Threatened green sturgeon population estimate and assessment of bycatch impact.

Background/Question/Methods

There are many species with life histories that use a variety of habitats. This type of life history may make these species difficult to monitor as each habitat may require a different censusing technique and the total population of the species may be divvied over multiple habitat types. Long-lived anadromous fish species, such as sturgeon, fit this category as use both ocean and riverine environment, and the population is often divided between habitats. To estimate the population of threated green sturgeon in California, we have been conducting a sonar-based census of spawners on the Sacramento River since 2010. We use an ingratiated population model to calculate the total adult population. We then combine those results with a stochastic life table model to estimate the entire population. We also use this methodology to conduct a population viability assessment with respect to the threat from fishing bycatch.

Results/Conclusions

The adult population is currently just below NOAA’s recovery goal (3000), and that the population over all is currently approximately 10,000 individuals. Pressure from the California halibut trawl fishery would reduce a stable population of green sturgeon by between 0.9 and 0.3% per year. These methods have proven useful for monitoring the population level of green sturgeon and assessing threats. We will continue to develop this modeling framework to assess the effects of other management actions on this sturgeon population.