Migration Range of Sharks Presents Challenges for Conservation 

Many migratory shark populations are threatened by a range of factors, and understanding their movement patterns across borders is critical for effective management and conservation.

To support this need, Dr. Ryan Daly of the Oceanographic Research Institute in South Africa led a team of researchers from several institutions to investigate transboundary movements of threatened shark species between South Africa and Mozambique. 

Challenge 

Migratory sharks play a key ecological role in marine ecosystems, yet many populations are declining due to various causes including climate change and overfishing.  

Addressing the decline is even more challenging for wide-ranging species, like sharks, that undertake long-term migrations, which typically take them between countries that may have different conservation priorities.

Understanding how these endangered species move between South Africa and Mozambique during the year is essential to develop a comprehensive, cooperative conservation plan between the countries. 

Solution 

The research team used Innovasea’s passive acoustic telemetry to monitor four species of shark with varying IUCN Red List statuses and habitat preferences: the Vulnerable bull shark and blacktip shark, representing medium to large coastal species; the Near Threatened tiger shark, representing a large coastal and open-ocean species; and the Endangered grey reef shark, representing a relatively small reef-associated species. 

A total of 102 sharks – 38 bull sharks, 20 blacktip sharks, 21 tiger sharks and 23 grey reef sharks – were fitted with long-life V13 and V16 acoustic transmitters. They were monitored for four years from 2018 to 2022 by leveraging an existing network of 350 acoustic receiver gates and arrays that spanned more than 2,000 kilometers of coastline off South Africa and Mozambique. 

The objectives of the investigation were to quantify the frequency and persistence of transboundary movements, discuss the implications of transboundary movements for threatened species and use the results to suggest ways to improve cooperative transboundary management. 

Result 

The research data showed that individuals from all four species of tagged sharks undertook transboundary movements with varying degrees of frequency between the neighboring areas of Breede River Estuary in South Africa and Bazaruto Island in Mozambique. 

In addition, blacktip, bull and tiger sharks all traveled vast distances beyond this area with migrations ranging from 980 to 2256 kilometers. Several individuals were detected at the northern limit of the receiver network making it very likely that these sharks moved even further north along the Mozambique coastline. 

These results confirmed frequent cross-border movement by the sharks between the neighboring countries, emphasizing a need for cooperative conservation. Aligning regional management plans and interventions would be a positive step towards mitigating declining shark populations in this region.