Modelling transport of inshore and deep-spawned chokka squid (Loligo reynaudi) paralarvae off South Africa: the potential contribution of deep spawning to recruitment
- Downey-Breedt, Nicola, Roberts, Michael J, Sauer, Warwick H H, Chang, N
- Authors: Downey-Breedt, Nicola , Roberts, Michael J , Sauer, Warwick H H , Chang, N
- Date: 2016
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/125183 , vital:35742 , https://doi.10.1111/fog.12132
- Description: The South African chokka squid, Loligo reynaudi, spawns both inshore (≤70 m) and on the mid-shelf (71–130 m) of the Eastern Agulhas Bank. The fate of these deep-spawned hatchlings and their potential contribution to recruitment is as yet unknown. Lagrangian ROMS-IBM (Regional Ocean Modelling System-Individual-Based Model) simulations confirm westward transport of inshore and deep-spawned hatchlings, but also indicate that the potential exists for paralarvae hatched on the Eastern Agulhas Bank deep spawning grounds to be removed from the shelf ecosystem. Using a ROMS-IBM, this study determined the transport and recruitment success of deepspawned hatchlings relative to inshore-hatched paralarvae. A total of 12 release sites were incorporated into the model, six inshore and six deep-spawning sites. Paralarval survival was estimated based on timely transport to nursery grounds, adequate retention within the nursery grounds and retention on the Agulhas Bank shelf. Paralarval transport and survival were dependent on both spawning location and time of hatching. Results suggest the importance of the south coast as a nursery area for inshore-hatched paralarvae, and similarly the cold ridge nursery grounds for deep-hatched paralarvae. Possible relationships between periods of highest recruitment success and spawning peaks were identified for both spawning habitats. Based on the likely autumn increase in deep spawning off the Tsitsikamma coast, and the beneficial currents during this period (as indicated by the model results) it can be concluded that deep spawning may at times contribute significantly to recruitment.
- Full Text:
- Authors: Downey-Breedt, Nicola , Roberts, Michael J , Sauer, Warwick H H , Chang, N
- Date: 2016
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/125183 , vital:35742 , https://doi.10.1111/fog.12132
- Description: The South African chokka squid, Loligo reynaudi, spawns both inshore (≤70 m) and on the mid-shelf (71–130 m) of the Eastern Agulhas Bank. The fate of these deep-spawned hatchlings and their potential contribution to recruitment is as yet unknown. Lagrangian ROMS-IBM (Regional Ocean Modelling System-Individual-Based Model) simulations confirm westward transport of inshore and deep-spawned hatchlings, but also indicate that the potential exists for paralarvae hatched on the Eastern Agulhas Bank deep spawning grounds to be removed from the shelf ecosystem. Using a ROMS-IBM, this study determined the transport and recruitment success of deepspawned hatchlings relative to inshore-hatched paralarvae. A total of 12 release sites were incorporated into the model, six inshore and six deep-spawning sites. Paralarval survival was estimated based on timely transport to nursery grounds, adequate retention within the nursery grounds and retention on the Agulhas Bank shelf. Paralarval transport and survival were dependent on both spawning location and time of hatching. Results suggest the importance of the south coast as a nursery area for inshore-hatched paralarvae, and similarly the cold ridge nursery grounds for deep-hatched paralarvae. Possible relationships between periods of highest recruitment success and spawning peaks were identified for both spawning habitats. Based on the likely autumn increase in deep spawning off the Tsitsikamma coast, and the beneficial currents during this period (as indicated by the model results) it can be concluded that deep spawning may at times contribute significantly to recruitment.
- Full Text:
Molecular genetic, life-history and morphological variation in a coastal warm-temperate sciaenid fish: evidence for an upwelling-driven speciation event
- Henriques, Romina, Potts, Warren M, Sauer, Warwick H H, Santos, Carmen V D, Kruger, Jerraleigh, Thomas, Jessica A, Shaw, Paul W
- Authors: Henriques, Romina , Potts, Warren M , Sauer, Warwick H H , Santos, Carmen V D , Kruger, Jerraleigh , Thomas, Jessica A , Shaw, Paul W
- Date: 2016
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/125252 , vital:35750 , http://dx.doi.10.1111/jbi.12829
- Description: The marine environment is punctuated by biogeographical barriers that limit dispersal and gene flow in otherwise widespread species (Teske et al., 2011a,b; Briggs & Bowen, 2012; Luiz et al., 2012). These barriers may be physical obstacles such as landmasses (e.g. Isthmus of Panama) or less intuitive features such as deep water (Lessios et al., 2003), freshwater outflows (Floeter et al., 2008) or oceanographic features (Shaw et al., 2004; Galarza et al., 2009; von der Heyden et al., 2011). Upwelling cells and sea surface temperature (SSTs) gradients in particular are known to disrupt gene flow, leading to divergence of allopatric populations and species (Waters & Roy, 2004; Teske et al., 2011a; Henriques et al., 2012, 2014, 2015). However, as oceanographic features are seldom permanent and frequently subject to considerable environmental variability, many barriers often permit some level of permeability to dispersal (Floeter et al., 2008). Other processes may influence the persistence of differentiated allopatric taxa across such physical barriers (Bradbury et al., 2008), with ecological divergence (and diversifying selection) being reported as a major evolutionary process influencing the biogeographical distributions of marine species (Pelc et al., 2009; Teske et al., 2011a; Gaither et al., 2015).
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- Authors: Henriques, Romina , Potts, Warren M , Sauer, Warwick H H , Santos, Carmen V D , Kruger, Jerraleigh , Thomas, Jessica A , Shaw, Paul W
- Date: 2016
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/125252 , vital:35750 , http://dx.doi.10.1111/jbi.12829
- Description: The marine environment is punctuated by biogeographical barriers that limit dispersal and gene flow in otherwise widespread species (Teske et al., 2011a,b; Briggs & Bowen, 2012; Luiz et al., 2012). These barriers may be physical obstacles such as landmasses (e.g. Isthmus of Panama) or less intuitive features such as deep water (Lessios et al., 2003), freshwater outflows (Floeter et al., 2008) or oceanographic features (Shaw et al., 2004; Galarza et al., 2009; von der Heyden et al., 2011). Upwelling cells and sea surface temperature (SSTs) gradients in particular are known to disrupt gene flow, leading to divergence of allopatric populations and species (Waters & Roy, 2004; Teske et al., 2011a; Henriques et al., 2012, 2014, 2015). However, as oceanographic features are seldom permanent and frequently subject to considerable environmental variability, many barriers often permit some level of permeability to dispersal (Floeter et al., 2008). Other processes may influence the persistence of differentiated allopatric taxa across such physical barriers (Bradbury et al., 2008), with ecological divergence (and diversifying selection) being reported as a major evolutionary process influencing the biogeographical distributions of marine species (Pelc et al., 2009; Teske et al., 2011a; Gaither et al., 2015).
