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Low Summer River Flows Associated with Low Productivity of Chinook Salmon in a Watershed with Shifting Hydrology

File(s): 
Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2022-01-20
Abstract: 
  1. Climate change and human activities are transforming river flows globally, with potentially large consequences for freshwater life. To help inform watershed and flow management, there is a need for empirical studies linking flows and fish productivity.
  2. We tested the effects of river conditions and other factors on 22 years of Chinook salmon productivity in a watershed in British Columbia, Canada.
  3. Freshwater conditions during adult salmon migration and spawning, as well as during juvenile rearing, explained a large amount of variation in productivity.
  4. August river flows while salmon fry reared had the strongest effect on productivity—our model predicted that cohorts that experience 50% below average flow in the August of rearing have 21% lower productivity.
  5. These contemporary relationships are set within long-term changes in climate, land use, and hydrology. Over the last century, average August river discharge decreased by 26%, air temperatures warmed, and water withdrawals increased. Seventeen percent of the watershed was logged in the last 20 years.
  6. Our results suggest that, in order to remain stable, this Chinook salmon population being assessed for legal protection requires substantially higher August flow than previously recommended. Changing flow regimes—driven by watershed impacts and climate change—can threaten imperilled fish populations.
Document type: 
Article

Emergent Trophic Interactions Following the Chinook Salmon Invasion of Patagonia

File(s): 
Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2022-02-03
Abstract: 

In their native range, Pacific salmon (Oncorhynchus spp.) have strong interactions with a multitude of species due to the annual pulse of marine-derived nutrients that they deliver to streams and forests when they spawn and die. Over the past few decades, Chinook salmon (Oncorhynchus tshawytscha) has established non-native populations throughout the Patagonia region of southern South America. Here, we provide the first assessment of the pathways through which salmon-derived nutrients enter stream and forest food webs in Patagonia by surveying multiple streams in southern Chile to identify invertebrate and vertebrate consumers of salmon carcasses and summarizing all documented trophic interactions of Chinook salmon in Patagonia. Blowflies (Calliphoridae) were the dominant colonizer of carcasses in the riparian zone, and midge flies (Chironomidae) were the most common invertebrate on submerged carcasses. Camera trap monitoring in the riparian zone revealed consumption of carcasses or carcass-associated invertebrates by the insectivorous passerine bird “chucao” (Scelorchilis rubecula), small rodents (black rat Rattus rattus, house mouse Mus musculus, and/or colilargo Oligoryzomys longicaudatus), the South American fox “culpeo” (Lycalopex culpaeus), and the invasive American mink (Neovison vison). A mink was filmed transferring a carcass from stream to streambank, indicating that vertebrate scavenging likely increases the degree to which marine-derived nutrients enter terrestrial food webs. The native taxa that consume salmon are closely related to species that benefit from salmon consumption in North America, suggesting that the pathways of salmon nutrient incorporation in North American food webs have functionally re-emerged in South America. Similarly, non-native trout (Oncorhynchus mykiss and Salmo trutta) and mink consume salmon in Patagonia, and their eco-evolutionary history of coexistence with salmon could mean that they are preadapted for salmon consumption and could thus be key beneficiaries of this invasion. Expanded monitoring of the abundance and impacts of salmon will be vital for understanding how these novel inputs of marine-derived nutrients alter Patagonian food webs.

Document type: 
Article

Data for Use of Shell Hash to Mitigate the Acidification of Intertidal Sediments - Doyle and Bendell

File(s): 
Peer reviewed: 
No, item is not peer reviewed.
Date created: 
2022-01-09
Abstract: 

