Distribution patterns of mobile organisms can affect the outcome of population, community, and ecosystem interactions. For example, confluences have been considered ecological hotspots, but how confluence “sites” affect the distribution of organisms, especially predators, is rarely tested. Site fidelity is heuristically linked to ecological theory. However, site fidelity is ambiguously defined as staying in or returning to (i.e. fidelity) some generically defined area (i.e. site) for some variably defined period. The generality and utility of this concept is limited by the lack of specific empirical hypothesis about relative components of site fidelity. Here we test empirical patterns of site fidelity using telemetry data from migratory striped bass that seasonally feed in Plum Island Estuary (PIE LTER), MA. Specifically, we ask whether fish predators (1) stay in specific locations longer than would be predicted, (2) differentially use confluence “sites”, (3) exhibit patterns of site fidelity that differ with spatial scale, (4) move differentially within and between sites, and (5) display individual variability? These five questions were tested using residence time (hours detected) for 59 acoustically tagged striped bass at 29 stationary within-estuary receivers over 2 years.
Tagged fish spent more time at some specific receiver locations than others, suggesting that striped bass “favor” a discontinuous distribution within the estuary. Fish exhibited more fidelity to some confluence sites and to some locations within confluences. Elsewhere, in the estuary, fish resided within a regional “site” rather than a habitat “site” (e.g. confluence or non-confluence). At all scales, fish never stayed exclusively at any site, but periodically moved throughout the estuary. The concept of animals staying in or returning to a specific location has substantial implications for understanding animal behavior (e.g. how they forage), organismal-habitat associations (e.g. where they are), predator-prey interactions (e.g. impacts of predators on prey), how predators influence the routing of energy and nutrients (e.g. ecosystem effects), differences across scales, and patterns of natural selection. However, to use the concept of site fidelity effectively, researchers need to better understand empirical patterns of residence and movement associated with both “site” and “fidelity”. Our study represents novel empirical results that can help refine this ecological theory.