Residence time and habitat duration for predators in a small mid-Atlantic estuary

Abstract

Residence times of individ-ual fishes should reflect the durations over which habitat resources support survival, metabolic maintenance, and adequate growth. From May to Octo-ber in 2006 and 2007, we measured residencies of ultrasonically tagged age-1+ Striped Bass (Morone saxati-lis; n=46), age-0 and age-1+ Bluefish (Pomatomus saltatrix; n=45 and 35) and age-1+ Weakfish (Cynoscion rega- lis; n=41) in a small estuarine tribu-tary in New Jersey with 32 ultrasonic receivers to monitor movements and sensors to measure habitat resources. Striped Bass and age-1+ Bluefish used the estuary for medians of 9.5 days (d) (max=58 d) and 22 d (max=88 d), and age-0 Bluefish and Weakfish were resident for medians of 30 d (max=52 d) and 41 d (max=88 d), respectively. Small individuals <500 mm TL were likely to remain in the estuary longer at warmer temperatures than were large individuals. Size-dependent temperature responses were similar to optimal temperatures for growth reported in previous studies. Freshwa-ter discharge also influenced residence time. All species were likely to remain in the estuary until freshwater dis-charge rates fell to a value associated with the transition of the estuarine state from a partially to fully mixed state. This transition weakens flows into the upstream salt front where prey concentrations usually are high. Time of estuarine residence appeared to be regulated by temperatures that controlled scopes for growth and the indirect effects of freshwater discharge on prey productivity and concentration. Changes in the seasonal phenology of temperature, precipitation, and human water use could alter the durations over which small estuarine tributar-ies serve as suitable habitats.