Population genetics of selected whitebait species : Galaxias maculatus (Jenyns) and Lovettia sealii (Johnston).

Population Genetics of Selected Whitebait Species: Galaxias maculatus (Jenyns) and Lovettia sealii (Johnston). Populations of diadromous G. maculatus and anadromous L. sealii fishes have been studied for genetic variation by cellulose acetate electrophoresis. L. sealii is a small member of the family Aplochitonidae endemic to Tasmania. In contrast, G. maculatus a salmoniform fish of the Family Galaxiidae, is found throughout the southern temperate zone (Australia, New Zealand and South America). Together these species are the predominant components of Tasmanian whitebait. A significant commercial fishery for Tasmanian whitebait began in 1941 and rapidly declined after 1947 probably due to overfishing (Blackburn, 1950), until its closure in 1974. Encouraging runs of whitebait in the early 1980s prompted a major study to investigate the potential yield and present status of this resource. The lack of data regarding the genetic structure of the species prompted the following study. Eight populations of G. maculatus extending from Western Australia to New Zealand were investigated. Twenty seven samples of L. sealii representing thirteen different river populations from Tasmania were included to capture genetic data both within and between three successive spawning seasons. An analysis of the gene frequency data using Nei's genetic distance (D) and identity (I) , G-test and F-statistics indicated population substructuring in the two species. Morphometric and meristic analysis of L. sealii was also undertaken and supported the genetic data. Within G. maculatus, the Western Australian population was genetically distinct primarily based on allele frequencies observed at the ADH locus. Three genetic pools of G. maculatus were identified which have zoo-geographic implications for this species. In particular they appear to confirm the potential of marine larval dispersal between Australia and New Zealand. A clear genetic discontinuity was observed between north and south Tasmanian L. sealii primarily based on the allele frequency data at the PEPD locus. These fmdings were consistent with those of Blackburn (1950) based on differences in growth rate and pigmentation. However, many southern rivers were found to carry unique stocks. A major contributing factor to this genetic diversity is thought to be the prevailing local hydrographic conditions. The results of this study have implications for the management of the recreational whitebait fishery which has re-opened in Tasmania and possibly the commercial whitebait fishery in New Zealand which is dominated by G. maculatus.