Fishery Biological Characteristics and Changes in the Annual Biomass of Bigeye Kilka (Clupeonella grimmi) in the Caspian Sea

Through most of the last century, three endemic kilka species supported the major commercial species in the Caspian Sea. Recent changes in the Caspian Sea ecosystem have occurred as a consequence of climate change and ecological change caused by the invasive ctenophore Mnemiopsis leidyi. We examined the impact of these changes on the population biology of bigeye kilka (Clupeonella grimmi) in Iranian waters of the Caspian Sea from 1995 to 2001. The overall sex ratio (male:female) was 1.65:1. The length-weight regression was W = 0.00922L2.851 (females) and W = 0.008021L2.907 (males) indicating a negative growth for both sexes. Growth parameters were estimated as L∞ = 142 mm, K = 0.28 yr^-1, t0 = -1.39 yr. The instantaneous coefficient of natural mortality was estimated as 0.460 yr^-1 and the instantaneous coefficient of fishing mortality varied between 0.469 to 0.980 yr^-1. Biomass of the bigeye kilka increased from about 36,900 mt in 1995 to more than 53,500 mt in 1998, but declined to less than 5,900 mt in 2001. This decrease in bigeye kilka was simultaneous with a sharp reduction in anchovy kilka due to the combined effects of fishing and changes in zooplankton abundance and composition soon after the appearance of Mnemiopsis leidyi in the Caspian Sea.