The bycatch of cetaceans and other protected species in fisheries across continental waters is a current cause for concern. Whether via fixed gillnets, long lines or other fishing methods, they can frequently become entangled in fishing gear suspended from vessels, an undesirable byproduct of commercial fishing that can harm cetacean populations and also potentially foodwebs.
As a frontline issue for both policy makers and the relevant specialist ICES working groups and their members, steps are now being taken to counter the trend, including the fitting of sound-emitting devices to fishing apparatus in order to frighten off incoming marine mammals.
The three-pronged advice document issued today centres around the Data Collection Framework (DCF) and fisheries monitoring schemes, the use and effectiveness of acoustic deterrent devices (also known as pingers), and the proposal of the optimum ways for defining bycatch limits or threshold standards (reference points) that could be worked into Common Fisheries Policy (CFP) management targets. Generally speaking, the advice group took into account all threatened species listed under Annex II of the EU's Habitat Directive.
Advisory Committee (ACOM) Vice-Chair and Chair of the advice drafting group Mark Tasker explained one of the challenges in compiling the data.
"The difficulty is that most of the DCF monitoring is of the fisheries that have the most discards in terms of tonnage of fish, and those are not necessarily the same fisheries that are catching the most cetaceans."
"We've got plenty of sampling from trawl nets, which have the most discards, but you'd particularly need to be looking at things like fixed gill nets and long lines which don't have much discard (because they're designed not to) but do catch cetaceans."
The EU's Data Collection Framework is insufficient as a sole means of sampling, partly because it doesn't satisfactorily cover all fisheries that incidentally catch marine mammals. ICES Member Countries have also been monitoring bycatch under EU Regulation 812/2004, a more cetacean-specific measure. ICES advice is that at present both of these methods are together insufficient and that further observations would be needed in future. ICES recommended that remote electronic video recording is an economic method for future bycatch evaluation.
Tasker continued to explain that the Review Group had examined the specifications of acoustic deterrent devices such as high-frequency transmitting pingers and found that they should be broadened.
"The problem is that the current legislation is somewhat constraining. Let's say we know that a set of frequencies and characteristics of pingers work, but probably that's just part of a much bigger picture of what works. It might be that something else works better. So our advice really is try not to constrain – and the best way to do that is really to set some sort of a goal to reduce bycatch by X amount. So it's an objective rather than a prescription."
"The essence of the final advice is based around where you should set bycatch limits. Now, many people might say you don't want any bycatch of cetaceans at all, but more or less if you put a net in the water then, at some point, you're going to catch something. It's where you put the play off between the two, and that is a societal choice."
Harbour porpoisem, one of the species covered in the advice, in Sognefjord, Norway; © Florian Granar