Use of Passive Integrated Transponder (PIT) Tag Antennas to Monitor Movements of Mummichogs Fundulus heteroclitus in a Tidal Saltwater Creek

Relatively few studies have used passive integrated transponder (PIT) tags for monitoring fishes in saltwater environments compared with freshwater systems.  However, recent advances in PIT tags and associated detection equipment have allowed their application in estuarine systems to examine fish abundance and movement patterns.  PIT tags permit greater ‘recapture’ rates than non-electronic tags and can be used to mark small fishes.  Our goal was to estimate movement rates and patterns of tagged mummichog (Fundulus heteroclitus), a resident fish species in southeast United States estuaries, using an autonomous PIT tag antenna system.  We tagged fish in Porters Creek, North Carolina, a 600 meter-long sub-estuary characterized by fringing intertidal marsh, spring tide amplitudes of ~1 meter, and nearly complete tidal flushing.  In November 2010, forty-three mummichogs were captured throughout the creek (above and below the detection array), surgically implanted with 12 mm full-duplex tags, released at their capture sites, and monitored for one month.  Water depth was measured at the three-antenna array located 50 m above the creek mouth.  The array recaptured ninety-three percent (40 of 43) of tagged fish and recorded 20,170 individual detections during the 30 d period.  Daily detection probability averaged 50 percent during the first week, generally increased through the third week, and then decreased to 11 percent at the end of the monitoring period, coinciding with a fall in water temperatures to 0°C.  Thirty-nine tagged fish were still detected in the final week of monitoring, indicating high survival rates over this period.  Ingress appeared to occur early during flood tide, with a mean depth of detection = 0.24 m.  Correspondingly, egress appeared to occur late during ebb tide, with a mean depth of detection = 0.35 m.  Mean times spent above the array more closely tracked the semi-diurnal tidal pattern around spring tides than neap tides.  Results indicate that mummichogs ingress into the creek before the marsh floods and egress from the creek after the marsh drains.  These movement patterns appear to maximize access to the flooded marsh.  This work represents the initial findings of a broader study relating residence and survival patterns of estuarine fishes to habitat alteration of North Carolina tidal creeks.