Effect of pulsed gastric lavage on apparent survival of a juvenile fish in a natural system

Abstract

Dietary studies are essential for studying trophic dynamics, and are often based on analysis of stomach contents. A popular method to collect stomach contents is the use of pulsed gastric lavage (PGL), wherein a stream of pressurized water forces an individual to regurgitate food items. Most past experimental studies have shown no effect of PGL on survival, but these studies are limited to laboratory or cage experiments, thereby controlling for natural effects such as predation or emigration. Using a mark–recapture/resighting approach, we determined the effect of PGL on apparent survival (ϕ=1−mortality−emigration) in a natural system. In two study sites, we marked a total of 200 juvenile common snook, Centropomus undecimalis (Bloch 1792) (mean=251.7mm standard length, sd=30.7, range=202–320mm) with PIT tags, lavaged 89 of these snook, and resighted 90% of marked fish at least once with a telemetry array. Using the Barker survival model, we determined a significant effect of PGL on apparent survival through QAICc model selection, 95% confidence intervals of parameter estimates, and likelihood ratio testing (P=0.017). The PGL effect reduced QAICc model averaged maximum likelihood estimates of apparent survival by 12.0–17.4%. Since we estimated apparent as opposed to true survival, we could not fully partition lethal and sublethal (emigration) effects; however, a lower incidence of emigration in lavaged individuals suggests that emigration did not drive the declines in apparent survival. Regardless of the mechanism, we found that PGL affected individuals, which is contrary to most previous controlled studies. Future researchers using PGL must consider the influence of potential lethal/sublethal effects in natural settings.