Yellowfin tuna, aptly named for their bright yellow dorsal and anal fins, are quite striking visually, much more so than the other tropical tunas that inhabit the Phoenix Islands. This is the tuna commonly referred to as “ahi” on sushi menus, though ahi can sometimes refer to bigeye tuna as well.

Credit: NOAA Fishwatch via

The metallic blue/green of their backs are separated from their silvery white bellies by a thick, yellow stripe starting at the upper jaw and ending near the tail. Also notable are the bright yellow finlets outlined in black, which run from the second dorsal and anal fins to the tail. As they age, the long second dorsal and anal fins become prominent and may reach lengths greater than 20 percent of the fish’s total length, but as juveniles, yellowfin look quite similar to both skipjack and bigeye tuna, and the three species often school together when they are young.

Like skipjack tuna, yellowfin are batch spawners, capable of spawning every few days once they’ve reached maturity at about 3 feet (100 cm) in length. Because they mature at a relatively young age (1–2 years) and spawn frequently, they are fairly resistant to fishing pressure. However, the segment of the population that inhabits the tropical Pacific, where 95 percent of landings occur has been heavily impacted by the explosive growth of the purse seine fleet and the use of FADs. Though conservation measures have been enacted to keep the stock from becoming overexploited, proper monitoring and compliance by fishing fleets must be ensured to maintain the population at healthy levels.

Yellowfin tuna is often called "ahi" from the Hawaiian word for tuna ʻahi.

In the waters of Kiribati, yellowfin are caught by both purse seine vessels and longline vessels. Kiribati has a small domestic longline fleet, but most yellowfin caught within its territorial waters are landed by vessels from distant water fishing nations (DWFNs). An average of 35,000 metric tons (more than 77-million pounds) of yellowfin are landed annually by all gear types (purse seine, longline, other artisanal methods), with a value of around $28.4 million USD [1]. Though tuna catches contribute only minimally to the Kiribati GDP (because very little tuna is landed or processed in Kiribati), licensing fees paid by DWFNs to fish for yellowfin and other tuna species in Kiribati account for greater than 40 percent of government revenues. Obviously, maintaining healthy populations of yellowfin and other tuna species will be essential for the economy and welfare of the Kiribati people.

Currently the only legal commercial activity going on inside this marine protected area—an area the size of California—is tuna fishing by Distant Water Fishing Nations (DWFN) under bilateral and multilateral treaties. Purse seine and longline vessels target yellowfin, big eye and skipjack tunas destined for, among other countries, markets and restaurants here in the United States.

Climate change, which is projected to affect the abundance and distribution of yellowfin and many other important commercial species in the Pacific, will be another added stressor that could have negative long-term impact on revenue from tuna fisheries. Current model projections are optimistic for Kiribati, indicating that increasing water temperatures and other factors that go hand-in-hand with climate change are likely to increase the abundance of skipjack and yellowfin in the region.

Credit National Undersea Research Program via

However, there is substantial uncertainty around these projections due to the complexity of interactions among climate change variables, so they must be viewed with caution. Closing PIPA to tuna fishing is an important part of Kiribati’s commitment to maintain sustainable tuna fisheries within its territorial waters in the face of inevitable changes in the near future. Implementing the closure, along with other measures to control fishing effort and FAD use, can offset fishing excesses in other areas and some of the changes likely to occur with an increasingly warm ocean.