Discontinuities concentrate mobile predators: quantifying organism–environment interactions at a seascape scale

Abstract

Understanding environmental drivers of spatial patterns is an enduring ecological problem that is critical for effective biological conservation. Discontinuities (ecologically meaningful habitat breaks), both naturally occurring (e.g., river confluence, forest edge, drop‐off) and anthropogenic (e.g., dams, roads), can influence the distribution of highly mobile organisms that have land‐ or seascape scale ranges. A geomorphic discontinuity framework, expanded to include ecological patterns, provides a way to incorporate important but irregularly distributed physical features into organism–environment relationships. Here, we test if migratory striped bass (Morone saxatilis) are consistently concentrated by spatial discontinuities and why. We quantified the distribution of 50 acoustically tagged striped bass at 40 sites within Plum Island Estuary, Massachusetts during four‐monthly surveys relative to four physical discontinuities (sandbar, confluence, channel network, drop‐off), one continuous physical feature (depth variation), and a geographic location variable (region). Despite moving throughout the estuary, striped bass were consistently clustered in the middle geographic region at sites with high sandbar area, close to channel networks, adjacent to complex confluences, with intermediate levels of bottom unevenness, and medium sized drop‐offs. In addition, the highest striped bass concentrations occurred at sites with the greatest additive physical heterogeneity (i.e., where multiple discontinuities co‐occurred). The need to incorporate irregularly distributed features in organism–environment relationships will increase as high‐quality telemetry and GIS data accumulate for mobile organisms. The spatially explicit approach we used to address this challenge can aid both researchers who seek to understand the impact of predators on ecosystems and resource managers who require new approaches for biological conservation.

Could spatial heterogeneity in flow disturbance drive temporal stability of native–invasive species co‐occurrence in riverscapes?

“…Stability has many meanings in ecology (Grimm & Wissel, 1997), but here we quantify it as temporal variation in fish assemblage composition. In rivers, habitat diversity could be increased through the spatial juxtaposition of habitats with very different disturbance regimes (Kennedy et al., 2016). Because floods are a major form of disturbance to rivers (Hart & Finelli, 1999; Bunn & Arthington, 2002; Poff & Zimmerman, 2010), variation in flood disturbance regimes should be a primary source of coarse‐scale differences between river branches.…”

Merging Scientific Silos: Integrating Specialized Approaches for Thinking about and Using Spatial Data That Can Provide New Directions for Persistent Fisheries Problems

“…Striped Bass spawned in the Chesapeake, Delaware, and Hudson Bay estuaries can make annual spring foraging migrations north along the Atlantic coast after reaching about 2–4 years of age (Mather et al 2010; Pautzke et al 2010). From spring to fall, these migrating Striped Bass may reside and feed in one or more New England estuaries for several months before returning south to overwinter (Walter et al 2003; Kennedy et al 2016). Here we review Striped Bass research, conducted over 15 years at the National Science Foundation‐sponsored Plum Island Ecosystems (PIE) Long term Ecological Research Site (LTER) in northeastern Massachusetts that has contributed to and benefitted from interdisciplinary collaborations using multiple approaches (Figure 2A).…”

“…At a regional, across‐estuary scale, Striped Bass on a foraging migration had a heterogeneous across‐estuary distribution and consumed a diverse diet across New England estuaries that resulted in high but variable prey consumption (Ferry and Mather 2012). At the whole‐estuary scale, a consistently large number of migrating Striped Bass seasonally resided in PIE for a prolonged period in summer (mean: 51–72 days; Pautzke et al 2010; Kennedy et al 2016; Taylor et al 2019). At a within‐estuary scale, Striped Bass that were seasonally resident in PIE exhibited spatially explicit distribution patterns that had distinct behaviors (Pautzke et al 2010; Taylor et al 2019).…”

“…We combined telemetry data that quantified fish dynamic distribution with geomorphology to understand the relationship between Striped Bass and physical drivers (Figure 2C). At the whole‐estuary scale, we connected concentrations of Striped Bass feeding within PIE to whole‐estuary physical discontinuities such as sand bars, drop‐offs, and confluences that can act to concentrate forage (Kennedy et al 2016; Taylor et al 2019). This approach required development of metrics for whole‐estuary scale heterogeneity (Kennedy et al 2017).…”

“…For Blue Catfish, reservoir discontinuities were differences in depth and drop‐offs. For Alewife, river discontinuities were differences in within‐stream habitat types (pools, runs, and riffles; Mather et al 2012) and water withdrawals (Mass GIS, available: https://bit.ly/36C3h1k; Additional details can be found in Kennedy et al 2016, 2017; Peterson 2015; Frank et al 2011).…”