Paul Joseph Rudershausen

The mummichog Fundulus heteroclitus is a trophically important fish inhabiting Atlantic coastal salt marshes, with few in situ estimates of overwinter survival throughout the species range. We estimated overwinter apparent survival rates of F. heteroclitus at the approximate mid‐latitudinal species range [coastal North Carolina (USA)] in four tidal creeks that experience variable winter water temperatures. To estimate apparent survival, we fitted a Cormack‐Jolly‐Seber model to daily mark‐resight data autonomously obtained from fish marked with passive integrated transponder tags. Creek, year, mean daily water temperature, change in mean daily temperature, fish length and fish condition were considered for effects on the modelled parameters: apparent survival (Φ) (product of true survival and site fidelity) and detection probability (p). Modelling showed that water temperature and fish metrics were not related to Φ. Water temperature was directly related to p, indicating reduced fish activity and thus reduced detection probability or poor antenna detection performance at low temperatures. Creek was related to Φ and p, and the creek most open to its downstream estuary (lacking a culvert) had lower rates than the others. Greater loss (fish mortality plus emigration) in this one creek may more effectively transfer production of F. heteroclitus to larger waterbodies via emigration or predation. Conversely, lower Φ may reflect reduced detection efficiency. The results suggest that F. heteroclitus survival is insensitive to variable winter water temperatures typical of thermal dynamics in shallow estuaries in this region of its range. Median creek‐specific overwinter Φ rates (range of median values, 2 × 10⁻⁸, 0.04) were roughly equal to previously published rates for these creeks during the growing season (April–October). At these latitudes and with increasingly moderate winters, the results indicate that natural mortality could arise equally or more so from predation during the growing season than mechanisms such as starvation, direct mortality, thermal morbidity and stress‐related susceptibility to predation resulting from intermittently low water temperatures during the overwinter season.

Organisms that rely on salt marsh habitat are an important trophic link, helping to maintain estuarine ecosystem productivity. We used GIS to quantify intertidal (assumed salt marsh) area from aerial photographs taken in 1939 and from software-supplied satellite imagery taken in 2021 for tidal creeks in North Carolina (USA) that have experienced minor (60%) losses of intertidal habitat over the 8 decades. The current (2022) absolute abundance of adult Fundulus heteroclitus, a trophically important resident fish in US Atlantic estuaries, was estimated over each season in each creek by fitting a Lincoln-Petersen model to tag-recapture data. Current abundances of F. heteroclitus were lowest in creeks with the lowest intertidal area. The median and 2.5/97.5 credible intervals of the posterior probability distribution for the slope of a regression model relating current fish abundance to current intertidal area were positive, demonstrating that intertidal area was a meaningful covariate of abundance. Loss of intertidal area in the creeks between 1939 and 2021 ranged from 8 to 93%. The correlation between current intertidal area and historical loss of this habitat was negative and significant (Pearson r = -0.91, p = 0.012). Parameters from the regression relating current abundance to intertidal area were used to estimate historic F. heteroclitus abundances in each creek using GIS-derived estimates of historic intertidal area. Historic abundances were predicted to have been on average (across study creeks) 7.5 times greater in 1939 than in 2022. Reduced abundances, and thus reduced trophic relay by F. heteroclitus to higher-order consumers, can be expected in estuaries that have lost salt marsh due to inter-decadal development.

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.

It is unclear how urbanization affects secondary biological production in estuaries in the southeastern USA. We estimated production of larval/juvenile Fundulus heteroclitus in salt marsh areas of North Carolina tidal creeks and tested for factors influencing production. F. heteroclitus were collected with a throw trap in salt marshes of 5 creeks subjected to a range of urbanization intensities. Multiple factor analysis (MFA) was used to reduce dimensionality of habitat and urbanization effects in the creeks and their watersheds. Production was then related to the first 2 dimensions of the MFA, month, and year. Lastly, we determined the relationship between creek-wide larval/juvenile production and abundance from spring and abundance of adults from autumn of the same year. Production in marsh (g m^-2 d^-1) varied between years and was negatively related to the MFA dimension that indexed salt marsh; higher rates of production were related to creeks with higher percentages of marsh. An asymptotic relationship was found between abundance of adults and creek-wide production of larvae/juveniles and an even stronger density-dependent relationship was found between abundance of adults and creek-wide larval/juvenile abundance. Results demonstrate (1) the ability of F. heteroclitus to maintain production within salt marsh in creeks with a lesser percentage of marsh as long as this habitat is not removed altogether and (2) a density-dependent link between age-0 production/abundance and subsequent adult recruitment. Given the relationship between production and marsh area, natural resource agencies should consider impacts of development on production when permitting construction in the southeastern USA.

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.