Campana et al. (2009; Mar Ecol Prog Ser 387:241–253) explored the survival of blue sharks (Prionace glauca) captured and released from the North Atlantic commercial longline fishery. We think that their comments and comparisons do not accurately reflect a previous survival study of blue sharks in Hawaii (Moyes et al. 2006; Trans Am Fish Soc 135:1389–1397). The differences in mortality between the studies, ~5% in the Hawaii-based fishery and ~35% in the North Atlantic fishery,
Sharks, turtles, billfish, and marine mammals are frequently caught accidentally in commercial fisheries. Although conservationists and fisheries managers encourage the release of these nontarget species, the long-term outcome of released animals is uncertain. Using blue sharks (Prionace glauca), we developed a model to predict the long-term survival of released animals based on analysis of small blood samples. About 5% of the sharks were landed in obviously poor condition (lethargic and unresponsive to handling); these moribund sharks were sampled and euthanized.
In October 2013, researchers and fishermen from the United States, Europe, South America, Australia, and the Indian Ocean came together to identify reseach priorities for marine mammal bycatch mitigation techniques in longline fisheries.
The workshop covered topics such as time-area closures, as well as several methods under evaluation in different parts of the world for reducing the bycatch and subsequent mortality of odontocetes in longline gear, including acoustic deterrents, weak hooks, and net sleeves. Many questions remain in understanding the efficacy of these mitigation methods, and how practical they may be to the fishing industry.
Seabird bycatch in the tuna and billfish longline fishery in South African waters has had one of the highest seabird bycatch rates in the world. Research was carried out aboard two Japanese longline vessels in the South African EEZ in 2010. Half of the branch lines on each vessel were weighted using the double-weight configuration, which consists of a weighted section that was inserted into the monofilament section of a branch line 2m above the hook. Each vessel also deployed two "hybrid" bird-scaring lines during every set. the lines had a mix of long and short streamers.