Carcass Analog Research Articles

Combination of Acoustic Telemetry and Side‐Scan Sonar Advances Suppression Efforts for Invasive Lake Trout in a Submontane Lake

AbstractExpansion of an invasive Lake Trout Salvelinus namaycush population in Swan Lake, Montana, threatens a core area population of Bull Trout S. confluentus. Given the recent development of novel suppression methods, such as use of carcass analog pellets to cause high mortality of embryos, there was a need to quantify spawning season aggregation sites, site use, and spawning habitat for Lake Trout in Swan Lake. Acoustic tags were implanted in 85 Lake Trout during the summer in 2018 and 2019. Nightly tracking efforts during autumn in both years resulted in 1,744 relocations for 49 individual Lake Trout. Kernel density analysis was used to evaluate Lake Trout aggregation sites, identifying 10 distinct sites. All spawning sites were located in the littoral zone along areas of steep bathymetric relief, and these sites composed 48% of total relocations during both spawning seasons. In 2019, side‐scan sonar imaging was used to classify and quantify the total area of spawning substrate, which constituted 12.8% of the total surface area estimated for spawning sites 1, 6, and 9 and 11.4% of the total surface area for aggregation sites 2–5, 7, 8, and 10. Simultaneous treatment of all spawning sites would require 205,709 ± 86 kg of carcass analog pellet material, resulting in 370.4 ± 0.2 kg of phosphorus inputs and 7,487.9 ± 3.1 kg of nitrogen inputs to Swan Lake. Thus, pellet treatment would increase the Carlson's trophic state index (TSI) values from 20.8 to 27.7 for total phosphorus and from 22.1 to 26.2 for total nitrogen. Based on a TSI threshold of less than 40 for an oligotrophic lake, the use of carcass analog pellets could be feasible for supplementing the gill‐netting suppression of Lake Trout in Swan Lake.

The fate of marine-derived nutrients: tracing δ13C and δ15N through oligotrophic freshwater and linked riparian ecosystems following salmon carcass analog additions

The oligotrophic condition of salmon-bearing catchments in the Columbia River Basin is a potential limiting factor for the recovery of Pacific salmon (Oncorhynchus spp.). To address this issue, nutrient supplementation programs attempt to mitigate for reduced marine-derived nutrients (MDN). We examined the assimilation of MDN in the biota of tributaries of the Salmon River Basin, Idaho, USA, following the addition of salmon carcass analogs (SCA). We measured carbon (C) and nitrogen (N) stable isotopes from biofilm, macroinvertebrate, salmonid fish, and riparian vegetation samples and found significant 15N enrichment and substantial assimilation of SCA material in all aquatic trophic levels and in riparian vegetation. Our results suggest that SCA are incorporated primarily through indirect pathways and provide a source of MDN to multiple trophic levels in freshwater and linked riparian ecosystems.

Bioenergetic calculations evaluate changes to habitat quality for salmonid fishes in streams treated with salmon carcass analog

Nutrient supplementation in oligotrophic streams is proposed as a means of mitigating losses of marine-derived subsidies from declining or extirpated populations of anadromous fishes. One of the central predictions of nutrient addition is an increased production of fish through bottom-up increases in invertebrate abundance. Such changes in food availability may increase growth and production rates for stream fishes by increasing habitat quality. In this study we apply bioenergetic calculations to estimate changes to habitat quality based on predicted increases in net energy intake. We compared invertebrate drift abundance and estimated changes in energy availability in streams treated with salmon carcass analog versus untreated controls. Our results revealed a two- to threefold increase in invertebrate drift abundance following the addition of salmon carcass analog; however, this effect appeared to be short-term. Measures of the energetic profitability of stream habitat for salmonid fishes revealed small, yet significant, increases in net energy availability in streams that received analog additions, but only after controlling for differences in physical habitat features such as temperature and stream flow.

