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- About Bycatch
The Consortium for Wildlife Bycatch Reduction conducts research to understand the nature of interactions between endangered non-target species and fishing operations.
Short-finned Pilot Whales and False Killer Whales
Duke University scientists have been working with longline fishermen within the Cape Hatteras Special Research Area (CHSRA) to study pilot whale (Globicephala spp.) interactions with the longline fishery. Their initial findings were that short-finned pilot whales (Globicephala macrorhynchus) are the main species that interact with longline vessels during the fall season, that interactions within this fishery occur frequently and most often occur during the evening through the early morning, and that there is substantial depredation of tuna (target species) by pilot whales.
Researchers at Duke are currently trying to quantify the extent of pilot whale depredation on tuna off North Carolina and to determine the proportion of the population that engages in depredation. They are examining the relative importance of tuna in the diet of pilot whales in the CHSRA using stable isotope analysis.
Both short-finned pilot whales and false killer whales (Pseudorca crassidens) can be hooked by pelagic longline gear. Researchers at Duke University and the University of North Carolina are assessing the "hook pulling" jaw strength of pilot whales and false killer whales to provide biological guidance for "whale-safe" hooks by understanding the thresholds of hook bending capacity of the jaws of these odontocetes. The target bending threshold strength is determined by the minimum required to retain the target catch. Owing to the large disparity in weight between an average or large-bodied target fish (e.g. yellowfin tuna) and that of pilot or killer whales, reducing hook strength to this threshold should result in retention of target catch while mouth-hooked whales should be able to pull on the hook, straighten it, and de-hook themselves.
Bottlenose dolphins (Tursiops truncatus) are known to remove captured fish (depredate) from gillnets set for Spanish mackerel in North Carolina; this behavior increases the dolphins' risk of entanglement. Danielle Waples, at Duke University, conducted a field evaluation of SaveWave acoustic deterrent devices on these gillnets. She recorded interactions between dolphins and Spanish mackerel gillnets equipped with the devices and found that dolphins were less likely to approach or interact with nets that had active SaveWave devices, but their presence did not eliminate interactions completely. She also found that dolphins were echolocating more when active SaveWave devices were present. This may mean that the dolphins used echolocation to invistigate the nets with SaveWave devices, which may improve their ability to detect and avoid the nets.
Loggerhead Sea Turtles
Bottom-set gillnet fisheries that target flounder in the Pamlico Sound, North Carolina are responsible for incidentally taking juvenile sea turtles during the fall months. This is especially problematic given that it is the State's most valuable finfish fishery. The Division of Marine Fisheries has employed a variety of management tools to address this problem including: closed areas, mandatory permits, reporting and observer coverage, gear restrictions, net attendance, goals for reduced strandings, and incidental take limits. In 2002, the National Marine Fisheries Service was forced to permanently close the deepwater portion of the fishery due to sea turtle takes. Shallow water areas remain open, with portions closed seasonally when takes exceed certain levels.
Catherine McClellan, while at Duke University, tracked loggerhead sea turtles, Caretta caretta, using satellite telemetry to determine how their movements interacted with the inshore large-mesh gillnet fishery. In Pamlico Sound, loggerheads spent 64 to 70 percent of their time in the deep water areas that are closed to gillnet fishing.