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Planning adaptation to climate change in fast-warming marine regions with seafood-dependent coastal communities
- Hobday, Alistair J, Cochrane, Kevern L, Howard, James, Aswani, Shankar, Byfield, Val, Duggan, Greg, Duna, Elethu, Dutra, Leo X C, Frusher, Stewart D, Fulton, Elizabeth A, Gammage, Louise, Gasalla, Maria A, Griffiths, Chevon, Guissamulo, Almeida, Haward, Marcus, Jarre, Astrid, Jennings, Sarah M, Jordan, Tia, Joyner, Jessica, Ramani, Narayana K, Shanmugasundaram, Swathi L P, Malherbe, Willem, Ortega-Cisneros, Kelly, Paytan, Adina, Pecl, Gretta T, Plagányi, Éva E, Popova, Ekaterina E, Razafindrainibe, Haja, Roberts, Michael J, Rohit, Prathiba, Sainulabdeen, Shyam S, Sauer, Warwick H H, Valappil, Sathianandan T, Zacharia, Paryiappanal U, Van Putten, E Ingrid
- Authors: Hobday, Alistair J , Cochrane, Kevern L , Howard, James , Aswani, Shankar , Byfield, Val , Duggan, Greg , Duna, Elethu , Dutra, Leo X C , Frusher, Stewart D , Fulton, Elizabeth A , Gammage, Louise , Gasalla, Maria A , Griffiths, Chevon , Guissamulo, Almeida , Haward, Marcus , Jarre, Astrid , Jennings, Sarah M , Jordan, Tia , Joyner, Jessica , Ramani, Narayana K , Shanmugasundaram, Swathi L P , Malherbe, Willem , Ortega-Cisneros, Kelly , Paytan, Adina , Pecl, Gretta T , Plagányi, Éva E , Popova, Ekaterina E , Razafindrainibe, Haja , Roberts, Michael J , Rohit, Prathiba , Sainulabdeen, Shyam S , Sauer, Warwick H H , Valappil, Sathianandan T , Zacharia, Paryiappanal U , Van Putten, E Ingrid
- Date: 2016
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/125675 , vital:35806 , https://doi.10.1007/s11160-016-9419-0
- Description: Many coastal communities rely on living marine resources for livelihoods and food security. These resources are commonly under stress from overfishing, pollution, coastal development and habitat degradation. Climate change is an additional stressor beginning to impact coastal systems and communities, but may also lead to opportunities for some species and the people they sustain. We describe the research approach for a multi-country project, focused on the southern hemisphere, designed to contribute to improving fishing community adaptation efforts by characterizing, assessing and predicting the future of coastal-marine food resources, and codeveloping adaptation options through the provision and sharing of knowledge across fast-warming marine regions (i.e. marine ‘hotspots’). These hotspots represent natural laboratories for observing change and concomitant human adaptive responses, and for developing adaptation options and management strategies. Focusing on adaptation options and strategies for enhancing coastal resilience at the local level will contribute to capacity building and local empowerment in order to minimise negative outcomes and take advantage of opportunities arising from climate change. However, developing comparative approaches across regions that differ in political institutions, socio-economic community demographics, resource dependency and research capacity is challenging. Here, we describe physical, biological, social and governance tools to allow hotspot comparisons, and several methods to evaluate and enhance interactions within a multi-nation research team. Strong partnerships within and between the focal regions are critical to scientific and political support for development of effective approaches to reduce future vulnerability. Comparing these hotspot regions will enhance local adaptation responses and generate outcomes applicable to other regions.
- Full Text:
- Authors: Hobday, Alistair J , Cochrane, Kevern L , Howard, James , Aswani, Shankar , Byfield, Val , Duggan, Greg , Duna, Elethu , Dutra, Leo X C , Frusher, Stewart D , Fulton, Elizabeth A , Gammage, Louise , Gasalla, Maria A , Griffiths, Chevon , Guissamulo, Almeida , Haward, Marcus , Jarre, Astrid , Jennings, Sarah M , Jordan, Tia , Joyner, Jessica , Ramani, Narayana K , Shanmugasundaram, Swathi L P , Malherbe, Willem , Ortega-Cisneros, Kelly , Paytan, Adina , Pecl, Gretta T , Plagányi, Éva E , Popova, Ekaterina E , Razafindrainibe, Haja , Roberts, Michael J , Rohit, Prathiba , Sainulabdeen, Shyam S , Sauer, Warwick H H , Valappil, Sathianandan T , Zacharia, Paryiappanal U , Van Putten, E Ingrid
- Date: 2016
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/125675 , vital:35806 , https://doi.10.1007/s11160-016-9419-0
- Description: Many coastal communities rely on living marine resources for livelihoods and food security. These resources are commonly under stress from overfishing, pollution, coastal development and habitat degradation. Climate change is an additional stressor beginning to impact coastal systems and communities, but may also lead to opportunities for some species and the people they sustain. We describe the research approach for a multi-country project, focused on the southern hemisphere, designed to contribute to improving fishing community adaptation efforts by characterizing, assessing and predicting the future of coastal-marine food resources, and codeveloping adaptation options through the provision and sharing of knowledge across fast-warming marine regions (i.e. marine ‘hotspots’). These hotspots represent natural laboratories for observing change and concomitant human adaptive responses, and for developing adaptation options and management strategies. Focusing on adaptation options and strategies for enhancing coastal resilience at the local level will contribute to capacity building and local empowerment in order to minimise negative outcomes and take advantage of opportunities arising from climate change. However, developing comparative approaches across regions that differ in political institutions, socio-economic community demographics, resource dependency and research capacity is challenging. Here, we describe physical, biological, social and governance tools to allow hotspot comparisons, and several methods to evaluate and enhance interactions within a multi-nation research team. Strong partnerships within and between the focal regions are critical to scientific and political support for development of effective approaches to reduce future vulnerability. Comparing these hotspot regions will enhance local adaptation responses and generate outcomes applicable to other regions.
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The GULLS project: a comparison of vulnerabilities across selected ocean hotspots and implications for adaptation to global change
- Cochrane, Kevern L, Hobday, Alistair J, Aswani, Shankar, Byfield, Val, Dutra, Leo X C, Gasalla, Maria A, Haward, Marcus, Paytan, Adina, Pecl, Gretta T, Popova, Katya, Sainulabdeen, Shyam S, Savage, Candida, Sauer, Warwick H H, van Putten, Ingrid E, Visser, Natascha, TG Team
- Authors: Cochrane, Kevern L , Hobday, Alistair J , Aswani, Shankar , Byfield, Val , Dutra, Leo X C , Gasalla, Maria A , Haward, Marcus , Paytan, Adina , Pecl, Gretta T , Popova, Katya , Sainulabdeen, Shyam S , Savage, Candida , Sauer, Warwick H H , van Putten, Ingrid E , Visser, Natascha , TG Team
- Date: 2016
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/422037 , vital:71906
- Description: The GULLS project, `Global learning for local solutions: Reducing vulnerability of marine-dependent coastal communities' has been underway since October 2014. The project has been investigating six regional `hotspots': marine areas experiencing rapid warming. These are south-east Australia, Brazil, India, Solomon Islands, South Africa, and the Mozambique Channel and Madagascar. Rapid warming could be expected to have social, cultural and economic impacts that could affect these countries in different ways and may already be doing so. GULLS has focused on contributing to assessing and reducing the vulnerability of coastal communities and other stakeholders dependent on marine resources and to facilitate adaptation to climate change and variability through an integrated and trans-disciplinary approach. It includes participants from Australia, Brazil, India, Madagascar, New Zealand, South Africa, the United Kingdom and the United States of America. The research programme has been divided into six inter-linked components: ocean models, biological and ecological sensitivity analyses, system models, social vulnerability, policy mapping, and communication and education. This presentation will provide a brief overview of each of these components and describe the benefits that have resulted from the collaborative and transdisciplinary approach of GULLS. Following the standard vulnerability elements of exposure, sensitivity and adaptive capacity, the vulnerabilities of coastal communities and other stakeholders dependent on marine resources in the five hotspots will be compared using a set of indicators derived and populated from results of the research programme. The implications of similarities and differences between the hotspots for adaptation planning and options will be described.
