The population biology of tench, Tinca tinca (L.), in two gravel pit lakes.
The populations of tench from two gravel pit lakes of contrasting habitat type were studied. The population density of tench from St Peter's Lake, which has abundant aquatic vegetation was 176 individuals ha-1 (102.2 kg ha-1) compared to 0.3 individuals ha-1 (0.5 kg ha-1) in the Main Lake which has very little aquatic vegetation. The results of ageing tench by scales, opercular bones and otoliths were compared; all three structures gave similar results up to 9 years of age, but thereafter there were difficulties in ageing using scales and care was needed in counting annuli. The oldest tench caught was 15 years old. Growth of male and female tench was similar and fitted the von Bertalanffy model; for female tench Lx=573 mm, K=0.122 and for male tench Lx=586 mm, K=0.114. Recruitment was variable and strong year classes occurred in years with warm summers.