Effects of IUU fishing and stock enhancement on and restoration strategies for the stellate sturgeon fishery in the Caspian Sea

Sturgeon is the most valuable fish species because of the high demand for their roe. The sturgeon fishery was historically the most important fishery in the Caspian Sea, but the major sturgeon species have now been classified as “critically endangered” by the International Union for Conservation of Nature. Considering commercial importance and data availability, we focus this study on stellate sturgeon. By applying a Depletion-Based Stock Reduction Analysis to model the population dynamics of the stellate sturgeon in the Caspian Sea, we estimate that the current stock is only 16% of the biomass (BMSY) that can produce the maximum sustainable yield (MSY). If all fish removals are stopped and no more stock enhancement takes place in the future, the stock would recover to BMSY by 2035 on average, with a 50% probability of it occurring between 2029 and 2058. If stock enhancement continues at the 2010 level, the rebuilding process will be 5 years faster, reaching BMSY by 2030. In contrast, if IUU fishing continues at the current level and only legal fishing is stopped, the stellate sturgeon will fail to recover and become extinct by 2042 without stock enhancement. Therefore, the priority of conserving the stellate sturgeon stock in the Caspian Sea is to eliminate IUU fishing. Practical rebuilding plans need also to include a combination of reducing fishing removals and restoring the spawning potential of the stock that has been lost by human interruptions in the ecosystem such as destruction of spawning grounds and overfishing.