SOME BIOLOGICAL ASPECTS OF MELICERTUS KERATHURUS (FORSKÅL, 1775) (DECAPODA, PENAEIDAE) INHABITING IZM˙ IR˙ BAY (AEGEAN SEA), TURKEY BY GUREL TURKMEN1,2) and HAKAN YILMAZYERLI1) 1) Faculty of Fisheries, Ege University, TR-35100 Bornova-Izmir,˙ Turkey ABSTRACT Some biological aspects of Melicertus kerathurus, a shrimp of high commercial value, were studied in Izmir˙ Bay from April 2004 to December 2004. A seasonal reproduction pattern was observed from April to September with a high percentage of mature females occurring between May and July, when water temperature was relatively high. During the study, a total of 1050 specimens was captured: 612 (58.3%) females and 438 (41.7%) males. The largest female and male were 22.7 cm and 17.0 cm, respectively. The minimum size attained at first maturity was estimated to be 3.9 cm carapace length (CL) and 14.1 cm total length (TL). Sexual differences related to the length-weight relationship were noted. The onset of sexual maturity for females was estimated to be CL50% = 4.6 cm and TL50% = 16.5 cm. RÉSUMÉ Certains aspects biologiques de Melicertus kerathurus, une crevette de forte valeur commerciale ont été étudiés dans la baie d’Izmir˙ d’Avril 2004 à Décembre 2005. Un rythme de reproduction saisonnier a été observé d’Avril à Septembre avec un fort pourcentage de femelles mâtures entre Mai et Juillet, quand la température de l’eau est relativement élevée. Durant l’étude, un total de 1050 spécimens ont été capturés: 612 (58,3%) femelles et 438 (41,7%) mâles. La femelle et le mâle les plus grands mesuraient respectivement 22,7 cm et 17,0 cm. La taille minimum à la maturité a été estimée à 3,9 cm de longueur de carapace (CL) et 14,1 cm de longueur totale (TL). Des différences entre sexe portant sur la relation taille-poids ont été notées. Le début de la maturité sexuelle pour les femelles a été estimé à CL50% = 4,6 cm et TL50% = 16,5 cm. INTRODUCTION Out of 62 shrimp species identified to date in Turkish seas, ten, i.e., Penaeus semisulcatus De Haan, 1844, Melicertus kerathurus (Forskål, 1775), Marsupe- naeus japonicus (Bate, 1888), Metapenaeus monoceros (Fabricius, 1798), Metape- 2) Author for correspondence; Fax: +90.2323883685; e-mail: [email protected] © Koninklijke Brill NV, Leiden, 2006 Crustaceana 79 (5): 583-591 Also available online: www.brill.nl 584 GUREL TURKMEN & HAKAN YILMAZYERLI naeus stebbingi (Nobili, 1904), Parapenaeus longirostris (Lucas, 1846), Trachype- naeus curvirostris (Stimpson, 1860), Melicertus hathor Burkenroad, 1959, Aris- taeomorpha foliacea (Risso, 1827), and Plesionika heterocarpus (Costa, 1871) have been reported to be commercially important for Turkish fisheries (Kocatas et al., 1991; Bayhan et al., 2003). Melicertus kerathurus is found from the south coast of England down the entire eastern Atlantic coastline, as far south as Angola. It is also found throughout the Mediterranean Sea. The species lives in shallow water, marine and estuarine, down to 40 meters, on sandy-mud bottoms (Dore & Frimodt, 1987). In Turkey, this species is distributed in coastal areas of the Mar- mara, Aegean, and Mediterranean seas, and it is commercially one of the most important species in coastal fisheries (Kocatas et al., 1991). This species is fished for all along the above-mentioned sea coasts, because of its large size and excellent taste. It is also a target species for fishermen using trammel nets in Izmir˙ Bay in western Turkey. Studies on the biological aspects of penaeid shrimps in Turkey are scarce. Among these, only three studies (Kumlu et al., 1999; Bayhan et al., 2003; Bayhan et al., 2005) are concerned with their biology, whereas the rest dealt with their systematics. Although the biology and fisheries of M. kerathurus have been studied in other countries (Rodriguez, 1985; Ben Mariem, 1993, 1995, 2004; Lumare & Scordella, 2001; Scordella & Lumare, 2001; N.C.M.R., 2002), there is little basic information on the seasonal trends of reproduction for this species in Izmir˙ Bay (Alpbaz & Hossucu, 1990). Hence, the present investigation was carried out to study some biological aspects dealing with size frequency, length-weight relationship, size at first maturity, and sexual maturity of M. kerathurus inhabiting the Izmir˙ Bay, for one fishing season. MATERIAL AND METHODS During the fishing period of 2004 (April 20-November 20), a fortnightly sampling (n = 70) schedule was followed on board a commercial fishing boat, following the fishermen’s practice. Shrimps were collected on a boat (9 m long and powered with a 25 HP engine), and also obtained from local fishermen, who were using trammel nets with an inner mesh size of 40 mm (polyamide 0.24 mm twine diameter) and an outer mesh size of 220 mm (polyamide 0.50 mm twine diameter). Fishing operations were carried out between 10 and 20 m depth in Izmir˙ Bay (from 38◦2900N26◦4900Eto38◦2700N26◦5200E) where the bottom is covered with sand (fig. 1). During each cruise, surface water temperature and salinity were measured. All sampled individuals were sorted according to sex, weighed to the nearest 0.01 g, measured for their carapace length (CL) from the postorbital margin to.