Survival and density of a dominant fish species across a gradient of urbanization in North Carolina tidal creeks

Development in the southeastern U.S. coastal plain generates the need for a better understanding of how demographics (survival and abundance) of estuarine nekton respond to urbanization. Apparent survival and density of the dominant Atlantic coast salt marsh fish, Fundulus heteroclitus, were estimated in four North Carolina tidal creeks using a model simultaneously fitted to mark-resight and mark-recapture data. Rates of weekly loss (mortality plus emigration) were high (~10%). Sampling for tagged fish within- and outside of study creeks showed high site fidelity to each creek, suggesting that loss largely result from mortality rather than emigration. Estimated rates of apparent survival were lowest in the creek with the least instream- and watershed-level impacts relative to creeks with greater impacts; this was also the creek with direct (non-culvert) access downstream to a larger waterbody, suggesting that enhanced access by predators and/or greater rates of permanent emigration may have contributed to loss there. There was a positive relationship between minnow trap catch-per-unit-effort (CPUE) and density; CPUE was used to index density so that the relationship between it and habitat and urbanization effects could be examined in two additional (six total) study creeks. Highest CPUE estimates occurred early in each growing season and were associated with creeks possessing characteristics most representative of undisturbed salt marsh mosaics: high percentages of marsh coverage instream and downstream and greatest percentages of marsh edge. Given generally limited movement outside of creeks, differences in abundance among creeks likely result from different levels of recruitment that are related to salt marsh availability. Natural resource planners should prioritize preservation of salt marsh habitats to maintain abundance levels of this trophically important species.