Our objectives were twofold; (1) to determine if the addition of shell hash to intertidal sediments would mitigate porewater acidification, and (2) whether its effectiveness was dependent on the type of sediment as described by organic matter (OM) and particle grain size (PGS). Field experiments were conducted at two sites within Burrard Inlet, British Columbia; Maplewood Mudflats (MM), high in OM and silt and Whey-ah-Wichen/Cates Park (WAW), low in OM and an equal PGS among very coarse, coarse, fine sand and silt. Shell hash was added to triplicate treatment plots matched with triplicate controls at each site and porewater pH measured at flood and ebb tide over 8 tidal cycles. Sampling occurred during June and July when tidal cycles were at their maximum inundation and exposure. Porewater pH was significantly greater for ebb versus flood tide and also between sites with MM significantly lower (7.59) as compared to WAW (8.03). Although pH was not mitigated by the shell hash, for WAW, variation in pH was reduced as compared to MM, as indicated by coefficients of variation over the 6-week sampling period. We suggest that the application of shell hash to reduce the impact of ocean acidification (OA) on intertidal sediments, will be site dependent. The combined processes of eutrophication in sediments with high OM and respiration of infauna, especially at high densities could act in concert with OA to create an intertidal region unsuitable for bivalve larvae settlement and development.4

Document type: 
Dataset

Effects of Spawning Pacific Salmon on Terrestrial Invertebrates: Insects near Spawning Habitat Are Isotopically Enriched with Nitrogen-15 but Display No Differences in Body Size

File(s): 
Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2021-08-24
Abstract: 

When Pacific salmon (Oncorhynchus spp.) spawn and die, they deliver marine-derived nutrient subsidies to freshwater and riparian ecosystems. These subsidies can alter the behavior, productivity, and abundance of recipient species and their habitats. Isotopes, such as nitrogen-15 (15N), are often used to trace the destination of marine-derived nutrients in riparian habitats. However, few studies have tested for correlations between stable isotopes and physiological responses of riparian organisms. We examined whether increases in δ15N in terrestrial insect bodies adjacent to salmon spawning habitat translate to changes in percent nitrogen content and body size. This involved comparisons between distance from a salmon-bearing river, marine-derived nutrients in soils and insects, soil moisture content, and body size and nitrogen content in two common beetle families (Coleoptera: Curculionidae, Carabidae). As predicted, δ15N in riparian soils attenuated with distance from the river but was unaffected by soil moisture. This gradient was mirrored by δ15N in the herbivorous curculionid beetles, whereas carabid beetles, which feed at a higher trophic level and are more mobile, did not show discernable patterns in their δ15N content. Additionally, neither distance from the river nor body δ15N content was related to beetle body size. We also found that nitrogen-15 was not correlated with total percent nitrogen in insect bodies, meaning that the presence of spawning salmon did not increase the percent nitrogen content of these insects. We conclude that while salmon-derived nutrients had entered terrestrial food webs, the presence of δ15N alone did not indicate meaningful physiological changes in these insects in terms of percent nitrogen nor body size. While stable isotopes may be useful tracers of marine-derived nutrients, they cannot necessarily be used as a proxy for physiologically important response variables.

Document type: 
Article

Impacts of Run-of-river Hydropower on Coho Salmon (Oncorhynchus Kisutch): The Role of Density-dependent Survival

File(s): 
Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2021-08-09
Abstract: 

Predicting whether anthropogenic sources of mortality have negative consequences at the level of population dynamics is challenged by mechanisms like density-dependent survival that can amplify or offset the loss of individuals from anthropogenic disturbances. Run-of-river (RoR) hydropower is a growing industry that can cause frequent mortality of salmonid fry through rapid reductions in streamflow, leading to stranding on dewatered shores. However, whether individual-level impacts reduce population growth rates or increase local extinction risk is difficult to predict. We used a stochastic stage-structured matrix model to evaluate how the timing and magnitude of anthropogenic flow fluctuations impacted population abundance and extinction risk of coho salmon (Oncorhynchus kisutch), which spend up to 1.5 yr in many streams regulated by RoR hydropower. We additionally assessed how the timing (spring, winter) and strength (weak, moderate, high) of natural density-dependent bottlenecks experienced by salmon in freshwaters tempers or amplifies the potential for RoR-induced mortality to scale to emergent population dynamics. We compared population sizes and the 45-yr probability of quasi-extinction under 12 scenarios that varied the frequency (0–20 events per year) and magnitude (1–10% mortality per event) of RoR-induced flow fluctuations, as well as the timing and strength of density-dependent bottlenecks occurring during the first year in freshwater. We found that even mild flow fluctuations by RoR hydropower can impact coho salmon population dynamics, especially if density dependence is weak or occurs early in freshwater residency (spring). When density dependence was strong and during winter, the potential for population-level impact was lessened, but populations still declined by 13–42% when RoR-induced mortality was severe (5–10%) or frequent (10–20 events/yr). We conclude that strong density-dependent survival bottlenecks could partially mitigate the loss of fry from anthropogenic flow fluctuations, especially if bottlenecks occur late in freshwater residency, but not for all intensities of flow fluctuations. Even with strong density dependence in winter, our models predict declining populations by up to 70% under strong and very frequent flow fluctuations, which should serve to caution those tasked with regulating flows in streams affected by RoR hydropower.

