Entanglement

The extent of cetacean entanglement and bycatch in fishing gear and lines in BC waters is not well understood.  Entanglement usually refers to animals becoming tangled in gear and towing it along with them, while bycatch usually refers to the unintentional capture of small cetaceans in fishing nets.  Worldwide, entanglement/bycatch in fisheries operations poses a major risk for 86% of the world’s toothed whales, according to the Convention on the Conservation of Migratory Species of Wild Animals (UNEP/CMS).  Baleen whales are greatly impacted as well.

THE PROBLEM:

Bycatch: Bycatch is the primary threat for 62 of the 71 extant species of toothed cetaceans in the world and is increasing. Various forms of fishing gear such as gillnets, driftnets, traps, weirs, purse-seine nets, long-lines, trawls and others were implicated with causing entanglement that may lead to suffocation and death of whales, dolphins and porpoises. Globally, over 300,000 small cetaceans die each year due to entanglement in fishing gear (WWF 2011).  Several species are at risk of extinction due to bycatch, including the vaquita in the Gulf of Mexico and Maui’s dolphins in New Zealand.

Possible below-surface scenario of a humpback whale entangled around it’s pecotral fins.

Sea turtles are also significantly affected by bycatch.  Between 1990 and 2008, ~85,000 sea turtles were reported caught in global fisheries.  Unfortunately, due to low observer coverage and reporting (<1% of all fisheries) this number grossly under-represents true levels of turtle bycatch (Wallace et al 2010).

Sea turtle caught up in fishing gear.

In BC, harbour porpoises are probably the most affected small cetacean.  In 2002, Anna Hall and colleagues estimated that approximately 80 harbour porpoises died in the South Coast salmon gillnet fishery the year before (Hall et al 2002) .  Of the confirmed cases of porpoise bycatch, almost half were released alive.  Between 1996 and 2006, the Pacific trawl fishery reported catching cetaceans in 14 incidents.  This bycatch included Pacific white-sided dolphins, common dolphins, and unidentified dolphin and porpoise species (Living Oceans 2009).

Entanglement: With a large and mostly uninhabited coastline, many entangled animals likely go undetected or unreported; therefore understanding the scope of the problem is difficult.  However, even considering the small likelihood of detection, 54 reports of entanglements of cetacean species have been received by the BC Marine Mammal Response Network since 2008 (Spaven 2012 pers comm).  Humpback whales have been the mostly commonly reported species entangled in BC, though many other species are likely affected as well.

Entangled whale “Canuck” in the Strait of Georgia during the summer of 2011. The whale lice that can be seen as beige patches behind the dorsal fin is evidence of poor health. This whale was never successfully disentangled.

Entanglement can happen with a variety of gear, such as crab and prawn traps and gillnets. The majority of entanglements involve line wrapped through the animals’ mouth, around their pectoral flippers, or around the tail peduncle (stock) or flukes.  While entanglement can cause drowning right away, entanglement can also cause long-term impairment and a slow decline in body condition.  Long term entanglements can affect the animal’s ability to properly feed or swim and the line can cut into the animal’s body, causing infection or deformation.

Humpback whale locally known as “Twister” entangled in prawn traps through the mouth. (Photo Doug Sandilands)

Entanglement response in BC is coordinated by the BC Marine Mammal Response Network, a program of Fisheries and Oceans Canada.  Due to the remote nature of most of the coast, mounting a quick response can be very difficult; however where a quick response has been initiated there has been success. In the summer of 2011, two humpback whales were successfully disentangled by professionals off the coast of BC (one on the central coast and one on the west side of Vancouver Island), and a third entangled humpback was reported in the Strait of Georgia but disentanglement attempts have not yet been successful.  More notoriously, one whale, nick-named ‘Twister’ (BCY0710) was entangled and successfully released twice in less than three weeks in 2009!  Both times the entangling gear on Twister was prawn pots.  Disentangling whales can be very dangerous and should ONLY be attempted by trained and authorized professionals.

In other parts of North America, the issue of cetacean entanglement is better understood.  Dr. Jon Lien, a scientist at Memorial University in Newfoundland, first disentangled a whale in 1976 and brought light to the issue in Newfoundland.  Between 1979 and 2008, 1,209 large whale entanglements were recorded in Newfoundland and Labrador, mostly humpback whales (80%) and minke whales (15%). The fisheries implicated in these entanglements have shifted from primarily cod prior to the early ‘90s to the offshore snow crab fishery ( Benjamins et al 2011).  This program, the Whale Release and Stranding Network, continues operations in Newfoundland and Labrador today and also works directly with fishermen to find solutions to the problem.

