Population structure, growth, mortality and estimated stock size of the introduced tench, Tinca tinca (L.), population in Lake Beysehir, Turkey

Abstract

Population structure, growth, length-weight relationship, mortality and stock size of tench, Tinca tinca (L.), was studied in Lake Beysehir, Turkey in 2005. Totals of 3360 tench (1865 males; 1795 females) were captured with gill- and trammel-nets of various mesh sizes. Male to female ratio was 1.04 : 1. The study covered length year classes. Fork lengths and total weights ranged from 9 to 37 cm and 13 to 815 g. For all individuals, the von Bertalanffy growth equation and length-weight relationship were L-t = 54.2[1-exp(-0.1350(t + 1.0281)] and W = 0.0151 L-2.9993, respectively. Growth performance index and mean condition factor of the tench population were 2.598 and 1.513, respectively. Mortality rates were Z = 1.97 year(-1), M = 0.29 year(-1) and F = 1.68 year(-1) for total, natural, and fishing mortality, respectively. The exploitation rate was E = 0.85, and the percentage of surviving fish was 13.9%. Tench stock was assessed as about 6-7 million individuals and 1450-1500 tonnes in biomass. It was determined that maximum sustainable yield could be obtained with an 80% level of the current fishing effort.