Population ecological parameters and biomass of anchovy kilka Clupeonella engrauliformis in the Caspian Sea

TLDR: Investigation of the population biology and biomass of anchovy kilka Clupeonella engrauliformis in Iranian waters of the Caspian found that catches and abundance of all species have changed, but catch and sampling data are limited and stock assessments are inadequate.

Abstract: Through most of the last century, three endemic kilka species supported major commercial species in the Caspian Sea. It is clear that catches and abundance of all species have changed, but catch and sampling data are limited and stock assessments are inadequate. Recent changes in the Caspian Sea ecosystem have occurred as a consequence of climatic environmental change (sea level change) and ecologic change caused by the invasive ctenophore Mnemiopsis leidyi. This paper examines the effects of these changes on the population biology and biomass of anchovy kilka Clupeonella engrauliformis in Iranian waters of the Caspian of catch, length-weight relationship, von Bertalanffy growth parameters, condition factors, sex ratios, maturity stages determined from ovarian analysis, natural and fishing mortality, age at first capture, and spawning biomass. The instantaneous coefficient of natural mortality was estimated as 0.473/year and the instantaneous coefficient of fishing mortality varied during the 10-year period between 0.541 and 2.690/year. Biomass of anchovy kilka declined from about 186000 t in 1996 to less than 12000 t in 2004. Recent high fishing rates were not sustainable after the introduction of Mnemiopsis, so overfishing is part of the explanation for the collapse of anchovy kilka in the Caspian Sea.