Is marine animal entanglement in Scottish waters really a problem?

As I work my way around the coast interviewing fishermen about their experiences, knowledge and perceptions of marine animal entanglements, some have questioned just how big a problem this might be. While a few fishermen have told me that they have experienced several animals caught in their gear over the years others have referred to this as a ‘once in a generation’ occurrence. But many fishermen have never witnessed an entanglement or the consequences of these events, which can make it difficult to understand why the Scottish Entanglement Alliance (SEA) exists.

Scottish inshore waters are inhabited by an array of resident and visiting large marine animals including over 20 species of cetacean (whales, dolphins and porpoise) as well as basking sharks, seals and turtles. These waters also provide world-class fishing grounds for creel fishermen targeting a variety of shellfish species year-round. Associated with this industry as much as 25, 000km of rope is deployed in inshore waters at any one time (Northridge 2010), and on occasion these animals come in to contact with this and subsequently become entangled.

Since 1992 SEA partner the Scottish Marine Animal Stranding Scheme (SMASS) has performed almost 3000 necropsies to establish cause of death of marine animals found stranded around the Scottish coast. Overall, entanglements has been diagnosed as the cause of death in less than 2% of these cases, and for some species e.g. harbour porpoise and bottlenose dolphins, entanglement does not seem to pose a threat. However for Mysticetes (baleen whales including minke and humpback whales) entanglement accounts for 46% of known deaths in Scottish waters. For basking sharks and turtles, 100% of known human-caused deaths have been the result of entanglement.

Cause of death diagnosed in Mysticetes in Scottish waters since 1992 (left), and anthropogenic (human-induced) causes of death in marine animals (right). SMASS 2018

 

Minke whales

SMASS has diagnosed entanglement as the cause of death in 29 minke whales that have washed ashore around the Scottish coast in recent years, and this species accounts for 87% of entangled cetaceans reported.

Locations of minke whales reported to SMASS that have died as a result of entanglement in fishing gear.

From these reports, it is known that minke whales suffer both acute entanglements (71% of reported cases) where the animal drowns quickly as a result of becoming caught in gear, and chronic entanglements (21% of reported cases) where the animal remains entangled in ropes and/or netting for a prolonged period of time. Chronic entanglements can cause serious injuries and as such represent a significant welfare concern.

Chronic entanglement – this young male minke whale discovered on the west coast of Scotland suffered a debilitating chronic entanglement which resulted in deep tissue lacerations and a fractured jaw. This animal died of starvation and sepsis approximately six months after first becoming entangled.

Acute entanglement – A female minke whale discovered by divers off Shetland entangled around the jaw. This animal likely drowned very quickly. Entanglements can also have an economic impact, for example the fishing gear this animal became caught in was potentially not recoverable, meaning the owner of this has lost not just this gear but also any catch associated with this.

Humpback whales

Since 2012 British Divers Marine Life Rescue (BDMLR), another SEA partner which has the only trained disentanglement response team in Europe, have been involved in the successful disentanglement of five humpback whales. A further three humpbacks are known to have died as a result of entanglement within the same period. Though when compared to minke whales fewer humpback entanglements have been reported in Scottish seas, a recent study conducted by Ryan et al (2016) to calculate the probability of humpback whale entanglement in our inshore waters suggests that as a source of mortality, entanglement of humpback whales in static fishing gear in this area may be occurring at a rate that is an order of magnitude higher than sustainable levels for this species. Therefore Scottish waters may be acting as a mortality sink (where deaths exceed births) for this species in the North East Atlantic.

An 8.9m 7000kg female humpback whale that died on the east coast of Scotland in 2015 as a result of a chronic debilitating entanglement and an acute second entanglement in actively fished gear. This animal was discovered alive but drowned before it could be rescued. This animal was reported to BDMLR’s large whale disentanglement team by the fisherman whose gear it was caught in. He provided invaluable information and support to the team during the rescue attempt and subsequent recovery of the animal for necropsy.

Mitigating entanglements

In order to better understand and ultimately mitigate marine animal entanglements in fishing gear, meaningful engagement with the Scottish inshore fishing fleet is essential. So far I have conducted approximately 65 anonymous interviews with creel fishermen and gained a unique insight into this issue and the potential solutions to it. Many fishermen have offered advice and ideas on how they think this problem could be addressed, and are already taking measures to reduce the risk of animals becoming caught in their gear. Fishermen are not deliberately entangling large marine animals, instead they are disentangling them, working hard to keep the marine environment clean, and providing important data on species distributions and populations by recording and reporting their wildlife sightings. For example many ensure that their ropes are adjusted appropriately for the depths they are fishing in, and/or using leaded or negatively buoyant rope to minimise the amount of excess rope floating in the water column. Many regularly maintain and replace their gear and do their very best to retrieve gear that has been displaced due to rough weather or other fishing boats. Others report their marine animal sightings using the WhaleTrack app, designed by our partner the Hebridean Whale and Dolphin Trust (HWDT) and delay deploying their fishing gear when they see large marine animals in their fishing grounds. I have also met several fishermen who participate in the ‘Fishing for Litter’ scheme (www.fishingforlitter.org.uk) and many others who conduct their own regular derelict gear and litter collections.

In addition fishermen have also been sharing their experiences of rescuing live animals that they have discovered caught in their fishing gear. During these incidents their skills and expertise in boat handling and rope work, and their knowledge of their gear and local seascape have proved vital in ensuring that they, their boat, crew and gear are safe and the animal in question is released unharmed. Receiving this sort of extremely useful information from the fishing community is a major strength of this SEA project and we welcome detailed accounts of other successful releases at sea. As the SEA project progresses, fishermen will be invited to participate in training and knowledge exchange workshops in photographing live entangled marine animals and sampling those that have been discovered dead. This will enable SEA partners to build our knowledge of how animals become entangled, assist in future rescue attempts and gear recovery, and improve our ability to assess the impacts of other threats including chemical pollutants, disease, plastic waste and underwater noise. These events will also provide a platform for fisherman-led discussions and exchange of ideas on what potential approaches could be taken to minimise the risk of entanglements occurring which are practical, flexible, and do not interfere with or disrupt fishing activity.

If you are a creel fisherman and would be willing to participate in a short anonymous interview, or you have any stories or ideas relating to marine animal entanglement please contact Ellie MacLennan (SEA project co-ordinator) at entanglement@sac.co.uk or on 07393 798153. Any information shared will be treated sensitively, positively and confidentially.

 

References

  • Ryan, C., Leaper, R., Evans, P.G.H., Dyke, K., Robinson, K.P., Haskins, G.N., Calderan, S., van Geel, N., Harries, O., Froud, K., Brownlow, A. and Jack, A. (2016). Entanglement: an emerging threat to humpback whales in Scottish waters. Report to the Scientific Committee of the International Whaling Commission, SC/66b/HIM/01, 1-12.
  • Northridge, S, Cargill, A, Coram, A, Mandleberg, L, Calderan, S. and Reid, B. (2010). Entanglement of minke whales in Scottish waters; an investigation into occurrence, causes and mitigation. Final Report to Scottish Government CR/2007/49. 57pp.

 

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