Temporal and spatial variations in the spawning activity of the micronektonic shrimp,Sergia lucens (hansen) in Suruga Bay,Japan |
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| Authors: | Gretchen H Bishop Makoto Omori Fumio Muranaka |
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| Institution: | (1) Research Laboratory of Fisheries Resources, Tokyo University of Fisheries, 4-5-7, Konan, Minato-ku, 108 Tokyo, Japan;(2) Present address: 12175 Mendenhall Loop Rd., 99801 Juneau, AK, U. S. A.;(3) Shizuoka Prefectural Fisheries Experimental Station, 3690 Kogawashioiri, 425 Yaizu, Shizuoka, Japan |
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| Abstract: | Temporal and spatial variations in the spawning activity ofSergia lucens were investigated in relation to some environmental conditions of Suruga Bay. The daily egg abundance varied considerably with the coefficient of variation from 81% to 269% in July. The spawning activity was most clearly affected by temperature, but the relationship to lunar period and content of chlorophylla were not obvious. Timing of the July spawning is predictable with increase of the surface temperature to 24°C and strong vertical movements of the 18°C isotherm depth; it is also related to modal length of the shrimp in June. It is suggested that intrusion of cold water at 20–50 m affects reproduction of the shrimps and vertical distribution of eggs and larvae. The shrimp population seemed to relate principally to two spawning grounds,i.e. the head part and the western part of the bay. The timing of spawning is not always synchronous throughout the bay. The spawning is sporadic and the distribution of eggs is patchy. This may reflect a recent decrease in the population of the shrimp due to increased fishing pressure.A part of the present paper is based on the thesis submitted by G. H. B. in partial fulfilment of the requirements for her degree of Master of Science at the Tokyo University of Fisheries in 1986. |
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