Size at Sexual Maturity and the Reproductive Biology of Two Species of Scyllarid Lobster from New South Wales and Victoria, Australia

SIZE AT SEXUAL MATURITY AND THE REPRODUCTIVE BIOLOGY OF TWO SPECIES OF SCYLLARID LOBSTER FROM NEW SOUTH WALES AND VICTORIA, AUSTRALIA

J. STEWART1), S. J. KENNELLY1) and O. HOEGH-GULDBERG2) 1) New South Wales Fisheries Research Institute, P.O. Box 21, Cronulla, NSW 2230, Australia 2) School of Biological Sciences A08, University of Sydney, NSW 2006, Australia

ABSTRACT

Various aspects of the reproductive biology of the Australian scyllarid lobsters Ibacus peronii and Ibacus sp. were studied for the first time. Sizes at physiological and physical maturity were estimated for males and females of each species and we provide the first documented observations of their reproductive anatomy, mating, oviposition and hatching. Size at physiological maturity was determined via histological examination of ovaries and testes and by identifying the smallest ovigerous females captured in the field. This was estimated (±95% confidence intervals) as 50.4 mm±0.7 mm carapace length (C.L.) for female I. peronii from Coffs Harbour and 50.2 mm± 0.4 mm C.L. for female I. peronii from Lakes Entrance. Male I. peronii and Ibacus sp. were estimated to be physiologically mature when as small as 38.5 mm and 47.4 mm C.L., respectively. All female Ibacus sp. sampled in the study were found to be immature. Size at physical maturity was estimated by examining changes in the relative growth rates of various body parts and, for female I. peronii, was estimated as 54.9 mm±4.0 mm C.L. from Coffs Harbour and 56.6 mm±3.1 mm C.L. from Lakes Entrance. For male I. peronii, size at physical maturity may be approximately 55 mm C.L. The results are discussed in terms of the similarity of these species' reproductive biology with other species of scyllarid and palinurid lobsters, and the consequences of their sizes at sexual maturity for setting a minimum legal size for the fishery of these species.

RÉSUMÉ

Divers aspects de la reproduction des scyllares australiens Ibacus peronii et Ibacus sp. ont été étudiés pour la premièrie fois. Les tailles à la maturité physique et physiologique ont été évaluées pour les mâles et pour les femelles de chaque espèce, et nous fournissons les premières observations documentées sur l'anatomie de la reproduction, l'accouplement, l'oviposition et l'éclosion. La taille à la maturité physiologique a été déterminée par l'examen histologique des ovaires et des testicules et par l'identification des plus petites femelles ovigères capturées. Ceci a été estimé (±95% d'intervalles de confiance) à 50,4 mm±0,7 mm de longuer de carapace (C.L.) pour Ibacus peronii femelle de Coffs Harbour et à 50,2 mm± 0,4 mm pour celle de Lakes Entrance. Les mâles d'I. peronii et d'Ibacus sp. ont été estimés physiologiquement mûrs à partir de 38,5 mm et de 47,4 mm C.L. respectivement. Toutes les femelles d'Ibacus sp. échantillonnées pendant l'étude ont été trouvées immatures. La taille à la maturité physique a été estimée par l'examen des 345 changements dans les taux de croissance relative de différentes parties du corps et, pour I. peronii femelle, a été évaluée à 54,9 mm± 4,0 mm C.L. pour Coffs Harbour et 56,6 mm±3,1 mm C.L. pour Lakes Entrance. Pour I. peronii mâle, la taille à la maturité physique peut être d'environ 55 mm C.L. Les résultats ont été discutés en termes de similarité de la biologie reproductive de ces espèces avec celle d'autres scyllarides et palinurides, avec les conséquences de leurs tailles à la maturité sexuelle pour la fixation d'un minimum de taille légal pour leur pêche.

INTRODUCTION

Ibacus peronii Leach, 1815 and Ibacus sp. are commercially important scyllarid lobsters occurring off the east coast of Australia (George & Griffin, 1972). Also referred to as "bugs," "shovelnosed lobsters," "flapjacks" and "sand lobsters," these two species are landed as by-catch from prawn and fish trawling and are marketed as "Balmain Bugs." I. peronii and Ibacus sp. are morphologically similar and have only recently been identified as different species. There is also some overlap in their distributions: I. peronii are found predominantly in rela- tively shallow inshore waters (less than 80 m deep) from northern New South Wales around the south of the continent to Western Australia; and Ibacus sp. are found predominantly in mid-shelf waters (from 50 to 150 m deep) from northern New South Wales to southern Queensland (Kailola et al., 1993). Little is known about the biology of scyllarid lobsters and studies of their reproductive biology are limited to a few commercially important species. Fecundities and spawning seasons have been described for the Mediterranean Locust Lob- ster, Scyllarides latus (Latreille, 1803) (cf. Martins, 1985), and the Slipper Lob- ster, Scyllarides nodifer (Stimpson, 18f 6) from the northeastern Gulf of Mexico (Lyons, 1970; Hardwick & Cline, 1990). In Australia, the reproductive anatomy, fecundity and size at first maturity of the Moreton Bay Bug, Thenus orientalis (Lund, 1793) has been well documented (Kniepp, 1974; Hossain, 1978a, b, 1979; Branford, 1980; Jones, 1988). However, despite the importance of the fisheries for Ibacus spp. in New South Wales and Victoria, there have been no published studies on any aspects of their reproductive biology. Along the east coast of Australia, Ibacus spp. historically have been considered as an incidental by-catch when fishing for more lucrative species such as prawns. However, the recent combination of an expanding market, increased consumer awareness and higher prices has resulted in fishers specifically targeting these animals. This increase in fishing effort, and claims by fishers that the total catch and average size of Ibacus spp. have both decreased, has led to concerns that stocks are over-exploited and calls for improved fishery management. The only management regulation that protects Ibacus spp. in New South Wales or Victoria is that females carrying eggs may not be landed in New South Wales. The