Casting the net for cetacean bycatch solutions

Rob Deaville

ZSL's cetacean strandings expert, Rob Deaville, summarises our scientific event on cetacean bycatch. 

Bycatch can be defined as ‘the incidental capture of non-target species during fishing activity’. It affects many species globally, including fish, sea birds, pinnipeds and of course cetaceans. On Tuesday 10 April, we held our ZSL Science and Conservation event ‘Cetacean bycatch: casting the net for solutions’ to try to look in more detail at this issue.

George Eustice, MP and Minister of State for Agriculture, Fisheries and Food at Defra opened the meeting with a video message, reiterating the government’s support for efforts to reduce the impact of cetacean bycatch within UK fisheries. 

Dr Paul Jepson from ZSL began the evening’s presentations by discussing the work of the UK Cetacean Strandings Investigation Programme, which is coordinated by ZSL. Since the inception of the CSIP in 1990, bycatch/entanglement has been a consistent finding every year and is the single most common cause of mortality we have found during post-mortem investigation of UK strandings (n=718, data 1990-2015).

Cases of diagnosed bycatch were most prevalent in southwest England, particularly in Cornwall, as evidenced by collaborations with our partners in this region, the Cornwall Wildlife Trust Marine Strandings Network and the University of Exeter.  Bycatch was also a particularly common finding in short-beaked common dolphins (n=301 or 46% of examined animals) and in harbour porpoises (n=360, or 17% of examined animals) (data 1990-2015).  Paul also demonstrated that the pathology of these cases, illustrates the significant welfare implications of bycatch as a cause of death. Paul concluded by indicating that small, isolated populations of cetaceans are those at most risk of serious conservation impacts from bycatch. In the UK, this would include inshore populations of bottlenose dolphins (such as those in Cornwall) and the west coast community of killer whales in Scotland, which now only numbers eight individuals.

Sarah Dolman from Whale and Dolphin Conservation then moved onto the issue of entanglement in large whales, opening her presentation with the sobering line that ‘entanglement is the single most significant marine mammal welfare issue of our time’. Sarah began with the example of the North Atlantic right whale, which is one of the most endangered species of whale on the planet. Since the impacts of commercial whaling decimated this species over the previous two centuries, significant conservation efforts helped increase the estimated population size to around 500 individuals by 2011.

Entangled minke whale

However, an increase in mortality over recent years, partly associated with increased entanglement in creel fisheries in the Bay of Fundy, has lead to a population decline, with around 400 individuals now thought to remain. The species now faces a perilous future, with some predictions of potential extinction by 2040.

Sarah discussed both acute and chronic cases of entanglement and highlighted the significant welfare issue of the latter, with some chronic entanglements lasting months or longer, leading to debilitating impacts on the individual whales and eventual death in many instances. Sarah also discussed entanglements in the UK, where both acute and chronic cases have been documented. She then finished by discussing the policy relevance of this issue, current research to mitigate entanglement and the significant efforts made globally to disentangle whales.

Dr Simon Northridge from the Sea Mammal Research Unit and the University of St. Andrews closed the meeting by discussing the work of the UK bycatch observer scheme coordinated by SMRU and how this helps inform efforts to determine the potential scale of bycatch across the UK fleet. Simon also discussed how they work with fishermen, to try to mitigate the impact of bycatch and the current focus on the use of acoustic deterrent devices (ADDs or pingers as they are also known).

Pingers have proved successful in mitigating bycatch in a number of species in some regions and have proved a useful addition to the ‘toolbox’ of options to address this issue. Our existing toolbox of options is still relatively limited however and further ones need to be researched and developed.

Monofilament netmarks on harbour porpoise

Simon also began and closed his presentation with discussion of another international example of a cetacean species endangered as a result of bycatch impact. The critically endangered vaquita is a small porpoise species endemic to the northern Gulf of California, which has been severely impacted by bycatch as a result of the illegal fishery for the totoaba, whose swim bladders are highly valued in the traditional Chinese medicine industry. Last-ditch efforts to save the few remaining vaquita failed last year and there are now thought to be less than 20 individuals left. It seems likely that the vaquita may soon become extinct and this would follow on from the loss of the baiji, which was declared functionally extinct in 2006, again in large part due to the impacts of bycatch.

A panel discussion took place at the end of the meeting, with the three speakers and Catherine Bell from Defra fielding questions from the audience.  

In conclusion, bycatch is a difficult and complex issue to address. But it’s only through collaboration between fishermen and industry, researchers and the wider public that we can address and hopefully reduce the impact of this globally significant issue, which has serious welfare implications and is the cause of major conservation impacts in some species and regions.

Learn more about the Cetacean Strandings Investigation Programme (CSIP)

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