- Full Text:
- Authors: Cochrane, Kevern L , Hobday, Alistair J , Aswani, Shankar , Byfield, Val , Dutra, Leo X C , Gasalla, Maria A , Haward, Marcus , Paytan, Adina , Pecl, Gretta T , Popova, Katya , Sainulabdeen, Shyam S , Savage, Candida , Sauer, Warwick H H , van Putten, Ingrid E , Visser, Natascha , TG Team
- Date: 2016
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/422037 , vital:71906
- Description: The GULLS project, `Global learning for local solutions: Reducing vulnerability of marine-dependent coastal communities' has been underway since October 2014. The project has been investigating six regional `hotspots': marine areas experiencing rapid warming. These are south-east Australia, Brazil, India, Solomon Islands, South Africa, and the Mozambique Channel and Madagascar. Rapid warming could be expected to have social, cultural and economic impacts that could affect these countries in different ways and may already be doing so. GULLS has focused on contributing to assessing and reducing the vulnerability of coastal communities and other stakeholders dependent on marine resources and to facilitate adaptation to climate change and variability through an integrated and trans-disciplinary approach. It includes participants from Australia, Brazil, India, Madagascar, New Zealand, South Africa, the United Kingdom and the United States of America. The research programme has been divided into six inter-linked components: ocean models, biological and ecological sensitivity analyses, system models, social vulnerability, policy mapping, and communication and education. This presentation will provide a brief overview of each of these components and describe the benefits that have resulted from the collaborative and transdisciplinary approach of GULLS. Following the standard vulnerability elements of exposure, sensitivity and adaptive capacity, the vulnerabilities of coastal communities and other stakeholders dependent on marine resources in the five hotspots will be compared using a set of indicators derived and populated from results of the research programme. The implications of similarities and differences between the hotspots for adaptation planning and options will be described.
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Incipient genetic isolation of a temperate migratory coastal sciaenid fish (Argyrosomus inodorus) within the Benguela Cold Current system
- Henriques, Romina, Potts, Warren M, Sauer, Warwick H H, Shaw, Paul W
- Authors: Henriques, Romina , Potts, Warren M , Sauer, Warwick H H , Shaw, Paul W
- Date: 2015
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124710 , vital:35652 , https://doi.10.1080/17451000.2014.952309
- Description: The Benguela Cold Current system, located in the south-eastern Atlantic, features cold sea surface temperatures, bounded to the north and south by tropical currents (the Angola and Agulhas Currents, respectively) and a perennial upwelling cell off central Namibia that divides the region into two sub-systems with different characteristics (Shannon 1985; Hutchings et al. 2009). The colder sea surface temperatures of the Benguela Current have been considered an important biogeographic barrier, isolating tropical and warm-temperate fauna of the Atlantic and Indo-Pacific Oceans (Avise 2000; Floeter et al. 2008). However, recent studies revealed that other oceanographic features, such as the perennial upwelling cell, may also play an important role in shaping the population structure of warm temperate fish populations within the Benguela system, as complete disruption of gene flow was documented both in Lichia amia (Linnaeus, 1758) and Atractoscion aequidens (Cuvier, 1830) (Henriques et al. 2012, 2014). Little is known, however, regarding the influence of the Benguela system on genetic population connectivity of cold-water-tolerant species.
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- Authors: Henriques, Romina , Potts, Warren M , Sauer, Warwick H H , Shaw, Paul W
- Date: 2015
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124710 , vital:35652 , https://doi.10.1080/17451000.2014.952309
- Description: The Benguela Cold Current system, located in the south-eastern Atlantic, features cold sea surface temperatures, bounded to the north and south by tropical currents (the Angola and Agulhas Currents, respectively) and a perennial upwelling cell off central Namibia that divides the region into two sub-systems with different characteristics (Shannon 1985; Hutchings et al. 2009). The colder sea surface temperatures of the Benguela Current have been considered an important biogeographic barrier, isolating tropical and warm-temperate fauna of the Atlantic and Indo-Pacific Oceans (Avise 2000; Floeter et al. 2008). However, recent studies revealed that other oceanographic features, such as the perennial upwelling cell, may also play an important role in shaping the population structure of warm temperate fish populations within the Benguela system, as complete disruption of gene flow was documented both in Lichia amia (Linnaeus, 1758) and Atractoscion aequidens (Cuvier, 1830) (Henriques et al. 2012, 2014). Little is known, however, regarding the influence of the Benguela system on genetic population connectivity of cold-water-tolerant species.
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Ocean warming affects the distribution and abundance of resident fishes by changing their reproductive scope
- Potts, Warren M, Booth, Anthony J, Richardson, Timothy J, Sauer, Warwick H H
- Authors: Potts, Warren M , Booth, Anthony J , Richardson, Timothy J , Sauer, Warwick H H
- Date: 2014
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/125352 , vital:35775 , https://doi.10.1007/s11160-013-9329-3
- Description: With ocean warming predicted globally, one of the mechanisms driving distributional shifts and changes in the abundance of resident fishes is reproductive output. The relationship between sea surface temperature and the reproductive activity of a eurythermic, resident coastal species, blacktail seabream Diplodus sargus capensis, was examined in the ‘‘ocean warming’’ hotspot of the northern Benguela. Reproductive activity was found to be restricted to periods when the water temperature dropped below 20 _C. A metadata analysis conducted on the D. sargus sub-species complex similarly showed that reproductive activity was restricted to temperatures between 15 and 20 _C, regardless of the range in ambient water temperature. Based on these findings and using satellite derived SST information, we examined D. s. capensis’s total and seasonal ‘‘reproductive scope’’ that is defined as either the area suitable for spawning each year or the duration of its potential spawning season at a fixed geographical locality, respectively. Trends were examined over the last three decades. Reproductive scope by area was found to be shrinking at a rate of 7 % per decade in southern Angola and expanding at a rate of 6 % per decade in northern Namibia. Reproductive scope by season decreased by 1.05 months per decade in Namibe, southern Angola and increased by 0.76 months per decade in Hentiesbaai, northern Namibia. Changes in reproductive scope may be a driving mechanism of distributional shifts in resident fishes, although the rate of the shifts is likely to be slow. More importantly, changes in reproductive scope will not be uniform throughout fish distributions and will most likely result in heterogeneous variations in fish abundance.
- Full Text:
- Authors: Potts, Warren M , Booth, Anthony J , Richardson, Timothy J , Sauer, Warwick H H
- Date: 2014
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/125352 , vital:35775 , https://doi.10.1007/s11160-013-9329-3
- Description: With ocean warming predicted globally, one of the mechanisms driving distributional shifts and changes in the abundance of resident fishes is reproductive output. The relationship between sea surface temperature and the reproductive activity of a eurythermic, resident coastal species, blacktail seabream Diplodus sargus capensis, was examined in the ‘‘ocean warming’’ hotspot of the northern Benguela. Reproductive activity was found to be restricted to periods when the water temperature dropped below 20 _C. A metadata analysis conducted on the D. sargus sub-species complex similarly showed that reproductive activity was restricted to temperatures between 15 and 20 _C, regardless of the range in ambient water temperature. Based on these findings and using satellite derived SST information, we examined D. s. capensis’s total and seasonal ‘‘reproductive scope’’ that is defined as either the area suitable for spawning each year or the duration of its potential spawning season at a fixed geographical locality, respectively. Trends were examined over the last three decades. Reproductive scope by area was found to be shrinking at a rate of 7 % per decade in southern Angola and expanding at a rate of 6 % per decade in northern Namibia. Reproductive scope by season decreased by 1.05 months per decade in Namibe, southern Angola and increased by 0.76 months per decade in Hentiesbaai, northern Namibia. Changes in reproductive scope may be a driving mechanism of distributional shifts in resident fishes, although the rate of the shifts is likely to be slow. More importantly, changes in reproductive scope will not be uniform throughout fish distributions and will most likely result in heterogeneous variations in fish abundance.
