More than 16,600 tuna were tagged in a recent scientific tagging expedition in ocean generally north of Papua New Guinea.
The voyage targeted skipjack tuna, which makes up 70% of the volume of tuna caught in the Western and Central Pacific Ocean (WCPO).
Tuna tagging helps the Western and Central Pacific Fisheries Commission (WCPFC) and national fisheries managers assess numbers of tuna. The assessments are used to set catch limits.
This voyage was conducted largely in the exclusive economic zones (EEZs) of Papua New Guinea, Solomon Islands, Palau, and Federated States of Micronesia, with a little time spent also in two pockets of high seas.
In its most recent fisheries newsletter, SPC reported that fisheries authorities in PNG, Palau and FSM provided research permits and gave support to the research being done in their EEZs.
An average of almost 450 tuna were tagged and released each fishing day. Most – 93% – were skipjack, the rest being yellowfin (6%) and bigeye (1%). Most came from free-swimming schools (i.e. the tuna were not caught near fish-aggregating devices, or FADs).
Some fish were implanted with what is known as an archival tag, a physical device which must be inserted using small surgery and a very fast turnaround – no more than 30 seconds – so that the tuna doesn’t become too stressed and lacking in oxygen.
SPC reported that it expected some of the tuna tagged in this way would be recovered and would provide good data on the behaviour and movement of the fish.
The agency also reported that some tuna were injected with strontium chloride, a slightly radioactive salt that becomes incorporated into a part of the tuna’s skeleton known as the otolith (or ‘ear stone’). As the fish grows, scientists can use the mark left by the strontium chloride in the otolith to estimate how old the fish is. (Otoliths help fish to balance and to understand how fast they are swimming.)
To conduct the tagging cruise, SPC chartered a pole-and-line vessel from Noro, in Solomon Islands.
This was the fifth western Pacific tagging cruise, and it lasted from July to September 2019.
Tuna tagging has been carried out regularly since the Pacific Tuna Tagging Programme ran its first voyage in 2006.
This trip came under a new tagging experiment introduced by the Pacific Community (SPC) to implement a recommendation of the 12th meeting of the Scientific Committee of the Western and Central Pacific Fisheries Commission (WCPFC).