The small pelagic fishery of the Pemba Channel, Tanzania: what we know and what we need to know for management under climate change
- Sekadende, Baraka, Scott, Lucy E P, Anderson, Jim, Aswani, Shankar, Francis, Julius, Jacobs, Zoe, Jebri, Fatma, Jiddawi, Narriman, Kamukuru, Albogast T, Kelly, Stephen, Kizenga, Hellen, Kuguru, Baraka, Kyewalyanga, Margareth, Noyon, Margaux, Nyandwi, Ntahondi, Painter, Stuart C, Palmer, Matthew, Raitsos, Dionysios, Roberts, Michael J, Sailley, Sévrine F, Samoilys, Melita, Sauer, Warwick H H, Shayo, Salome, Shaghude, Yohana W, Taylor, Sarah F W, Wihsgott, Juliane U, Ekaterina Popova
- Authors: Sekadende, Baraka , Scott, Lucy E P , Anderson, Jim , Aswani, Shankar , Francis, Julius , Jacobs, Zoe , Jebri, Fatma , Jiddawi, Narriman , Kamukuru, Albogast T , Kelly, Stephen , Kizenga, Hellen , Kuguru, Baraka , Kyewalyanga, Margareth , Noyon, Margaux , Nyandwi, Ntahondi , Painter, Stuart C , Palmer, Matthew , Raitsos, Dionysios , Roberts, Michael J , Sailley, Sévrine F , Samoilys, Melita , Sauer, Warwick H H , Shayo, Salome , Shaghude, Yohana W , Taylor, Sarah F W , Wihsgott, Juliane U , Ekaterina Popova
- Date: 2020
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/178986 , vital:40102 , https://doi.org/10.1016/j.ocecoaman.2020.105322
- Description: Small pelagic fish, including anchovies, sardines and sardinellas, mackerels, capelin, hilsa, sprats and herrings, are distributed widely, from the tropics to the far north Atlantic Ocean and to the southern oceans off Chile and South Africa. They are most abundant in the highly productive major eastern boundary upwelling systems and are characterised by significant natural variations in biomass. Overall, small pelagic fisheries represent about one third of global fish landings although a large proportion of the catch is processed into animal feeds. Nonetheless, in some developing countries in addition to their economic value, small pelagic fisheries also make an important contribution to human diets and the food security of many low-income households. Such is the case for many communities in the Zanzibar Archipelago and on mainland Tanzania in the Western Indian Ocean. Of great concern in this region, as elsewhere, is the potential impact of climate change on marine and coastal ecosystems in general, and on small pelagic fisheries in particular. This paper describes data and information available on Tanzania's small pelagic fisheries, including catch and effort, management protocols and socio-economic significance.
- Full Text:
- Authors: Sekadende, Baraka , Scott, Lucy E P , Anderson, Jim , Aswani, Shankar , Francis, Julius , Jacobs, Zoe , Jebri, Fatma , Jiddawi, Narriman , Kamukuru, Albogast T , Kelly, Stephen , Kizenga, Hellen , Kuguru, Baraka , Kyewalyanga, Margareth , Noyon, Margaux , Nyandwi, Ntahondi , Painter, Stuart C , Palmer, Matthew , Raitsos, Dionysios , Roberts, Michael J , Sailley, Sévrine F , Samoilys, Melita , Sauer, Warwick H H , Shayo, Salome , Shaghude, Yohana W , Taylor, Sarah F W , Wihsgott, Juliane U , Ekaterina Popova
- Date: 2020
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/178986 , vital:40102 , https://doi.org/10.1016/j.ocecoaman.2020.105322
- Description: Small pelagic fish, including anchovies, sardines and sardinellas, mackerels, capelin, hilsa, sprats and herrings, are distributed widely, from the tropics to the far north Atlantic Ocean and to the southern oceans off Chile and South Africa. They are most abundant in the highly productive major eastern boundary upwelling systems and are characterised by significant natural variations in biomass. Overall, small pelagic fisheries represent about one third of global fish landings although a large proportion of the catch is processed into animal feeds. Nonetheless, in some developing countries in addition to their economic value, small pelagic fisheries also make an important contribution to human diets and the food security of many low-income households. Such is the case for many communities in the Zanzibar Archipelago and on mainland Tanzania in the Western Indian Ocean. Of great concern in this region, as elsewhere, is the potential impact of climate change on marine and coastal ecosystems in general, and on small pelagic fisheries in particular. This paper describes data and information available on Tanzania's small pelagic fisheries, including catch and effort, management protocols and socio-economic significance.
