Movement and growth of the spotted gully shark Triakis megalopterus in South African waters

Abstract

The movement and growth of spotted gully sharks Triakis megalopterus (family Triakidae) along the coast of South Africa were investigated using external dart tagging. Of a total of 7 211 sharks tagged, 657 (9.1%) were recaptured over a 37-year period, from 1984 to 2021. Average distance moved by recaptured sharks was 31 (SD 82) km, with a maximum distance moved of 911 km. The longest time at liberty was 6 332 days (17.3 years). Most recaptures (66.9%) displayed resident, philopatric behaviour, although adults moved significantly more than juveniles. There was strong seasonality in the catches, with more individuals caught during summer months (October–March); however, there was no evidence to suggest that adults undertook seasonal migrations to and from mating or pupping areas. Similarly, the findings suggested that pupping likely takes place throughout their distribution and is not confined to a particular region. Growth of recaptured individuals was slow, with an average growth rate of 50 mm year⁻¹. This was similar to the growth rate determined by vertebral band counts but suggested that individuals could reach a theoretical maximum age of 41 years. Based on the species’ resident behaviour and slow growth rate, we advocate for maintenance of the current fishing regulations and greater protection in no-take marine protected areas with suitable habitat within their distribution. Further research using acoustic telemetry is also recommended.