Movement of summer flounder (Paralichthys dentatus): Application of telemetry to understand ecology and bycatch discard mortality

• Main Author: Yergey, Matthew E
• Format: Dissertation
• Language: English
• Subjects: biology, oceanography
• ISBN: 1267255471; 9781267255471

Summer flounder, Paralichthys dentatus, is a commercially and recreationally important flatfish species along the east coast of the United States. There are some clear and important data gaps in our understanding of summer flounder and their ecology. In this study we address two of those data gaps using acoustic telemetry; discard mortality in the commercial trawl fishery and the potential for pelagic behavior. Discard mortality studies to date rely on potentially biased on-deck evaluation of immediate mortality, and evaluation of delayed mortality through holding captured fish to determine survival. Telemetry of ultrasonically tagged fish provides a technique for evaluating fish bycatch discard mortality, and especially latent mortality, under natural conditions in the sea. For summer flounder along the eastern United States, an 80% discard mortality is assumed but not verified. There is also a growing body of literature on flatfish species exhibiting pelagic behaviors for various essential functions. In captivity, summer flounder use "stroke and glide" behavior in the water column and they can feed actively there. To determine the discard mortality, and explore their potential vertical movement, adult summer flounder were collected from a commercial trawl vessel and tagged and released in a fixed hydrophone array on 15 September 2009 off Brigantine, New Jersey. In 2010, an additional set of summer flounder were collected in the Great Bay - Mullica River estuary, tagged, and released into an array nearby the 2009 site for further examination of pelagic behaviors. Fish were re-detected both alive and dead within the array and during mobile tracking. Pressure sensing tags recorded depth at a resolution of 0.68 meters. Signal values indicating depths two meters or greater above an individual's greatest depth were considered to be pelagic in nature. Fish of poor initial health and dead individuals were redetected after the storm in a concentrated area inshore of the release site and were presumed dead. The final discard mortality estimate from the commercial trawl, combining on-deck mortality (32.7%) and latent mortality (49.0%), was 81.7%; similar to prior estimates. Latent mortality contributed at least as much to total discard mortality as on-deck mortality. The individual depth profiles show clear patterns of active pelagic behavior in 6 out of 14 live fish in 2009 and 6 out of 11 live fish in 2010. The mean percent of time above a 2-meter floor was 16.8% with a standard deviation of 24.4% in 2009, and 1.2%, with a standard deviation of 3.0% in 2010. This pelagic behavior occurred more frequently (86.0%) during nighttime, but there were no other obvious environmental correlates.