Effects of experimentally added salmon subsidies on resident fishes via direct and indirect pathways

AbstractArtificial additions of nutrients of differing forms such as salmon carcasses and analog pellets (i.e. pasteurized fishmeal) have been proposed as a means of stimulating aquatic productivity and enhancing populations of anadromous and resident fishes. Nutrient mitigation to enhance fish production in stream ecosystems assumes that the central pathway by which effects occur is bottom‐up, through aquatic primary and secondary production, with little consideration of reciprocal aquatic‐terrestrial pathways. The net outcome (i.e. bottom‐up vs. top‐down) of adding salmon‐derived materials to streams depend on whether or not these subsidies indirectly intensify predation on in situ prey via increases in a shared predator or alleviate such predation pressure. We conducted a 3‐year experiment across nine tributaries of the N. Fork Boise River, Idaho, USA, consisting of 500‐m stream reaches treated with salmon carcasses (n = 3), salmon carcass analog (n = 3), and untreated control reaches (n = 3). We observed 2–8 fold increases in streambed biofilms in the 2–6 weeks following additions of both salmon subsidy treatments in years 1 and 2 and a 1.5‐fold increase in standing crop biomass of aquatic invertebrates to carcass additions in the second year of our experiment. The consumption of benthic invertebrates by stream fishes increased 110–140% and 44–66% in carcass and analog streams in the same time frame, which may have masked invertebrate standing crop responses in years 3 and 4. Resident trout directly consumed 10.0–24.0 g·m−2·yr−1 of salmon carcass and <1–11.0 g·m−2·yr−1 of analog material, which resulted in 1.2–2.9 g·m−2·yr−1 and 0.03–1.4 g·m−2·yr−1 of tissue produced. In addition, a feedback flux of terrestrial maggots to streams contributed 0.0–2.0 g·m−2·yr−1 to trout production. Overall, treatments increased annual trout production by 2–3 fold, though density and biomass were unaffected. Our results indicate the strength of bottom‐up and top‐down responses to subsidy additions was asymmetrical, with top‐down forces masking bottom‐up effects that required multiple years to manifest. The findings also highlight the need for nutrient mitigation programs to consider multiple pathways of energy and nutrient flow to account for the complex effects of salmon subsidies in stream‐riparian ecosystems.

Feeding and Growth of Larval Pacific Lamprey Reared in Captivity

AbstractPacific Lampreys Entosphenus tridentatus are declining in the Columbia River basin as well as in much of their broader range. To mitigate for reductions in abundance, strategies such as hatchery propagation and captive rearing of lamprey larvae are currently being considered. We conducted a series of experiments using captive larval Pacific Lampreys at Eagle Creek National Fish Hatchery to investigate the effect of different food types and different food concentrations on the growth of larvae. In our first experiment, we evaluated the growth of larvae (TL range, 59–145 mm) given four different food types (algae, leaves, yeast–larval fish food, and salmon carcass analogs) and a control group that was not fed. Assimilation of food types was evaluated by tracking unique stable isotope signatures of δ13C and δ15N within larval tissues. Results from experiment 1 indicated that lampreys fed a diet of salmon carcass analog or algae had positive growth (up to 0.16 mm/d and 42% proportional change in length) over approximately 6 months. Isotopic analyses of larval tissues showed unique signatures that matched those of their specific food treatment. Based on the results of experiment 1, we conducted a second experiment to evaluate the growth of larvae fed four different quantities of salmon carcass analog. Results from this experiment indicated larval growth rate increased with increasing rations of food, but positive growth was observed in all feeding treatments. The highest dose of salmon carcass analog resulted in the highest growth (up to 0.15 mm/d and 36% proportional change in length) over 6 months. We successfully reared larval Pacific Lampreys in captivity with minimal mortality and positive growth, which highlights the potential to use captive rearing and propagation as a conservation tool for this ecologically and culturally important species.

