Unanswered Forum Topics

The ability of acoustic alarms to alert migrating humpback whales (Megaptera novaeangliae) to fishing gear was tested. Two alarms were used, each with a distinct tone. One alarm had a 5 kHz tone (5 s emission interval and 400 ms emission duration), and one had a 2-2.1 kHz swept tone (8 s emission interval and 1.5 s emission duration). The response of the whales in terms of changes to surface behavior and travel direction were investigated. A total of 108 migration tracks were collected using a theodolite. The study was conducted at Cape Solander, Sydney, Australia.

Documented entanglements, long-term population studies and mark-recapture studies were evaluated to determine the impact of cryptic mortality on North Atlantic right whales. Results suggest entangled adults had low initial survival (0.749). Adults that did survive the first year had survival rates similar (0.952) to those animals never entangled (0.961 female and 0.986 male). Juveniles had post entanglement survival rates similar to initial survival rates of entangled adults, 0.733, but lower than un-impacted juveniles (0.978).

Bryde's whale (Balaenoptera edeni) behavior was studied using suction-cup attached tags. Behavior was studied to identify potential mitigation measures that could reduce lethal vessel strikes in the Hauraki Gulf, New Zealand. Tagged whales spent 91% of their time at depths within the maximum draft of vessels. This behavior could increase the potential for vessel strikes. Analysis of vessel transits and whale sightings suggested that re-routing of vessel traffic in the Gulf would not be beneficial because whales are distributed throughout the Gulf.

A spatially and temporally explicit Productivity and Susceptibility Analysis (PSA) was developed to screen cetacean species for bycatch risk. This PSA can be included under Ecosystem Based Fisheries Management (EBFM). The potential risk to harbor porpoises and minke whales from static fishing gear was investigated. Harbor porpoise's had a low to moderate biological risk from bycatch compared to other cetacean species. Minke whales are less productive than harbor porpoise's but also have a low to moderate biological risk to bycatch.

This study provides a summary of methods that can be used to reduce depredation and bycatch of marine mammals in longline fisheries. Methods include 1) spatial management methods, 2) acoustic methods, 3) physical methods and 4) 'other methods'. The results indicate that some methods can be used with both pelagic and demersal longlines, while others can be used with only one or the other. In addition to the methods investigated, the results highlight significant knowledge gaps.These include survivability after hooking and entanglement.