Changing estuaries and impacts on juvenile salmon: A systematic review

Abstract

Estuaries are productive ecosystems providing important habitat for a diversity of species, yet they also experience intense levels of anthropogenic development. To inform decision‐making, it is essential to understand the pathways of impacts of particular human activities, especially those that affect species such as salmon, which have high ecological, social‐cultural and economic values. Salmon systems provide an opportunity to build from the substantial body of research on responses to estuary developments and take stock of what is known. We conducted a systematic English‐language literature review on the responses of juvenile salmon to anthropogenic activities in estuaries and nearshore areas asking: what has been studied, where are the major knowledge gaps and how do stressors affect salmon? We found a substantial body of research (n = 167 studies; 1,369 comparative tests) to help understand responses of juvenile salmon to 24 activities and their 14 stressors. Across studies, 82% of the research was conducted in the eastern Pacific (Oregon and Washington, USA and British Columbia, Canada) showing a limited geographical scope. Using a semiquantitative approach to summarize the literature, including a weight‐of‐evidence metric, we found a range of results from low to moderate–high confidence in the consequences of the stressors. For example, we found moderate–high confidence in the negative impacts of pollutants and sea lice and moderate confidence in negative impacts from connectivity loss and changes in flow. Our results suggest that overall, multiple anthropogenic activities cause negative impacts across ecological scales. However, our results also reveal knowledge gaps resulting from minimal research on particular species (e.g. sockeye salmon), regions (e.g. Atlantic) or stressors (e.g. entrainment) that would be expedient areas for future research. With estuaries acting as a nexus of biological and societal importance and hotspots of ongoing development, the insights gained here can contribute to informed decision‐making.

Urban seas as hotspots of stress in the Anthropocene ocean: The Salish Sea example

“…Balanced against these positive signs is the drumbeat of warning signs: disappearing kelp beds (Berry et al, 2021), seagrass meadows threatened by disease (Groner et al, 2021), endangered resident orca whales (Wasser et al, 2017), changed flow in the Fraser River (Shrestha et al, 2012), habitat loss in its delta (Kehoe et al, 2020) and in the deltas of many other important rivers and streams (Brophy et al, 2019), and declining salmon runs (Figure 3; Losee et al, 2019;Pearsall et al, 2021), which exhibit lower marine survival in stocks from within the urban sea than from those outside. Salmon are an iconic species within this ecosystem and have been integral to Indigenous community identities for thousands of years; their decline is an important indicator of ecosystem change and one that integrates stressors across the urban estuarine landscape (Hodgson et al, 2020) and serves as an opportunity for innovative and time-tested management solutions (Atlas et al, 2021).…”

Practical implementation of cumulative‐effects management of marine ecosystems in western North America

“…), for example, move through many different ecosystems, jurisdictions, and political boundaries over the course of their lives. As stocks continue to decline over much of their range, many are pointing to the CE of a multitude of stressors as the culprits of this decline, though management actions continue to be narrow in scale in most jurisdictions (Price et al 2008;Lacy et al 2016;Hodgson et al 2020). Like spatial scale, the specified temporal scale can also greatly influence the conclusions of a CEA, but notably, Korpinen and Anderson (2016) found that no published CEA contains acknowledgment of or includes historical modifications to the environment.…”

“…2016 ; Hodgson et al. 2020 ). Like spatial scale, the specified temporal scale can also greatly influence the conclusions of a CEA, but notably, Korpinen and Anderson ( 2016 ) found that no published CEA contains acknowledgment of or includes historical modifications to the environment.…”

Evaluating ecosystem-based management alternatives for the Puget Sound, U.S.A. social-ecological system using qualitative watershed models

“…Streams and rivers are essential corridors for water, species, sediment, human activities, and other constituents of coastal watersheds. In heavily urbanized and agricultural watersheds, stormwater runoff (rain and melted snow) accumulates pollutants, such as bacteria, toxics, and excess nutrients, as it flows over landscapes en route to receiving waters, causing cascading impacts across the freshwater-estuarine gradient (Kennish, 2002;Hodgson et al, 2020). The quantity and toxicity of stormwater runoff is exacerbated by impervious surfaces and land conversion, and stormwater is the fastest growing cause of water quality degradation in coastal systems (Walsh et al, 2005;McCarthy et al, 2008).…”