Document type: 
Article

Analytical Methods Matter Too: Establishing a Framework for Estimating Maximum Metabolic Rate for Fishes

File(s): 
Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2021-07-13
Abstract: 

Advances in experimental design and equipment have simplified the collection of maximum metabolic rate (MMR) data for a more diverse array of water-breathing animals. However, little attention has been given to the consequences of analytical choices in the estimation of MMR. Using different analytical methods can reduce the comparability of MMR estimates across species and studies and has consequences for the burgeoning number of macroecological meta-analyses using metabolic rate data. Two key analytical choices that require standardization are the time interval, or regression window width, over which MMR is estimated, and the method used to locate that regression window within the raw oxygen depletion trace. Here, we consider the effect of both choices by estimating MMR for two shark and two salmonid species of different activity levels using multiple regression window widths and three analytical methods: rolling regression, sequential regression, and segmented regression. Shorter regression windows yielded higher metabolic rate estimates, with a risk that the shortest windows (<1-min) reflect more system noise than MMR signal. Rolling regression was the best candidate model and produced the highest MMR estimates. Sequential regression models consistently produced lower relative estimates than rolling regression models, while the segmented regression model was unable to produce consistent MMR estimates across individuals. The time-point of the MMR regression window along the oxygen consumption trace varied considerably across individuals but not across models. We show that choice of analytical method, in addition to more widely understood experimental choices, profoundly affect the resultant estimates of MMR. We recommend that researchers (1) employ a rolling regression model with a reliable regression window tailored to their experimental system and (2) explicitly report their analytical methods, including publishing raw data and code.

Document type: 
Article

Links Between Fluctuations in Sockeye Salmon Abundance and Riparian Forest Productivity Identified by Remote Sensing

File(s): 
Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2021-08-08
Abstract: 

Pacific salmon (Oncorhynchus spp.) carcasses can fertilize riparian forests with marine-derived nutrients when populations make their annual return to natal streams to spawn; however, the strength of this cross-system linkage likely varies substantially among years due to the interannual fluctuations in abundance that characterize most salmon populations. Here, we used a 36-yr time series (1984–2019) of satellite imagery and salmon abundance estimates to assess spatiotemporal associations between forest greenness (a measure of plant productivity) and adult sockeye salmon (Oncorhynchus nerka) abundance in the lower Adams River, British Columbia, Canada. The Adams River sockeye population displays a quadrennial pattern of abundance, with a dominant cohort that spawns every four years in numbers that are typically two to three orders of magnitude larger than non-dominant cohorts. We found that variation in forest greenness was consistently explained best by models including dominant cohort year, whereas models lacking an index of salmon abundance were the lowest-ranked. Greenness of riparian vegetation increased by an average of 0.015 NDVI units (approximately 1%) in the summer after a dominant cohort return, and this effect on greenness persisted into the subsequent fall (11–13 months after spawning). The positive association between quadrennial pulses of salmon and riparian greenness occurred in plots both within 30 m of the stream and 95–125 m away from the stream, indicating that the spatial extent of fertilization may occur well beyond areas directly adjacent to the riverbank. These results suggest that forests respond to cyclical variation in salmon abundance and that overwinter storage of marine-derived nutrients within catchments allows plants to capitalize on these nutrients in the following growing season. Continued advances in remote sensing technology will enhance our understanding of cross-system resource linkages and can inform the ecosystem-based management of Pacific salmon.

