Using geomorphology and animal “individuality” to understand ‘scape-scale predator distributions

Abstract

Determining patterns and drivers of organismal distribution and abundance are fundamental and enduring challenges in ecology, especially for mobile organisms at a ‘scape scale. To address the problem presented by individuals whose distributions are dynamic across large geographic areas, here I tracked 59 acoustically-tagged migratory striped bass (Morone saxatilis) with an array of 26 stationary receivers in Plum Island Estuary (PIE), MA. Specifically, I asked (1) how these predators were distributed across the estuarine seascape, (2) if these fish used three types of geomorphic sites (exits, confluences, and non-confluences) differently, (3) if distinct types of individual distributional “types” existed, and (4) if fish within distinct distributional groups used geomorphic site types and regions differently. Based on three components of predator trajectories (site specific numbers of individuals, residence time, and number of movements), striped bass were not distributed evenly throughout PIE. Confluences attracted tagged striped bass although not all confluences or all parts of confluences were used equally. Use of non-confluences sites was more variable than exits or confluences. Thus, geomorphic drivers and regions link mobile organisms to physical conditions across the seascape. Based on spatial and spatial-temporal cluster analyses, these striped bass predators clustered into four seasonally-resident distributional types. These included the (1) Rowley River group (fish that primarily resided in the Rowley River), (2) Plum Island Sound group (fish that primarily resided in the Middle Sound region), (3) Extreme Fidelity group (fish that spent most of their time in PIE at a single receiver location), and (4) the Exploratory group (fish that showed no affiliation with any particular location). These distributional groups used geomorphic site types and regions differently. Thus, my data show a rare link between behavioral (i.e., individual animal personalities) and field ecology (seascape geomorphology) that can advance the understanding of field-based patterns and drivers of organismal distribution.