Interspecific differences in the distribution of adult and juvenile ponyfish (Leiognathidae) in the Gulf of Carpentaria, Australia

Abstract

The distribution of leiognathids was investigated at 261 sites spread throughout the Gulf of Carpentaria. Eight species, Gazza minuta, Leiognathus decorus, L. equulus, L. fasciatus, L. leuciscus, L. smithursti, L. splendens and Secutor ruconius, were usually restricted to coastal areas, whereas four species, L. bindus, L. moretoniensis, Leiognathus sp. and S. insidiator, were not. Two other species, L. aureus and L. elongatus, were caught at only one site each. The relationships between size of fish and depth in Albatross Bay were investigated by examining the mean weight and minimum and maximum lengths of different species in 356 trawls. Six of the coastal species showed the common pattern of linear increase in size with depth. This pattern is consistent with the existence of estuarine and/or inshore nursery areas, and supports previous observations of these species. In contrast, three of the widespread species exhibited approximately quadratic relationships between size and depth. This unusual pattern resulted from small fish living in both the shallow inshore areas and deeper offshore areas, and it may reduce competition among the juveniles of the large number of very abundant, coexisting species of leiognathid.