Juvenile fishes show fidelity to intertidal creeks
Salt marshes are coastal wetlands found along the sheltered shorelines of estuaries in temperate regions around the world (Figure 1). These marshes are dominated by salt tolerant grasses that withstand being regularly flooded by the tides. Long considered to be “wastelands”, many marshes were filled in for agriculture or development. In recent years, salt marshes in the United States have been protected due to their numerous ecosystem services.
Estuaries are important nurseries and feeding grounds for many fish and shellfish species. The sheltered waters around salt marshes and eelgrass beds provide refuge, and the plants and detritus (decaying organic matter) provide the basis for a rich food web. The fish species that occupy estuaries are commonly categorized as either resident or transient species. Resident fishes occupy the estuary for all their lives. Transient species only live in the estuary for part of their life cycle. For most transient species, the fish live and feed in estuaries as larvae and juveniles before entering the ocean as water temperatures begin to cool during the fall.
Many fish species have been observed in intertidal salt marsh creeks (small creeks that are exposed at low tide), but the importance of these creeks as nurseries or feeding habitats is not well understood. To investigate this, researchers from the University of South Carolina and Florida International University conducted two tagging studies to examine the habitat use and site fidelity (tendency to return to a location) of several common transient fish species in the southeastern United States. The studies took place in the North Inlet estuary in South Carolina, a large estuarine system that is mostly comprised of salt marsh and intertidal habitats.
In 2008, the researchers used seine nets to capture juvenile spot (Leiostomus xanthurus; Figure 2), silver perch (Bairdiella chrysoura), and mullet (Mugil spp.) in pools along the beds of three intertidal creeks at low tide. The fish were tagged with coded microwire tags and released where they were originally captured. Microwire tags can only detected using a metal detection wand so the fish must be recaptured. To do so, the team returned periodically throughout the summer and into the fall to seine the pools along the creek beds at low tide. Since the detection wand only detects if a tag is present or not, tagged fish were brought back to the lab so the tag could be removed to identify the individual fish.
Four years later, the researchers returned to the estuary and captured juvenile silver perch (Figure 3), spot, pinfish (Lagodon rhomboides), and pigfish (Orthopristis chrysoptera) using the same protocols from the previous survey. Instead of using microwire tags, the fish were tagged with Passive Integrated Transponder (PIT) tags. By using PIT tags, the scientists could identify individual fish immediately upon recapture instead of if they were simply tagged or not. All captured fish were released to document additional recaptures as the summer went on.
The results indicate that all the species in the study exhibit strong site fidelity in specific intertidal creeks. Two of the creeks surveyed flow into a larger subtidal creek (that contains water at low tide) only 15 m from each other. Despite the close proximity of these creeks, over 74% of the recaptured fish were caught in the creek they were tagged in. The third creek was over 150 m from the other two and all the tagged fish that were recaptured were from that creek.
High rates of site fidelity in small intertidal creeks may be influenced by food availability and habitat quality. Fluctuations in fidelity can be indicative of changes to the habitat of the creek. This can be important when assessing essential fish habitat for species that utilize estuarine environments. As salt marsh restoration projects become more widespread, further work will be needed to understand the role of intertidal creeks to the development of juvenile fish.
Garwood, J.A., D.M. Allen, M.E. Kimball, and K.M. Boswell. 2019. Site fidelity and habitat use by young-of-the-year transient fishes in salt marsh intertidal creeks. Estuaries and Coasts 42(5): 1387-1396.