en Stock assessment Stock assessment پژوهشي Orginal research papers There have been recent changes in the Caspian Sea ecosystem, such as those due to changes in sea level or those caused by the invasive ctenophore, <em>Mnemiopsis leidyi</em>. It is believed that these changes had significant impacts on the absolute and relative abundance of the commercially important anchovy kilka (<em>Clupeonella engrauliformis</em>) and common kilka (<em>C. cultriventris caspia</em>) leading to decline in the former and increase in the latter species in the Iranian waters. Consequently, more rigorous management is required. The mixed-species yield-per-recruit was applied to the Iranian conical lift-net. This study showed that the pooled fishing mortality at <em>F</em>_40% was 0.70 yr^-1 which is higher than fishing mortality of main species of anchovy kilka, but lower than the pooled fishing mortality at <em>F</em>_0.1(0.75 yr^-1). The ABC under the best information available, at pooled species reference points for two species of anchovy and common kilkas, was estimated to be 8260mt. An analogous goal in a multispecies situation would be fishing at a fishing level, denoted <em>F</em>_ws, such that the fishing rate for the weakest stock (in this case; anchovy kilka) does not exceed its <em>F</em>_40% rate. Under this harvest strategy at F_40% for anchovy kilka, it is suggested that the ABC of pooled species of anchovy and common kilkas was estimated 7920mt to be selected in kilka fishery in Iranian waters. Multi-species fishery, Yield per recruit, Spawning biomass per recruit, Reference point, Acceptable biological catch 141 154 http://jifro.ir/browse.php?a_code=A-10-120-3&slc_lang=en&sid=1 H. Fazli hn_fazli@yahoo.com 100319475328460024151 100319475328460024151 Yes C.I. Zhang 100319475328460024152 100319475328460024152 No D.E. Hay 100319475328460024153 100319475328460024153 No C.W. Lee 100319475328460024154 100319475328460024154 No