Movements and growth rates of tagged bronze whaler sharks (Carcharhinus brachyurus) in southern Africa

Context: Shark species that are targeted by recreational anglers and commercial fisheries are vulnerable to over exploitation when fishing effort is not informed or regulated by data on the relative distribution and growth of different age/size classes.

Aims: We investigate the spatiotemporal distribution, movement patterns and growth rates of Carcharhinus brachyurus in southern Africa. 

Methods: We analysed a 36-year cooperative shore-angling tag-recapture dataset.

Key results: Distribution was centred in Namibia and the South Coast of South Africa during the austral summer. Large-scale regional movement of individual sharks (n = 21) supports the lack of population structure in southern African. The South Coast of South Africa represented a potentially important nursery region where 96% of all juveniles were tagged. Sub-adults and adults were more widely distributed and recorded significantly greater time at liberty than juveniles, but the distance moved for adults was significantly lower, indicating higher site fidelity. Growth model predictions showed annual growth rates of C. brachyurus were among the slowest when compared to other carcharhinids.

Conclusions and implications: These slow life-history traits, affinity to coastal regions and cross-border movements leave the southern African C. brachyurus population vulnerable to overexploitation in the absence of regionally aligned research and management.