抄録
The strawberry conch, Strombus luhuanus, is exploited as a fishery resource during its reproductive season in Japan, and the degree of fishery exploitation might therefore affect the reproductive potential of this species. From May to August in 2003 and 2004, we compared population and reproductive parameters of S. luhuanus, including population density, size frequency, density of egg masses, egg tube length and diameter, and egg size and number, between a highly exploited population in Uranouchi Inlet and a less exploited population around Okinoshima island. Both sites are located along the Pacific coast of Shikoku. Mean shell length of the Uranouchi population was greater than that of the Okinoshima population, and egg tube length and diameter of the Uranouchi population were larger than those of the Okinoshima population, but the density of egg masses was much lower in Uranouchi than at Okinoshima. This suggests that fishery operations can disturb the mating and/or breeding of this species resulting in reduced fecundity of the Uranouchi population. Conchs engaged in reproductive behavior, as well as conch egg masses, were observed more frequently on mixed sediment with sand and pebbles than on uniform sediment composed either of mud, sand, or pebbles. Sediment type might be important for the reproduction of S. luhuanus; but immature conchs were also most abundant on mixed sediment. This type of sediment might, however, be preferred by S. luhuanus irrespective of state of maturity, for other reasons such as ease of burrowing to avoid predation.
