Putative fishery-induced changes in biomass and population size structures of demersal deep-sea fishes in ICES Sub-area VII, Northeast Atlantic Ocean

J A Godbold,M A Collins,D M Bailey,W A Spallek,J D M Gordon,I G Priede

doi:10.5194/bg-10-529-2013

J A Godbold, M A Collins + Show 4 more

Open Access

https://doi.org/10.5194/bg-10-529-2013

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Abstract

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.

Highlights

Humans have used the oceans over millennia and significant technological advances allow exploitation of fisheries’ resources, hydrocarbons and minerals below a depth of 2000 m (Ramirez-Llodra et al, 2011)
The results show a significant decline in total demersal fish biomass with depth in both periods
At 1000 m, within the depth zone of the commercial fishery, the results show that total biomass decreased from 1126 kg km−2 in the early period to 727 kg km−2 in the late period

Summary

Introduction

Humans have used the oceans over millennia and significant technological advances allow exploitation of fisheries’ resources, hydrocarbons and minerals below a depth of 2000 m (Ramirez-Llodra et al, 2011). The environmental impacts of human activities on the deep-sea benthos are of increasing concern; of these, trawling appears to be the most significant, certainly in terms of the area affected. Godbold et al.: Putative fishery-induced changes in biomass and population size structures only impact the target (and non-target) fish species, and affect the abundance and diversity of the benthic epi- and infauna Godbold et al.: Putative fishery-induced changes in biomass and population size structures only impact the target (and non-target) fish species, and affect the abundance and diversity of the benthic epi- and infauna (e.g. Koslow et al, 2000; Gage et al, 2005; Clark and Koslow, 2007), which can have knock-on effects on the food web and for the functioning of the ecosystem (Watling and Norse, 1998; Hinz et al, 2009)

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