GROWTH OF THE DEEP-WATER MUD SHRIMP MELANTHO DE MAN, 1907 (, , SOLENOCERIDAE) IN KAGOSHIMA BAY, SOUTHERN JAPAN

BY

JUN OHTOMI and SHINYA IRIEDA Faculty of Fisheries, Kagoshima University, Shimoarata 4-50-20, Kagoshima 890, Japan

ABSTRACT

The deep-water mud shrimp Solenocera melantho is commercially important as the main target species for small-scale trawlers in Kagoshima Bay, southern Japan. A total of 4,837 specimens were collected from the central area of the bay from January 1993 to June 1994. Length frequency analysis was used to examine the growth and longevity of S. melantho. Both males and females were first recruited in winter with modal sizes of around 15 mm carapace length. Growth was best described by the Pauly & Gaschütz growth equation as Lt = 33.09{1 - exp[-0.857(t/12 + 0.525) - (0.538/2π) sin(2π (t/12 - 0.404))]} for males and Lt = 45.76{1- exp[-0.777(t/12 + 0.401) - (0.452/2π) sin(2π (t/12 - 0.583))]} for females, where Lt is carapace length (mm) at age t (months). Females grow faster and reach larger sizes earlier than males of the same age group. Growth rates and the occurrence of soft-shelled individuals in both sexes were highest between winter and spring, and lowest during the spawning season between summer and early winter (June to December). The longevity of both malc and female S. melantho was estimated to be around 37 months. The allometric relationship between body weight and carapace length was represented by sig- nificantly different equations between sexes.

RÉSUMÉ

Le Pénéide d'eau profonde Solenocera melantho est commercialement important comme prin- cipal objectif de pêche pour les petits chalutiers de la baie de Kagoshima, Japon méridional. Un total de 4837 spécimens a été recueilli dans la partie centrale de la baie de janvier 1993 à juin 1994. L'analyse de fréquence des longueurs a été utilisée pour examiner la croissance et la longévité de l'espèce. Des mâles et des femelles ont d'abord été recrutés en hiver avec des tailles modales de 15 mm environ de longueur de carapace. La croissance a été mieux décrite par l'équation de Pauly & Gaschütz, comme Lt 33,09{1-exp[-0,857(t/12+0,525) - (0,538/2π) sin(2π(t/12-0,404))]} pour les mâles et Lt =45,76{1-exp[-0,777(t/12+0,401) - (0,452/2π) sin(2π (t/12-0,583))]} pour les femelles, où Lt est la longueur de la carapace (mm) à l'âge de t (mois). Les femelles croissent plus rapidement et atteignent de plus grandes tailles que les mâles du même groupe d'âge. Les taux de croissance et le nombre d'individus des deux sexes à carapace molle étaient plus élevés entre l'hiver et le printemps, et plus faibles pendant la saison de ponte entre l'été et le 46 début de l'hiver (juin à décembre). La longévité des mâles et des femelles de S. melantho a été évaluée à 37 mois environ. La relation allométrique entre le poids du corps et la longueur de la carapace était représentée par des équations présentant des différences significatives entre les sexes.

INTRODUCTION

Many species of the family Solenoceridae inhabit muddy bottoms on the edge of the continental shelf or the upper continental slope (Hayashi, 1992). The biology of several solenocerid species has been studied: Solenocera crassicornis (H. Milne Edwards, 1837) by Cheung (1963); S. membranacea (Risso, 1816) by Heegaard (1966, 1967, 1972) and Froglia & Gramitto (1981, 1987); S. prominen- tis Kubo, 1949 by Chalayondeja & Tanoue (1971); Pleoticus robustus (Smith, 1885) by Anderson & Lindner (1971; as r.); Haliporoides sibo- gae (De Man, 1907) by Baelde (1992, 1994). The deep-water mud shrimp Solenocera melantho De Man, 1907 is widely distributed in the Indo-Pacific region including the Pacific coast of southern Japan at depths of 150 to 400 m (De Man, 1907; Kubo, 1949; Toriyama & Hayashi, 1982; Crosnier, 1985, 1989). In Kagoshima Bay, S. melantho, as well as Plesionika semilaevis Bate, 1888 (Pandalidae), is one of the most dominant species in the benthic community, especially in the central area of the bay and is also commercially important as the main target species for small-scale trawlers (Ohtomi & Hayashi, 1995). More than 70 years ago, Urita (1921) reported the occurrence of what he thought to be S. distincta De Haan, 1849 in Kagoshima Bay, but which seems to be the same species as the one treated here. Chalayondeja & Tanoue (1971) studied the fisheries biology of this species in Kagoshima Bay under the name of S. prominentis which at present is considered a junior synonym of S. melantho (cf. Baba et al., 1986). However, they rarely captured individuals smaller than 15 mm in carapace length and could not obtain the proper successive length fre- quency distributions (figs. 9, 10 in Chalayondeja & Tanoue, 1971). Consequently they were unable to estimate the growth parameters. Although biological infor- mation such as growth parameters are required for appropriate stock management of this commercially important species, biological aspects of S. melantho have not been sufficiently examined yet. The main purpose of this paper is to describe the growth patterns of the S. melantho population in Kagoshima Bay by measuring a large number of spec- imens collected over 18 months. The relationship between body weight and carapace length was also examined.