Assessing Effects of the Nonindigenous Pike Killifish on Indigenous Fishes in Tampa Bay, Florida, Using a Weighted‐Evidence Approach

Abstract

AbstractNonindigenous fish introductions may result in significant negative ecological and economic effects. Pike killifish Belonesox belizanus, a small‐bodied piscivorous fish native to Central America, was introduced into South Florida in 1957 and raised concerns because of its consumption of small‐bodied fishes. The present study examined the negative effects on indigenous fishes from a second pike killifish population that invaded Tampa Bay several decades later. Four data sets were used to test several hypotheses based on earlier observations from South Florida: potential indigenous prey fish populations are less abundant or less frequently occurring or have a larger size composition (1) in invaded water bodies than in uninvaded water bodies and (2) following invasion than before invasion (with no concurrent change in uninvaded systems). For each prey species, the result of each hypothesis test was scored (2 = accept, 1 = tentatively accept, and 0 = reject) and the average score of all hypotheses was calculated, weighted by the relative rankings of the factors influencing the scope of inference from each data set (e.g., number of samples, years, and water bodies). Three resident (nonmigratory or potamodromous) small‐bodied species (sailfin molly Poecilia latipinna, eastern mosquitofish Gambusia holbrooki, and sheepshead minnow Cyprinodon variegatus) showed the most evidence of potential effects and had overall weighted‐evidence scores of around 50% (i.e., as much evidence for pike killifish effects as against). There was much greater evidence of effects of pike killifish when calculating scores based only on the abundance and frequency‐of‐occurrence hypotheses because the three species were two to six times less abundant or frequently occurring in the presence of, or after invasion by, pike killifish. Migratory species showed little evidence of negative effects, probably because they recruit from larger source populations and are not year‐round residents of pike killifish habitat.