Vulnerability of skates and rays caught by the longline fishery targeting Patagonian toothfish in the Crozet and Kerguelen EEZs
Chondrichthyans (sharks, skates and rays and chimaeras) represent the group of marine vertebrates most threatened by fisheries worldwide. Almost 50% of global catch is indeed composed of bycatch (unintentional catch of non-targeted species). In Kerguelen and Crozet EEZs, skates are among the main by...
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| Other Authors: | , , , , |
| Format: | Doctoral or Postdoctoral Thesis |
| Language: | French |
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CCSD
2023
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| Subjects: | |
| Online Access: | https://theses.hal.science/tel-04965649 https://theses.hal.science/tel-04965649v1/document https://theses.hal.science/tel-04965649v1/file/FAURE_2023_These_vfinale_pour_impression.pdf |
| Summary: | Chondrichthyans (sharks, skates and rays and chimaeras) represent the group of marine vertebrates most threatened by fisheries worldwide. Almost 50% of global catch is indeed composed of bycatch (unintentional catch of non-targeted species). In Kerguelen and Crozet EEZs, skates are among the main bycatch species of demersal longline fisheries targeting Patagonian toothfish (Dissostichus eleginoides). The aim of this PhD thesis was to i) obtain knowledge about biology and ecology attributes of these skate species in order to constitute a basic understanding allowing to ii) evaluate vulnerability to fishing and iii) propose operational solution to mitigate fishing impacts.We composed a large dataset of reporting fishery data, data routinely collected by fishery observers and to answer particular protocols implemented as part of this thesis. Using these data, we were able to estimate a large variety of attributes such as life-history traits of species, their abundance in the fishery area and their post-release survival.We first study life-history traits of the three species and results highlighted that the Kerguelen Sandpaper skate (Bathyraja irrasa) was less productive species than the Eaton skate (Bathyraja eatonii). Relatively, the Whiteleg skate (Amblyraja taaf) was more productive.We then examined species ecology and their interaction with the fishery and results showed that B. irrasa was more susceptible to capture than the two other species. Its feeding ecology has indeed suggested a strong affiliation to the benthic habitat where fishing lines are set and mean size of capture is lower than size-at-maturity implying a large part of juveniles are captured. In contrast, B. eatonii showed a limited accessibility to fishery with a refuge area from 0 to 500 m deep (where fishing is prohibited) and post-release survival estimates of A. taaf revealed a low fishing mortality (0.001).Acquirement of these basic knowledge allowed us to evaluate vulnerability to longline fishing of the three species and conclude on ... |
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