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Ocean warming hotspots provide early warning laboratories for climate change impacts
- Pecl, Gretta T, Hobday, Alistair J, Frusher, Stewart, Sauer, Warwick H H, Bates, Amanda E
- Authors: Pecl, Gretta T , Hobday, Alistair J , Frusher, Stewart , Sauer, Warwick H H , Bates, Amanda E
- Date: 2014
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/125363 , vital:35776 , https://doi.10.1007/s11160-014-9355-9
- Description: A growing literature describes a wide range of negative impacts of climate change on marine resources and the people and communities they support, including species range changes, changes in productivity of fisheries and declines in economic performance (Doney et al. 2012; Poloczanska et al. 2013). These impacts, many of which are projected to increase in future, are compounded by growing pressures on marine resources (Halpern et al. 2008; Maxwell et al. 2013). An estimated 260 million people are involved directly or indirectly in global marine fisheries (Teh and Sumaila 2013) with many of the resources for capture fisheries already fully (&57 % in 2009) or over exploited (30 %) (FAO 2012). Nevertheless, production of marine resources will need to increase to accommodate the demands of a growing population, and the impacts of climate change on food security will need to be minimised (FAO 2009). Identifying opportunities and threats, and developing adaptation options in response to climate change impacts in the marine realm, is essential for optimising the benefits that society can continue to derive from the goods and services provided by marine resources.
- Full Text:
- Authors: Pecl, Gretta T , Hobday, Alistair J , Frusher, Stewart , Sauer, Warwick H H , Bates, Amanda E
- Date: 2014
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/125363 , vital:35776 , https://doi.10.1007/s11160-014-9355-9
- Description: A growing literature describes a wide range of negative impacts of climate change on marine resources and the people and communities they support, including species range changes, changes in productivity of fisheries and declines in economic performance (Doney et al. 2012; Poloczanska et al. 2013). These impacts, many of which are projected to increase in future, are compounded by growing pressures on marine resources (Halpern et al. 2008; Maxwell et al. 2013). An estimated 260 million people are involved directly or indirectly in global marine fisheries (Teh and Sumaila 2013) with many of the resources for capture fisheries already fully (&57 % in 2009) or over exploited (30 %) (FAO 2012). Nevertheless, production of marine resources will need to increase to accommodate the demands of a growing population, and the impacts of climate change on food security will need to be minimised (FAO 2009). Identifying opportunities and threats, and developing adaptation options in response to climate change impacts in the marine realm, is essential for optimising the benefits that society can continue to derive from the goods and services provided by marine resources.
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Ocean warming, a rapid distributional shift, and the hybridization of a coastal fish species
- Potts, Warren M, Henriques, Romina, Santos, Carmen V D, Munnik, Kate, Ansorge, Isabelle J, Dufois, Francois, Sauer, Warwick H H, Booth, Anthony J, Kirchner, Carola, Sauer, Warwick, Shaw, Paul W
- Authors: Potts, Warren M , Henriques, Romina , Santos, Carmen V D , Munnik, Kate , Ansorge, Isabelle J , Dufois, Francois , Sauer, Warwick H H , Booth, Anthony J , Kirchner, Carola , Sauer, Warwick , Shaw, Paul W
- Date: 2014
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/125375 , vital:35777 , https://doi.10.1111/gcb.12612
- Description: Despite increasing awareness of large-scale climate-driven distribution shifts in the marine environment, no study has linked rapid ocean warming to a shift in distribution and consequent hybridization of a marine fish species. This study describes rapid warming (0.8 °C per decade) in the coastal waters of the Angola-Benguela Frontal Zone over the last three decades and a concomitant shift by a temperature sensitive coastal fish species (Argyrosomus coronus) southward from Angola into Namibia. In this context, rapid shifts in distribution across Economic Exclusive Zones will complicate the management of fishes, particularly when there is a lack of congruence in the fisheries policy between nations. Evidence for recent hybridization between A. coronus and a congener, A. inodorus, indicate that the rapid shift in distribution of A. coronus has placed adults of the two species in contact during their spawning events. Ocean warming may therefore revert established species isolation mechanisms and alter the evolutionary history of fishes. While the consequences of the hybridization on the production of the resource remain unclear, this will most likely introduce additional layers of complexity to their management.
- Full Text:
- Authors: Potts, Warren M , Henriques, Romina , Santos, Carmen V D , Munnik, Kate , Ansorge, Isabelle J , Dufois, Francois , Sauer, Warwick H H , Booth, Anthony J , Kirchner, Carola , Sauer, Warwick , Shaw, Paul W
- Date: 2014
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/125375 , vital:35777 , https://doi.10.1111/gcb.12612
- Description: Despite increasing awareness of large-scale climate-driven distribution shifts in the marine environment, no study has linked rapid ocean warming to a shift in distribution and consequent hybridization of a marine fish species. This study describes rapid warming (0.8 °C per decade) in the coastal waters of the Angola-Benguela Frontal Zone over the last three decades and a concomitant shift by a temperature sensitive coastal fish species (Argyrosomus coronus) southward from Angola into Namibia. In this context, rapid shifts in distribution across Economic Exclusive Zones will complicate the management of fishes, particularly when there is a lack of congruence in the fisheries policy between nations. Evidence for recent hybridization between A. coronus and a congener, A. inodorus, indicate that the rapid shift in distribution of A. coronus has placed adults of the two species in contact during their spawning events. Ocean warming may therefore revert established species isolation mechanisms and alter the evolutionary history of fishes. While the consequences of the hybridization on the production of the resource remain unclear, this will most likely introduce additional layers of complexity to their management.
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Ontogenetic dietary shift and morphological correlates for Diplodus capensis (Teleostei Sparidae) in southern Angola
- Richardson, Timothy J, Potts, Warren M, Santos, Carmen V D, Sauer, Warwick H H
- Authors: Richardson, Timothy J , Potts, Warren M , Santos, Carmen V D , Sauer, Warwick H H
- Date: 2011
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/443984 , vital:74176 , https://doi.org/10.1080/15627020.2011.11407501
- Description: Allometric growth patterns of functional morphological variables that reflect resource use in fish were correlated with the diet of Diplodus capensis in southern Angola. A total of 114 individuals (76–336 mm FL) were collected for stomach content analysis and a further 35 individuals (80–320 mm FL) for morphometric analysis. The major dietary components belonged to the groups Chlorophyta, Cirripedia, Rhodophyta and Bivalvia, and made up 71.7% of the diet in terms of a computed ranking index. There was a clear ontogenetic dietary shift with small fish feeding predominantly on algae and large fish on barnacles and mussels. This increasingly durophagous diet corresponded with a positive allometric growth pattern in the gape dimensions (width, height and surface area), adductor mandibulae muscle process and incisor width. Conversely, the relative gut length followed an isometric growth pattern, suggesting a decreased absorptive capacity. This isometric growth pattern is attributed to the better digestibility of the durophagous prey items when compared with algae and further corroborates a link between the morphology and an ontogenetic dietary shift observed in this species.
