Status, ecology and conservation of an endemic fish, Oreochromis niloticus baringoensis, in Lake Baringo, Kenya

Britton, J. Robert and Jackson, MC and Muchiri, M. and Tarras-Wahlberg, H. and Harper, D.M. and Grey, Jonathan (2009) Status, ecology and conservation of an endemic fish, Oreochromis niloticus baringoensis, in Lake Baringo, Kenya. Aquatic Conservation: Marine and Freshwater Ecosystems, 19 (5). pp. 487-496. ISSN 1052-7613

Abstract

1. The tilapia Oreochromis niloticus baringoensis is a genetically and morphologically distinct sub-species of Oreochromis niloticus endemic to Lake Baringo, Kenya. In recent years, concern has been expressed as to its status. Recent declines in catch returns suggest the population may be threatened, with conservation action required to safeguard it. 2. Catch returns from the Baringo fishery since 1964 have shown considerable fluctuations for all species, but especially O. n. baringoensis. From a peak of 712 t in 1970, their total catch was only 5 t in 2005, despite a 2 year period of closure in 2002 and 2003. Changes in fishery catch and relative abundance were independent of exploitation in the fishery but were significantly correlated with lake level. 3. Few individuals were captured at lengths >250 mm, with no fish sampled >284 mm. During periods of high lake level, individuals matured at smaller sizes and were capable of growing to larger ultimate sizes. With maturity at lengths <130 mm and fishery regulations preventing removal of fish <180 mm, there was a relatively large proportion of mature fish that was below exploitation size each year (19 to 44%). In most years, the proportion of fish available for exploitation was <10%. 4. Stable isotope analyses revealed O. n. baringoensis was reliant upon planktonic basal resources and zooplankton carbon. There was only minimal trophic overlap with other fish species in the lake, indicating little potential for competition for food resources. 5. These data suggest that the population status of O. n. baringoensis is not threatened per se, but subject to an unpredictable and unstable environment that strongly influences their life-history traits and, ultimately, their population abundance, and should be managed accordingly.