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

Abstract

Nonindigenous 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.

Received January 25, 2011; accepted May 9, 2011

ACKNOWLEDGMENTS

Thanks to personnel from the Fish and Wildlife Conservation Commission–Fish and Wildlife Research Institute Fisheries-Independent Monitoring Program for collection and processing of fish samples. Richard Sullivan and Ross Dickerson (Hillsborough County Parks, Recreation, and Conservation Department), and Wendy Anastasiou (Tampa Electric Company) facilitated access to several sampling sites. Data used in this study were derived from projects supported in part by funding from State of Florida Saltwater Fishing License sales; by the Department of the Interior, U.S. Fish and Wildlife Service, Federal Aid for Sport Fish Restoration grant F-43; by the Pinellas County Environmental Fund, Tidal Tributary Habitat Initiative grant 2005-0003-003; by the Southwest Florida Water Management District; by Tampa Bay Water; by State Wildlife grant SWG05-015; and by grants CM-254 and CM-280 from the Florida Office of Coastal Management, Department of Environmental Regulation, with funds provided by the U.S. Office of Ocean and Coastal Resource Management, National Oceanic and Atmospheric Administration, under the Coastal Zone Management Act of 1972, as amended. David Jude (University of Michigan) and several anonymous reviewers greatly improved earlier versions of the manuscript.