Catch sampling

The ear bone of a snapper holds a wealth of information. However, it is not until you look at thousands of them that the picture of a population reveals itself. So where do you get 10,000 snapper ear bones from?

It’s just after 4am and the Sanford Fish Processing shed in Auckland is a riot of activity. 

The snapper landed a few hours earlier are meeting the knives on the processing line. Skilled hands are preparing fillets for the dinner menus of restaurants, supermarket chilled sections and whole fish are being readied to be sent overseas. Also, on the processing line are two NIWA fisheries scientists.

“The boats that are coming in are our sampling lens. They are going out there and fishing. We are working in partnership to get a good view of what is happening in the water right now.” Darren Parsons – NIWA Marine Ecologist

Everyday thousands of fish are caught then readied for market in fish processing sheds across the country. This provides an opportunity for NIWA to take a snapshot of what is happening beneath the waves. The primary means to do this is by measuring the fish and removing their otoliths, or ear bones.

Commercial catch sampling

Fisheries managers in Aotearoa New Zealand need to understand how healthy each stock is to be able to set the total allowable commercial catch (TACC). To do this they need data - lots and lots of data. This is why NIWA fisheries scientists are up at 4am across the country measuring and removing otoliths. 

“Every little bit of data counts. We measure one fish here today, that will be one line of data. But this builds into a huge data set that goes to the Ministry (Fisheries New Zealand) and makes a difference so that when you or I go out fishing on the weekend, I know there are going to be fish there from the research we have done.”  Rikki Taylor – NIWA Fisheries Technician.

Since the 1980’s NIWA has been providing Fisheries New Zealand independent data to make sustainability decisions. Marc Griffiths, Principal Science Advisor at Fisheries New Zealand says, “Obtaining information on the age structure of the commercial fishery is crucial to successful stock assessments”. The otolith is key to providing this age data.

What is in a fish’s ear?

Fish produce growth increments in various calcified structures, most notably in their otoliths, but also in scales, spines, vertebrae, and other bones. Like the human ear drum, otoliths are part of the fish's sensory and balance system, and the name 'otolith' comes from two Greek words meaning ear and stone.

It is estimated that well over a million fish are aged each year worldwide, highlighting the importance of age information in fisheries science. All ageing investigations involve a count of microscopic contrasting light and dark zones, though methods vary between species and structures. Because ageing information contributes in so many ways to population modelling and management, any inaccuracies in age data can result in management actions which could impact seriously on the population being fished. 

“We don’t let a snapper otolith go until two readers agree on an age, so we can give the best possible information to Fisheries New Zealand so they can manage the fishery” - Helena Armiger. Principal Technician – Fisheries Modelling and Recreational Fisheries.

10,000 snapper ear-bones

In the noise of the Sanford processing shed In Auckland, NIWA scientists Rikki Taylor and Darren Parsons are measuring hundreds of fish from a catch that has just landed as well as removing otoliths to be measured back at the laboratory. 

In the last year NIWA removed over 17,000 otoliths from key species like snapper, tarakihi, trevally, hoki, and blue cod in processing sheds from Leigh in the North to Bluff in the south.This creates a picture of age and length distributions to assess fish stocks and allows fishery managers to balance conservation and utilisation.