The effect of overfishing on the life-history strategies of Nile tilapia, Oreochromis niloticus (L.) in the Nyanza Gulf of Lake Victoria, Kenya

Abstract

Studies were conducted on reproductive characteristics of Oreochromis niloticus from 1998 to 2000. The results were combined with published work on growth parameters of O. niloticus from 1985 to 1999 in order to establish the current survival strategies exhibited by O. niloticus in the Nyanza Gulf of Lake Victoria. The study revealed that size at maturity had decreased concurrently with increasing fishing mortality. Observations on reproductive effort point to a fish species under stress. It is observed that the behavioural change in O. niloticus is not due to size selective predation but due to size selective exploitation. Indications that O. niloticus in the Nyanza Gulf of Lake Victoria allocates more energy for reproduction than for somatic growth (i.e. increased turnover rate) are multiple. It is concluded that O. niloticus in the Nyanza Gulf exhibits an ‘r’-selected life history strategy in order to survive stressful conditions.