Hydrobiologia

, 606:187

Effects of fishing methods on deep water shark species caught as by-catch off southern Portugal

CHALLENGES TO MARINE ECOSYSTEMS

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.

Keywords

Size distribution Sex ratio Maturity Deep water sharks Fishing gears By-catch 

References

  1. Abdulla, A., 2004. Status and Conservation of Sharks in the Mediterranean Sea. IUCN Technical Paper, 1–7.Google Scholar
  2. Anderson, E. D., 1990. Fishery models as applied to elasmobranch fisheries. In Pratt, H. L., S. H. Gruber & T. S. Taniuchi (eds), Elasmobranchs as Living Resources: Advances in the Biology, Ecology, Systematics, and the Status of Fisheries. NOAA Technical Report NMFS 90, 473–484.Google Scholar
  3. Baum, J. K., R. A. Myers, D. G. Kehler, B. Worm, S. J. Harley & P. A. Doherty, 2003. Collapse and conservation of shark populations in the Northwest Atlantic. Science 299: 389–392.PubMedCrossRefGoogle Scholar
  4. Bonfil, R., 1997. Status of shark resources in the southern Gulf of Mexico and Caribbean: implications for management. Fisheries Research 29: 101–117.CrossRefGoogle Scholar
  5. Campos, A. & P. Fonseca, 2004. The use of separator panels and square mesh windows for by-catch reduction in the crustacean trawl fishery off the Algarve (South Portugal). Fisheries Research 69: 147–156.CrossRefGoogle Scholar
  6. Clarke, M. W., P. L. Connolly & J. J. Bracken, 2001. Aspects of reproduction of the deep water sharks Centroscymnus coelolepis and Centrophorus squamosus from west of Ireland and Scotland. Journal of the Marine Biological Association of the United Kingdom 81: 1019–1029.Google Scholar
  7. Coelho, R., L. Bentes, J. M. S. Gonçalves, P. G. Lino, J. Ribeiro & K. Erzini, 2003. Reduction of elasmobranch by-catch in the hake semipelagic near-bottom longline fishery in the Algarve (Southern Portugal). Fisheries Science 69: 293–299.CrossRefGoogle Scholar
  8. Coelho, R., K. Erzini, L. Bentes, C. Correia, P. G. Lino, P. Monteiro, J. Ribeiro & J. M. S. Gonçalves, 2005. Semi-pelagic longline and trammel net elasmobranch catches in southern Portugal: catch composition, catch rates and discards. Journal of Northwest Atlantic Fishery Science 35: 531–537.CrossRefGoogle Scholar
  9. Compagno, L. J. V., 2001. Sharks of the World. An Annotated and Illustrated Catalogue of Shark Species known to Date, Vol. 2: Bullhead, Mackerel and Carpet Sharks (Heterodontiformes, Lamniformes and Orectolobiformes). FAO, Rome.Google Scholar
  10. Compagno, L. J. V., M. Dando & S. Fowler, 2005. Sharks of the World. Collins, London.Google Scholar
  11. Cortés, E., 2000. Life history patterns and correlations in sharks. Reviews in Fisheries Science 8: 299–344.Google Scholar
  12. Costa, M. E., K. Erzini & T. C. Borges, 2005. Reproductive biology of the blackmouth catshark, Galeus melastomus (Chondrichthyes: Scyliorhinidae) off the south coast of Portugal. Journal of the Marine Biological Association of the United Kingdom 85: 1173–1183.CrossRefGoogle Scholar
  13. Dulvy, N. K., J. D. Metcalfe, J. Glanville, M. G. Pawson & J. D. Reynolds, 2000. Fishery stability, local extinctions, and shifts in community structure in skates. Conservation Biology 14: 283–293.CrossRefGoogle Scholar
  14. Erzini, K., J. M. S. Gonçalves, L. Bentes, P. G. Lino & J. Ribeiro, 2001. The hake deepwater semi-pelagic (“pedra-bola”) longline fishery in the Algarve (southern Portugal). Fisheries Research 51: 327–336.CrossRefGoogle Scholar
  15. Ford, E., 1921. A contribution to our knowledge of the life-histories of the dogfishes landed at Plymouth. Journal of the Marine Biological Association of the United Kingdom 12: 468–505.CrossRefGoogle Scholar
  16. Gordon, J. D. M., 1999. Management considerations of deep-water shark fisheries. In Shotton, R. S. (ed.), Case Studies of the Management of Elasmobranch Fisheries. FAO, Rome.Google Scholar
  17. Hammond, T. R. & J. R. Ellis, 2005. Bayesian assessment of northeast Atlantic spurdog using a stock production model, with prior for intrinsic population growth rate set by demographic methods. Journal of Northwest Atlantic Fishery Science 35: 299–308.Google Scholar
  18. Hilborn, R. & C. J. Walters, 1992. Quantitative Fisheries Stock Assessment: Choice, Dynamics and Uncertainty. Chapman and Hall, London.Google Scholar
  19. Monteiro, P., A. Araujo, K. Erzini & M. Castro, 2001. Discards of the Algarve (southern Portugal) crustacean trawl fishery. Hydrobiologia 449: 267–277.CrossRefGoogle Scholar
  20. Rey, J., B. Séret, D. Lloris, R. Coelho & L. Gil de Sola, 2006. A new redescription of Galeus atlanticus (Vaillant, 1888) (Chondrichthyes: Scyliorhinidae) based on field marks. Cybium 30(4) (Supplement): 7–14.Google Scholar
  21. StatSoft, 2004. Electronic Statistics Textbook. StatSoft, Tulsa.Google Scholar
  22. Stevens, J. D., R. Bonfil, N. K. Dulvy & P. A. Walker, 2000. The effects of fishing on sharks, rays, and chimaeras (chondrichthyans), and the implications for marine ecosystems. ICES Journal of Marine Science 57: 476–494.CrossRefGoogle Scholar

Copyright information

© Springer Science+Business Media B.V. 2008

Authors and Affiliations

  1. 1.FCMA/CCMARUniversity of the AlgarveFaroPortugal

Personalised recommendations