Environmental context and contaminant biotransport by Pacific salmon interact to mediate the bioaccumulation of contaminants by stream‐resident fish

Abstract

The extent to which environmental context mediates the bioaccumulation of biotransported contaminants by stream‐resident organisms is poorly understood. For example, it is unclear the extent to which contaminant type, instream characteristics or resident fish identity interact to influence the uptake of contaminants deposited by Pacific salmon (Oncorhynchus spp.) during their spawning runs. To address this uncertainty, we sampled four stream‐resident fish species from 13 watersheds of the Laurentian Great Lakes in locations with and without salmon runs across a gradient of instream and watershed characteristics. We determined the polychlorinated biphenyl (PCB) and mercury (Hg) concentration along with the stable isotope ratios for salmon and stream‐resident fish. We found that stream‐resident fish PCB concentrations were higher in reaches with salmon and were positively related to δ15N. In contrast, resident fish Hg concentrations were similar or lower in reaches with salmon compared with reaches lacking salmon and either exhibited a negative or no relationship with δ15N. Based on AICc, resident fish exhibited species‐specific PCB concentrations that were positively related to salmon PCB flux. Hg burdens exhibited an interaction between fish length and salmon Hg flux—as salmon Hg inputs increased, Hg levels decreased with increasing resident fish length. Because salmon eggs are enriched in PCBs but depleted in Hg, contaminant loads of resident fish appear to be driven by consumption of salmon eggs. We found no support for models that included the mediating influence of instream or watershed factors. Synthesis and applications. Our results highlight that contaminants bioaccumulate differently depending on contaminant type, species identity and the trophic pathway to contamination. Consequently, consideration of the recipient food web and route of exposure is critical to understanding the fate of biotransported contaminants in ecosystems. The transfer of contaminants by migratory organisms represents an understudied stressor in ecology. Effective management of biotransported contaminants will require the delineation of hotspots of biotransport and implementation of best management practices to reduce inputs of salmon‐derived pollutants.

Microbial Community Response to a Novel Salmon Resource Subsidy

“…A Before-After-Control-Intervention field study design was implemented for this study (Stewart-Oaten et al, 1986). Chinook and Coho (n = 120; 50/50 species split) salmon carcasses were introduced into the same salmon "treatment" reach in October 2014 and October 2015 (the typical timing of Michigan salmon runs; Gerig et al, 2018) using loading rates (∼1 kg m −2 of stream) approximate to that of a typical salmon run in a Lake Michigan tributary (Janetski et al, 2012;Gerig, 2017). Michigan Department of Natural Resources hatcheries were the source of the salmon carcasses, and salmon died of natural causes.…”

Contaminant Biotransport by Pacific Salmon in the Great Lakes

“…The process of contaminant biotransport is characterized by several steps including: (1) contaminant bioaccumulation by a migratory organism; (2) contaminant transport across an ecosystem boundary; and (3) contaminant deposition into the recipient ecosystem (Blais et al, 2007;Kallenborn and Blais, 2015). This process can include a fourth step related to variables that control how biotransported contaminants are accumulated in the recipient food web (Gerig et al, 2018). Furthermore, life history traits of the biovector including breeding strategy (e.g., semelparity), large size, high trophic position, increased fecundity, and synchronicity of movement enhance the likelihood an organism will biologically transport contaminants (Janetski et al, 2012;Schiesari et al, 2018).…”

“…As a consequence, many Great Lakes tributaries have annual runs of Pacific salmon that facilitate the translocation of contaminants from lake to tributary (Figure 1). Thus, migratory salmon can be considered a source of contaminants to tributaries of the Great Lakes region, now and in the future (Janetski et al, 2012;Gerig et al, 2018).…”

“…Research from the Great Lakes over the last decade has increased our understanding of contaminant biotransport by Pacific salmon. We now appreciate that stream-resident fish can acquire contaminants from salmon spawners (Janetski et al, 2012;Gerig et al, 2018). Moreover, the primary mechanism by which salmon facilitate contaminant dispersal and bioaccumulation is through their eggs, which are consumed readily by streamresident fish (Gerig et al, 2019).…”

“…With this mini-review, we will describe the process of contaminant biotransport, using Pacific salmon in the Laurentian Great Lakes as a case-study to describe factors controlling contaminant biotransport. The Laurentian Great Lakes are useful for this task because of the large amount of information that has been generated on contaminants, including their biotransport (Janetski et al, 2012;Murphy et al, 2012;Gerig et al, 2018), while being a globally important freshwater resource (Bunnell et al, 2014).…”