Takapu Charters backs Fiordland blue cod research with Charter clients helping unravel Fiordland's blue cod mystery.
The blue cod on the dinner table after a Fiordland fishing trip this summer could help decide how the fishery is managed for the next generation.
Clients aboard Takapu Charters' vessel Yuwindi II will measure every blue cod they catch from 1 December to 31 May, and record the sex of every fish they keep, as part of a new population study.
The project is run by the Fiordland Marine Guardians, the Ministry for Primary Industries and the University of Otago.
It is the first look at blue cod population structure inside Dusky Sound since the last published survey in 2014.
University of Otago marine science student Tim Willans, who grew up in Te Anau, is leading the work as part of his Masters degree.
He said the gap in knowledge mattered because the Southland and Fiordland stock was under pressure, with recent cuts to both the commercial catch limit and recreational daily bag limits.
Females that become males
Blue cod have an unusual biology. Some are born male, but females can also change sex. "This is thought to happen when there is no dominant male in an area, which leads to the largest and most dominant female changing sex to male," Mr Willans said.
"In areas exposed to high fishing effort, the large male is often caught. If this happens repeatedly, the next female to change is smaller each time, and the number of females in the area drops."
The only reliable way to sex a blue cod is to check its gonads after it has been gutted, which is why the study relies on fish clients were already keeping. No extra fish are killed for the research.
Blue cod also rarely travel far. Populations within the fiords are highly residential, leaving them vulnerable to heavy fishing in small areas.
Sampling is expected to focus on Dusky Sound, Chalky Inlet and the open coast. Dusky Sound receives far more charter fishing pressure than other areas, and comparing it with quieter spots will be a key part of the study.
Local knowledge
Mr Willans said working from charter boats rather than a research vessel brought fishers into the science.
"The skippers and crew are out experiencing the fishery day to day. They have a wealth of knowledge on the Fiordland Marine Area and fisheries in other areas, which is hugely valuable for understanding how fish stocks are coping with fishing pressure."
He recently ran through the sexing protocols with the Takapu Charters crew off the coast of Dog Island in Foveaux Strait.
"The Takapu crew have been awesome to work with. We had a great time catching a few blue cod and sexing them, alongside some really insightful conversations about how the fishery is doing in Fiordland, particularly in the fiords."
Takapu Charters managing director Paul Jones said backing the research was an easy call.
"We've been fishing Fiordland for years and we want our clients, and their kids, to be able to do the same. The more we understand about how the cod are doing, the better we can all look after them."
Fish for a feed
Mr Willans said recreational fishers could help by fishing for a feed rather than the freezer, using as much of each fish as possible, and mixing up their spots.
The Free Fish Heads app was one way to pass on heads and frames that would otherwise be thrown out, he said, while drift fishing helped spread effort across localised populations.
The project is due to finish by early 2028, with results expected to be released through the Fiordland Marine Guardians.
"Research and fishers working together is what will create the best outcomes for fish stocks," Mr Willans said.
"With more understanding comes more informed management, right down to a fisher-to-fisher scale."