Biofilm nutrient limitation, metabolism, and standing crop responses to experimental application of salmon carcass analog in Idaho streams

Dramatic declines of Pacific salmon (Oncorhynchus spp.) populations have decreased delivery of marine-derived material to Pacific Northwest streams where juvenile salmon reside. Managers use artificial nutrient additions to increase juvenile salmon growth and survival and typically assume nutrient-driven increases in biofilm production are an important pathway by which nutrients become available to higher trophic levels. To evaluate how biofilms respond to additions of salmon carcass analog, a pasteurized, processed form of nutrient mitigation materials, we quantified biofilm nutrient limitation, benthic and whole-stream metabolism, and biofilm standing crops before and following experimental additions in tributaries of the Salmon River, Idaho, USA. Biofilm nutrient limitation did not change and standing crop did not increase in response to analog additions at two different levels (low, 30 g·m−2; or high, 150 g·m−2) within 1 month of addition. In contrast, whole-stream and benthic primary productivity and respiration increased in a high-analog treated segment, but did not increase in a low-analog treated segment. Together, our results suggest that metabolism may be a more appropriate tool for assessing the ecosystem effects of nutrient additions than biofilm standing crop or nutrient limitation, which are constrained by a variety of abiotic and biotic factors like hydrology and grazing.

Use of an Ecosystem‐Based Model to Evaluate Alternative Conservation Strategies for Juvenile Chinook Salmon in a Headwater Stream

AbstractDeclining abundance of Chinook Salmon Oncorhynchus tshawytscha across the Pacific Northwest is an issue of great concern ecologically, culturally, and economically. Growth during the first summer is vitally important for juvenile Chinook Salmon, as it influences not only life history decisions (to smolt or not to smolt) but also subsequent river and ocean survival. Using Ecopath with Ecosim, we developed a food web model for a representative stream in the Salmon River basin, Idaho, to evaluate potential species‐specific and food web effects of three management strategies: (1) adding salmon carcasses or carcass analogs to promote primary production and detrital availability that were lost due to declining salmon returns; (2) removal of nonnative Brook Trout Salvelinus fontinalis, which are competitors with and predators on juvenile Chinook Salmon; and (3) stocking hatchery Chinook Salmon into streams to supplement wild production. Overall, juvenile Chinook Salmon responded strongly to increases in basal resources. Removal of Brook Trout had little effect on potential production for juvenile Chinook Salmon, but the responses of sculpins Cottus spp. were strong, primarily due to the sculpins’ high degree of dietary overlap with and predation by Brook Trout. Supplementation with hatchery‐origin juveniles depressed the production of wild juvenile Chinook Salmon, especially at the densities commonly applied to streams in this region. Our results suggest that efforts to enhance basal resources are likely to be the most effective in promoting the production of juvenile Chinook Salmon and nearly all food web groups considered in our model system. Removal of nonnative Brook Trout is unlikely to substantially affect salmon but could have a disproportionately large effect on nongame species, which are generally overlooked in single‐species management approaches.Received October 2, 2013; accepted March 24, 2014

Nutrient additions to mitigate for loss of Pacific salmon: consequences for stream biofilm and nutrient dynamics

Mitigation activities designed to supplement nutrient and organic matter inputs to streams experiencing decline or loss of Pacific salmon typically presuppose that an important pathway by which salmon nutrients are moved to fish (anadromous and/or resident) is via nutrient incorporation by biofilms and subsequent bottom‐up stimulation of biofilm production, which is nutrient‐limited in many ecosystems where salmon returns have declined. Our objective was to quantify the magnitude of nutrient incorporation and biofilm dynamics that underpin this indirect pathway in response to experimental additions of salmon carcasses and pelletized fish meal (a.k.a., salmon carcass analogs) to 500‐m reaches of central Idaho streams over three years. Biofilm standing crops increased 2–8‐fold and incorporated marine‐derived nutrients (measured using 15N and 13C) in the month following treatment, but these responses did not persist year‐to‐year. Biofilms were nitrogen (N) limited before treatments, and remained N limited in analog, but not carcass‐treated reaches. Despite these biofilm responses, in the month following treatment total N load was equal to 33–47% of the N added to the treated reaches, and N spiraling measurements suggested that as much as 20%, but more likely 2–3% of added N was taken up by microbes. Design of biologically and cost‐effective strategies for nutrient addition will require understanding the rates at which stream microbes take up nutrients and the downstream distance traveled by exported nutrients.

