Fisheries 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 of whales caused by deterrent methods, entanglement, or accidental hooking. Because it provides an additional food supply, depredation also has the potential to cause whale populations to increase beyond their natural carrying capacity, and/or for previously-existing behaviours related to hunting or seasonal movements to be lost.
In 2002, a workshop in Samoa produced a report entitled Interactions between Cetaceans and Longline Fisheries, which focuses on the South Pacific and contains background papers on specific fisheries affected by depredation. The report provides general recommendations regarding possible methods for reducing depredation, improving data collection, identifying whale species involved in depredation, and increasing the awareness of depredation among governmental and non-governmental agencies.
Symposium Objectives The 2006 symposium focused on depredation by killer and sperm whales, and built on progress made in Samoa. Its objectives were:
A) to broaden understanding of :
· cues and behaviours whales use to locate gear and remove fish · variability of depredation behaviours within and between species · spread of depredation between groups of whales · extent of losses resulting from depredation · implications of depredation for fisheries management
B) to produce specific guidelines for the fishing industry and fisheries management agencies on:
· how fishing operations can be modified to reduce or eliminate depredation · preventing depredation from spreading to new or existing fisheries experiencing no depredation at this time
The first part of the symposium consisted of presentations focused on:
· aspects of natural behaviour and social organisation of killer and sperm whales, with emphasis on populations involved in depredation · case-history examples of killer and sperm whale depredation with special emphasis on the behaviour of the whales involved and associated changes in their social structure, ecology, or demography · impacts of depredation on the fishing industry · methods of passive deterrence, including modification of fishing behaviours, timing, and /or gear · methods of active deterrence · examples of successful measures used to reduce human conflict with species other than cetaceans.
The second part of the meeting was comprised of in-depth, workshop-style group discussions focused on reducing the extent of the problem where it currently exists, limiting its spread to other fisheries and other regions, and producing guidelines for fishermen and fisheries managers affected by killer and sperm whale depredation.