Effects of Alien Species on the Abundance and Condition Status of the Endangered Killifish Fundulus lima

The abundance and the residual somatic condition index (Kr) as an expression  of fitness status of the population was analyzed for the endangered endemic Fundulus lima, using catch-per-unit-effort and residuals obtained from the least square regression of total mass and total length, respectively. The fish catches were performed during rainy and dry seasons at six stations through the main river course of the San Ignacio and La Purísima drainages. Five fish species were recorded: the native killifish and four exotics (Cyprinus carpio, Poecilia reticulata, Xiphophorus hellerii, and Tilapia sp. cf. zillii). Killifish showed a population decline in both basins as consequence of the expansion and competition of exotic fish species. The relationships between the Kr of killifish and 21 environmental variables were analyzed using multiple regressions. Values of Kr for the killifish varied among sampling sites. The biomasses of T. sp. cf. zillii and C. carpio were the ecological variables that better explained the variation of Kr for the killifish. T. sp. cf. zillii is indirectly responsible for the low abundances of the four coexisting species into the oases, dominating the habitat and pushing to these species for occupying smaller habitat units, causing a higher competition for food among them and reducing the condition factor of the endemic killifish. We conclude that Kr for the populations of killifish is a good indicator of the competitive interactions by exotic fishes in oases of Baja California peninsula and could be considered when such stocks are subject to recovery plans or any other management program.