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Depredation mitigation projectEffect of catch depredation on longline fisheries Since the late 1980s, many major commercial fisheries have experienced ever declining profits, due to (i) declining fish stocks (caused principally by over fishing), (ii) greater management restrictions (caused by the need to manage the finite resource) and (iii) increased operational costs (mainly fuel and crew). In addition, some fisheries have found themselves in competition with other marine predators, such as Odontocetes, which include small toothed whales, dolphins and porpoises. Odontocetes may depredate caught fish from fishing gear because (i) the caught fish are a part of their natural diet, (ii) they have learned to opportunistically or habitually target this easily obtainable food source, or (iii) their natural prey species have been reduced by commercial fishing activities, forcing them to switch to alternative food items. Depredation is particularly prevalent to longline fisheries, where recent anecdotal reports suggest that catch value is regularly reduced when depredating odontocetes (i) deter target fish from taking baited hooks, (ii) completely remove caught fish, or (iii) cause damage to caught fish that renders them unsalable. These events appear to have become widespread and are now rated as a matter of principal economic concern among the global longline fishing community.
Effect of by-catch on depredating Odontocetes The activity of catch depredation from longline gear may also have negative impacts on the Odontocetes involved, at an individual or population level. In addition, the welfare of depredating individuals is at stake, especially if they accidentally ingest a hook. Such events may, in the short term, result in the individuals drowning, or, in the long term, result in individuals dieing from infections or starvation caused by internal injuries (if they break away, or are cut loose by the crew of the vessel). The extent of the impact that these events have on the conservation of Odontocete populations or species is difficult to determine, due to the paucity of information on their breeding and foraging ecology and population structure, and the level of mortalities sustained. Despite the perception by many fishers that Odontocetes are responsible for significant losses of target fish, other marine predators (i.e. sharks) and scavengers (i.e. small pelagic fish and squid) may also be responsible for reducing the number of fish caught on longlines. Nonetheless, Odontocetes are conspicuous (mainly because they are large and spend periods of time at the surface), which may have biased the perception of some fishers, who believe that Odontocetes are the main cause of catch loss and damage.
Finding a solution Given the impact that depredation has on the longline fisheries involved and that by-catch has on the Odontocetes involved, there is a need to search for effective ways to mitigate the interaction. Derek Hamer is a marine biologist at the Australian Marine Mammal Centre (AMMC) who has extensive experience in assisting fisheries to mitigate operational interactions with marine mammals. Derek heads up this project and will work closely with affected pelagic longline fisheries in the Australian and Indo-Pacific regions to develop mitigation options to address this problem. To date, considerable effort has been directed toward the use of acoustic deterrents. However, few formal studies have confirmed their effectiveness and anecdotal resports suggest there are unresolved problems relating to effective practical application. In contrast, physical deterrence has received much less attention. Recently, a physical depredation mitigation device (PDMD), known as the Cachalotera, was shown to significantly reduce sperm whale and killer whale depredation in a South American demersal longline fishery, while another PDMD was used with some success to reduce bottlenose depredation in a US troll fishery. These two examples offer insights and hope that a similar approach may assist in mitigating Odontocete depredation in pelagic longline fisheries. The aim of this project is to indentify, develop and test a suite of PDMDs through rigorous sea trials, that will (i) mitigate Odnotocete by-catch and (ii) mitigate fish catch depredation, while (ii) having no effect on fish catch rate. During the course of developing the PDMDs, additional criteria will be considered, including durability, cost and efficient operational integration. The advice of key stakeholders, especially those from within the fishing community, will be sought regulalry throughout the life of the project.
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 (August 2010) 7. Update: PDMD Tank Trials (December 2010) 8. Update: Gearing Up for Sea Trials (March 2011) 9. Update: First gear trial completed in Coral Sea (September 2011) 10. Update: Second gear trial completed in Fijian waters (available soon)
Project supporters Fisheries agencies Australian Fisheries Management Authority (AFMA) Conservation agencies Worldwide Fund for Nature (WWF)
Related reports and journal publications Hamer, D.J., Childerhouse, S.J., Gales, N.J., 2010. Mitigating operational interactions between odontocetes and the longline fishing industry: a preliminary review of the problem and of potential solutions. Report to the International Whaling Commission (IWC) Scientific Committee, Report no. SC/62/BC3. 30pp. (An updated draft has been submitted to a peer reviewed journal and hopefully will be accepted for publication soon). |
 
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