Where Predators and Prey Meet: Anthropogenic Contact Points Between Fishes in a Freshwater Estuary

Brendan Lehman,Cyril Michel,Meagan Gary,Nicholas Demetras

doi:10.15447/sfews.2019v17iss4art3

Brendan Lehman, Cyril Michel + Show 2 more

Open Access

https://doi.org/10.15447/sfews.2019v17iss4art3

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Abstract

The Sacramento–San Joaquin Delta has been invaded by several species of non-native predatory fish that are presumed to be impeding native fish population recovery efforts. Since eradication of predators is unlikely, there is substantial interest in removing or altering manmade structures in the Delta that may exacerbate predation on native fish (contact points). It is presumed that these physical structures influence predator-prey dynamics, but how habitat features influence species interactions is poorly understood, and physical structures in the Delta that could be remediated to benefit native fish have not been inventoried completely. To inform future research efforts, we reviewed literature that focused on determining the effects of predator-prey interactions between fish, based on contact points that are commonly found in the Delta. We also performed a geospatial analysis to determine the extent of potential contact points in the Delta. We found that the effects of submerged aquatic vegetation (SAV) and artificial illumination are well studied and documented to influence predation in other freshwater systems worldwide. Conversely, other common structures in the Delta—such as docks, pilings, woody debris, revetment, and water diversions—did not have the same breadth of research. In the Delta, the spatial extent of the different types of contact points differed considerably. For example, 22% of the Delta water surface area is occupied by SAV, whereas docks only cover 0.44%. Our conclusion, based on both the literature review and spatial analysis, is that the effects of SAV and artificial illumination on predation warrant the most immediate future investigation in the Delta.

Highlights

Human development in the 19th and 20th century has significantly altered the landscape in which wild organisms interact with each other (Dudgeon et al 2006)
Submerged Aquatic Vegetation our search was intended to capture studies that described all forms of aquatic vegetation, all of the relevant articles (n = 19) we found described the effects of submerged aquatic vegetation (SAV)
Restoration actions aimed at improving native fish populations by altering the physical habitat of rivers and estuaries must consider the existing literature and local habitat and species compositions

Summary

Introduction

Human development in the 19th and 20th century has significantly altered the landscape in which wild organisms interact with each other (Dudgeon et al 2006). Freshwater ecosystems have been dramatically altered by anthropogenic activities such as dam construction, water diversions, revetment, shoreline development, and dredging (Meybeck 2003). Physical habitat alterations can become points of contact between predators and prey that either concentrate fish or influence the outcome of their interactions These “contact points” can take many shapes and forms: they can be nearly continuously distributed (such as submerged aquatic vegetation [SAV]), discretely spaced (docks), or fall somewhere in-between (artificial lighting). These changes in habitat structure can influence the interaction between organisms in different ways. Artificial nighttime lighting may aggregate prey and increase predator efficiency (Becker et al 2013) while invasive SAV may aggregate both predators and prey into the same areas (Annett 1998)

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