Characterisation of the Mitochondrial Genome and the Population Genetics of Polyprion Oxygeneios (Hapuku) from Around New Zealand

Abstract

Polyprion oxygeneios (hapuku) is an important commercial and recreational fishery species within New Zealand. Moreover, P. oxygeneios are currently being developed as a high-value New Zealand aquaculture species. There have been no previous studies on New Zealand’s P. oxygeneios that have been able to detect genetic differences among samples, which may be of use to either broodstock or fisheries managers. An understanding of the genetic structure of commercially harvested species maximises the potential for sustainable harvesting through effective management schemes. The primary goal of this thesis was to investigate the population genetic structure of P. oxygeneios using molecular markers to analyse samples collected from sites within New Zealand’s Exclusive Economic Zone (EEZ). The DNA sequence of the whole mitochondrial genome of P. oxygeneios was determined and it showed a similar structure and gene organisation to that of other species across a wide range of taxa. A set of species-specific control region primers was developed for P. oxygeneios and Polyprion americanus, and additional primers were designed for the 16S and ND6 genes of P. oxygeneios. A ~488 bp portion of the mitochondrial DNA (mtDNA) control region sequence from 274 individuals, and genotypes from 259 individuals using nine polymorphic microsatellite loci, were used to investigate the phylogeography and population genetic structure of P. oxygeneios. The mitochondrial DNA data failed to detect any significant differentiation between sample sites. However, the microsatellite DNA analyses showed that individuals sampled from the west coast of the South Island (Hokitika) were genetically distinct from individuals sampled at all other New Zealand sites. These two groups might be representative of two discrete populations of P. oxygeneios within New Zealand’s EEZ. These results suggest that the west coast South Island P. oxygeneios fishery should continue to be managed as a separate stock, with some possible revision of the Cook Strait fishery required. Analyses of the mtDNA and microsatellite DNA data of P. oxygeneios broodstock held at NIWA’s Bream Bay Aquaculture Park showed that they were not significantly differentiated from the wild populations (excluding Hokitika). Simulations also described the appropriate sampling efforts required to capture an appropriate level of genetic diversity when either establishing a new broodstock or supplementing an existing broodstock with new individuals. Continued management of the broodstock will be required to maintain the high levels of genetic diversity that have been captured in the founding broodstock in future generations.