Age-related movement patterns and population structuring in southern garfish, Hyporhamphus melanochir, inferred from otolith chemistry

Abstract

<jats:p><jats:bold>Abstract </jats:bold> The southern garfish, <jats:italic>Hyporhamphus melanochir</jats:italic> (Val.), is an important inshore fishery species in South Australia. Over the past few years there have been concerns with this fishery, which is now considered to be over‐exploited. Currently, the fishery is assumed to consist of two separate stocks, but there is no understanding of movement patterns both within and between these two stocks to justify this assumption. Otolith chemistry was used to infer age‐related patterns of movement, delineate potential sub‐populations and determine the extent of mixing within South Australian coastal waters. Results indicated that the population structuring of garfish is more complex than previously assumed and it seems that stocks can be discriminated at a much finer spatial scale. Garfish collected from sites separated by &lt;60 km displayed significantly different chemical signatures (relative concentrations of <jats:sup>7</jats:sup>Li, <jats:sup>24</jats:sup>Mg, <jats:sup>55</jats:sup>Mn, <jats:sup>88</jats:sup>Sr and <jats:sup>138</jats:sup>Ba) in their otoliths, especially during their second year of growth, indicating that they had inhabited different water bodies. From a broader perspective, South Australian garfish can be partitioned into six regional components with various levels of inter‐mixing. From these results, it was suggested that assessment and management of the fishery may have to be restructured to align with the smaller spatial units.</jats:p>