Hey there! I’m Joni and I am a 3rd year PhD candidate in The Fish Lab at Macquarie University in Sydney, Australia. My PhD research is focussed on understanding the behavioural ecology of stingrays, with a particular focus on their interactions with humans. Specifically, I study the smooth stingray, which is Australia’s largest species of stingray. These charismatic megafauna are common at boat ramps in southern Australia, where they scavenge fish waste discarded by recreational anglers from fish cleaning tables. They’re also often the target unregulated tourism attractions based on these aggregations. My research uses passive acoustic telemetry to track their space use around these areas, and stable isotope analysis to look at how much of their diets are made up of this provisioned resource. The day I have chosen to highlight for this blog is from my latest fieldtrip to Jervis Bay on the south coast of NSW. This fieldtrip was the last of my PhD *cries* and our goal was to collect tissue samples from potential prey items for our stable isotope analysis and to tag juvenile smooth stingrays with acoustic transmitters to track their movements. Fieldwork is how I spend about 10% of my time. The other 90% is either in the lab processing our tissue samples or behind a computer analysing data. Fieldwork is certainly my favourite part of being a marine biologist, which is why I have decided to share a day in the field:
Fieldwork for me usually involves roughing it with 3-5 volunteers in cramped 6-berth cabins in caravan parks. Fortunately, our regular accommodation, the Jervis Bay Holiday Park, comes with a killer view and some beautiful sunrises. My morning starts with a cup of coffee sitting with the ducks here on the shores of Currambene Creek.
The next step is to pack the car. For this trip, our gear included crab traps, nipper pumps, wetsuits, booties, an esky full of fish scraps, a cooler bag for storing tissue samples, my tagging pole (aka Badass Lady Trident), acoustic tags, and lots and lots of cable ties.
Then it’s time to hook up our research boat, Sea Wasp, and head to the boat ramp. Here, we load all out gear and do all out checks before launching and heading upstream.
Our first task was to drop the crab traps along the edges of mangroves in the hope of catching mud and blue swimmer crabs. These traps stay in overnight and are checked each morning.
Once the traps are in, we headed to the mudflats. In creeks like Currambene, these mudflats resemble the surface of the moon (left) due to all the feeding pits left by rays. On the right, a common stingaree has left a perfect imprint of its body after trying to excavate some delicious invertebrate from the sand underneath. On these mudflats, the rays would be feeding on things like nippers, bivalves, crabs and polychaete worms. Larger species of rays, like my smooth stingrays, may also be eating larger crustaceans and oysters. Our mission on this mudflat was to collect nippers, polychaete worms and oysters.
Then it is back onto the boat where I sat on the floor to crack open the oysters we collected and extract their muscle tissue. The idea behind stable isotope analysis is “you are what you eat.” The isotope signatures of different organisms gives us an idea of what trophic level it feeds at (primary producer, consumer, high order consumers, etc). Different tissue types also give us an idea of when they were eating at a trophic level. For example, the turnover rate of stable isotopes in blood is a lot faster than in muscle tissue so using blood gives an idea of what an organism recently ate, whereas muscle gives an idea of what an organism has been eating over the past 6-12 months. We use muscle tissue because we are interested in these longer-term diets.
Back on shore, we then processed the rest of our prey samples in our al fresco laboratory – the fish cleaning table. In this photo we are extracting muscle tissue from the tails of the nippers we caught that morning. These samples are put into small tubes, labelled and put into the cooler bag. Back at camp they go into the freezer, and then back at the real lab after fieldwork we dry and crush them into powder for the stable isotope analysis.
We finished off the afternoon watching my beloved smooth stingrays at the boat ramp. Some local anglers had come back from their day of fishing and the smooth stingrays were busy cleaning up the scraps. This female here is a sub-adult we tagged in November 2019. You can see her tag in her left wing. These tags are attached to small umbrella-like dart heads that are implanted into the wing muscle using a tagging pole. After about 6 months, the tags fall out and the rays fully heal within a week or two.
Back at home base, we took over the camp kitchen to cook a quality BBQ and watch Survivor with a couple of beers, because that’s the best way to end a day in the field. I’d also like to give a shout out to my superstar volunteers, Tim (left) and Alyssa (middle) and my supervisor, Culum Brown (right), for all their help on this trip, and all our other trips!