STONY BROOK (US)—Reducing adult mortality of beluga sturgeon would be more effective than hatchery supplementation in easing a worldwide shortage of caviar.
A joint study by American and Kazakhstani scientists of a Caspian Sea beluga sturgeon (Huso huso) fishery demonstrates current harvest rates are four to five times higher than those that would sustain population abundance.
The study’s results, which will be published in an upcoming issue of the journal Conservation Biology, suggest that conservation strategies for beluga sturgeon should focus on reducing the overfishing of adults rather than heavily relying upon hatchery supplementation.
Populations of beluga sturgeon have declined by nearly 90 percent in the past several decades due to the high demand for black caviar, inadequate management, and habitat degradation.
There has been concern about increasingly dwindling numbers of the already depleted species, which has gone extinct in the Adriatic Sea and is on the brink of extinction in the Azov Sea.
Black caviar, the unfertilized roe (eggs) of the beluga sturgeon, is the most valuable of all caviar, and can be sold for as much as $8,000 for one kilogram (2.2 pounds).
Data used in the quantitative analysis were collected in the Ural River, the only remaining Caspian Sea river where beluga sturgeon reproduce unhindered by dams.
“This is the first time that anyone has calculated sustainable harvest limits for Caspian Sea beluga sturgeon and compared them to present fishing pressure,” says Phaedra Doukakis, senior research scientist with the Institute for Ocean Conservation Science at Stony Brook University and lead author of the study.
“We can finally attach numbers to what people have suspected—that current management of Caspian Sea sturgeon fisheries will not prevent further population decline. We hope that this study provides the evidence needed to shift mindsets and management practices.”
Fishing pressure far exceeds sustainable levels. Limiting the take of adult and subadult sturgeon will contribute more to the population growth rate as compared with hatchery supplementation.
The beluga sturgeon can live more than 100 years, and do not reach maturity until 9 to 20 years of age. The optimal age of first harvest is 31 years because older and larger fish produce more eggs.
Conservation efforts would be much more effective than current practices if minimum size limits for fishing targeted this optimum age for first capture and if the illegal harvest of subadult fish were reduced, allowing for the survival of subadult and adult females.
Doing so would increase population productivity by 10 times that achieved by hatchery supplementation.
Currently the fishery management focus for beluga sturgeon conservation is on using hatcheries to sustain the population. However, survival of hatchery-reared fish in the wild is thought to be very low.
Additionally, genetic diversity may be compromised by hatchery practices, which can potentially jeopardize the long-term survival of all beluga sturgeon. Despite the potential threats posed by hatchery fish, regulatory agencies allow more fishing (higher quotas) by countries with higher hatchery output.
“Reducing the mortality of wild beluga sturgeon adults is a much more effective conservation strategy than hatchery supplementation,” says Ellen Pikitch, Executive Director of the Institute for Ocean Conservation Science and a coauthor of the study.
“Ten hatchery fish would need to be produced to achieve the same conservation benefit as preventing the kill of a single wild beluga sturgeon.
“It’s clear that the focus of sturgeon management in the region has been misplaced and must change. A shift in practices could prevent further declines in beluga sturgeon and ultimately promote recovery,” she adds.
The Convention on International Trade in Endangered Species (CITES) listed beluga and most other species of sturgeon as threatened in 1998.
However, beluga sturgeon numbers have declined by approximately 60 percent from the time of the listing through 2005 showing that existing management of beluga sturgeon fisheries has not been effective.
The new research results suggest that a change in management focus is critical to stabilization and recovery of the species.
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