| Project/Area Number |
59560178
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
General fisheries
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| Research Institution | University of Tokyo |
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Principal Investigator |
TANIUCHI Toru Lecturer, Faculty of Agriculture, University of Tokyo, 農学部, 講師 (00012021)
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| Project Period (FY) |
1984 – 1986
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| Project Status |
Completed (Fiscal Year 1986)
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| Budget Amount *help |
¥2,500,000 (Direct Cost: ¥2,500,000)
Fiscal Year 1986: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 1985: ¥800,000 (Direct Cost: ¥800,000)
Fiscal Year 1984: ¥1,200,000 (Direct Cost: ¥1,200,000)
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| Keywords | Age / Growth / Reproduction / Food habits / Geographical variation / Choshi / Squalidae / 繁殖 |
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| Research Abstract |
Specimens of Squalus mitsukurii were collected from Choshi, the Ogasawara Islands, Masseiba, and Hancock Seamounts to reveal age, growth, reproduction and food habits. Age determination was undertaken using the 2nd dorsal fin. As a result differences in growth parameters were observed. Similarly, size and age at maturity differed greatly by regions. Clasper lengths and testis weights showed a rapid increase with the onset of maturity. Litter size and the number of large ova per female increased with the size of the parent and showed a large difference among regions. However, this species seemed to possess an united reproductive strategy since the difference arose from differences in the size at maturity. Stomach content analysis revealed that this species was piscivorous. Prey species were different by regions.
Three species of small Aqualoids sharks were investigated to elucidate some aspects of reproduction and food habits. Females showed predominance over males in the size at maturity and the maximum size. The number of large ova per female appeared to indicate true litter size rather than apparent litter size. It is conjectured that these species showed no well defined reproductive cycle. The three species indicated high percentage occurrence of empty stomachs. Ratios of stomach content weight to total weight were usually less than 3 %. Important diets were squids and fishes.
Two species of scyliorhinid sharks were collected from Choshi to study reproduction and food habits. Both species showed little differences in the size at maturity and the maximum length. A well defined reproductive cycle was not found. Analysis of diet compositions showed overlapping in higher category of food but the two species seemed to avoid competition for prey by changing percentage occurrence and feeding on different prey species.
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