Biological Characteristics of a Subtropical Nemipterid (Pentapodus vitta) Established in a Temperate Embayment

The biological characteristics of the Western Butterfish (Pentapodus vitta), a subtropical nemipterid, were determined in a temperate embayment (Cockburn Sound) and compared to those from a previous study in a subtropical embayment (Shark Bay), 700 km northward, to test predictions from the temperature-size-rule (TSR). In Cockburn Sound, P. vitta displayed sexually dimorphic growth with females attaining significantly smaller lengths at age and total length at maturity than males (127 vs. 147 mm), but a greater maximum age (12 vs. 9 years). Analysis of monthly trends in reproductive data indicates peak spawning occurs from October to December. Pentapodus vitta grows more slowly to a larger maximum size (265 vs. 240 mm) and attains an older age (12 vs. 8 years) in the temperate than the subtropical embayment. These findings are consistent with the predictions of both the MTE and the TSR, where fish in cooler waters grow more slowly but reach larger sizes than those in warmer waters, which grow faster but attain smaller maximum sizes. There was a 30-fold increase in the mean abundance of P. vitta in Cockburn Sound between 2007/08 and 2021–2023, and an increase in the frequency of occurrence in otter trawl samples from 44% to almost 100%, making this species among the most abundant and ubiquitous teleosts in this embayment. These results enable a better understanding of the impact of the increasing abundance of a subtropical generalist in a temperate embayment.