Influence of selectivity of sampling gears on an estimation of the population structure of shirauo, Salangichthys microdon
1994
Miura, M. (Tohoku Univ., Sendai (Japan). Faculty of Agriculture) | Omori, M. | Okata, A.
In studies on the structure of fish population, it is necessary to collect suitable samples which represent the real structure of the natural fish population. Owing to the selectivity of sampling gears, there often appears a great lacuna between the size composition of sampled fish and that of natural fish. The object of this report is to make clear the influence of the selectivity of sampling gears on the size composition of shirauo, Salangichthys microdon, as well as to examine the suitability of a method of estimation for the natural fish size composition in the fishery ground of Lake Ogawara. In Lake Ogawara, Shirauo is mainly caught by seine net. The net is composed of mesh which is suitable to catch commercial-sized fish. It is not available for sampling larvae. Therefore, in this study, shirauo larvae were sampled during their hatching period by the use of larva nets. By way of the factors affecting the size composition of fish caught by seine net and larva net, the authors assumed the following three: the mesh size selection of the seine net, the escape of fish from the larva net owing to an over-flow caused by clogged mesh, and the difference in the fish size composition due to the vertical distribution patterns of the fish. In the present study, we compared the size composition of shirauo sampled by seine net and larva net. In order to estimate the selection rate made by both the seine net and larva nets, sampling was done by the use of two gears: the seine net covered by fine mesh net over the cod-end and the multiple layer sampling larva net. Thus we concluded that the problem of size selection can be pretty well solved by the combination of gears which have different characteristics
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