Population Size and Site Fidelity of Fundulus heteroclitus in a Macrotidal Saltmarsh Creek

Fundulus heteroclitus (mummichog) is the numerically dominant fish species found in salt marshes from Florida to Nova Scotia. These areas exhibit a wide range of fluctuation in environmental conditions such as temperature, salinity, and tidal range. Mummichogs are known to be eurythermal and euryhaline, but there is little information about the influence of tidal range on population dynamics. Our purpose was to determine whether extreme tides (>3 m) in a tidal creek system would affect the population density and site fidelity of F. heteroclitus. Both population density and site fidelity were measured by mark-recapture experiments in a primary saltmarsh creek (named here Sweeney Creek) off the Rowley River in Plum Island Estuary, a macrotidal (>3 m) estuary (Fig. 1). Both branches were approximately 300 m long from the confluence to the upland end. From 18 June to 3 I July 1998, temperature (data logger), salinity (refractometer), and fish abundance were monitored. Six, 6.35mm-mesh minnow traps were set in the center and randomly apart on both branches at around 180 m (East) and 120 m (West) from the confluence (Fig. 1). Specimens of F. heteroclitus 2 40 mm caught in the traps were counted and marked yellow (West) and blue (East) by injection of acrylic dye under the skin on the left dorsal side, then released. Population size was estimated using the Bailey model (1). Site fidelity was measured as the number of marked fish recaptured in different locations. Opposite-colored fish found in a marking zone were recorded and remarked on the opposite dorsal side with the color of the branch in which captured. To determine how far and by what path fish moved, we set traps in three locations. In the secondary creek, two traps were set at five stations 22 to 106 m from the confluence. Nine traps were set in the mosquito ditches, and traps were set upstream of the marking locations. The pannes and secondary creek were also seined. Time intervals between mark and recapture were variable, averaging a 14.75 hour catch per unit effort. Temperature and salinity were within the normal range for F. heteroclitus. Water temperature averaged 20°C at night and 26°C during the day for both branches. Salinity ranged from 8 to 25 ppt for the East branch, and 10 to 26 ppt for the West.