Aside from cleaning tanks, feeding mussels out to the fish and carrying out regular water changes we were also able to help with two exciting projects during our internship – inducing tonic immobility in benthic sharks and a maze experiment to assess the cognitive abilities of benthic sharks.
The first of the two projects that we were able to gain experience with was inducing tonic in a leopard catshark named “Zimzi”. We first received an informative introduction to the phenomenon of tonic immobility by the aquarium manager Alan, who told us that it is thought to be related to reproduction in various elasmobranch species (so that the female relaxes during copulation). Since Claudia had experience with putting sharks in tonic from her previous month as an intern, she guided Megan and I as we learnt how to safely and gently handle the shark.
We were instructed to ensure we had the right grip on the shark – not too soft so that they can move around and potentially create too much stress for both ourselves and the shark and also not too tight as it would cause discomfort to the shark. Our first grab should be with our dominant hand on the body (behind the gill slits) and the other hand on the underside of the tail so that we could then flip the shark over in one smooth movement, always holding both parts firmly.
I was excited but also slightly nervous to try it the first time – I wanted to reach for and grab Zimzi in a quick and gentle manner that would cause as little stress possible. I was a little hesitant going for my first grab and got startled when he started moving but had success the second time. It was such an amazing feeling holding him in tonic – he completely laxed out and I took a couple seconds to gently stroke his belly which was soft and squishy to touch.
Once tonic was induced one of the other interns would keep track of time in tonic while the other would count how many breaths the shark would take (as seen by movement of the gills). We took turns rotating our duties around so that we would each get a turn at the various roles for collecting the data.
The maze experiment was really interesting – we were testing whether sharks were able to learn and be conditioned. We worked out in the back room at the aquarium in the rectangular tank lined with fibreglass and after the shark was collected from the main benthic tank, it was placed in the far right in a holding area which had a removable door. At the other end of the tank there was a wall divided into two sections which had a picture on each side – on the left there was a circle and on the right a picture of a fish (both A4 sized and laminated).
The shark would be released from the holding section when Alan (the aquarium manager) opened the door, and the stopwatch started by one of us interns. If the shark chose to swim to the side with the fish picture, it would be rewarded with food (fish) and if it went to the circle it wouldn’t receive anything. We were assisting with testing whether females learn faster than males.
For our first time at the maze experiment we worked with a male leopard catshark named “Spock” and carried out ten trials while each being assigned to specific tasks – one on providing the fish reward, one on stopwatch and the other on data.