Phenotypic changes in reproductive traits with changes in stock size of the starspotted smooth-hound Mustelus manazo in
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ORIGINAL ARTICLE
Biology
Phenotypic changes in reproductive traits with changes in stock size of the starspotted smooth-hound Mustelus manazo in Tokyo Bay, Japan Jeong-Chae Park • Masaaki Oyama • Jeong-Hoon Lee Keita Kodama • Yasuhiko Ohta • Atsuko Yamaguchi • Hiroaki Shiraishi • Toshihiro Horiguchi
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Received: 23 September 2012 / Accepted: 27 November 2012 / Published online: 19 December 2012 Ó The Japanese Society of Fisheries Science 2012
Abstract Reproductive traits are among the primary determinants of population dynamics, and their changes could affect stock size. We investigated differences in reproductive traits of the starspotted smooth-hound Mustelus manazo in Tokyo Bay between the 1990s (a lowstock period) and the 2000s (a high-stock period). Peak timings of mating (May–July), ovulation (May–June), and parturition (May–June) were similar between the two periods. However, the size at first maturity in the 2000s was smaller than that in the 1990s for both sexes. In addition, embryo-related parameters differed greatly between the two periods. Slopes of size–fecundity regression in the 2000s decreased to 43–73 % of the 1990–1996
J.-C. Park The United Graduate School of Veterinary Science, Yamaguchi University, Yoshida, Yamaguchi 753-8511, Japan J.-C. Park M. Oyama J.-H. Lee K. Kodama H. Shiraishi T. Horiguchi (&) Center for Environmental Risk Research, National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba, Ibaraki 305-8506, Japan e-mail: [email protected] Present Address: J.-H. Lee Southeast Sea Fisheries Research Institute, National Fisheries Research and Development Institute, Tongyeong, Gyeongnam 650-943, Korea Y. Ohta Laboratory of Experimental Animals, Department of Veterinary Medicine, Faculty of Agriculture, Tottori University, Koyama, Tottori 680-8553, Japan A. Yamaguchi Faculty of Fisheries, Nagasaki University, Nagasaki, Nagasaki 852-8521, Japan
values, suggesting a substantial decline in fecundity during the 2000s. Frequency distribution of the maximum ovum diameter during the ovulation season showed two distinct two modes in 1990s while it showed a substantial dispersion during the 2000s, implying that changes occurred in the developmental pattern of ova in the ovary. Undeveloped eggs were present in the uteri with low frequency from September to May during the 2000s, but they were totally absent from September through May in the 1990s. The increased number of remnant undeveloped eggs that did not become embryos may explain the fecundity decline during the 2000s. Keywords Density dependence Elasmobranch Embryo Fecundity Mustelus manazo Phenotypic plasticity Reproduction Tokyo Bay
Introduction The stock size and species composition of biotic communities in marine ecosystems usually show large fluctuations [1, 2]. In Tokyo Bay, substantial changes in the stock size of megabenthic species have been observed during the last three decades [2], with the stock size of small to mid-sized dominant species increasing until the mid-1980s and then decreasing in th
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