- Full Text:
Ecological connectivity between the areas beyond national jurisdiction and coastal waters: Safeguarding interests of coastal communities in developing countries
- Popova, Ekaterina, Vousden, David, Sauer, Warwick H H, Mohammed, Essam Y, Allain, Valerie, Downey-Breedt, Nicola, Fletcher, Ruth, Gjerde, Kristina M, Halpin, Patrick, Kelly, Stephen, Obura, David, Pecl, Gretta T, Roberts, Michael J, Raitsos, Dionysios E, Rogers, Alex, Samoilys, Melita, Sumaila , Ussif Rashid, Tracey, Sean, Yool, Andrew
- Authors: Popova, Ekaterina , Vousden, David , Sauer, Warwick H H , Mohammed, Essam Y , Allain, Valerie , Downey-Breedt, Nicola , Fletcher, Ruth , Gjerde, Kristina M , Halpin, Patrick , Kelly, Stephen , Obura, David , Pecl, Gretta T , Roberts, Michael J , Raitsos, Dionysios E , Rogers, Alex , Samoilys, Melita , Sumaila , Ussif Rashid , Tracey, Sean , Yool, Andrew
- Date: 2019
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124331 , vital:35594 , https://doi.10.1016/j.marpol.2019.02.050
- Description: The UN General Assembly has made a unanimous decision to start negotiations to establish an international, legally-binding instrument for the conservation and sustainable use of marine biological diversity within Areas Beyond National Jurisdiction (ABNJ). However, there has of yet been little discussion on the importance of this move to the ecosystem services provided by coastal zones in their downstream zone of influence. Here, we identify the ecological connectivity between ABNJ and coastal zones as critically important in the negotiation process and apply several approaches to identify some priority areas for protection from the perspective of coastal populations of Least Developed Countries (LDCs). Initially, we review the scientific evidence that demonstrates ecological connectivity between ABNJ and the coastal zones with a focus on the LDCs. We then use ocean modelling to develop a number of metrics and spatial maps that serve to quantify the connectivity of the ABNJ to the coastal zone. We find that the level of exposure to the ABNJ influences varies strongly between countries. Similarly, not all areas of the ABNJ are equal in their impacts on the coastline. Using this method, we identify the areas of the ABNJ that are in the most urgent need of protection on the grounds of the strength of their potential downstream impacts on the coastal populations of LDCs. We argue that indirect negative impacts of the ABNJ fishing, industrialisation and pollution, communicated via oceanographic, cultural and ecological connectivity to the coastal waters of the developing countries should be of concern.
- Full Text:
- Authors: Popova, Ekaterina , Vousden, David , Sauer, Warwick H H , Mohammed, Essam Y , Allain, Valerie , Downey-Breedt, Nicola , Fletcher, Ruth , Gjerde, Kristina M , Halpin, Patrick , Kelly, Stephen , Obura, David , Pecl, Gretta T , Roberts, Michael J , Raitsos, Dionysios E , Rogers, Alex , Samoilys, Melita , Sumaila , Ussif Rashid , Tracey, Sean , Yool, Andrew
- Date: 2019
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124331 , vital:35594 , https://doi.10.1016/j.marpol.2019.02.050
- Description: The UN General Assembly has made a unanimous decision to start negotiations to establish an international, legally-binding instrument for the conservation and sustainable use of marine biological diversity within Areas Beyond National Jurisdiction (ABNJ). However, there has of yet been little discussion on the importance of this move to the ecosystem services provided by coastal zones in their downstream zone of influence. Here, we identify the ecological connectivity between ABNJ and coastal zones as critically important in the negotiation process and apply several approaches to identify some priority areas for protection from the perspective of coastal populations of Least Developed Countries (LDCs). Initially, we review the scientific evidence that demonstrates ecological connectivity between ABNJ and the coastal zones with a focus on the LDCs. We then use ocean modelling to develop a number of metrics and spatial maps that serve to quantify the connectivity of the ABNJ to the coastal zone. We find that the level of exposure to the ABNJ influences varies strongly between countries. Similarly, not all areas of the ABNJ are equal in their impacts on the coastline. Using this method, we identify the areas of the ABNJ that are in the most urgent need of protection on the grounds of the strength of their potential downstream impacts on the coastal populations of LDCs. We argue that indirect negative impacts of the ABNJ fishing, industrialisation and pollution, communicated via oceanographic, cultural and ecological connectivity to the coastal waters of the developing countries should be of concern.
