Surface and subsurface oceanographic features drive forage fish
distributions and aggregations: Implications for prey availability to
top predators in the US Northeast Shelf ecosystem
Abstract
Forage fishes are a critical food web link in marine ecosystems,
aggregating in a hierarchical patch structure over multiple spatial and
temporal scales. Surface-level forage fish aggregations (FFAs) represent
a concentrated source of available prey for surface- and
shallow-foraging marine predators. Existing survey and analysis methods
are often imperfect for studying forage fishes at scales appropriate to
foraging predators, making it difficult to quantify predator-prey
interactions. In many cases, general distributions of forage fish
species are known; however, these may not represent surface-level prey
availability to predators. Likewise, we lack an understanding of the
oceanographic drivers of spatial patterns of prey aggregation and
availability or forage fish community patterns, generally. Specifically,
we applied Bayesian joint species distribution models to bottom trawl
survey data to assess species- and community-level forage fish
distribution patterns across the US Northeast Continental Shelf (NES)
ecosystem. Aerial digital surveys gathered data on surface FFAs at two
project sites within the NES, which we used in a spatially explicit
hierarchical Bayesian model to estimate the abundance and size of
surface FFAs. We used these models to examine the oceanographic drivers
of forage fish distributions and aggregations. Our results suggest that,
in the NES, regions of high community species richness are spatially
consistent with regions of high surface FFA abundance. Bathymetric depth
drove both patterns, while subsurface features, such as mixed layer
depth, primarily influenced aggregation behavior and surface features,
such as sea surface temperature, sub-mesoscale eddies, and fronts
influenced forage fish diversity. In combination, these models help
quantify the availability of forage fishes to marine predators and
represent a novel application of spatial models to aerial digital survey
data.