Carcass analog addition enhances juvenile Atlantic salmon (Salmo salar) growth and condition

Our study used historic marine-derived nutrient (MDN) delivery timing to simulate potential effects of restored connectivity on juvenile Atlantic salmon (ATS; Salmo salar) growth and condition. Four headwater streams were stocked with ATS young of the year (YOY) and received carcass analog additions (0.10 kg·m–2wetted area) in treatment reaches to match the timing of sea lamprey (Petromyzon marinus) spawning. Individual ATS mass was 33%–48% greater and standard length was 9%–15% greater in treatment reaches relative to control reaches for 4 months following nutrient additions. Percent total lipids in YOY ATS were twice as great in treatment reaches 1 month following carcass analog additions and remained elevated in treatment fish for 2 more months. Absolute growth rates, based on otolith microstructure analysis, correlated with water temperature fluctuations in all reaches and were elevated by an average of 0.07 mm·day–1in treatment reaches for 1 month following carcass analog additions. Simulated sea lamprey MDNs increased juvenile ATS growth, which, via potential increases in overwinter survival and decreases in smolt age, may contribute to population persistence and ecosystem productivity.

Nutrient Enrichment with Salmon Carcass Analogs in the Columbia River Basin, USA: A Stream Food Web Analysis

AbstractAnadromous fishes represent an important ecosystem linkage between marine and inland aquatic and terrestrial habitats. These fishes carry organic matter and marine‐derived nutrient (MDN) subsidies across a vast landscape, often with profound influences on recipient ecosystem food web structure and function. In the Columbia River basin, century‐long declines in the abundance of anadromous fish populations have focused attention on potential mitigation efforts to address MDN deficits. In this study, we evaluate components of the stream food web response (periphyton, macroinvertebrate, and fish) to pasteurized salmon carcass analog (SCA) treatments in 15 streams across the Columbia River basin. Periphyton standing crop, macroinvertebrate density, and salmonid fish growth rates and stomach fullness measures increased following the addition of SCA. We found no significant change in dissolved nutrient concentrations after treatment, suggesting that biological demand exceeded supply. Nitrogen stable isotope signatures confirmed trophic transfer from SCA to lower trophic levels but were noticeably weak in fish tissue samples despite our marked growth and stomach fullness measures. These data indicate that SCA has the potential to increase the productivity of nutrient‐limited freshwater ecosystems and may provide a nutrient mitigation tool in ecosystems where MDNs are severely limited or unavailable.

Aquatic Community Responses to Salmon Carcass Analog and Wood Bundle Additions in Restored Floodplain Habitats in an Alaskan Stream

AbstractLand use activities often directly and indirectly limit the capacity of freshwater habitats to produce fish. Consequently, habitat creation and enhancement actions are often undertaken to increase the quantity and quality of resources available to aquatic communities within these impaired systems, with the intent to increase fish production. The objectives of this study were to (1) determine whether aquatic community colonization and development could be accelerated through additions of woody debris bundles and marine‐derived nutrients (via salmon carcass analog pellets) and (2) measure how aquatic communities (biofilm, invertebrates, and fish) respond to these additions after the creation of off‐channel (alcove) fish habitat in a stream in south‐central Alaska. Biofilm, invertebrates, and juvenile coho salmon Oncorhynchus kisutch were sampled in four treatments (control, wood, analog, and analog plus wood). Biofilm chlorophyll‐a concentrations were 4–10 times higher in analog‐enriched treatments than in the control and wood treatments. No treatment effects were detected in benthic invertebrate density; however, treatment differences were detected in coho salmon diets, with nearly twice the amount of invertebrate abundance and biomass (primarily various dipteran, ephemeropteran, and plecopteran larvae) in the analog and analog plus wood treatments compared with the control and wood treatments. Juvenile coho salmon density and biomass were significantly higher in the wood treatment than in the analog plus wood treatment, and fish in the control showed possible signs of density‐dependent limitation. Further, body condition of juvenile coho salmon was highest in the two analog‐enriched treatments at the end of the study; juveniles in these habitats showed nearly two times the condition increase of fish inhabiting the control and wood treatment alcoves. These results demonstrate that the combination of salmon carcass analog and woody debris bundle additions aids in the short‐term development of aquatic communities in newly created off‐channel habitats, providing a boost in limited resources such as food and shelter.

