Mature females key to beluga sturgeon survival

Hatchery fish unlikely to restore caviar-producing fish populations

Saving grown females first — not fry — is crucial to preventing extinction of the beluga sturgeon, suggests a new conservation assessment of the fish that’s been pushed to the brink by demand for its roe, known as black caviar.

ROE HARVEST Hatcheries breed beluga sturgeon and collect eggs from adult females (above). The “Padushka massage” method allows eggs to be extracted without killing the adult, but it is seldom used for caviar because the collected roe doesn’t have the desired crunch. The Institute for Ocean Conservation Science

PRE-CAVIAR Management of the Caspian Sea’s beluga sturgeon population relies heavily on hatchery-bred fish, such as this youngster from a facility in Kazakhstan. The dwindling population would be better boosted by protecting older females, a new analysis finds. The Institute for Ocean Conservation Science

Current harvest rates are four to five times higher than the population can handle and management practices must change if the species is to survive, scientists report in an upcoming Conservation Biology.

“In this case, it’s a no-brainer,” says fisheries biologist Dylan Fraser of Concordia University in Montreal, who was not involved with the study. “The data are saying if you want to save the species, stop fishing — or drastically reduce it. The evidence is overwhelming.”

The new study concludes that current conservation efforts, which rely mostly on introducing young fish bred in hatcheries into the wild, are unlikely to succeed. Instead, it finds the survival of the species depends on protecting the mature females that are most prized for their copious roe.

Beluga sturgeon, Huso huso, used to swim the Adriatic, Azov, Black and Caspian seas. But dams, pollution and demand for eggs that sold for $8,000 per kilogram in 2009 have pummeled populations. The fish is gone entirely from parts of its range and is critically endangered in others, but commercial fishing is still allowed in the Caspian Sea.

Using life history traits such as age of maturity and population data on the sturgeon that return to the Ural River to spawn, the researchers examined the implications of keeping different age classes of fish in the population. For fishing to have minimal effects, they concluded, sturgeon shouldn’t be harvested until they are at least 31 years old in order to assure the females have had a sufficient chance to produce eggs.

Saving mature and nearly adult females was 10 times more effective for maintaining a healthy population than supplementing the population with hatchery fish, says Phaedra Doukakis of the Institute for Ocean Conservation Science at Stony Brook University in New York, who led the study.

In fact, Fraser says, introducing hatchery-raised fry may harm the fragile population further, because hatchery stocks derive from only a handful of fish; their genetic blandness could swamp out whatever diversity remains in the existing population.

“There’s always the argument that if we are fishing more, we’ll just stock more,” Fraser says, but the new analysis demonstrates that hatchery supplementation “can’t be viewed as a cure-all.”

The Caspian Sea sturgeon fishery “has been a bit of a black box,” says Doukakis, who hopes the new analysis will help guide management strategies. Efforts are complicated by the fact that five countries border the Caspian Sea and must work together to manage the fishery.

Beluga sturgeons are protected under Appendix 2 of the Convention on International Trade in Endangered Species, which allows regulated trade. But they are a good candidate for Appendix 1, Doukakis says, which bans all commercial trade of the creature in question.

The species’ status is not on the docket for this year’s CITES meeting, which begins March 13 in Doha, Qatar. The animal committee will review the fish’s standing early next year, says David Morgan, chief of the CITES scientific support unit in Geneva.

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