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Source: NIWA – National Institute of Water and Atmospheric Research

Down on the Viaduct processing line, Taylor and Parsons are carefully working their way through a randomly selected sample of the catch, measuring each fish and then meticulously removing their tiny ear bones for detailed investigation.

“The boats that are coming in are part of our sampling lens,” says marine ecologist Parsons.

“They are going out there fishing and they see what is happening first hand. We are in partnership, piggy backing along to get a good view of what is happening in the water right now.”

Later, back in one of NIWA’s Auckland laboratories, fisheries modelling technician Helena Armiger puts those ear bones under the spotlight.

Like trees, fish produce annual growth rings. These rings are most pronounced in their ear bone – or to give them their scientific name, the otolith. Using her microscope, Armiger can carefully count the individual rings and work out a range of factors, including the exact age of each fish.

It takes about 10 minutes to age one otolith. Examine a large enough sample from each catch and you start to build a picture of the age structure and the health of the target fishery.

In the last year alone, in processing sheds from Leigh to Bluff, NIWA researchers extracted over 17,000 ear bones, from key species like snapper, tarakihi, trevally and blue cod.

“We don’t let an otolith go until two readers agree on an age, so we can give the best possible information to FNZ,” says Armiger.

If you know how many fish you are catching and how the age structure of your fish population changes over time, you can track the sustainability of your fishery. Lots of young fish, for example, is a sign of strong recruitment and a growing population.

Combine the information gathered from the otoliths, with other data sources such as biomass estimates from standardised research surveys or catch rates from commercial operations, and fisheries modellers can build a detailed picture of the health of specific fish populations.