- Full Text:
- Authors: Richardson, Timothy J , Potts, Warren M , Santos, Carmen V D , Sauer, Warwick H H
- Date: 2011
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/443984 , vital:74176 , https://doi.org/10.1080/15627020.2011.11407501
- Description: Allometric growth patterns of functional morphological variables that reflect resource use in fish were correlated with the diet of Diplodus capensis in southern Angola. A total of 114 individuals (76–336 mm FL) were collected for stomach content analysis and a further 35 individuals (80–320 mm FL) for morphometric analysis. The major dietary components belonged to the groups Chlorophyta, Cirripedia, Rhodophyta and Bivalvia, and made up 71.7% of the diet in terms of a computed ranking index. There was a clear ontogenetic dietary shift with small fish feeding predominantly on algae and large fish on barnacles and mussels. This increasingly durophagous diet corresponded with a positive allometric growth pattern in the gape dimensions (width, height and surface area), adductor mandibulae muscle process and incisor width. Conversely, the relative gut length followed an isometric growth pattern, suggesting a decreased absorptive capacity. This isometric growth pattern is attributed to the better digestibility of the durophagous prey items when compared with algae and further corroborates a link between the morphology and an ontogenetic dietary shift observed in this species.
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Aspects of the biology and fisheries of an economically important sparid Dentex macrophthalmus (Bloch 1791) in the Namibe province, Angola
- Potts, Warren M, Inácio, L A, Santos, Carmen V D, Richardson, Timothy J, Sauer, Warwick H H
- Authors: Potts, Warren M , Inácio, L A , Santos, Carmen V D , Richardson, Timothy J , Sauer, Warwick H H
- Date: 2010
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/123096 , vital:35405 , https://doi.org/10.2989/1814232X.2010.538160
- Description: Dentex macrophthalmus is a small, commercially important sparid fish that is abundant in the deeper waters (range 50–500 m) of the Mediterranean Sea (Trunov 1970), the North-West African shelf (Goode and Bean 1896, Fowler 1936), including the Cape Verde and Canary Islands, and the south-eastern Atlantic from the Equator to just south of Lüderitz (27°40′ S) (Trunov 1970). Because of its high abundance, it is of considerable economic importance and is captured in large numbers in both artisanal and commercial fisheries in many countries. Although it is the most important artisanal species along the entire Angolan coast, it is most abundant in the southern region (Kilongo et al. 2007). Despite its economic importance in Angola and elsewhere, relatively little is known on its abundance, fisheries and biology.
- Full Text:
- Authors: Potts, Warren M , Inácio, L A , Santos, Carmen V D , Richardson, Timothy J , Sauer, Warwick H H
- Date: 2010
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/123096 , vital:35405 , https://doi.org/10.2989/1814232X.2010.538160
- Description: Dentex macrophthalmus is a small, commercially important sparid fish that is abundant in the deeper waters (range 50–500 m) of the Mediterranean Sea (Trunov 1970), the North-West African shelf (Goode and Bean 1896, Fowler 1936), including the Cape Verde and Canary Islands, and the south-eastern Atlantic from the Equator to just south of Lüderitz (27°40′ S) (Trunov 1970). Because of its high abundance, it is of considerable economic importance and is captured in large numbers in both artisanal and commercial fisheries in many countries. Although it is the most important artisanal species along the entire Angolan coast, it is most abundant in the southern region (Kilongo et al. 2007). Despite its economic importance in Angola and elsewhere, relatively little is known on its abundance, fisheries and biology.
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Semi-submersible rigs: a vector transporting entire marine communities around the world
- Wanless, Ross M, Scott, Sue, Sauer, Warwick H H, Andrew, Timothy G, Glass, James P, Godfrey, Brian, Griffiths, Charles, Yeld, Eleanor
- Authors: Wanless, Ross M , Scott, Sue , Sauer, Warwick H H , Andrew, Timothy G , Glass, James P , Godfrey, Brian , Griffiths, Charles , Yeld, Eleanor
- Date: 2010
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/126920 , vital:35935 , https://doi.10.1007/s10530-009-9666-2
- Description: A virtually intact subtropical reef community (14 phyla, 40 families and 62 non-native taxa) was associated with a rig under tow from Brazil that became stranded on the remote island of Tristan da Cunha. This exposes rigs as a significant vector spreading alien marine organisms, and includes the first records of free-swimming marine finfish populations becoming established after unintentional movement. With relatively trivial effort, a pre-tow clean would have obviated the need to salvage and dispose of the rig (undertaken largely to address concerns about invasive species), at a cost of *US$20 million. Our findings show that towing biofouled structures across biogeographic boundaries present unexcelled opportunities for invasion to a wide diversity of marine species. Better control and management of this vector is required urgently. Simultaneous, unintentional introductions of viable populations of multiple marine organisms are rare events, and we develop a basic framework for rapid assessment of invasion risks.
- Full Text:
- Authors: Wanless, Ross M , Scott, Sue , Sauer, Warwick H H , Andrew, Timothy G , Glass, James P , Godfrey, Brian , Griffiths, Charles , Yeld, Eleanor
- Date: 2010
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/126920 , vital:35935 , https://doi.10.1007/s10530-009-9666-2
- Description: A virtually intact subtropical reef community (14 phyla, 40 families and 62 non-native taxa) was associated with a rig under tow from Brazil that became stranded on the remote island of Tristan da Cunha. This exposes rigs as a significant vector spreading alien marine organisms, and includes the first records of free-swimming marine finfish populations becoming established after unintentional movement. With relatively trivial effort, a pre-tow clean would have obviated the need to salvage and dispose of the rig (undertaken largely to address concerns about invasive species), at a cost of *US$20 million. Our findings show that towing biofouled structures across biogeographic boundaries present unexcelled opportunities for invasion to a wide diversity of marine species. Better control and management of this vector is required urgently. Simultaneous, unintentional introductions of viable populations of multiple marine organisms are rare events, and we develop a basic framework for rapid assessment of invasion risks.
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Spatial description of hake-directed fishing activity off the west coast of South Africa
- Fairweather, T P, Booth, Anthony J, Sauer, Warwick H H, Leslie, Rob W
- Authors: Fairweather, T P , Booth, Anthony J , Sauer, Warwick H H , Leslie, Rob W
- Date: 2010
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/127031 , vital:35945 , https://doi.10.2989/18142320609504129
- Description: Historically, the two species of Cape hakes Merluccius capensis and M. paradoxus off South Africa were commercially exploited exclusively by demersal trawling. In 1994, hake-directed demersal longline was introduced on an experimental basis, and in 1998 was initiated as a commercial fishing sector. The effect of a combined fleet composed of both trawlers and longliners on the Cape hake resource is not fully understood. Analysis of fishing intensity and catch-rate data revealed that the highest catch rates were found around the 400m and 500m isobaths for the trawl and longline fisheries respectively. Catch rates from both fishing sectors were also noted to be higher over sediments with a sand component. Differences between areas of the highest fishing intensity and highest catch rates were noted. In addition to other factors, it is suggested that a ‘friction of distance’ effect applies — vessels will trade-off higher catch rates with the increased costs associated with fishing in deeper waters.
- Full Text:
- Authors: Fairweather, T P , Booth, Anthony J , Sauer, Warwick H H , Leslie, Rob W
- Date: 2010
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/127031 , vital:35945 , https://doi.10.2989/18142320609504129
- Description: Historically, the two species of Cape hakes Merluccius capensis and M. paradoxus off South Africa were commercially exploited exclusively by demersal trawling. In 1994, hake-directed demersal longline was introduced on an experimental basis, and in 1998 was initiated as a commercial fishing sector. The effect of a combined fleet composed of both trawlers and longliners on the Cape hake resource is not fully understood. Analysis of fishing intensity and catch-rate data revealed that the highest catch rates were found around the 400m and 500m isobaths for the trawl and longline fisheries respectively. Catch rates from both fishing sectors were also noted to be higher over sediments with a sand component. Differences between areas of the highest fishing intensity and highest catch rates were noted. In addition to other factors, it is suggested that a ‘friction of distance’ effect applies — vessels will trade-off higher catch rates with the increased costs associated with fishing in deeper waters.
