MEPS 403:193-203 (2010)  -  DOI: https://doi.org/10.3354/meps08469

ABSTRACT: Fish spawning aggregations (FSA) are generally spatially and temporally predictable, making them particularly vulnerable to fishing, which is capable of rapidly removing a significant proportion of the aggregated adults and reducing egg production. These effects may cause the loss of the aggregation altogether. In the Northern Territory (NT), Australia, repeated fishing of known aggregations of the tropical sciaenid species, the blackspotted croaker Protonibea diacanthus, is probably unsustainable, particularly given this species’ decline elsewhere. Acoustic monitoring was used to examine the temporal and spatial movement patterns and site fidelity of P. diacanthus in the NT. Fish were only detected at their respective aggregations, providing no evidence of large-scale movements between FSA. There was evidence for behavioural polymorphism in the aggregations, and fish monitored for ≥1 yr showed decreased presence during cooler months and increased presence during warmer months when peak spawning occurs. The tidal cycle significantly influenced the detection of tagged fish, with detections peaking on running tides, the peak period for catching P. diacanthus, suggesting that this is when they feed. This study has provided important information on the connectivity and dynamics of P. diacanthus aggregations in the NT, including crucial information for implementing appropriate management strategies for this vulnerable species. There appears to be little interchange of adult P. diacanthus at the spatial scale examined, which suggests that the separate FSA examined support separate adult populations. The presence of seemingly separate spawning populations of P. diacanthus has significant implications for their management, with the potential for each aggregation to be vulnerable to localised depletion.

KEY WORDS: Spawning aggregation · Site fidelity · Acoustic monitoring · Sciaenidae · Fisheries management · Movement · Tidal cycle