A fishy business

When we catch up with PSA member Tom Trnski, he’s analysing a small cardinal fish that’s new to science, one of two new discoveries from a recent expedition he led to the Kermadecs. The other was a species of pipe fish that looks a bit like a straightened-out seahorse.

Tom TrnskiTom is a marine scientist and head of natural sciences at the Auckland Museum. He’s a go-to person when television wants an expert to explain why fish are behaving in a particular way or, most recently, to make sense of the tragic death of a swimmer by shark attack.

Tom’s speciality – the one he’s written about in books and papers – is the larval stage of fish. He goes to considerable lengths underwater to monitor their movements and determine the influences on their distribution and population size.

“Larvae swim around in the water column and then, at the juvenile stage, settle in their preferred habitat,” he explains. “For example, snapper prefer sea grass. If the sea grass is reduced in scale or quality, it will have an impact on how many snapper there will be to catch three years later.”

Fifty years ago, snapper could be caught fairly close to shore but now people have to go a lot further out, and most of the fish they catch will be undersized, he says. “The snapper stock in the Hauraki Gulf is now very low, only 15 per cent of what it was historically.”


Marine Reserves

Tom says much more needs to be done to protect fish species against the ravages of commercial and recreational fishing so populations have a chance to grow. That would mean more fish and bigger fish.

“New Zealand has a very small number of small marine reserves near the mainland. In terms of a network of reserves that would preserve our marine stocks, we have a very poor record.”

Part of the problem is that changes to the ocean have happened gradually and people’s perceptions of what’s normal have changed, he says.

It underlines the importance of museums which keep collections for the long term and can tell us a lot about change over time. It’s an important record that can be used to look at changes in chemical composition and where species historically occurred and no longer occur.

“For example, our collection documents the first arrival of exotic plants in the Auckland region. We have the first plant here,” says Tom.

The museum has a reference collection from around the world. When a strange-looking snail was found in a pond in the Auckland Domain, they were able to tell Biosecurity what it was and that it had arrived from South America.


Icing on the cake

Tom says it’s the diversity of activities and the people he meets at the museum that keep him really  interested in his work. “And being able to do some research and science is the icing on the cake for me.”

Four years ago, the museum invited the public to watch Tom and a shark expert from DOC dissect a three-metre-long great white shark. Over 4,000 people flocked to the museum to see what was inside it.

The shark had been found tangled and dead in a gill net. Given its size, Tom had expected to find remains of seal in its stomach. “All we found was fish remains and a few fish hooks, though it did have the scars from interaction with seals.”

Sharks are threatened around the world but have an important role as the top predator in the marine environment, he says. “We wouldn’t imagine an African savannah without lions and tigers. They keep the numbers of big herbivores down. Sharks play the same role.”

Tom says his work on fish is his hobby. “I love it and would do it if I didn’t get paid. That’s true for a lot of scientists. Science demands a big commitment and dedication and that makes people passionate about what they are doing.

“I am very fortunate in having a broad understanding of how the marine environment works. Teasing out some of that information to inform others about how it works, that’s what really floats my boat.”


This article is from the March 2013 issue of the PSA Journal. You can read back issues of the Journal by clicking here.