Fishing for the secret lives of trout
Gutting and cleaning trout is helping research into the daily lives of trout, writes
Georgia Third spent her Christmas holidays gutting and cleaning other people’s fish on boat ramps around Lake Taupo¯. It might seem like a waste of the PhD student’s talents, but it was all in aid of an important research project she’s conducting into the lives and habits of trout in the lake, in the hopes of understanding how scientists and fishers can keep their populations strong.
There’s a lot still to learn about the lake’s rainbow trout, and Third hopes her work will help improve understanding of how they choose what to eat, their growth rate, and how they migrate.
To do that, she needs samples, so has spent the festive period offering to do the undesirable task of cleaning fishers’ catches in exchange for taking a range of information and samples.
“As people come in after they’ve been fishing, I’ve been offering to clean people’s fish for them and take all the guts out.
“At the same time, I’m taking photos of the fish, taking length and weight, [and] stomach samples to see what they’ve been eating.”
Third also took muscle samples for stable isotope analysis, which is a test that allows her to see what the fish has been feeding on for the previous six to 12 months, giving a better picture of the whole food web in the lake.
As well as potentially changing the way fisheries are managed for the better, Third’s research may give a scientific explanation to what generations of fishers have observed about Taupo¯‘s trout population.
“A lot of fishers will talk about there being smelt specialists or ko¯ura specialists, and I’m interested in why.
“What makes a trout decide and how much do they switch between these prey types over time or even over a few hours? Are they feeding sometimes at the bottom and other times in the water column?”
Although originally from the rural outskirts of Auckland, Third made the long journey to collect samples from her current home in America, where she’s studying at University of California, Santa Cruz.
It might seem a long way from the Central North Island, but the Californian
institute is a fitting place to look at how Lake Taupo¯‘s trout are put together, said Third, because it’s where they originally came from.
“Trout in Taupo¯ were introduced from California and I’m studying around the area that trout came from in Santa Cruz.
“I’m studying the trout in the ancestral population and in the introduced population.
“University of California Santa Cruz have found a few different genes that are of importance to trout over there, to whether they migrate or stay resident, and how fast they grow.
“One of the things I’m doing is seeing whether those genes are relevant in the introduced population here.”
Although Third’s research isn’t directly concerned with pollution and litter, one catch particularly caught her attention, she said.
“There was a fish that came in through the gutting station and it looked really sickly, it was an almost green colour and it was really thin.
“The people who caught it said they couldn’t even tell it was on the line. When I opened it, I saw a glint of purple and I thought ‘Oh, it’s swallowed a hook and lure’.
“When I fully opened the stomach it was a Cadbury Caramello wrapper. It had completely blocked the stomach and meant the fish couldn’t eat.”
It was frightening to think how many fish might be ingesting litter in this way, she said.
“When you scale that up to thousands of fish, that’s a huge amount of potential plastic.”
During her time around Lake Taupo¯ , Third had set a lofty target of 150 samples and was happy to end up with about 145.
It will take a good few years to complete the project and her PhD, but the fishers she interacted with were happy to help, she said.
“People were so good at the boat ramps, I had a lot of great feedback and people were really interested.”