Reproductive biology and diet of the southern fiddler ray, Trygonorrhina fasciata (Batoidea:Rhinobatidae), an important trawl bycatch species

Abstract

The reproductive cycle of Trygonorrhina fasciata females in south-western Australian waters is shown to include a protracted period of embryonic diapause or delayed development. This characteristic is typically regarded as enabling young to be born when conditions are optimal. The birth of T. fasciata occurs in April/May, when water temperatures are still high and conducive to rapid growth. Furthermore, because gut fullness in this and subsequent months was similar to other times of the year, the prey of neonates, i.e. mysids, carids, pinnotherids, amphipods and isopods, were presumably abundant in that period. Ovulation occurs in April/May and embryos grow rapidly between December and birth in April/May. Females grew to greater lengths than males, i.e. 1460 v. 890 mm, and matured (L50) at larger lengths, i.e. 892 v. 678 mm respectively. As body size increased, teleosts, pilumnid and portunid crabs and molluscs became important dietary components. Overall, the diet consisted predominantly of crustaceans, fish, polychaetes and molluscs, with volumetric contributions of 73.4, 17.2, 5.3 and 2.8% respectively. Dietary composition underwent a cyclical seasonal change and differed among locations, indicating some degree of opportunistic feeding. Interspecific comparisons indicate that benthic food resources are partitioned among and within the main batoid species in south-western Australian waters.