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%. Survival estimates were 90%, 95%, and 100% for the small, medium, and large 8.4‐mm tagged Mummichogs; and tag retention was 100% for the survivors. Within the medium and large sized Spot and Mummichogs (for both 8.4‐mm and 12.5‐mm tags), there was no effect of PIT tag presence on growth (length or weight). Spot should be >68 mm TL to obtain a tag success of >90% using 12.5‐mm PIT tags. Tagging was successful for Mummichogs in the smallest sized groups examined but there was also an indication of lower growth rates for Mummichogs <50 mm marked with 12.5‐mm PIT tags. Mummichogs should thereby be >50 mm when initially tagged with 12.5‐mm PIT tags and more than ~36 mm TL when tagged with 8.4‐mm PIT tags. PIT tags can be used to successfully mark relatively small Spot and Mummichogs, potentially allowing for robust estimates of their demographic rates. Received April 2, 2015; accepted December 16, 2015 Published online May 31, 2016

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.

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We estimated rates of survival as well as effects of habitat on catch rates of juvenile yellow‐phase American Eels Anguilla rostrata in southeastern U.S. tidal creeks. We trapped and marked eels with PIT tags at 24 fixed sites in eight North Carolina tidal creeks and then recaptured and resighted the tagged individuals to estimate apparent survival. Separate Cormack–Jolly–Seber (CJS) models were fitted to mark–recapture data (eight creeks) versus mark–resight data (four creeks) to estimate apparent survival. Median annual apparent survival (Φ) was higher when the CJS model was fitted to mark–resight data (Φ = 0.15) than to mark–recapture data (Φ = 0.013). Negative binomially distributed models were fitted to catch rates of both tagged and untagged eels to test for habitat, development, and seasonal effects. The presence/absence of culverts and season were meaningful covariates of catch rates; greater catches were found at sites possessing culverts and during the spring. Other habitat and development factors at the site, creek, and watershed levels were not important covariates of catch rates. Partitioning the sources of loss of yellow‐phase American Eels from these systems into mortality versus emigration would be useful future research in the southeastern U.S. coastal region. Further study into how culverts affect yellow‐phase American Eel habitation and movement in southeastern U.S. estuaries is also warranted.

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