Evidence for protandry in Polydactylus quadrifilis in the Kwanza Estuary, Angola, and its implications for local fisheries
- Butler, Edward C, Childs, Amber-Robyn, Winkler, Alexander C, Milner, Marianne V, Potts, Warren M
- Authors: Butler, Edward C , Childs, Amber-Robyn , Winkler, Alexander C , Milner, Marianne V , Potts, Warren M
- Date: 2018
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124451 , vital:35614 , https://doi.10.1007/s10641-017-0699-6
- Description: A total of 141 Polydactylus quadrifilis were sampled from the Kwanza Estuary in Angola ranging in size from 436 to 1360 mm fork-length (FL). Of these, 124 were male, six intersex and 11 female. Female fish were significantly longer (mm, FL) and heavier (kg) than males and had significantly higher gonadosomatic indices (GSI’s) than those of males and intersex fish. Transitional (intersex) gonads were delimited, with testicular and ovarian regions separated by connective tissue. The first signs of ovarian tissue appeared on the outer ventral surface of the gonad. A second layer of ovarian tissue was first noticeable at either end of the initial ovarian region and developed back towards the centre of the ventral wall to form a luminal space. Early-stage oocytes were commonly found in the outer area of male regions and residual late-stage spermatids and spermatozoa were found in the luminal space of ovarian regions, suggesting a process of sex change from the outside inwards. A loss of male function was noted with increased ovarian prevalence. Based on this evidence it is suggested that P. quadrifilis in the Kwanza Estuary are protandrous. Owing to the reliance of P. quadrifilis on large highly fecund females for egg production, it is likely that they will be sensitive to fishing practices that target larger individuals within the population.
- Full Text:
- Date Issued: 2018
- Authors: Butler, Edward C , Childs, Amber-Robyn , Winkler, Alexander C , Milner, Marianne V , Potts, Warren M
- Date: 2018
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124451 , vital:35614 , https://doi.10.1007/s10641-017-0699-6
- Description: A total of 141 Polydactylus quadrifilis were sampled from the Kwanza Estuary in Angola ranging in size from 436 to 1360 mm fork-length (FL). Of these, 124 were male, six intersex and 11 female. Female fish were significantly longer (mm, FL) and heavier (kg) than males and had significantly higher gonadosomatic indices (GSI’s) than those of males and intersex fish. Transitional (intersex) gonads were delimited, with testicular and ovarian regions separated by connective tissue. The first signs of ovarian tissue appeared on the outer ventral surface of the gonad. A second layer of ovarian tissue was first noticeable at either end of the initial ovarian region and developed back towards the centre of the ventral wall to form a luminal space. Early-stage oocytes were commonly found in the outer area of male regions and residual late-stage spermatids and spermatozoa were found in the luminal space of ovarian regions, suggesting a process of sex change from the outside inwards. A loss of male function was noted with increased ovarian prevalence. Based on this evidence it is suggested that P. quadrifilis in the Kwanza Estuary are protandrous. Owing to the reliance of P. quadrifilis on large highly fecund females for egg production, it is likely that they will be sensitive to fishing practices that target larger individuals within the population.
- Full Text:
- Date Issued: 2018
Integrated genetic and morphological data support eco‐evolutionary divergence of Angolan and South African populations of Diplodus hottentotus
- Gwilliam, Michael P, Winkler, Alexander C, Potts, Warren M, Santos, Carmen V D, Sauer, Warwick H H, Shaw, Paul W, McKeown, Niall J
- Authors: Gwilliam, Michael P , Winkler, Alexander C , Potts, Warren M , Santos, Carmen V D , Sauer, Warwick H H , Shaw, Paul W , McKeown, Niall J
- Date: 2018
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124833 , vital:35702 , https://doi.10.1111/jfb.13582
- Description: The genus Diplodus presents multiple cases of taxonomic conjecture. Among these the D. cervinus complex was previously described as comprising three subspecies that are now regarded as separate species: Diplodus cervinus, Diplodus hottentotus and Diplodus omanensis. Diplodus hottentotus exhibits a clear break in its distribution around the Benguela Current system, prompting speculation that Angolan and South African populations flanking this area may be isolated and warrant formal taxonomic distinction. This study reports the first integrated genetic [mitochondrial (mt)DNA and nuclear microsatellite] and morphological (morphometric, meristic and colouration) study to assess patterns of divergence between populations in the two regions. High levels of cytonuclear divergence between the populations support a prolonged period of genetic isolation, with the sharing of only one mtDNA haplotype (12 haplotypes were fully sorted between regions) attributed to retention of ancestral polymorphism. Fish from the two regions were significantly differentiated at a number of morphometric (69·5%) and meristic (46%) characters. In addition, Angolan and South African fish exhibited reciprocally diagnostic colouration patterns that were more similar to Mediterranean and Indian Ocean congeners, respectively. Based on the congruent genetic and phenotypic diversity we suggest that the use of hottentotus, whether for full species or subspecies status, should be restricted to South African D. cervinus to reflect their status as a distinct species-like unit, while the relationship between Angolan and Atlantic–Mediterranean D. cervinus will require further demo-genetic analysis. This study highlights the utility of integrated genetic and morphological approaches to assess taxonomic diversity within the biogeographically dynamic Benguela Current region.
