Bycatch Rates (bycatch + rate)

Distribution by Scientific Domains

Selected Abstracts

Characterizing seabird bycatch in the eastern Australian tuna and billfish pelagic longline fishery in relation to temporal, spatial and biological influences

Rowan Trebilco
Abstract 1.Seabirds killed incidentally in Australia's eastern tuna and billfish (ETBF) longline fishery between September 2001 and June 2006 were examined to evaluate species composition and to relate, where possible, capture events to operational and environmental factors. 2.During this period 2.129 million hooks on 2202 shots were observed, and 369 birds were reported killed. The majority (78%) of these were flesh-footed shearwaters (Puffinus carniepes), 53% of which were male and 44% female. Smaller numbers of medium to large sized albatrosses (Diomedeidae, predominantly female) and other shearwaters (Puffinus spp.) and petrels (Pterodroma spp.) dominated the remainder of the bycatch. 3.Of the 369 birds reported taken as bycatch, 280 were available for necropsy, and species identifications performed in situ by observers were assessed. While observer identifications were generally correct for common species, performance was poor for less common ones. 4.The geographical location (latitude) of shots, season, time of day at which shots were set, and bait type and life status (dead or alive) influenced the seabird bycatch rate. The majority of captures (87% overall) occurred between 30 and 35S, with bycatch being lowest in winter, and remaining at similar levels across the other seasons. 5.The use of live fish bait was generally associated with increased captures of both seabirds overall, and flesh-footed shearwaters in particular. Copyright 2010 John Wiley & Sons, Ltd. [source]

Global patterns of marine turtle bycatch

Bryan P. Wallace
Abstract Fisheries bycatch is a primary driver of population declines in several species of marine megafauna (e.g., elasmobranchs, mammals, seabirds, turtles). Characterizing the global bycatch seascape using data on bycatch rates across fisheries is essential for highlighting conservation priorities. We compiled a comprehensive database of reported data on marine turtle bycatch in gillnet, longline, and trawl fisheries worldwide from 1990 to 2008. The total reported global marine turtle bycatch was ,85,000 turtles, but due to the small percentage of fishing effort observed and reported (typically <1% of total fleets), and to a global lack of bycatch information from small-scale fisheries, this likely underestimates the true total by at least two orders of magnitude. Our synthesis also highlights an apparently universal pattern across fishing gears and regions where high bycatch rates were associated with low observed effort, which emphasizes the need for strategic bycatch data collection and reporting. This study provides the first global perspective of fisheries bycatch for marine turtles and highlights region,gear combinations that warrant urgent conservation action (e.g., gillnets, longlines, and trawls in the Mediterranean Sea and eastern Pacific Ocean) and region,gear combinations in need of enhanced observation and reporting efforts (e.g., eastern Indian Ocean gillnets, West African trawls). [source]

Reducing seabird bycatch in longline, trawl and gillnet fisheries

Leigh S. Bull
Abstract With an increasing number of seabird species, particularly albatross and petrels, becoming threatened, a reduction of fishery impacts on these species is essential for their future survival. Here, mitigation methods to reduce and avoid seabird bycatch are assessed in terms of their ability to reduce bycatch rates and their economic viability for longline, trawl and gillnet fisheries worldwide. Factors influencing the appropriateness and effectiveness of a mitigation device include the fishery, vessel, location, seabird assemblage present and season of year. As yet, there is no single magic solution to reduce or eliminate seabird bycatch across all fisheries: a combination of measures is required, and even within a fishery there is likely to be refinement of techniques by individual vessels in order to maximize their effectiveness at reducing seabird bycatch. In longline demersal and pelagic fisheries, a minimum requirement of line weighting that achieves hook sink rates minimizing seabird bycatch rates should be tailored with a combination of strategic offal and discard management, bird-scaring lines (BSLs) and night-setting, particulary in Southern Hemisphere fisheries. Urgent investigation is needed into more effective measures at reducing seabird interactions with trawl nets and gill nets. In trawl fisheries, a combination of offal and discard management, the banning of net monitoring cables, paired BSLs, and a reduction in the time the net is on or near the surface are likely to be the most effective in reducing seabird interactions with the warp cables and net. Few seabird bycatch reduction methods have been developed for gillnet fisheries, although increasing the visibility of the net has been shown to reduce seabird bycatch. Further studies are required to determine the efficacy of this technique and its influence on target species catch rates. [source]


Jay Barlow
Abstract A controlled experiment was carried out in 1996,1997 to determine whether acoustic deterrent devices (pingers) reduce marine mammal bycatch in the California drift gill net fishery for swordfish and sharks. Using Fisher's exact test, bycatch rates with pingers were significantly less for all cetacean species combined (P < 0.001) and for all pinniped species combined (P= 0.003). For species tested separately with this test, bycatch reduction was statistically significant for short-beaked common dolphins (P= 0.001) and California sea lions (P= 0.02). Bycatch reduction is not statistically significant for the other species tested separately, but sample sizes and statistical power were low, and bycatch rates were lower in pingered nets for six of the eight other cetacean and pinniped species. A log-linear model relating the mean rate of entanglement to the number of pingers deployed was fit to the data for three groups: short-beaked common dolphins, other cetaceans, and pinnipeds. For a net with 40 pingers, the models predict approximately a 12-fold decrease in entanglement for short-beaked common dolphins, a 4-fold decrease for other cetaceans, and a 3-fold decrease for pinnipeds. No other variables were found that could explain this effect. The pinger experiment ended when regulations were enacted to make pingers mandatory in this fishery. [source]