The study, published in the journal Nature Communications, suggests new reforms to the European Union's Common Fisheries Policy (CFP) – which bans the practice of throwing away unwanted fish caught at sea – may have unintended consequences.
The aim of the ban is to improve fish stocks – however the researcher team led by Professor Mike Heath from the University of Strathclyde, Scotland, said this outcome was uncertain.
"Wildlife everywhere capitalises on waste from human activity, and discarded fish are food for a wide range of seabirds, marine mammals, seabed animals and other fish. Therefore, banning discards of fish could have unintended effects on the ecosystem," he said.
"Our results highlight the importance of considering the broader ecosystem consequences of fishery management,” commented Dr Robin Cook, who also worked on the study. “Policy changes to reduce discards affect the food web and, without careful consideration, may dissipate or negate intended benefits.”
The new CFP took effect on 1 January 2014 and will phase out the discarding of fish between 2015 and 2019.
The team developed a computer simulation model of the North Sea marine ecosystem and used it to investigate the effects of changes in the fishing pressure and the proportion of fishery catch which is discarded at sea.
The modelling found that forcing vessels to land fish which are currently discarded could lead to adverse effects on seabirds and marine mammals – and on seabed animals – but without any improvements in fish stocks.
In contrast, changing fishing practices – so that unwanted fish are no longer captured – had dramatic effects in the model which affected the entire food web, with major benefits for birds, mammals, and fish stocks, said the team.
This could be achieved by ‘improved selectivity’, through the use of fishing gear designed to avoid unwanted catches and judicious timing and location of fishing.
Heath and his team said although both approaches to eliminating discarding satisfy the societal demand for reductions in waste of natural resources, the conservation benefits are quite different.
"Inflating landing quotas to accommodate the entire catch is an inadequate solution with few conservation benefits,” said Cook. “On the other hand, the effective reductions in harvest rates resulting from changes in fishing practices to eliminate the capture of unwanted fish can deliver conservation benefits, especially in heavily exploited systems.”
"These ecological effects need to be considered alongside the practical, societal and economic issues in developing a sustainable policy."
Source: Nature Communications
Published online ahead of print, doi: 10.1038/ncomms4893
“Cascading ecological effects of eliminating fishery discards”
Authors: Michael R. Heath, Robin M. Cook, et al