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Unaccounted mortality and overview of the Hawaiian Kona crab Ranina ranina (Linnaeus) fishery
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2020
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Source: Fisheries Research, 226, 105517
Details:
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Journal Title:Fisheries Research
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Description:Injuries sustained by Kona crabs Ranina ranina Linnaeus through tangle-nets were quantified during 17 fishing trips on 4 of the Main Hawaiian Islands: Oahu, Hawaii, Maui, and Niihau. Of the 1160 crabs assessed by onboard observers, 30 % were damaged via the fishing process, either through predation of crabs stuck to the tangle-nets or disentanglement by the fishermen. Effects of the most common injuries on crab mortality were then evaluated during a laboratory experiment. Aquaria were used to hold damaged crabs along with undamaged controls to compare the resulting mortalities during two rounds of experiments. The loss of one or more dactyli resulted in 0–8.7 % mortality; one limb pulled off resulted in 62.5 % mortality; one limb cut cleanly off resulted in 8.3 % mortality; and crabs kept out of water under the sun for two hours resulted in 16.7 % mortality. The demonstrated care in aquarium husbandry underscores that estimated mortality rates are potentially very sensitive to aquarium setup, explaining differences between similar studies. Additionally, predation on crabs stuck to the tangle-nets and on those sinking back to the sea floor after release were monitored via small high definition cameras. Post-release mortality was calculated by multiplying the number of injuries observed in the field by the corresponding mortality rate from the lab. Unaccounted mortality, the combined rates of post-release mortality and total predation, was calculated at 10.9 % for the Hawaiian Kona crab fishery. Using the ratio of landed and released crabs this results in the deaths of an additional 38.9 % of landed crabs. However, when catch rates are high, care in handling crabs is compromised, therefore unaccounted mortality is likely a minimum estimate.
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Source:Fisheries Research, 226, 105517
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ISSN:0165-7836
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Rights Information:Accepted Manuscript
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Compliance:Library
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