Development of a Carcass Analog for Nutrient Restoration in Streams

Abstract Resource managers are becoming more interested in restoring nutrients to food-limited salmonid bearing streams, but all of the current approaches have some shortcomings. The objective of our work was to develop a nutrient restoration product that reduced these shortcomings. The product we developed, a carcass analog, was made from fall Chinook salmon (Oncorhynchits tshawytscha) from Spring Creek Hatchery, Underwood, Washington. These fish were pasteurized during the process that dried the ground salmon carcasses into a fishmeal. No known fish pathogens were detected in the pasteurized product. The analogs were easy to transport and distribute throughout the stream channel, generally sank to the bottom, and were retained within the channel. Approximately half of the analog had dissolved or been eaten after being in streams two weeks, and the analog was almost gone after four weeks. We discuss other studies that have demonstrated that carcass analogs reproduce the main food pathways historically pr...

Ecological and water quality consequences of nutrient addition for salmon restoration in the Pacific Northwest

Salmon runs have declined over the past two centuries in the Pacific Northwest region of North America. Reduced inputs of salmon-derived organic matter and nutrients (SDN) may limit freshwater production and thus establish a negative feedback loop affecting future generations of fish. Restoration efforts use the rationale of declining SDN to justify artificial nutrient additions, with the goal of reversing salmon decline. The forms of nutrient addition include introducing salmon carcasses, carcass analogs (processed fish cakes), or inorganic fertilizers. While evidence suggests that fish and wildlife may benefit from increases in food availability as a result of carcass additions, stream ecosystems vary in their ability to use nutrients to benefit salmon. Moreover, the practice may introduce excess nutrients, disease, and toxic substances to streams that may already exceed proposed water quality standards. Restoration efforts involving nutrient addition must balance the potential benefits of increased food resources with the possible harm caused by increased nutrient and toxin loads.

Restoring Productivity of Salmon‐Based Food Webs: Contrasting Effects of Salmon Carcass and Salmon Carcass Analog Additions on Stream‐Resident Salmonids

We tested the hypotheses that salmon carcasses and salmon carcass analogs (dried, processed hatchery salmon) increase the condition factor, production, and whole-body lipid content of stream-resident salmonids and that stream shading affects responses to enrichment. Two enrichment treatments (salmon carcass, salmon analog) and a control, each with and without simulated riparian shading (95% shade), were replicated six times in once-through artificial channels (mesocosms). Each channel was stocked with three live young-of-the-year coho salmon Oncorhynchus kisutch. The experiment spanned 30 July through 18 2002. Production and lipid content significantly increased in both carcass and analog treatments. Condition was generally unchanged. Stream shading significantly reduced the magnitude of production and lipid responses. In addition, in a small stream where salmon carcasses and analogs were added to two separate tributaries, cutthroat trout O. clarki had higher mean condition, production, and lipid content than fish in stream sections that were not enriched (6 August to 20 2002). Furthermore, coho salmon production was also higher in an analog-enriched reach than in control reaches. This study illustrates that marine subsidies from salmon spawners and salmon analogs increase condition, production, and lipid concentrations of resident and anadromous salmonids. Larger and more lipid-rich fish may subsequently have higher survival and reproduction, thereby elevating freshwater and marine salmonid production. Salmon analogs appear to hold promise for restoring nutrients and productivity to freshwater ecosystems suffering reduced salmon runs and may prove to be a useful, albeit temporary, tool for improving aquatic productivity.