Depredation by whales

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Pacific Marine Mammal Bulletin #2

Depredation (removal of fish from fishing gear) by toothed whales is a widespread problem in many oceans of the world. The negative impacts of depredation include economic losses to fishermen, increased pressure on fish stocks, and injury or mortality to whales caused by deterrent methods, entanglement, or accidental hooking.

Depredation in the Northeast Pacific

In Alaska, longline fishers have been faced with significant losses for many years from depredation by killer whales and sperm whales. Here in British Columbia, depredation by killer whales and sperm whales has been observed and appears to be increasing. Fisheries & Oceans Canada (DFO) and fishermen alike are concerned and looking for ways to prevent its expansion. Depredation has been reported by halibut, rockfish, and sablefish longliners, salmon trollers and recreational anglers. While hook and line fisheries appear to be most frequently targeted, other fisheries including pot fishing and trawl, contribute to the problem through release by discarding offal in the presence of whales. Cetaceans are highly intelligent, and once learned, these behaviours are very difficult to extinguish. Fishermen around the world have struggled to find universal solutions to this problem with little success. There is no gear modification, deterrent device or fishing strategy that has proved entirely successful at stopping depredation once established.

Depredation may also impact natural whale foraging behaviour and seasonal movement patterns.

Fishermen, Researchers and Managers Working Together

At the Depredation Workshop in 2006, presentations on current research on the nature of depredation and experiments to avoid or stop depredation were given. Workshop participants explored ideas for new research, strategies to avoid depredation and means of communicating on this issue. A website (http://www.depredation.org) has been established by the Vancouver Aquarium Marine Science Centre to house the workshop results and host a forum where fishers here in B.C. and around the world can learn about depredation, and share their experiences and best practices.

An International Workshop

At an international workshop in 2006 in Vancouver, B.C., fishers, managers and researchers from around the world agreed that the most practical and cost effective way to limit depredation is to prevent it from becoming firmly established and widespread. It is critical that ALL fishers work together and agree to “not feed the whales”, as once these animals are trained to a new food source, the problem will continue to grow.

Report Depredation

Avoiding this problem will take the efforts and cooperation of fishers, researchers and managers. Doing your part to discourage depredation is essential and several suggestions are presented in this bulletin. Sharing information on when, where and how depredation occurs will allow other fishers to avoid problem areas and researchers to understand the problem better with the hope of finding solutions. A confidential reporting email address has been established by DFO at:  marinemammals@dfo-mpo.gc.ca.

Resources and Contacts

Depredation Reports
Vancouver Aquarium Depredation website
BC Commercial Fishing Industry Contacts
Sport Fishing Advisory Board and Sport Fishing Institute
DFO Marine Mammal Incident Response Network
  • Sick, Injured, or Dead Marine Mammals or Sea Turtles:  1-800-465-4336
BC Cetacean & Sea Turtle Sightings Network (to report a sighting)

Depredation: "The removal of fish from gear by whales."

The solution is prevention.

The consequences:

  • Reductions in catch
  • Additional fishing time, fuel, and costs
  • Gear damage and loss
  • Loss of productive fishing grounds
  • Risk to whales from ingested gear and entanglements
  • Loss of whales’ feeding cultures and behaviours

What you can do:

  • Don’t feed whales
  • Don’t discard fish or offal in the presence of whales
  • Don’t set or haul gear when whales are present
  • If hauling groundline gear, drop gear until whales leave
  • Fish in a different area
  • Report all depredation events (confidential)

“It is critical that all fishers work together and agree to “not feed the whales”, otherwise the problem will continue to grow.”

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