Search

Tidal creeks along the southeastern U.S. and Gulf of Mexico coastlines provide nursery habitats for commercially and ecologically important nekton, including juvenile blue crabs Callinectes sapidus, a valuable and heavily landed seafood species. Instream and watershed urbanization may influence the habitat value that tidal creeks provide to blue crabs. We investigated natural and anthropogenic factors influencing juvenile blue crab occupancy dynamics in eight first-order tidal creeks in coastal North Carolina (USA). An auto-logistic hierarchical multi-season (dynamic) occupancy model with separate ecological and observation sub-models was fitted to juvenile blue crab presence/absence data collected over replicate sampling visits in multiple seasons at three fixed trapping sites in each creek. Colonization and survival are the processes operating on occupancy that are estimated with this formulation of the model. Covariates considered in the ecological sub-model included watershed imperviousness, the percent of salt marsh in each creek’s high tide area, percent salt marsh edge, site-level water depth, and site-level salinity. Temperature, salinity, and dissolved oxygen were covariates considered in the observation sub-model. In the ecological sub-model, watershed imperviousness was a meaningful negative covariate and site-level salinity was a positive covariate of survival probability. Imperviousness and salinity were each marginally meaningful on colonization probability. Water temperature was a positive covariate of detection probability in the observation sub-model. Mean estimated detection probability across all sites and seasons of the study was 0.186. The results suggest that development in tidal creek watersheds will impact occupancy dynamics of juvenile blue crabs. This places an emphasis on minimizing losses of natural land cover classes in tidal creek watersheds to reduce the negative impacts to populations of this important species. Future research should explore the relationship between imperviousness and salinity fluctuations in tidal creeks to better understand how changing land cover influences water chemistry and ultimately the demographics of juvenile blue crabs.

We conducted three laboratory studies to determine the effects of surgically implanted, passive integrated transponder (PIT) tags on survival, tag retention, and growth in two abundant estuarine fishes. The effects of the 12.5-mm PIT tags were examined in Spot Leiostomus xanthurus, and the effects of the 12.5-mm and 8.4-mm tags were examined in Mummichog Fundulus heteroclitus. For each experiment, Spot and Mummichogs were divided into three size-groups: small, medium, and large. Tagged Spot had lower survival rates than the untagged conspecifics with the exception of the larger Spot, where there was no difference in survival rates. Large Spot also had the highest tag retention (86%) and tagging “success” (i.e., 80% survived and retained their tag). There was no significant difference in the survival rate between the 12.5-mm tagged and untagged Mummichogs; there was no significant effect of Mummichog size on survival, tag retention, or success; and success for all 12.5-mm tagged Mummichogs was 87%....