Movement patterns and catch trends of the diamond ray Gymnura natalensis (Dasyatidae) in South African waters

The diamond ray Gymnura natalensis is endemic to southern Africa where its preference for shallow coastal habitats makes it vulnerable to recreational shore-based angling. Although it makes up approximately 1% of the shore-based tag numbers, little is known about its movements, reproduction or population status in South Africa. This study used three independent long-term (34-41 years) datasets, including tagging by recreational anglers, competitive shore angling catches and shark net catches, to investigate the species' movements, catch composition and population status in South Africa. Of the 3 739 individuals tagged (1984-2018), only 30 (1%) were recaptured after an average of 487 days at liberty. The majority (60%) of the recaptures occurred within 10 km of the release site, while 7% had moved more than 1 000 km along the coast. The longest recorded movements (1 577 and 1 756 km) were undertaken by adult rays tagged in the Western Cape Province moving to KwaZulu-Natal Province (KZN). The competitive shore angling catch (1977-2018; n = 9 150) from KZN was dominated by adult rays caught north of Durban, while the shark net catch in KZN (1981-2018; n = 584) was dominated by juvenile rays primarily from the central beaches of Durban. All the datasets exhibited strong seasonal trends with most catches taking place in summer. A risk assessment confirmed a stable to increasing population trend over four generations, suggesting that the population sampled along the east coast of South Africa should be classified as Least Concern.

Automated summary

This study investigated the movements, reproduction, and population status of the diamond ray Gymnura natalensis in South Africa. The findings showed that the species mainly inhabits the east coast of South Africa and despite the low number of individuals tagged, the population trend is stable to increasing, suggesting a classification of Least Concern.