Dynamics of summer flounder, Paralichthys dentatus, seasonal migrations based on ultrasonic telemetry

Abstract Migrations of summer flounder, Paralichthys dentatus, to and from estuaries to the continental shelf in the Mid-Atlantic Bight (MAB) occur seasonally but their dynamics are poorly understood. Ultrasonic telemetry, both passive and active, was used during 2003–2005 to determine timing and rate of juvenile and adult summer flounder (268–535 mm TL) migrating to and from the Mullica River–Great Bay estuary in southern New Jersey. Additionally, 7 years of inner continental shelf surveys off New Jersey were used to assess complementary seasonal movements. Most tagged fish emigrated from the estuary between July and September, though emigration lasted into December and appeared to be influenced by a number of factors. In July 2004, more tagged fish emigrated, at increased rates of movement, at low barometric pressure during a storm event. Trawl collections on the inner shelf demonstrated the same approximate immigration times as seen with telemetry. Later in the fall, increased numbers of tagged summer flounder emigrated from the estuary when dissolved oxygen was decreasing. Fall trawl surveys showed increased numbers of fish on the inner shelf when dissolved oxygen was decreasing in the Mullica River–Great Bay estuary, supporting the telemetry results. Fish emigrated from the estuary during the day and night but nighttime movements were in deeper water at slightly slower rates of movement. Exit and re-entry also occurred during the fall emigration. Ultrasonically tagged individuals demonstrated homing by returning to the same estuary, in March through June, in the second and third year of the study (39–6%, respectively). In summary, immigration may result from homing for a large proportion of summer flounder. Emigration may be associated with storms on an episodic scale, and dissolved oxygen and temperature on a seasonal scale.