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A change of the seaward boundary of Goukamma Marine Protected Area could increase conservation and fishery benefits
- Götz, Albrecht, Kerwath, Sven E, Attwood, Colin G, Sauer, Warwick H H
- Authors: Götz, Albrecht , Kerwath, Sven E , Attwood, Colin G , Sauer, Warwick H H
- Date: 2009
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/123503 , vital:35449 , https://doi10.4102/sajs.v105i9/10.102
- Description: Goukamma Marine Protected Area (MPA) on the South African temperate South Coast has been shown to be effective in maintaining a spawning stock of roman, Chrysoblephus laticeps (Sparidae). The larval ecology and the oceanographic conditions in the area suggest a good potential for the enhancement of roman stocks outside the reserve through larval dispersal. A high rate of illegal fishing just inside the seaward boundary of the MPA could severely compromise its function. We suggest that a change of the seaward boundary of the reserve to coincide with a latitudinal line could increase its function as a harvest refuge for resident reef fishes such as roman, facilitate voluntary compliance and monitoring and prosecution of illegal fishing without a significant negative impact on the commercial linefishing fleet in the area. Simple adjustments such as the one proposed here could be attempted at a number of South African MPAs as they would be beneficial to achieve fishery and conservation goals alike.
- Full Text:
- Authors: Götz, Albrecht , Kerwath, Sven E , Attwood, Colin G , Sauer, Warwick H H
- Date: 2009
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/123503 , vital:35449 , https://doi10.4102/sajs.v105i9/10.102
- Description: Goukamma Marine Protected Area (MPA) on the South African temperate South Coast has been shown to be effective in maintaining a spawning stock of roman, Chrysoblephus laticeps (Sparidae). The larval ecology and the oceanographic conditions in the area suggest a good potential for the enhancement of roman stocks outside the reserve through larval dispersal. A high rate of illegal fishing just inside the seaward boundary of the MPA could severely compromise its function. We suggest that a change of the seaward boundary of the reserve to coincide with a latitudinal line could increase its function as a harvest refuge for resident reef fishes such as roman, facilitate voluntary compliance and monitoring and prosecution of illegal fishing without a significant negative impact on the commercial linefishing fleet in the area. Simple adjustments such as the one proposed here could be attempted at a number of South African MPAs as they would be beneficial to achieve fishery and conservation goals alike.
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Establishing a basis for ecosystem management in the western Indian Ocean
- Vousden, David, Scott, Lucy E P, Sauer, Warwick H H, Bornman, T G, Ngoile, M, Stapley, J, Lutjeharms, Johan R E
- Authors: Vousden, David , Scott, Lucy E P , Sauer, Warwick H H , Bornman, T G , Ngoile, M , Stapley, J , Lutjeharms, Johan R E
- Date: 2008
- Language: English
- Type: Article
- Identifier: vital:6774 , http://hdl.handle.net/10962/d1008081
- Description: An ambitious multinational programme, with generous funding for an initial five years, aims to provide understanding of marine resources for the benefit of impoverished island and coastal populations in a much-neglected ocean region.
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- Authors: Vousden, David , Scott, Lucy E P , Sauer, Warwick H H , Bornman, T G , Ngoile, M , Stapley, J , Lutjeharms, Johan R E
- Date: 2008
- Language: English
- Type: Article
- Identifier: vital:6774 , http://hdl.handle.net/10962/d1008081
- Description: An ambitious multinational programme, with generous funding for an initial five years, aims to provide understanding of marine resources for the benefit of impoverished island and coastal populations in a much-neglected ocean region.
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Bycatch and discarding in the South African demersal trawl fishery
- Walmsley, Sarah A, Leslie, Rob W, Sauer, Warwick H H
- Authors: Walmsley, Sarah A , Leslie, Rob W , Sauer, Warwick H H
- Date: 2007
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/123944 , vital:35518 , https://doi.10.1016/j.fishres.2007.03.002
- Description: Observers aboard commercial trawlers collected data on the total catch composition of 614 and 479 hauls made by vessels operating off the south and west coasts of South Africa, respectively. On the south coast, four fishing areas were identified on the basis of target species and fishing depth. On the west coast, hauls were separated into those targeting hake Merluccius spp. in four depth ranges (0–300, 301–400, 401–500, and >500 m) and those targeting monkfish Lophius vomerinus. For each area, the catch composition was calculated and the species assemblages were investigated using cluster analysis and multi-dimensional scaling. Finally, for each coast, the weight of fish discarded annually was estimated. On the south coast, although hake dominated, between 21% and 47% of the catch was not hake, depending on the fishing area. In comparison, hake dominated west coast catches, the proportion of hake increasing with depth. For each fishery investigated, approximately 90% of the catch was processed and landed. However, estimates of annual discards indicate that the south and west coast fisheries may annually discard 9000 or 10,000 t and 17,000 or 25,000 t, of undersized and unutilizable fish and offal, respectively, depending on the estimation method used. When developing strategies to limit or enhance utilization of bycatch, cognisance should be taken of the differences in catch composition between the south and west coasts and of the importance of bycatch revenue to south coast fishing companies.
- Full Text:
- Authors: Walmsley, Sarah A , Leslie, Rob W , Sauer, Warwick H H
- Date: 2007
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/123944 , vital:35518 , https://doi.10.1016/j.fishres.2007.03.002
- Description: Observers aboard commercial trawlers collected data on the total catch composition of 614 and 479 hauls made by vessels operating off the south and west coasts of South Africa, respectively. On the south coast, four fishing areas were identified on the basis of target species and fishing depth. On the west coast, hauls were separated into those targeting hake Merluccius spp. in four depth ranges (0–300, 301–400, 401–500, and >500 m) and those targeting monkfish Lophius vomerinus. For each area, the catch composition was calculated and the species assemblages were investigated using cluster analysis and multi-dimensional scaling. Finally, for each coast, the weight of fish discarded annually was estimated. On the south coast, although hake dominated, between 21% and 47% of the catch was not hake, depending on the fishing area. In comparison, hake dominated west coast catches, the proportion of hake increasing with depth. For each fishery investigated, approximately 90% of the catch was processed and landed. However, estimates of annual discards indicate that the south and west coast fisheries may annually discard 9000 or 10,000 t and 17,000 or 25,000 t, of undersized and unutilizable fish and offal, respectively, depending on the estimation method used. When developing strategies to limit or enhance utilization of bycatch, cognisance should be taken of the differences in catch composition between the south and west coasts and of the importance of bycatch revenue to south coast fishing companies.
