Using Acoustic Telemetry, Stable Isotope Mixing Models, and Diet Analysis to Determine the Relationship between Resource Contribution and Habitat Use of Juvenile Red Drum in a Louisiana Estuary

Abstract

Estuaries are important areas for many species due to their high productivity. These ecosystems are made up of a patchy network of spatially distinct habitat complexes comprised of many habitat types. In Louisiana, estuaries that are essential for red drum and productive fisheries are experiencing serious land loss and habitat change. To determine how juvenile red drum use specific habitat types, acoustic telemetry was used to track fish at two spatial scales. Additionally, diet analysis and isotope mixing models were used to determine differences in diet and the sources of primary production contributing to red drum between marsh and hardened-shoreline habitats. Juvenile red drum tracked throughout this study showed high site fidelity. Telemetry also revealed that time of day and water level influenced movement. The contribution of different primary production sources to juvenile red drum and trophic level varied between foraging habitats, indicating differences in food web structure between habitat types. While particulate organic matter (POM) was the most important primary production source across both habitat types, fish sampled in hardened-shoreline areas were especially reliant on particulate organic matter derived production, compared to fish from marsh-dominated areas, who relied on POM and cordgrass more evenly. Results from the mixing model supported the high site fidelity seen in the telemetry results.

While the prey consumed by red drum were similar between habitat types, trophic level of marsh fish was over 1.5 trophic levels lower than hardened-shoreline fish. This means that there are less trophic transfers in the cordgrass energy pathway compared to the POM energy pathway. By combining stable isotope analysis and diet analysis with telemetry, I was able to uncover the mechanisms connecting movement and habitat use with resource contribution. This multiple method approach provides valuable information and can be used to help inform fisheries management and habitat restoration planning.