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From global to regional and back again: common climate stressors of marine ecosystems relevant for adaptation across five ocean warming hotspots
- Popova, Ekaterina, Yool, Andrew, Byfield, Valborg, Cochrane, Kevern L, Coward, Andrew C, Salim, Shyam S, Gasalla, Maria A, Henson, S.A, Hobday, Alistair J, Pecl, Gretta T, Sauer, Warwick H H, Roberts, Michael J
- Authors: Popova, Ekaterina , Yool, Andrew , Byfield, Valborg , Cochrane, Kevern L , Coward, Andrew C , Salim, Shyam S , Gasalla, Maria A , Henson, S.A , Hobday, Alistair J , Pecl, Gretta T , Sauer, Warwick H H , Roberts, Michael J
- Date: 2016
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124514 , vital:35623 , https://doi.10.1111/gcb.13247
- Description: Ocean warming ‘hotspots’ are regions characterized by above-average temperature increases over recent years, for which there are significant consequences for both living marine resources and the societies that depend on them. As such, they represent early warning systems for understanding the impacts of marine climate change, and test-beds for developing adaptation options for coping with those impacts. Here, we examine five hotspots off the coasts of eastern Australia, South Africa, Madagascar, India and Brazil. These particular hotspots have underpinned a large international partnership that is working towards improving community adaptation by characterizing, assessing and projecting the likely future of coastal-marine food resources through the provision and sharing of knowledge. To inform this effort, we employ a high-resolution global ocean model forced by Representative Concentration Pathway 8.5 and simulated to year 2099. In addition to the sea surface temperature, we analyse projected stratification, nutrient supply, primary production, anthropogenic CO2-driven ocean acidification, deoxygenation and ocean circulation. Our simulation finds that the temperature-defined hotspots studied here will continue to experience warming but, with the exception of eastern Australia, may not remain the fastest warming ocean areas over the next century as the strongest warming is projected to occur in the subpolar and polar areas of the Northern Hemisphere. Additionally, we find that recent rapid change in SST is not necessarily an indicator that these areas are also hotspots of the other climatic stressors examined. However, a consistent facet of the hotspots studied here is that they are all strongly influenced by ocean circulation, which has already shown changes in the recent past and is projected to undergo further strong change into the future. In addition to the fast warming, change in local ocean circulation represents a distinct feature of present and future climate change impacting marine ecosystems in these areas.
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- Authors: Popova, Ekaterina , Yool, Andrew , Byfield, Valborg , Cochrane, Kevern L , Coward, Andrew C , Salim, Shyam S , Gasalla, Maria A , Henson, S.A , Hobday, Alistair J , Pecl, Gretta T , Sauer, Warwick H H , Roberts, Michael J
- Date: 2016
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124514 , vital:35623 , https://doi.10.1111/gcb.13247
- Description: Ocean warming ‘hotspots’ are regions characterized by above-average temperature increases over recent years, for which there are significant consequences for both living marine resources and the societies that depend on them. As such, they represent early warning systems for understanding the impacts of marine climate change, and test-beds for developing adaptation options for coping with those impacts. Here, we examine five hotspots off the coasts of eastern Australia, South Africa, Madagascar, India and Brazil. These particular hotspots have underpinned a large international partnership that is working towards improving community adaptation by characterizing, assessing and projecting the likely future of coastal-marine food resources through the provision and sharing of knowledge. To inform this effort, we employ a high-resolution global ocean model forced by Representative Concentration Pathway 8.5 and simulated to year 2099. In addition to the sea surface temperature, we analyse projected stratification, nutrient supply, primary production, anthropogenic CO2-driven ocean acidification, deoxygenation and ocean circulation. Our simulation finds that the temperature-defined hotspots studied here will continue to experience warming but, with the exception of eastern Australia, may not remain the fastest warming ocean areas over the next century as the strongest warming is projected to occur in the subpolar and polar areas of the Northern Hemisphere. Additionally, we find that recent rapid change in SST is not necessarily an indicator that these areas are also hotspots of the other climatic stressors examined. However, a consistent facet of the hotspots studied here is that they are all strongly influenced by ocean circulation, which has already shown changes in the recent past and is projected to undergo further strong change into the future. In addition to the fast warming, change in local ocean circulation represents a distinct feature of present and future climate change impacting marine ecosystems in these areas.
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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.
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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.
- Full Text:
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:
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