The enigmatic weasel shark, will it disappear before we know it?

Methods

Summary

All caught specimens will be caught and handled using minimally invasive methods and with the aim to release them unharmed back to Cabo Verde’s waters. Collaborators on this project have worked extensively on techniques to minimize injury during capture and handling of live sharks. These methods will be employed and taught to local community members as part of our knowledge exchange. All sharks will be captured by live-release angling from boat or from shore using squid as bait. Specimens considered to be in bad condition (judged by experienced staff with practical experience handling sharks) will be released to the water immediately. Any specimens that are handled on board will be maintained in tonic immobility, quasi hypnosis, with a constant supply of water from the time of landing to the time of release. 

All individuals will be sexed and measured and, if possible, genetic and blood samples will be taken and the maturity status will be investigated.

Passive tagging with external visible passive marker tags, tags which are equipped with a unique individual identification number, will be attached in the musculature below the dorsal fin using a tagging pole.

Acoustic tags, called ‘individual coded acoustic transmitter tags’, will be implanted in the body of the animals, using aseptic surgery and sterile instruments. To insert transmitters, a small incision will be made with a sterile scalpel on the animal’s belly, then the transmitter will be inserted. The incision will be closed with surgical sutures. The entire surgical procedure will only take a few minutes. Since the incision is small and the handling time short, sharks are very unlikely to be negatively affected by this procedure. The procedure on internal tagging is therefore widely used by the international scientific community in acoustic telemetry studies of sharks. It has been applied successfully by the investigators on various shark species in the Northwest Atlantic Ocean.

The battery life of the acoustic tags is about 2 to 3 years. Already installed acoustic underwater receivers can identify all Vemco 69 kHz coded transmitters and will store data on the presence of any tag within a radius of approximately 800m. Hence, sea turtles, or any other species equipped with Vemco tags can also be detected, as well as any other species that might be tagged with Vemco tags in future.

All above described methods will only be applied by appropriately trained individuals to minimize the effect on the animals. Therefore, locals will also be trained by qualified individuals, particularly in terms of external passive tagging, catching, handling, live-release, size measurements, determining sex and species and fin clip DNA sampling of elasmobranchs for scientific research purposes.