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Determining the daily spawning cycle of the chokka squid, Loligo reynaudii off the South African Coast
- Authors: Melo, Y , Sauer, Warwick H H
- Date: 2007
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124275 , vital:35588 , https://doi.10.1007/s11160-006-9034-6
- Description: The study investigated the duration and peak of the daily spawning cycle of the chokka squid Loligo reynaudii, and the possibility of estimating the spawning frequency by means of classification and grouping (by age) of postovulatory follicles. Post-ovulatory follicles were classified into three types: new, intermediate or old, based in part on the degree of resorption of the follicles determined from histological sections. Ovulation in this species appears to be a rapid process, seen by the occurrence of both mature oocytes and post-ovulatory follicles in partially spent ovaries. Results suggest that chokka squid present a diel timing of spawning, with successive periods of egg accumulation at night, interrupted by periods of active spawning during the day. The ovarian cycle for this species appears typical of serial spawners. During the spawning phase ovaries go through ripe, partially spent and recovering stages by undergoing a process of maturation, ovulation and redeveloping, where a new batch of advanced oocytes is recruited. The cycle typically appears to last between 24 and 36 h, and may depend on a number of factors such as environmental conditions and the presence of predators. The short-lived (about 14 h) nature of the post-ovulatory follicles precludes the calculation of the exact spawning interval and does not allow us to accurately predict the spawning frequency. Together with the degree of oviduct fullness they do however give a good indication of imminent or recent spawning.
- Full Text:
- Authors: Melo, Y , Sauer, Warwick H H
- Date: 2007
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124275 , vital:35588 , https://doi.10.1007/s11160-006-9034-6
- Description: The study investigated the duration and peak of the daily spawning cycle of the chokka squid Loligo reynaudii, and the possibility of estimating the spawning frequency by means of classification and grouping (by age) of postovulatory follicles. Post-ovulatory follicles were classified into three types: new, intermediate or old, based in part on the degree of resorption of the follicles determined from histological sections. Ovulation in this species appears to be a rapid process, seen by the occurrence of both mature oocytes and post-ovulatory follicles in partially spent ovaries. Results suggest that chokka squid present a diel timing of spawning, with successive periods of egg accumulation at night, interrupted by periods of active spawning during the day. The ovarian cycle for this species appears typical of serial spawners. During the spawning phase ovaries go through ripe, partially spent and recovering stages by undergoing a process of maturation, ovulation and redeveloping, where a new batch of advanced oocytes is recruited. The cycle typically appears to last between 24 and 36 h, and may depend on a number of factors such as environmental conditions and the presence of predators. The short-lived (about 14 h) nature of the post-ovulatory follicles precludes the calculation of the exact spawning interval and does not allow us to accurately predict the spawning frequency. Together with the degree of oviduct fullness they do however give a good indication of imminent or recent spawning.
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Spatial patterns in the biology of the chokka squid, Loligo reynaudii on the Agulhas Bank, South Africa
- Olyott, L J H, Sauer, Warwick H H, Booth, Anthony J
- Authors: Olyott, L J H , Sauer, Warwick H H , Booth, Anthony J
- Date: 2007
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/127053 , vital:35947 , https://doi.10.1007/s11160-006-9027-5
- Description: Although migration patterns for various life history stages of the chokka squid (Loligo reynaudii) have been previously presented, there has been limited comparison of spatial variation in biological parameters. Based on data from research surveys; size ranges of juveniles, subadults and adults on the Agulhas Bank were estimated and presented spatially. The bulk of the results appear to largely support the current acceptance of the life cycle with an annual pattern of squid hatching in the east, migrating westwards to offshore feeding grounds on the Central and Western Agulhas Bank and the west coast and subsequent return migration to the eastern inshore areas to spawn. The number of adult animals in deeper water, particularly in autumn in the central study area probably represents squid spawning in deeper waters and over a greater area than is currently targeted by the fishery. The distribution of life history stages and different feeding areas does not rule out the possibility that discrete populations of L. reynaudii with different biological characteristics inhabit the western and eastern regions of the Agulhas Bank. In this hypothesis, some mixing of the populations does occur but generally squid from the western Agulhas Bank may occur in smaller numbers, grow more slowly and mature at a larger size. Spawning occurs on the western portion of the Agulhas Bank, and juveniles grow and mature on the west coast and the central Agulhas Bank. Future research requirements include the elucidation of the age structure of chokka squid both spatially and temporally, and a comparison of the statolith chemistry and genetic characterization between adults from different spawning areas across the Agulhas Bank.
- Full Text:
- Authors: Olyott, L J H , Sauer, Warwick H H , Booth, Anthony J
- Date: 2007
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/127053 , vital:35947 , https://doi.10.1007/s11160-006-9027-5
- Description: Although migration patterns for various life history stages of the chokka squid (Loligo reynaudii) have been previously presented, there has been limited comparison of spatial variation in biological parameters. Based on data from research surveys; size ranges of juveniles, subadults and adults on the Agulhas Bank were estimated and presented spatially. The bulk of the results appear to largely support the current acceptance of the life cycle with an annual pattern of squid hatching in the east, migrating westwards to offshore feeding grounds on the Central and Western Agulhas Bank and the west coast and subsequent return migration to the eastern inshore areas to spawn. The number of adult animals in deeper water, particularly in autumn in the central study area probably represents squid spawning in deeper waters and over a greater area than is currently targeted by the fishery. The distribution of life history stages and different feeding areas does not rule out the possibility that discrete populations of L. reynaudii with different biological characteristics inhabit the western and eastern regions of the Agulhas Bank. In this hypothesis, some mixing of the populations does occur but generally squid from the western Agulhas Bank may occur in smaller numbers, grow more slowly and mature at a larger size. Spawning occurs on the western portion of the Agulhas Bank, and juveniles grow and mature on the west coast and the central Agulhas Bank. Future research requirements include the elucidation of the age structure of chokka squid both spatially and temporally, and a comparison of the statolith chemistry and genetic characterization between adults from different spawning areas across the Agulhas Bank.
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Managing South Africa's trawl bycatch
- Walmsley, Sarah A, Leslie, Rob W, Sauer, Warwick H H
- Authors: Walmsley, Sarah A , Leslie, Rob W , Sauer, Warwick H H
- Date: 2006
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124954 , vital:35713 , https://doi.10.1093/icesjms/fsl022
- Description: Over the past few decades, it has become widely recognized that the management strategies of world fisheries must ensure sustainability of bycatch as well as of target species. South Africa implemented a pilot observer programme from 1995 to 2000 to collect data on the levels and patterns of bycatch and discards in the demersal trawl fishery. Here, the results of that programme are used in conjunction with information on bycatch value and compliance to assess the issues and problems regarding bycatch and discarding in the fishery. In general, bycatch components can be placed into one of three categories (discarded bycatch, retained bycatch, and processing waste), each of which present different management problems and require different management approaches. The results were used to formulate a bycatch management plan for the demersal trawl fishery in South Africa. Given the need to continue monitoring bycatch, the performance of the pilot observer programme is reviewed, and the levels of sampling effort required for a national programme are discussed.
- Full Text:
- Authors: Walmsley, Sarah A , Leslie, Rob W , Sauer, Warwick H H
- Date: 2006
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124954 , vital:35713 , https://doi.10.1093/icesjms/fsl022
- Description: Over the past few decades, it has become widely recognized that the management strategies of world fisheries must ensure sustainability of bycatch as well as of target species. South Africa implemented a pilot observer programme from 1995 to 2000 to collect data on the levels and patterns of bycatch and discards in the demersal trawl fishery. Here, the results of that programme are used in conjunction with information on bycatch value and compliance to assess the issues and problems regarding bycatch and discarding in the fishery. In general, bycatch components can be placed into one of three categories (discarded bycatch, retained bycatch, and processing waste), each of which present different management problems and require different management approaches. The results were used to formulate a bycatch management plan for the demersal trawl fishery in South Africa. Given the need to continue monitoring bycatch, the performance of the pilot observer programme is reviewed, and the levels of sampling effort required for a national programme are discussed.
