A working party on neritic tunas – one of seven working parties supporting the Scientific Committee of the Indian Ocean Tuna Commission (IOTC) – is trying to get a better handle on the state of the resource, for which detailed data has been lacking.
In contrast to oceanic tunas, which migrate over large areas, neritic tunas such as longtail tuna (Thunnus tonggol), eastern little tuna (Euthynnus affinis), frigate tuna (Auxis thazard), and bullet tuna (Auxis rochei) tend to stay in shallow waters within countries’ exclusive economic zones (EEZs) in the sub-regional seas of Southeast Asia. The working party, which met from 3 to 7 July on Eden Island, Seychelles, is trying to improve data collection on the various species.
Individual countries have recorded their domestic catches, but these domestic catches are not under the management of any regional fishery management organization (RFMO), like the IOTC or the Western and Central Pacific Fishery Commission (WCPFC), that deal with fishing on the high seas.
While the countries have reported their domestic catches to the United Nations Food and Agriculture Organization (FAO), The data is often presented in an “aggregated” form, with various species lumped together under one category. Some tuna-like mackerels or “seerfish” are often included as well, all under the single heading of “neritic tuna.”
A report, “Review of the Statistical Data Available for Indian Ocean Neritic Tuna and Seerfish Species under IOTC Management,” notes the uncertainties in retained catch data.
“Small or juvenile neritic tunas are often also treated commercially as the same species – particularly in the case of frigate and bullet tuna – and are often reported to the Secretariat as species aggregates or commercial categories, therefore requiring a disaggregation step to produce estimates at species level,” the report states.
Species like narrow-barred Spanish mackerel and Indo-Pacific king mackerel are also often combined and reported to the IOTC as one species called “seerfish.”
The data is organized this way because neritic tunas usually move in small schools, so mixed local fishing – rather than targeted fishing for one species – accounts for most of the catch. Fishing aimed at other species also takes many neritic tunas as bycatch. Detailed sorting and recording of the various species caught by fishers is more burdensome in a mixed fishery than when dealing with a single target species.
In recent years, RFMOs have recognized the need to collect and “disaggregate” this data. The IOTC Secretariat has had to estimate species and gear composition for some major countries, such as India and Indonesia, due to aggregation, which results in lower quality scores for the data.
Besides the aggregation issue, much of the catch is not reported at all. The amount of the total catch reported has oscillated between 37.2 and 72.2 percent of the actual total catch. Reporting improved from the mid-1990s to 2019, but then fell.
“The reporting quality has decreased since then and 59.1 percent of all retained catch was fully or partially reported to the Secretariat in 2021,” the report said.
As worldwide demand for tuna increases and the value of the neritic tunas is more broadly recognized, RFMOs like the IOTC are starting to place more importance on detailed breakdowns of data by species and the type of gear used to capture it, as well as fish-size data for each type of gear in each location.
“Information available from the [FAO] indicates that annual catches of six neritic tunas … and 12 seerfish species … exceeded two million metric [tons] in recent years,” said the report. “Some of these species are not under the management of any regional fishery body and catch data available from the tuna [RFMOs] may therefore misrepresent their socio-economic importance.”
Most of the catch goes to the local markets or to neighboring countries – in raw form or following processing at local canneries. An exception is longtail tuna, which exporters ship to the European Union (E.U.) or other markets in the region, like Saudi Arabia and Sri Lanka.
At the meeting, the working party received a report on longtail tuna. It showed that the largest proportion of the worldwide catch has repeatedly alternated over time between the Indian Ocean and the Western-Central Pacific. In 2020, the shares were about 35 percent and 65 percent, respectively. However, in 2014, the positions were the opposite, with 70 percent for the Indian Ocean and 30 percent for the Western-Central Pacific.
Catch volumes, while fluctuating, have been on a steeply rising trend, surpassing 350,000 metric tons (MT) in the two regions combined in 2020. Catches first surpassed 200,000 MT in 2003. In 2020, industrial fisheries took about 88 percent of the total catch in 2020, while artisanal fisheries took about 22 percent.
Between 2017 and 2021, gillnets accounted for 67.4 percent of the retained catch in the Indian Ocean. The most significant among other gear types were “other” (8.9 percent), handline (7.7 percent), purse seine (7.5 percent), trolling (4.9 percent), and coastal handline (3.3 percent).
During the period, Iran caught the most longtail tuna using gillnets, followed by Indonesia, Oman, and Pakistan. For catches by line, Indonesia and Oman were the leaders, followed by Iran and Yemen. Thailand, Malaysia, and Indonesia took the most by purse seine, followed by India. Much longfin tuna is taken in the Persian Gulf and in (and near) the northern part of the Strait of Malacca.
An early advocate of better data collection and more regional cooperation in managing neritic tuna was the Southeast Asian Fisheries Development Center (SEAFDEC) project, formed in 1967 by regional governments. The 45th SEAFDEC Council Meeting in 2013 called for the development of a plan of action for regional cooperation on neritic tunas in the Southeast Asian region, and this project continues despite a three-year pandemic-induced hiatus.
“We separate catch by species using average species compositions,” Tsutomu (Tom) Nishida of Japan, who leads a stock assessment software developing team for SEAFDEC, said. “But some countries have very crude composition (e.g., only one average species composition). That is why we recommend getting more specific species compositions by year, season, and area, so that more accurate catch by species can be estimated. This is on-going, thus we expect the situation will improve slowly.”
Photo coutesy of moointer/Shutterstock
