Late in 2014, the Two Oceans Aquarium donated funds to an acoustic telemetry study on leervis/garrick (Lichia amia) migrations. The study is a collaboration between the Oceanographic Research Institute (ORI) in Durban and the South African Institute for Aquatic Biodiversity (SAIAB) in Grahamstown.
Since October last year, 18 leervis have been successfully caught, tagged and released by the ORI’s senior scientist Bruce Mann and his team.
Ever wondered what it takes to tag and track leervis?
Here’s Bruce’s explanation:
The process of tagging these fish involves catching the fish from a boat or from the surf and landing it as quickly as possible.
Once landed, the fish is carefully handled and placed in a stretcher. On the beach we found it easiest to dig a hole in the sand in which to place the stretcher.
The stretcher contains fresh seawater, which is continually changed using a bucket.
The fish is turned upside down, inducing a state of tonic immobility, and a small incision is made in the abdomen just behind the pelvic fins using a sterile scalpel. The tag is then inserted into the coelomic cavity of the fish and the incision is stitched closed using two or three sutures. Wound gel powder is placed on the incision to assist with rapid healing and the whole procedure normally takes less than five minutes. The fish is measured, a small fin clip is taken for genetic analysis and the fish is then released.
And off they go!
The acoustic tag emits a unique ping every 45 seconds and can be recorded by underwater listening stations.
The Acoustic Telemetry Array Platform (ATAP) run by SAIAB with collaborating partners has approximately 120 listening stations placed at strategic locations along the Southern African coastline, from Hout Bay to Ponto do Oura. If a tagged fish swims within 500m of any listening station, its tag number is immediately recorded along with date and time. These listening stations are serviced every six to nine months, and all tag detection data recorded on them is downloaded for subsequent analysis.
The tags have a battery life of approximately eight years, allowing us to detect multiple year movements and migrations of tagged individuals.
Of the four fish we tagged at Port Shepstone in October 2014, three were recorded on listening stations in the Kowie and Bushman’s estuaries near Port Alfred (Eastern Cape) after a few months, and one moved as far south as Mossel Bay!
One of our tagged fish was recently recaptured by a recreational angler at Port Shepstone Sandspit on the 16 June. Therefore, after being tagged, this fish had swum all the way down to the Cape for summer and then returned to the exact locality where it was originally tagged seven months earlier!
We are currently rolling over the underwater listening stations deployed off the KwaZulu-Natal coast and are very excited to see which of our tagged fish have been detected. As data from other receivers deployed along the whole coast is made available, we will learn more about the underwater lives of our tagged garrick and once pooled with data collected from additional fish tagged by SAIAB in the Eastern Cape, we will obtain a greater understanding of the movement patterns of this popular gamefish species.