- Full Text:
- Date Issued: 2018
- Authors: Gwilliam, Michael P , Winkler, Alexander C , Potts, Warren M , Santos, Carmen V D , Sauer, Warwick H H , Shaw, Paul W , McKeown, Niall J
- Date: 2018
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124833 , vital:35702 , https://doi.10.1111/jfb.13582
- Description: The genus Diplodus presents multiple cases of taxonomic conjecture. Among these the D. cervinus complex was previously described as comprising three subspecies that are now regarded as separate species: Diplodus cervinus, Diplodus hottentotus and Diplodus omanensis. Diplodus hottentotus exhibits a clear break in its distribution around the Benguela Current system, prompting speculation that Angolan and South African populations flanking this area may be isolated and warrant formal taxonomic distinction. This study reports the first integrated genetic [mitochondrial (mt)DNA and nuclear microsatellite] and morphological (morphometric, meristic and colouration) study to assess patterns of divergence between populations in the two regions. High levels of cytonuclear divergence between the populations support a prolonged period of genetic isolation, with the sharing of only one mtDNA haplotype (12 haplotypes were fully sorted between regions) attributed to retention of ancestral polymorphism. Fish from the two regions were significantly differentiated at a number of morphometric (69·5%) and meristic (46%) characters. In addition, Angolan and South African fish exhibited reciprocally diagnostic colouration patterns that were more similar to Mediterranean and Indian Ocean congeners, respectively. Based on the congruent genetic and phenotypic diversity we suggest that the use of hottentotus, whether for full species or subspecies status, should be restricted to South African D. cervinus to reflect their status as a distinct species-like unit, while the relationship between Angolan and Atlantic–Mediterranean D. cervinus will require further demo-genetic analysis. This study highlights the utility of integrated genetic and morphological approaches to assess taxonomic diversity within the biogeographically dynamic Benguela Current region.
- Full Text:
- Date Issued: 2018
Assessing a social norms approach for improving recreational fisheries compliance
- Bova, Christopher S, Halse, Sarah J, Aswani, Shankar, Potts, Warren M
- Authors: Bova, Christopher S , Halse, Sarah J , Aswani, Shankar , Potts, Warren M
- Date: 2017
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/123122 , vital:35408 , https://doi.10.1111/fme.12218
- Description: This study aimed to assess the suitability of the Berkowitz’ (2005) social norms approach (SNA) for improving compliance behaviour amongst recreational fishers. A total of 138 recreational shore anglers were interviewed in Eastern Cape, South Africa and asked about their compliance, attitudes towards compliance, perceptions of compliance and the attitudes of other anglers. Results indicate that angler compliance for individual regulations was relatively high (75%–90%). Attitudes of anglers towards compliance was positive, with >80% feeling that “breaking any regulation is wrong.” Yet, as predicted by the SNA, interviewees often overestimated the non-compliance and negative attitudes of other anglers, particularly as their social proximity decreased. Interviewees with the greatest misperceptions were also less compliant. The social norms present in the Eastern Cape rock and surf fishery fulfil the criteria required for the application of the SNA, suggesting that this approach may provide a suitable normative intervention for improving compliance to be used in conjunction with instrumental approaches in recreational fisheries.
