Tuna tagging 'even more important' during Covid-19 pandemic

6:19 am on 2 October 2020

The tagging of over 6,000 tuna in the central Pacific over the past seven weeks is being hailed for the data it will provide to ensure accurate assessments of stocks in the region.

"The western and central Pacific is the only area in the world where tunas are sustainably harvested," said Dr Simon Nicol, the Pacific Community's (SPC) principle fisheries scientist who oversees stock assessments in the region.

"Without the information from tagging, we wouldn't be in a position to be confident that bigeye tuna is being sustainably harvested.

"Tagging data is fundamental in assessing the skipjack population. Without it, the assessment would be highly uncertain."

Large Yellowfin Tuna being tagged

Large Yellowfin Tuna being tagged Photo: SPC

The western and central Pacific tuna fishery - which involved fishing for skipjack, bigeye, yellowfin and albacore - was worth $US6 billion annually.

Most islands depend on a combination of fisheries and tourism revenue to fund national budgets, but the coronavirus pandemic has largely halted tourism.

"With global tourism effectively shutdown due to Covid-19, the income derived from tuna is even more critical for Pacific economies," said Graham Pilling, the SPC Deputy Director for the Oceanic Fisheries Program.

Nicol said the current tuna tagging effort, which started in August and was scheduled to finish this weekend, was of even more importance than usual because Covid-19 border closures had forced a halt to the use of independent fisheries observers on purse seine and some longline vessels fishing in the region.

This reduced the flow of data that scientists used for stock assessments.

SPC sponsored a tuna tagging program for two decades, with an estimated 450,000 tuna tagged and over 81,000 of those tags returned to the SPC, which is based in New Caledonia, for evaluation.

SPC pays a reward for returned tags, many of which are returned by cannery workers, stevedores handling tuna transshipment in island ports, and artisanal fishers.

The main challenge was getting the return of tags, particularly the electronic ones.

SPC offers a $US250 reward for return of the electronic tags and $US10 for the plastic tags.

"We use the returned tags to infer the level of harvest by the commercial fishery," said Nicol.

"The return rates of 10 to 20 percent are very useful to determining fishing mortality."

SPC combined the data gleaned from tuna tags with fisheries data from industry and independent fisheries observers to generate regular stock assessments used by island fisheries departments for management of the resource.

"Tuna is being fished well within sustainable limits," Nicol said.

The crew onboard SPC's chartered vessel the Gutsy Lady tagged 6,387 tuna on a seven-week voyage in Kiribati and the Phoenix Islands Protected Area that ends when the vessel returns to Honolulu Saturday.

A small yellowfin with attached electronic tag about to be returned to the water

A small yellowfin with attached electronic tag about to be returned to the water Photo: SPC

They have been using two types of tags. One was a conventional spaghetti-style plastic dart tag and the more sophisticated electronic tags that were surgically implanted, said SPC fisheries scientist Dr Joe Phillips.

"The electronic tags record information about the fish and the ocean environment," said Phillips.

"When the tags are returned, we evaluate the data stored on these electronic tags."

Scientists were able to learn things from the data stored on the electronic tags such as how much time tuna spend around fish aggregating devices (FADs), and school cohesion around the FADs.

The scientists said tagging was critical to show exactly how fishing pressure, climate change and improvements in fishing technology affected the health of the fishery.

Nicol said key to the success of the current tagging voyage was cooperation with the fishing industry.

"This is one of the most successful trips," he said, adding this reflected the "fantastic collaboration with industry, which has been providing daily updates from their electronic monitoring (of tuna schools) to direct us (crew on the Gutsy Lady) to areas of expected high tuna abundance."

Phillips said good support from the Kiribati government facilitated the voyage in Kiribati's vast exclusive economic zone.

The collaboration with the tuna industry and Tuna Commission members in the region was what made the tuna tagging programme work. "The tagging benefits everyone," Phillips said.

Because of the volume of tuna caught annually and the value to industry and the islands, credible stock assessments were essential to ensuring fishing rules and harvest limits could be made based on solid information, the two scientists said.

"By our estimate, the stocks are in good shape," said Phillips.