Diagram of an entangled humpback whale. Removing visible gear at the surface is not a good idea. Usually, there is extensive gear below the surface, and removing it reduces the likelihood of authorities re-spotting the whale to disentangle it. (Provincetown Centre for Coastal Studies)

Further south in U.S. waters, the Center for Coastal Studies in Provincetown, Massachusetts works cooperatively with other US agencies to locate and disentangle whales that have been caught in fishing gear. The Center for Coastal Studies has become a world leader in whale disentanglement, developing specialized equipment and techniques to ensure disentanglements are as safe as possible for both whales and humans. Over 90 whales have been freed from their gear using these methods. The Center for Coastal Studies has also undertaken studies trying to determine the scope and scale of entanglement.  A study done by Center researcher Dr. Jooke Robbins showed that over 90% of humpback whale entanglements go undetected or unreported.  She investigated the true level of entanglement by not only looking at animals that had obvious gear on them, but by also looking at characteristic scarring on humpbacks (Robbins 2009).

THE SOLUTION:

The best course of action for the public that finds an entangled whale is to contact authorities at 1800 465 4336 and to monitor the position of the whale at a distance so that the experts will be able to locate the distressed animal. Fisheries and Oceans Canada has a disentanglement team that specializes in whale disentanglements. The Vancouver Aquarium’s Cetacean Research Lab, Cetus Research and Conservation Society and Strawberry Isle Research are important partners in the efforts to reduce entanglements.

Changes to gear and timing of fisheries may also greatly reduce the bycatch of small cetaceans.  The World Wildlife Fund hosts a Smart Gear competition  each year to encourage new innovations in fishing gear to reduce this problem.

To reduce the amount of entanglements, further research is required to fully understand where and when most whales encounter fishing gear, as well as what gear-type is commonly involved.  Once this is better understood, working with the fishing industry to reduce this threat is paramount. Reporting incidents of entanglement and bycatch by the fishing industry and the public will help greatly in obtaining the necessary knowledge. 

WHAT YOU CAN DO:

-In BC, to report an entanglement for any marine mammal or sea turtle, call BC Marine Mammal Response Network hotline 1-800-465-4336, which operates 24 hours a day.

-Remain with the animal. If a disentanglement effort is to be successful we must know where the animal is located.

-Do not attempt to disentangle the whale yourself.

-Help reduce the amount of debris and abandoned fishing gear in BC waters by participating in the annual Great Canadian Shoreline Clean-up.

-Choose seafood from sustainable fisheries with minimal bycatch. The Vancouver Aquarium’s Ocean Wise program marks ocean-friendly options at restaurants and supermarkets. Learn more about Ocean Wise here.

REFERENCES:

Cassoff R.M., Moore K.M., McLellan W.A., Barco S.G., Rotstein, D.S., Moore, M.J. (2011).  Lethal entanglement in baleen whales. Dis Aquat Org 96:175-185 (link)

Benjamins, S., Ledwell, W, Huntington, J, & Davidson, A.R. (2011).  Assessing changes in numbers and distribution of large whale entanglements in Newfoundland and Labrador, Canada. Marine Mammal Science, 00(00): 1–23 (link)

Wallace, B.P., Lewison, R.L., McDonald, S.L., McDonald, R.K., Kot, C.Y., Kelez, S., Bjorkland, R.K., Finkbeiner, E,M., Helmbrecht,S., & Crowder, L.B. (2010).  Global patterns of marine turtle bycatch.  Conservation Letters 3(3): 1-12 (link)

Robbins, J. (2009).  Scar based inference into Gulf of Maine humpback whale entanglement: 2003-2006. Report to the National Marine Fisheries Service.  Order No. EA133F04SE0998. 34pp. (link)

Driscoll, J., Rob, C., and Bodtker, K. (2009).  Bycatch in Canada’s Pacific Groundfish Bottom Trawl Fishery: Trends and Ecosystem Perspectives. A Report by Living Oceans Society. (link)

Hall, A., Ellis, G., Trites, A.W. (2002).  Harbour Porpoise Interactions with the 2001 Selective Salmon Fisheries in Southern British Columbia and License Holder Reported Small Cetacean By-Catch. Selective Salmon Fisheries Science Program Report. Fisheries and Oceans Canada
Centre for Coastal Studies
Marine Education and Researc Society Entanglement Research
cetaceanbycatch.org