Putative fishery-induced changes in biomass and population size structures of demersal deep-sea fishes in ICES Sub-area VII, Northeast Atlantic Ocean
- 1Oceanlab, University of Aberdeen, Newburgh, Aberdeenshire AB41 6AA, UK
- 2National Oceanography Centre, Southampton, University of Southampton, Waterfront Campus, European Way, SO14 3ZH, UK
- 3Institute of Biodiversity, Animal Health and Comparative Medicine, University of Glasgow, Graham Kerr Building, Glasgow G12 8QQ, UK
- 4Government of South Georgia and the South Sandwich Islands, Government House, Port Stanley, Falkland Islands, FlQQ 1ZZ, UK
- 5Scottish Marine Institute, Scottish Association for Marine Science, Oban PA37 1QA, UK
- 6Faculty of Earth Science and Environmental Management, University of Wroclaw, pl. Uniwersytecki 1, 50-137 Wroclaw, Poland
Abstract. A time series from 1977–1989 and 2000–2002 of scientific trawl surveys in the Porcupine Seabight and adjacent abyssal plain of the NE Atlantic was analysed to assess changes in demersal fish biomass and length frequency. These two periods coincide with the onset of the commercial deep-water fishery in the late 1970s and the onset of the regulation of the fishery in the early 2000's, which allowed us to investigate changes in the relationship between total demersal fish biomass and depth between the pre- and post commercial fishing periods, as well as changes in the biomass (kg km−2) depth distribution and length frequency distribution of the most dominant fish species. Our results show a decline in total demersal fish biomass of 36% within the depth range of the commercial fishery (< 1500 m). Whilst there were significant declines in target (e.g. Coryphaenoides rupestris decreased by 57%) and non-target (e.g. C. guentheri and Antimora rostrata) species, not all species declined significantly. Changes in the overall length-frequency distribution were detected for 5 out of the 8 dominant species occupying depth ranges both within and outside the maximum depth for commercial trawling. This suggests that whilst there is evidence for likely fishery impacts on the biomass distribution of the demersal fish population as a whole, species-specific impacts are highly variable. It is clear that changes in population structure can extend beyond the depth at which fishing takes place, highlighting the importance for also considering the indirect effects on deep-sea fish populations.