Relationship between soak time and number of enmeshed animals in experimentally lost gill nets |
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Authors: | Seiji Akiyama Eriko Saito Toshihiro Watanabe |
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Institution: | (1) Faculty of Marine Science, Tokyo University of Marine Science and Technology, Konan, Minato, 108-8477 Tokyo, Japan;(2) National Research Institute of Fisheries Engineering, Hasaki, Kamisu, 314-0408 Ibaraki, Japan |
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Abstract: | In order to determine the effects of ghost fishing by lost gill nets, the relationship was examined between soak time and
number of enmeshed animals in experimentally lost gill nets by using diving observations. Two experimental gill nets were
set at 13 m depth in Tateyama Bay, Chiba Prefecture, Japan for approximately 200 days. One gill net was deployed in a small
trough surrounded by artificial reefs, and the other was deployed on an adjacent open sandy bed. Twelve species of crustaceans,
six species of gastropods, and five species of bony fish were enmeshed in the experimental gill nets. The number of enmeshed
animals in the artificial reef gill net was substantially larger than that in the sandy bed gill net. The number of enmeshed
animals in the experimental gill nets increased rapidly within one month after deployment, and then declined gradually showing
fluctuations caused by the decrease in newly enmeshed animals, and the drop off from gill nets caused by the decomposition
of dead animals. The decrease in the number of enmeshed animals was expressed by logarithmic equations, and based on these
equations, the duration of capture function for the lost gill nets was calculated to be 284–561 days in the artificial reef
gill net and 200 days in the sandy bed gill net. The duration of capture function for the lost gill nets for non-commercial
by-catch species such as small crustaceans and gastropods was longer than for commercial species such as Japanese spiny lobster
and bony fish. |
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Keywords: | ghost fishing gill net Japanese spiny lobster lost gear soak time |
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