Source: Islands Business
Since the 1950’s, when industrial fishing for tuna began, stocks have been depleted on a global scale. Total annual hauls have risen from 550,000 to more than 4 million tons.
In the western and central Pacific Ocean, the total catch in 2009 was over 2.4 million tons, an all-time record, representing 58% of global tuna production and valued at over USD3.8 billion.
For a number of years, major scientific research has been focused on improving data on the behavior, feeding patterns, migration and mortality of different tuna species to support an accurate assessment of the stocks.
The purpose is to ensure the sustainability of this vital renewable resource—a resource that can be easily damaged and, in the case of several popular tuna varieties, is already being commercially over-exploited.
In the Pacific, a focal point of this research work is the Oceanic Fisheries Program (OFP) of the Secretariat of the Pacific Community (SPC) based in Noumea, New Caledonia.
Supported by the New Zealand Aid Program, OFP was able to conduct a highly successful tuna tagging program in the Pacific.
This took place in phases across widely dispersed fisheries in the western and central Pacific Ocean between August 2006 and November 2009.
The Pacific Tuna Tagging Program has been a great success operationally, with 260,000 releases and 40,000 recaptures to-date.
These data are now being used to inform stock assessments of key tuna species for our region.
Tuna tagging involves catching, tagging and releasing tuna, then analyzing the data assembled from tags that are returned to SPC when the fish are caught.
The main objective is to improve the certainty and accuracy of the estimates of how much tuna can be sustainably harvested.
Harvesting at less than optimal levels results in lost economic opportunities; harvesting at more than these levels leads to reduced profitability and risks collapse of the fishery.
Tagging tuna
For example, the first SPC tagging program, some 30 years ago, revealed that the skipjack tuna resource was much larger than had been thought.
Without this information millions of tons of tuna harvested in the years since the tagging program could have been left to die of old age in the ocean.
These days, the emphasis is much more on setting accurate and scientifically-based catch limits.
As of July 2010, nearly 15% of all tags have been recovered and recaptures continue to come in from various unloading points.
As part of the program, about 4,000 fish stomachs were collected and almost 3,000 Fatmeter measurements were made, indicating the condition of the fish.
About half of the stomachs have since been analyzed to reveal nearly 200 different species out of some 55,000 prey counted.
The program has made use of nearly 1,000 ‘archival tags’ which are like miniature computers the size of a cigarette lighter.
These are placed just inside the belly and trail a pencil-length antenna outside it.
Archival tags provide invaluable details about the fish’s behavior, feeding times, depth habits, etc. Their use significantly augments the range of information gained from conventional tags, which provide data on growth, migration and mortality.
Recovering the tags
Recovering tags continues to be a major effort. This has involved considerable communication with fisheries authorities, major fishing associations and the tuna fishing industry in islands and countries covering a vast area.
Fish have already been caught up to 4,500km from the point at which they were released, and tagged fish can turn up in factories as far apart as Thailand and Ecuador.
It also involves significant outlay of reward money provided as an incentive to return tags from caught fish to SPC.
Posters are used to explain the program, illustrate the different tag types and advertise the rewards for returning them.
In the follow-up to the main program, SPC scientists have also made trips overseas to develop collaborative arrangements with members of the tuna industry across the region.
These visits have helped OFP personnel engage support and enthusiasm for the program and to put in place a network of tag recovery officers across the region.
About 10% of the archival tags have been recovered so far and more are expected.
This provides the Stock Assessment and Modeling section of OFP with about 5,500 days of data, offering some fascinating insights into tuna behavior. For example:
• tuna have been recorded diving to depths of more than 1,000 meters—perhaps to avoid predators;
• they adjust the depth at which they swim to maintain an ideal body temperature;
• each species has its own ‘favorite depth’ which shows up also in the different food they are eating; and
• tuna are known to congregate under floating objects; data revealed that those under such objects stay nearer the surface than those in free schools, making them more vulnerable to fishing.
PNG sees value
Papua New Guinea sees such value in the information resulting from the Pacific Tuna Tagging Program that it has agreed to fund a three-year continuation of the work in its exclusive economic zone. The program will be conducted by SPC in co-operation with Papua New Guinea’s National Fisheries Authority.
Costing USD3 million over three years, it will be part of an integrated fishery monitoring program that includes fisheries observers, in-port catch sampling and satellite-based vessel monitoring as well as tuna tagging.
In addition to the tagging in Papua New Guinea, the SPC’s tagging program will continue across the region with the support of several international and regional donors.