- Full Text:
- Date Issued: 2017
- Authors: Bova, Christopher S , Halse, Sarah J , Aswani, Shankar , Potts, Warren M
- Date: 2017
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/123122 , vital:35408 , https://doi.10.1111/fme.12218
- Description: This study aimed to assess the suitability of the Berkowitz’ (2005) social norms approach (SNA) for improving compliance behaviour amongst recreational fishers. A total of 138 recreational shore anglers were interviewed in Eastern Cape, South Africa and asked about their compliance, attitudes towards compliance, perceptions of compliance and the attitudes of other anglers. Results indicate that angler compliance for individual regulations was relatively high (75%–90%). Attitudes of anglers towards compliance was positive, with >80% feeling that “breaking any regulation is wrong.” Yet, as predicted by the SNA, interviewees often overestimated the non-compliance and negative attitudes of other anglers, particularly as their social proximity decreased. Interviewees with the greatest misperceptions were also less compliant. The social norms present in the Eastern Cape rock and surf fishery fulfil the criteria required for the application of the SNA, suggesting that this approach may provide a suitable normative intervention for improving compliance to be used in conjunction with instrumental approaches in recreational fisheries.
- Full Text:
- Date Issued: 2017
Phylogeny of the Sepia officinalis species complex in the eastern Atlantic extends the known distribution of Sepia vermiculata across the Benguela upwelling region
- Healey, Amy J E, McKeown, Niall J, Potts, Warren M, de Beer, Chénelle L, Sauer, Warwick H H, Shaw, Paul W
- Authors: Healey, Amy J E , McKeown, Niall J , Potts, Warren M , de Beer, Chénelle L , Sauer, Warwick H H , Shaw, Paul W
- Date: 2017
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/125631 , vital:35802 , https://doi.10.2989/1814232X.2017.1371076
- Description: Accurate species identification and biogeographic characterisation are fundamental for appropriate management of expanding cephalopod fisheries. This study addresses this topic within the common cuttlefish Sepia officinalis species complex (S. officinalis, S. hierredda and S. vermiculata), with an emphasis on occurrence in African waters. Tissue samples from the currently presumed distributions of S. vermiculata and S. hierredda (from South Africa and Ghana/Angola, respectively) were sequenced for the cytochrome c oxidase subunit I (COI) and the cytochrome b (cytb) genes of the mitochondrial genome and then compared to existing S. officinalis sequences. Three highly divergent and reciprocally monophyletic clades, corresponding to S. officinalis, S. hierredda and S. vermiculata, were resolved, representing the first molecular confirmation of the distinct species status of S. hierredda and S. vermiculata. The sequences also revealed that, contrary to expectations based on presently published information, all samples from southern Angola were S. vermiculata. These results indicate that the range of S. vermiculata extends beyond the currently described northern limit and that S. hierredda and S. vermiculata may be indiscriminately harvested in Angolan waters. Finer-scale patterns within S. vermiculata phylogeography also indicate that the Benguela Current System and/or other environmental factors serve to isolate northern and southern stocks.
- Full Text:
- Date Issued: 2017
- Authors: Healey, Amy J E , McKeown, Niall J , Potts, Warren M , de Beer, Chénelle L , Sauer, Warwick H H , Shaw, Paul W
- Date: 2017
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/125631 , vital:35802 , https://doi.10.2989/1814232X.2017.1371076
- Description: Accurate species identification and biogeographic characterisation are fundamental for appropriate management of expanding cephalopod fisheries. This study addresses this topic within the common cuttlefish Sepia officinalis species complex (S. officinalis, S. hierredda and S. vermiculata), with an emphasis on occurrence in African waters. Tissue samples from the currently presumed distributions of S. vermiculata and S. hierredda (from South Africa and Ghana/Angola, respectively) were sequenced for the cytochrome c oxidase subunit I (COI) and the cytochrome b (cytb) genes of the mitochondrial genome and then compared to existing S. officinalis sequences. Three highly divergent and reciprocally monophyletic clades, corresponding to S. officinalis, S. hierredda and S. vermiculata, were resolved, representing the first molecular confirmation of the distinct species status of S. hierredda and S. vermiculata. The sequences also revealed that, contrary to expectations based on presently published information, all samples from southern Angola were S. vermiculata. These results indicate that the range of S. vermiculata extends beyond the currently described northern limit and that S. hierredda and S. vermiculata may be indiscriminately harvested in Angolan waters. Finer-scale patterns within S. vermiculata phylogeography also indicate that the Benguela Current System and/or other environmental factors serve to isolate northern and southern stocks.
- Full Text:
- Date Issued: 2017
- «
- ‹
- 1
- ›
- »