Since the late 1980s, many commercial fisheries around the world have been faced with dwindling profit margins, due largely to increased fishing effort (due to declining fish stocks) and increased operational costs (i.e. fuel). Commercial whaling was banned at about the same time, in 1986, and some whale populations appear to have undergone population recovery. Consequently, there are now a growing number of reports that some of the smaller toothed species of whale and dolphin (Odontoceti) are opportunistically depredating from fishing gear. In particular, pelagic longline fishers consider depredation to be a major economic threat to their enterprises, because they remove and damage many of the fish they catch and may also scare others away from the hooks. This situation is now of central concern to longline fisheries generally and its occurrence has stimulated growing interest in the fishing, fisheries management and research communities.

Catch depredation may also have an adverse impact on the conservation of the species of toothed whale involved. Some individuals may accidentally ingest a hook, which may lead to internal injuries and infections that lead to starvation and eventual death. Other individuals may not be able to reach the surface if they become hooked or entangled and thus suffer a more immediate death. Given the paucity of literature available on the status, breeding and foraging biology of many toothed whale species and the difficulty in collecting these data and data on by-catch mortality rates, it is difficult to determine the impact these operational interactions may have on the conservation of the species involved. Despite the perception by many fishers that toothed whales are responsible for significant losses, other marine predators (i.e. sharks) and scavengers (i.e. small pelagic fish) may be responsible for reducing the number of fish landed by some vessels or fisheries. Nonetheless, toothed whales receive the brunt of the frustration of the fisheries affected, because they spend a considerable amount of time at the surface and are more conspicuous.

Given that catch depredation is likely to have negative impacts for both pelagic longline fisheries and the toothed whale species involved, there is a need to search for effective measures to mitigate the interaction. Derek Hamer joined the Australian Marine Mammal Centre (AMMC) in late 2009 as Project Coordinator: Marine Mammal – Fishery Interactions and his main focus is to assist surface longline fisheries in the Australian and Indo-Pacific regions to develop mitigation options to reduce catch depredation.

It is hoped that a solution can be found that is applicable to all pelagic longline fisheries, regardless of their peculiarities. To date, considerable effort and funding has been directed at describing where and how the problem occurs, with little effort dedicated to assessing potential tools for mitigating it. Acoustic deterrent and detection devices (ADDs) are one option that has been explored in recent times, but the results have been ambiguous at best, especially over longer time periods. In contrast, a physical depredation mitigation device (PDMD) known as the Cachalotera has proven very successful in reducing sperm whale and killer whale depredation in a South American demersal longline fishery. A PDMD has also been used with some success to reduce bottlenose depredation in a US troll fishery. We at the AMMC are confident that the principal of PDMDs may also offer solutions for pelagic longline fisheries.

The underpinning aim is to identify the most plausible suite of PDMDs, then test them through rigorous experimental trials to ensure they (i) reduce catch depredation by toothed whales and (ii) have minimal impact on catch rates. Although challenging, the chances of success will be increased by drawing upon the experience and knowledge of a diverse range of stakeholders such as fishing industry participants, researchers, conservationists and fishing gear technologists. Over the next few years, key stakeholders will become part of a working group that will provide advice, disseminate information and facilitate experimental trials. It is hoped that the AMMC, in cooperation with the working group, pelagic longline fisheries and other stakeholders, will bring about reductions in catch depredation by and mortality of toothed whales, through the development of an effective PDMD.

Below are a number of links to literature related to this project, including (i) specific project updates and (ii) peer reviewed publications.

PROJECT UPDATES:

1. Update: Project Background and Objectives (October 2009)

2. Update: Description of Problem and Possible Solutions (December 2009)

3. Update: Project Spreads to South Pacific (February 2010)

4. Update: Formation of Working Group (May 2010)

5. Update: Kobe II Bycatch Workshop (July 2010)

6. Update: PDMD Progress (July 2010)

RELATED REPORTS AND JOURNAL PUBLICATIONS:

Mitigating operational interactions between odontocetes and the longline fishing industry: a preliminary global review of the problem and of potential solutions

This paper has been formally presented at the 2010 IWC Scientific Committee meeting and at the 2010 Kobe II Bycatch Workshop. It is in draft form and is provided as a preliminary reference on the topic. The intention is to submit it to a peer reviewed journal in the near future for eventual publication. As such, constructive comments aimed at improving it are keenly welcomed. Please contact the lead author (derek.hamer@aad.gov.au).

Last updated: 15 July 2010.