Document type: 
Article

Century-Long Stomatal Density Record of the Nitrophyte, Rubus spectabilis L., From the Pacific Northwest Indicates No Effect of Changing Atmospheric Carbon Dioxide but a Strong Response to Nutrient Subsidy

File(s): 
Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2021-12-01
Abstract: 

Triangle Island on Canada's Pacific coast is home to a large, globally important sea-bird breeding colony. The shrub Salmonberry Rubus spectabilis and tussock-forming Tufted Hairgrass Deschampsia cespitosa together form ~70% of vegetation coverage and  contain  the  vast  majority  (~90%) of seabird nesting burrows. Salmonberry has in recent decades greatly expanded its coverage, while that of Tufted Hairgrass has receded.  Seabirds  prefer  not  to  burrow  under  Salmonberry,  making  its  ongoing  ex-pansion a potential conservation issue. We investigated three hypotheses proposed to  explain  Salmonberry's  expansion  (climate  change,  biopedturbation,  and  nutrient  input),  using  comparisons  of  stomatal  density  of  Salmonberry  leaves  sampled  from  Triangle  Island,  other  seabird  colonies,  other  coastal  locations,  and  from  historical  specimens in herbaria. Stomatal density helps regulate photosynthetic gain and con-trol water loss, and responds to light, nutrient, carbon dioxide, and water availability. Differing patterns of stomatal density are expected among sample locations depend-ing on which of the hypothesized factors most strongly affects Salmonberry's perfor-mance. Our data are most consistent with the nutrient input hypothesis. We discuss possible reasons why Salmonberry has expanded so recently, even though Triangle has been a large seabird colony for at least a century and likely much longer.

Document type: 
Article

Lethal and Sublethal Effects of the Anti-sea Lice Formulation Salmosan® on the Pacific Spot Prawn (Pandalus Platyceros)

File(s): 
Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2021-07-18
Abstract: 

The effects of the aquaculture chemotherapeutant Salmosan® (active ingredient [a.i.]: azamethiphos) were examined in Pacific spot prawns (Pandalus platyceros) at three temperatures (5, 11, and 17°C). Post-molt prawns were more sensitive to Salmosan® than intermolt prawns; repeated (3x) 1-hr LC50 values for post-molt prawns ranged from 17 (9.3–31 95% confident intervals) to 40 (25–63) μg/L a.i. while intermolt prawns survived 3 × 1-hr exposures up to 100 μg/L a.i. Using LC50 values, Salmosan® was approximately 2.4 times more toxic at 17 versus 5°C. Temperature significantly altered chemosensory and locomotory behaviors in intermolt prawns with the highest activity at the intermediate temperature. Significant decreases in antennule flicking (84 and 104% over controls) were seen at 17°C after 3 × 1-hr pulse exposures to 50 and 100 μg/L a.i., respectively. Temperature, but not Salmosan®, affected molting success: at 17°C significantly lower survival was seen during ecdysis (60% of those at 5°C) and at 5°C, molt time was longer (41 ± 3 days) compared to 11°C (34 ± 4 days) or 17°C (21 ± 4 days). Life stage (molt status) and environmental parameters (temperature) alter the effects of Salmosan® to non-target spot prawns.

Document type: 
Article

mDia1 Assembles a Linear F-Actin Coat at Membrane Invaginations To Drive Listeria monocytogenes Cell-to-Cell Spreading

File(s): 
Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2021-11-16
Abstract: 

Direct cell-to-cell spreading of Listeria monocytogenes requires the bacteria to induce actin-based finger-like membrane protrusions in donor host cells that are endocytosed through caveolin-rich membrane invaginations by adjacent receiving cells. An actin shell surrounds these endocytic sites; however, its structure, composition, and functional significance remain elusive. Here, we show that the formin mDia1, but surprisingly not the Arp2/3 complex, is enriched at the membrane invaginations generated by L. monocytogenes during HeLa and Jeg-3 cell infections. Electron microscopy reveals a band of linear actin filaments that run along the longitudinal axis of the invagination membrane. Mechanistically, mDia1 expression is vital for the assembly of this F-actin shell. mDia1 is also required for the recruitment of Filamin A, a caveola-associated F-actin cross-linking protein, and caveolin-1 to the invaginations. Importantly, mixed-cell infection assays show that optimal caveolin-based L. monocytogenes cell-to-cell spreading correlates with the formation of the linear actin filament-containing shell by mDia1.

Document type: 
Article