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Spatio-temporal patterns in maturation of the chokka squid (Loligo vulgaris reynaudii) off the coast of South Africa
- Olyott, L J H, Sauer, Warwick H H, Booth, Anthony J
- Authors: Olyott, L J H , Sauer, Warwick H H , Booth, Anthony J
- Date: 2006
- Language: English
- Type: Article
- Identifier: vital:6763 , http://hdl.handle.net/10962/d1007930
- Description: Knowledge of the temporal and spatial characteristics of chokka squid (Loligo vulgaris reynaudii) biology in South African waters is limited, so the possibility of there being a geographically fragmented stock was examined by investigating the distribution of maturity patterns for the species, covering all known spawning areas and using both historical and recent data. Gonadosomatic indices (GSI) varied between year-round consistency and apparent seasonal peaks in both summer and winter; there was no clear spatial pattern. Monthly percentage maturity provided further evidence for two peak reproductive periods each year, although mature squid were present throughout. Sex ratios demonstrated great variability between different areas and life history stages. Male-biased sex ratios were only apparent on the inshore spawning grounds and ranged between 1.118:1 and 4.267:1. Size at sexual maturity was also seasonal, squid maturing smaller in winter/spring than in summer/autumn. Also, squid in the east matured smaller than squid in the west. Although the results from the present study do not provide conclusive evidence of distinct geographic populations, squid likely spawn over a significantly larger area of the Agulhas Bank than previously estimated, and squid on the west coast of South Africa may return to spawn on the western portion of the Agulhas Bank. It remains likely, however, that the east and west coast populations are a single stock and that migration of juveniles to the west coast and their subsequent return as sub-adults is an integral but non-essential and variable part of the life history.
- Full Text:
- Authors: Olyott, L J H , Sauer, Warwick H H , Booth, Anthony J
- Date: 2006
- Language: English
- Type: Article
- Identifier: vital:6763 , http://hdl.handle.net/10962/d1007930
- Description: Knowledge of the temporal and spatial characteristics of chokka squid (Loligo vulgaris reynaudii) biology in South African waters is limited, so the possibility of there being a geographically fragmented stock was examined by investigating the distribution of maturity patterns for the species, covering all known spawning areas and using both historical and recent data. Gonadosomatic indices (GSI) varied between year-round consistency and apparent seasonal peaks in both summer and winter; there was no clear spatial pattern. Monthly percentage maturity provided further evidence for two peak reproductive periods each year, although mature squid were present throughout. Sex ratios demonstrated great variability between different areas and life history stages. Male-biased sex ratios were only apparent on the inshore spawning grounds and ranged between 1.118:1 and 4.267:1. Size at sexual maturity was also seasonal, squid maturing smaller in winter/spring than in summer/autumn. Also, squid in the east matured smaller than squid in the west. Although the results from the present study do not provide conclusive evidence of distinct geographic populations, squid likely spawn over a significantly larger area of the Agulhas Bank than previously estimated, and squid on the west coast of South Africa may return to spawn on the western portion of the Agulhas Bank. It remains likely, however, that the east and west coast populations are a single stock and that migration of juveniles to the west coast and their subsequent return as sub-adults is an integral but non-essential and variable part of the life history.
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Behavioural interactions of predators and spawning chokka squid off South Africa: towards quantification
- Smale, Malcolm J, Sauer, Warwick H H, Roberts, Michael J
- Authors: Smale, Malcolm J , Sauer, Warwick H H , Roberts, Michael J
- Date: 2001
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/123921 , vital:35516 , https://doi.10.1007/s002270100664
- Description: The interaction of a suite of predators with mating and spawning chokka squid (Loligo vulgaris reynaudii) was studied at inshore (<50 m) spawning grounds off South Africa. This study provides the first detailed records of predator–prey interactions of squids on their spawning grounds and is the first attempt to time disruptions caused by predators to the egg-laying behaviour of squids, thereby quantifying the perceived threat to the prey. The squids are focused on mate choice and reproduction while they aggregate over egg beds and they may be more vulnerable to predation than at other times. Their vulnerability to different predators in the field is examined and the tactics used against different predatory species are illustrated using recordings made with underwater video cameras. Predators recorded included two cephalopods (Octopus vulgaris and L. v. reynaudii), five teleosts (Pagellus bellotii natalensis, Spondyliosoma emarginatum, Pachymetopon aeneum, Cheimerius nufar and Pomatomus saltatrix), seven chondrichthyians (Squalus megalops, Mustelus mustelus, Carcharias taurus, Dasyatis brevicaudata, Gymnura natalensis, Poroderma africanum and P. pantherinum) and three marine mammals (Arctocephalus puscillus, Tursiops aduncus and Delphinus delphis). Analysis of behavioural interactions between predators and prey showed that predator disruption of egg laying may be quantified in terms of time. Marine mammals caused the most acute disruption, whereas other taxa had more chronic disruption effects because they spent more time on the spawning grounds. During November 1995, the suite of predators changed during the course of a 2-day period of underwater video recording, possibly because of an increase in water temperature. The hypothesis that predators would be concentrated around a spawning aggregation was tested by surveying the spawning ground using an underwater camera towed by a boat navigating with differential GPS. The results supported the hypothesis because predators were located only around the spawning sites. The serial spawning of chokka squids in recently upwelled water may reduce predation pressure. Furthermore, it may be difficult for predators to predict the specific spawning site on a particular day because squids disperse away from egg beds at night and use numerous spawning sites along the coast.
- Full Text:
- Authors: Smale, Malcolm J , Sauer, Warwick H H , Roberts, Michael J
- Date: 2001
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/123921 , vital:35516 , https://doi.10.1007/s002270100664
- Description: The interaction of a suite of predators with mating and spawning chokka squid (Loligo vulgaris reynaudii) was studied at inshore (<50 m) spawning grounds off South Africa. This study provides the first detailed records of predator–prey interactions of squids on their spawning grounds and is the first attempt to time disruptions caused by predators to the egg-laying behaviour of squids, thereby quantifying the perceived threat to the prey. The squids are focused on mate choice and reproduction while they aggregate over egg beds and they may be more vulnerable to predation than at other times. Their vulnerability to different predators in the field is examined and the tactics used against different predatory species are illustrated using recordings made with underwater video cameras. Predators recorded included two cephalopods (Octopus vulgaris and L. v. reynaudii), five teleosts (Pagellus bellotii natalensis, Spondyliosoma emarginatum, Pachymetopon aeneum, Cheimerius nufar and Pomatomus saltatrix), seven chondrichthyians (Squalus megalops, Mustelus mustelus, Carcharias taurus, Dasyatis brevicaudata, Gymnura natalensis, Poroderma africanum and P. pantherinum) and three marine mammals (Arctocephalus puscillus, Tursiops aduncus and Delphinus delphis). Analysis of behavioural interactions between predators and prey showed that predator disruption of egg laying may be quantified in terms of time. Marine mammals caused the most acute disruption, whereas other taxa had more chronic disruption effects because they spent more time on the spawning grounds. During November 1995, the suite of predators changed during the course of a 2-day period of underwater video recording, possibly because of an increase in water temperature. The hypothesis that predators would be concentrated around a spawning aggregation was tested by surveying the spawning ground using an underwater camera towed by a boat navigating with differential GPS. The results supported the hypothesis because predators were located only around the spawning sites. The serial spawning of chokka squids in recently upwelled water may reduce predation pressure. Furthermore, it may be difficult for predators to predict the specific spawning site on a particular day because squids disperse away from egg beds at night and use numerous spawning sites along the coast.
- Full Text: