Effects of fishing methods on deep water shark species caught as by-catch off southern Portugal
In: Hydrobiologia. Springer: The Hague. ISSN 0018-8158; e-ISSN 1573-5117, more Related to:Coelho, R.; Erzini, K. (2008). Effects of fishing methods on deep water shark species caught as by-catch off southern Portugal, in: Davenport, J. et al. Challenges to Marine Ecosystems: Proceedings of the 41st European Marine Biology Symposium, held in Cork, Ireland, 4-8 September 2005. Developments in Hydrobiology, 202: pp. 187-193. https://dx.doi.org/10.1007/978-1-4020-8808-7_16, more |  |
| Keywords | Animals > Chordata > Vertebrates > Fishes > Chondrichthyes > Marine fishes > Sharks
By-catch
Catching methods > Net fishing > Trawling
Equipment > Fishery industry equipment > Fishing gear
Fauna > Aquatic organisms > Aquatic animals > Fish
Fishing
Maturation
Population characteristics > Population structure > Sex ratio
Population characteristics > Population structure > Size distribution
Seawater
Sharks
Water > Deep water
Chondrichthyes [WoRMS]; Crustacea [WoRMS]; Etmopterus pusillus (Lowe, 1839) [WoRMS]; Etmopterus spinax (Linnaeus, 1758) [WoRMS]; Galeus melastomus Rafinesque, 1810 [WoRMS]; Actinopterygii [WoRMS]; Scyliorhinidae Gill, 1862 [WoRMS]
Marine/Coastal |
| Abstract | Deep water sharks are commonly caught as by-catch of longlines targeting bony fishes and trawlers targeting crustaceans in deep water off the southern Portuguese coast. Due to low or no commercial value, these species are most of the times discarded at sea, with only the larger specimens of some species commercialized at very low prices. In this study we present size distributions, maturity distributions, and sex ratios of 2,138 specimens belonging to four different species, namely the lantern sharks Etmopterus pusillus and Etmopterus spinax and the catsharks Galeus melastomus and Galeus atlanticus, caught with these two gears. Trawls generally caught smaller-sized specimens, in a wider length range than longlines. Trawls caught mostly immature specimens of all species, namely 83.7% immature of E. pusillus, 84.3% of E. spinax, 89.5% of G. melastomus, and 95.5% of G. atlanticus, while longlines caught mostly immature E. pusillus (69.2%) and G. melastomus (78.6%) and mostly mature E. spinax (88.2%) and G. atlanticus (87.2%). Trawls tended to catch more males than females of all species except E. spinax, while longlines caught more females than males of E. spinax and G. melastomus and more males than females of the other two species. The main conclusion of this work is that trawls are catching smaller-sized and mostly immature specimens when compared to longlines, meaning that they are probably having a more detrimental effect on these shark populations. The data presented here have significant implications for the conservation of these shark populations since sizes, sexes, and the immature and mature components of the populations are being affected differently by these two fishing gears. |
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