Spatial variation in shape of otoliths for southern garfish Hyporhamphus melanochir – Contribution to stock structure

Abstract

Otolith morphometrics and shape analyses were used to delineate the sub-population structure and determine the level of mixing of southern garfish in South Australian waters. Adult garfish from the 2+ age class were collected from three sites within each of six regions along the South Australian coast: Northern Gulf St Vincent, Southwest Gulf St Vincent, Kangaroo Island, Northern Spencer Gulf, Southern Spencer Gulf and the West Coast of Eyre Peninsula. This study adopted a multi-stage statistical approach exploring the spatial variation in gross otolith morphology and through elliptical Fourier analysis separately, and in combination, over both broad (regional) and fine (site) spatial scales. Stepwise discriminant function analysis revealed significant separation across both spatial scales; however, overall classification success of garfish to their site of capture was poor (<45%). Despite this, the results indicated some level of structuring within South Australia's southern garfish population, as fish were correctly classified at rates that were 32% better than would be expected by chance. At least six putative regional components with various levels of intermixing were detected based on differences in otolith shape. This result refines the spatial resolution of the fishery and consequently highlights the vulnerability of these regional components to localized depletion, particularly as the resource is currently considered to be over-exploited.

Key words:

• Hemiramphidae
• morphology
• otolith
• population structure
• shape

Acknowledgements

We thank Matt Lloyd, Bruce Jackson, David Schmarr and Jason Earl for valuable field and laboratory assistance.

Editorial responsibility: Geir Ottersen

Additional information

Funding

This work was funded by the Fisheries Research and Development Corporation (FRDC Project no. 2007/029) and logistical support was provided by the South Australian Research and Development Institute.