The latest report calculated that the best estimate is that between 1400 and 1700 porpoises were bycaught in UK fishing nets in 2014 [Northridge et al. 2015]. Previous analyses have suggested that porpoise bycatch rates may have increased slightly since 2010. There is not enough data to break this UK wider figure down into more meaningful sub-population figures.
276 common dolphins were estimated to be bycaught in set net fisheries and 417 seals (mainly grey seals) in tangle and trammel net fisheries in 2014.
The UK government invests considerable effort into monitoring the UK fishing fleet to understand the extent of bycatch (accidental capture) of porpoises, dolphins, whales and seals. The Sea Mammal Research Unit (SMRU) conduct the marine mammal bycatch monitoring and they also collect data on bycatch of seabirds (including fulmar and guillemot) and various elasmobranchs (including rare sharks and skates). There are a considerable number of caveats in the data (including that not enough monitoring occurs to be confident of the results). However, it is the best estimate that exists.
The use of pingers continues to reduce porpoise bycatch in nets up to 4 km, and compliance in pinger use has improved. Of course pingers introduce noise into the marine environment, and so are not without potential impacts themselves to noise sensitive species like porpoises – but perhaps they are the lesser of two evils in this case. Effective alternatives include implementing area or seasonal closures where fisheries overlap with bycatch concentrations.
Whilst pingers are successful at reducing porpoise bycatch where they are required, there are a number of limitations to their use, in addition to the noise generated, including their application to only a small section of the fleet and larger vessels. It is not known if pingers reduce dolphin or seal bycatch. WDC would like to see the UK government move towards other more reliable mitigation measures.
More detailed data are urgently required to be collected in logbooks and in landings data. The UK fleet is mostly made up of small vessels, yet currently small vessels have few obligations to report, which means we do not know what fishing is occurring where, let alone what marine species are being accidentally caught in nets. We need the support of fishermen to undertake this task.
Sampling observations were focused in the English Channel and Celtic Sea, with some effort in the static Irish Sea fisheries and long lines off Northwest Scotland. Sampling over a wider area and of more gear will be required to address uncertainties in bycatch in other regions.
The analysis conducted demonstrated that the future monitoring programme needs to be fit for purpose and the current EU Data Collection Framework (DCF) alone is not adequate to assess direct fisheries impacts on marine mammals.
Finally, these bycatch rates are only for UK boats and do not include non-UK boats fishing in UK waters. So better international collaboration is urgently required for adequate monitoring and effective mitigation – better quality data on bycatch rates and fishing effort from more fisheries is required from all EU Member Countries before any assessment can be refined and conclusions drawn as to the overall bycatch of harbour porpoise and other marine species in the North Sea, and elsewhere.
However action to reduce bycatch towards zero should not wait until such data are gathered.