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

1. The extent to which environmental context mediates the uptake of biotransported contaminants by stream-resident organisms is not understood. For example, there is no clear understanding of 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. 2. 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 across a gradient of instream and watershed characteristics. We determined the polychlorinated biphenyl (PCB) and mercury (Hg) concentration along with the stable isotope ratio of C and N for each stream-resident fish. 3. We found that stream-resident fish PCB concentrations were 24-fold higher in reaches with salmon and were positively related to δ15N. In contrast, stream-resident fish Hg concentrations were similar or lower in reaches with salmon and either exhibited a negative or no relationship with δ15N. 4. Based upon AICc, stream-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. We found no support for models that included the mediating influence of instream or watershed factors. Salmon eggs are enriched in PCBs but have very low Hg concentrations, so our results may be driven by the consumption of salmon eggs by stream-resident fish. 5. 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 “hot-spots” of biotransport and implementation of best management practices in those watersheds that receive contaminants from spawning salmon

SARS-CoV-2 Omicron is an immune escape variant with an altered cell entry pathway

Vaccines based on the spike protein of SARS-CoV-2 are a cornerstone of the public health response to COVID-19. The emergence of hypermutated, increasingly transmissible variants of concern (VOCs) threaten this strategy. Omicron (B.1.1.529), the fifth VOC to be described, harbours multiple amino acid mutations in spike, half of which lie within the receptor-binding domain. Here we demonstrate substantial evasion of neutralization by Omicron BA.1 and BA.2 variants in vitro using sera from individuals vaccinated with ChAdOx1, BNT162b2 and mRNA-1273. These data were mirrored by a substantial reduction in real-world vaccine effectiveness that was partially restored by booster vaccination. The Omicron variants BA.1 and BA.2 did not induce cell syncytia in vitro and favoured a TMPRSS2-independent endosomal entry pathway, these phenotypes mapping to distinct regions of the spike protein. Impaired cell fusion was determined by the receptor-binding domain, while endosomal entry mapped to the S2 domain. Such marked changes in antigenicity and replicative biology may underlie the rapid global spread and altered pathogenicity of the Omicron variant

Investigation of hospital discharge cases and SARS-CoV-2 introduction into Lothian care homes

Background The first epidemic wave of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) in Scotland resulted in high case numbers and mortality in care homes. In Lothian, over one-third of care homes reported an outbreak, while there was limited testing of hospital patients discharged to care homes. Aim To investigate patients discharged from hospitals as a source of SARS-CoV-2 introduction into care homes during the first epidemic wave. Methods A clinical review was performed for all patients discharges from hospitals to care homes from 1st March 2020 to 31st May 2020. Episodes were ruled out based on coronavirus disease 2019 (COVID-19) test history, clinical assessment at discharge, whole-genome sequencing (WGS) data and an infectious period of 14 days. Clinical samples were processed for WGS, and consensus genomes generated were used for analysis using Cluster Investigation and Virus Epidemiological Tool software. Patient timelines were obtained using electronic hospital records. Findings In total, 787 patients discharged from hospitals to care homes were identified. Of these, 776 (99%) were ruled out for subsequent introduction of SARS-CoV-2 into care homes. However, for 10 episodes, the results were inconclusive as there was low genomic diversity in consensus genomes or no sequencing data were available. Only one discharge episode had a genomic, time and location link to positive cases during hospital admission, leading to 10 positive cases in their care home. Conclusion The majority of patients discharged from hospitals were ruled out for introduction of SARS-CoV-2 into care homes, highlighting the importance of screening all new admissions when faced with a novel emerging virus and no available vaccine

Ecological consequences of Great Lakes salmon subsidies for stream-resident brook and brown trout

Introduced Pacific salmon (Oncorhynchus spp.) deliver novel, pulsed resource subsidies to Great Lakes streams. We explored interactions between native brook trout (Salvelinus fontinalis) and non-native brown trout (Salmo trutta) in the context of this resource pulse. Diets surveyed before and during salmon spawning showed that, regardless of species, trout consumed 4.5-fold more biomass during than before salmon runs. Brook trout grew more quickly than brown trout under controlled feeding regimes due, in part, to their higher food conversion efficiency of 36% compared to 21%. Bioenergetics model simulations explored the influence of temperature on the exploitation of resource pulses and found 35% lower growth rates and increased gorging at colder temperatures. Overall, we found evidence that brook trout and brown trout foraging and growth are modulated by the salmon resource pulse, especially through gorging on eggs. However, these species exhibit distinct physiological adaptations and environmental preferences that may influence their ultimate capacity to exploit resource pulses. The effects of environmental conditions and salmon subsidies on stream-resident trout have broader consequences for fisheries management and conservation efforts.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Marine subsidies in freshwater ecosystems: salmon carcasses increase the growth rates of stream-resident salmonids.

Abstract.-We tested the hypotheses that marine-derived resource subsidies (salmon carcasses) increase the growth rates of stream-resident salmonids in southeastern Alaska and that more carcasses translate into more growth. Five carcass treatments of pink salmon Oncorhynchus gorbuscha (0, 1, 2, 3, and 4 carcasses/m 2 or 0, 1.9, 3.7, 5.6, and 7.4 kg wet mass/m 2 ) were replicated six times in once-through artificial channels, then each channel was stocked with three live age-0 coho salmon O. kisutch. The experiment spanned more than 9 weeks: 16 August to 24 October 1998. The body mass and fork length of the young coho salmon significantly increased from carcass additions, but the incremental increases sharply diminished at carcass-loading levels above 1 carcass/m 2 . Further, in a small stream in which we added salmon carcasses to a cumulative density of 0.54 carcasses/m 2 , both cutthroat trout O. clarki and Dolly Varden Salvelinus malma grew significantly faster during the 2 months in which carcasses were added (September-October) compared with fish in control reaches. Fish maintained their assimilated body mass through winter into the following spring. This study illustrates that marine nutrients and energy from salmon spawners increase growth rates of resident and anadromous salmonids in streams. This elevated growth should translate into increased survival and reproduction, ultimately elevating freshwater and marine salmon production. Ecological relationships between salmon runs and aquatic community nutrition and productivity may be important considerations for salmon stock protection and restoration and for freshwater and marine ecosystem management

Pacific salmon as vectors of environmental contaminants: An experimental test confirms synoptic surveys in natural streams

Pacific salmon transfer large quantities of material to tributaries during their spawning migrations, including carcass tissue and labile nutrients but also persistent organic pollutants (POPs) and heavy metals. We conducted a Before-After-Control-Intervention experiment by adding salmon carcasses and eggs to a Michigan (USA) stream that had never received inputs from non-native salmon to understand the bioaccumulation and persistence of biotransported contaminants. Our experimental outcomes were compared to previous studies using meta-analysis. Coincident with the introduction of salmon, the PCB and DDE burden of resident trout significantly increased. However, we did not observe changes in total mercury (Hg). Two years after the salmon addition experiment concluded, resident trout POP concentrations had returned to pre-addition levels, with no difference between the treatment and control reaches. Analysis of effect sizes suggested that the contaminant response observed in our experiment is consistent with field survey observations. Our study suggested that the consumption of salmon eggs drove the increase in POP burden of resident trout while Hg bioaccumulation was influenced by watershed sources. Critically, our study suggests that ecosystems are capable of quickly recovering from POP inputs from species migrations if contaminant sources are removed