Discovering the secret lives of Namibia's sharks and rays

by Hayley Brand 

Sharks, skates and rays, collectively known as elasmobranchs, are a critical part of a healthy and balanced ecosystem. However, overfishing, climate change, habitat destruction and lack of knowledge are placing many species of elasmobranch at risk and worldwide, populations are declining. Little is known about the elasmobranchs that occur off Namibia’s coastline but if we want to protect them, we need to learn more about their lives, such as where they live, where they breed and their movement patterns. But how can we learn these things if we can’t see them or physically follow them around? 

For the first time the Namibia’s Rays and Sharks (NaRaS) project is using a method called passive acoustic telemetry to track the movements of elasmobranchs within the Namibian Islands Marine Protected (NIMPA) just off Lüderitz. Acoustic transmitters (also called tags) have been inserted under the skin of several sharks and skates by an experienced and authorised tagger, Dr. Matthew Parkinson, from the South African Institute of Aquatic Biodiversity (SAIAB). The procedure was overseen by Namibian veterinarian Dr. Andrea Klingelhöffer.

Matthew Parkinson and Ruth Leeney prepare to tag a bluntnose guitarfish. Tagging authorised under NCRST permit RCIV00012021 and authorised by the Namibian Veterinary Council.

Each tag emits a unique sound pattern, a bit like morse code, giving each tagged shark a unique identity. The NaRaS team have deployed four acoustic receivers in the NIMPA, where they are suspended in the water column (but anchored to the seafloor), ready to detect a tagged animal when it swims within range. When a tagged animal swims close enough, a receiver will record the unique identity of that tag, as well as the time and date that it was detected. After about 6 months, the receivers need fresh batteries, so they are retrieved from the depths, allowing us to replace the batteries and download the data. Fortunately, we don’t have to dive into the cold Benguela waters to retrieve them - a remotely triggered device releases the receiver from the anchor allowing it to float to the surface.

A whitespootted smoothhound (left) and biscuit skate (right) tagged by the NaRaS team in February 2023. (c) NaRaS.

The aim of this work is to assess whether tagging can be an effective long-term monitoring method for sharks, skates and rays in the NIMPA. This work will also give us insight into how some of Namibia’s elasmobranchs are using the country’s only marine protected area. The data collected will eventually contribute to a monitoring and management strategy for elasmobranchs as part of the broader NIMPA management plan. For the first time in Namibia, the NaRaS team tagged elasmobranchs with acoustic tags in February 2023. Several bluntnose guitarfish and biscuit skates were tagged, as well as two white spotted smoothhounds. All three of these species have rarely been tagged before (only one whitespotted smoothhound has been tagged in South Africa to date, and no bluntnose guitarfish), so the results of this study will, we hope, provide unique information on the lives of these species and how they move inside the Namibian Islands Marine Protected Area. We will return to Lüderitz in July to download the data from our receivers and re-deploy them. We are looking forward to sharing what we learn from the first 6 months of tracking data – keep an eye on our social media channels for updates! 

We are grateful to our collaborators at the South African Institute for Aquatic Biodiversity for their support of our acoustic tracking work. 

The NaRaS project is supported by the Shark Conservation Fund.