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Marine Ecology Progress Series

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MEPS 418:179-188 (2010)  -  DOI:

Impacts of shifts in spawning seasonality and size at maturation on the population growth of mantis shrimp in Tokyo Bay

Mifuyu Nakajima1,2,3,*, Keita Kodama1, Toshihiro Horiguchi1, Yoshinari Tanaka1, Hiroaki Shiraishi1

1Research Center for Environmental Risk, National Institute for Environmental Studies, Japan, 16-2 Onogawa, Tsukuba-City, Ibaraki 305-8506, Japan
2Department of Zoology, University of Hawaii, 2538 McCarthy Mall, Edmondson 152 Honolulu, Hawaii 96822, USA
3Present address: Department of Biology, Stanford University, Stanford, California 94305, USA

ABSTRACT: The spawning season of mantis shrimp Oratosquilla oratoria (Stomatopoda) in Tokyo Bay has changed from being unimodal (spring only) to bimodal (spring and summer).This shift in the pattern of spawning arose because reproductive maturation began to occur in smaller females, which presumably spawn in summer, and because the proportion of smaller mature females increased. Currently, recruitment appears to depend entirely on the summer cohort because of significantly lower juvenile survival in the spring cohort. In this study, we propose that the new summer spawning period and spawning by smaller-bodied individuals have supported the population. Our size- and age-structured mathematical model of O. oratoria population dynamics indicated that the number of eggs spawned in spring is lower than that in summer, and 98% of the annual recruitment is currently derived from summer spawning. The model also suggested that smaller-bodied spawners provided 84% of total recruitment and that if the proportion of smaller-bodied mature females had not increased, the population would have shown a larger decline than was observed. In reality, the stock size of O. oratoria has become extremely low, damaging the local fishery. Based on our model predictions, an efficient solution for population recovery is to reduce the mortality of small, unsalable individuals, which are currently fished and discarded.

KEY WORDS: Discarding · Life history · Oratosquilla oratoria · Recruitment · Seasonal survival · Settlement inhibition · Stomatopoda · Structured-population model

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Cite this article as: Nakajima M, Kodama K, Horiguchi T, Tanaka Y, Shiraishi H (2010) Impacts of shifts in spawning seasonality and size at maturation on the population growth of mantis shrimp in Tokyo Bay. Mar Ecol Prog Ser 418:179-188.

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