Prized ono carry international passports

Many anglers think of ono as a local, coastal fish, caught on ledges and dropoffs around the island, but a new genetic study shows they may be genetically more closely related worldwide than any other fish.

“They share genotypes between here and the Bahamas, which is unheard of in other tunas, billfish, and sharks,” said fish researcher Brian Bowen of the University of Hawai'i's Institute of Marine Biology.

(Image: a couple of anglers hold a fresh caught ono, also known as wahoo or Acanthocybium solandri. Photo: wahoosportfishing.com.)

The ono is a powerful, slim fish with tasty white meat. The fish is found throughout the world in warm to temperate waters. In Hawai'i, it is often caught trolling. Because ono do not school, they are not readily overfished by netting—and there are still quite a few of them as other fished species are declining in population.

A genetic study suggests all ono worldwide are comparatively closely related—much more so than many of the other fish with which they swim.

The study in the journal “Molecular Ecology” is entitled “High connectivity on a global scale in the pelagic wahoo, Acanthocybium solandri (tuna family Scombridae).” It was written by T. C. Theisen and J.D. Baldwin of Florida Atlantic University, Bowen of the University of Hawai'i's Hawai'i Institute of Marine Biology, and W. Lanier of the University of Iowa.

Hawai'i's Bowen said Hawaiian ono are very closely related to, for example, the ono swimming in the Bahamas, on the other side of the Americas. While a particular species of fish might be found both in different oceans, they normally are genetically quite different in distant locations—on account of having been isolated from each other for so long.

Not so with ono.

That doesn't mean Bahamian ono are cruising around the coast of South America or Africa for Hawaiian amorous vacations, but it does suggest there is something interesting going on.

One piece of the puzzle is that the fish do swim great distances. One O'ahu ono was tagged and was later recovered 2,700 kilometers away. That's about 1,700 miles.

But swimming isn't everything. It is also possible, the authors say, that the ono tend to spawn near oceanic currents that disperse their keiki dramatically.

“The combination of adult and larval dispersal yields the only globally-distributed animal with no population separations,” Bowen said.

That creates a unique challenge for fishery managers, who don't normally deal with fish that lack regional population boundaries.

“The challenge for managers is how to deal with a single worldwide stock. (Ono) are not overfished yet. Is it possible to overfish a global stock? We'll find out in the next few decades,” he said.

The paper does suggest that the ono seems to be the poster child arguing for international cooperation in protecting fisheries.

“The size of the wahoo population may still resemble pre-industrialized levels, and thus an increase in fishing pressure that reduces the overall size of the wahoo population and hence, the number of migrants per generation, may reduce or even eliminate their apparent global connectivity,” the authors write.

“For wahoo, an opportunity still exists for agencies to manage and study a pelagic fishery before it becomes over-exploited. Continued research on this apparently still-healthy pelagic fishery will almost certainly provide data valuable to the management of other, over-exploited pelagic species,” they write.

©2008 Jan TenBruggencate