The biological characteristics of Scorpis aequipinnis (Kyphosidae), including relevant comparisons with those of other species and particularly of a heavily exploited congener

Abstract

This study has determined the biological characteristics of Scorpis aequipinnis on the south coast of Western Australia. It thus supplements the limited amount of data for members of the widely distributed and speciose Kyphosidae, which contains species that make an important contribution to certain ecosystems and local commercial and recreational fisheries and have considerable aquaculture potential. S. aequipinnis was aged using the number of annuli in sectioned otoliths and its growth described using the Schnute growth equation. This species attains a greater maximum fork length (FL), i.e. 477 vs. 330mm, and greater maximum age, i.e. 68 vs. 54years, than S. lineolatus on the eastern Australian coast, where its stock has apparently experienced excessive exploitation. S. aequipinnis thus exhibits characteristics that would make it particularly susceptible to over-fishing should fishing effort on the south coast increase as anticipated. S. aequipinnis and S. lineolatus exhibit similar and very rapid growth initially, reaching 90% of their asymptotic fork lengths (FL∞) at 14-16 and 12years, respectively, and then grow only slightly for much of the remainder of their extensive life spans. The FL50s at maturity for female and male S. aequipinnis (363 and 379mm, respectively) and for both sexes of S. lineolatus combined (172mm) were each far greater than would be expected given their respective FL∞s. There have thus been strong selection pressures for the attainment by both species of a relatively large size prior to maturation. The main spawning period of S. aequipinnis, which occurs between late autumn and mid-winter when water temperatures are declining rapidly, and those of other recreational and commercial species on the south coast of Western Australia vary markedly, thereby reducing the potential for inter-specific competition for resources by their larvae and juveniles. The estimate of fishing mortality for male S. aequipinnis was greater than expected, possibly reflecting a combination of site fidelity and the localisation of commercial fishing.