Salmon Carcasses Research Articles

Juvenile coho salmon growth differences track biennial pink salmon spawning patterns

Abstract Spawning Pacific salmon (Oncorhynchus spp.) provide marine‐derived resources (MDR) to freshwater food webs in the form of eggs, flesh and maggots that consume salmon carcasses, all of which positively impact stream‐dwelling fish growth. Pink salmon (O. gorbuscha) are widely distributed throughout coastal catchments along the North Pacific Ocean and display increased spawning abundances in odd years, owing to a fixed 2‐year life history. While many studies have found that foraging and growth of stream‐dwelling salmonids are improved by increased adult salmon spawning abundance, few studies have investigated the importance of alternating pink salmon spawning abundance between years. Here, we examined how patterns of pink salmon spawning abundance impact the foraging and growth of juvenile coho salmon (O. kisutch). First, we used bioenergetic simulations to generate a hypothesis that coho salmon growth would increase during odd relative to even years. We then collected empirical juvenile coho salmon diet and growth data from a Southeast Alaska catchment in 2021 (pink salmon spawning) and 2022 (no pink salmon spawning). Field data were compared against simulation predictions to understand impacts of biennial pink salmon spawning patterns on juvenile coho salmon growth. Empirical growth data revealed similar patterns to bioenergetic simulations. Age‐1 coho salmon grew 16.6 mm longer and 5.5 g heavier on average in 2021 compared to 2022. Age‐0 coho salmon displayed minor growth differences between years. These results support bioenergetic model predictions and suggest that patterns of pink salmon spawning abundance can impart interannual growth disparities to juvenile coho salmon. Moreover, we show that distinct spawning characteristics of Pacific salmon species are important when understanding patterns of MDR transfer and growth responses in stream fishes.

Ecological implications of the pink salmon invasion in northern Norway-Aggregative responses and terrestrial transfer by white-tailed eagles.

Over the last 10 years, the spawning population of invasive pink salmon (Oncorhynchus gorbuscha) has increased in the river systems in northern Norway to a level that is causing concern about their impact on endemic fauna and ecosystem processes. The scale of transfer of pink salmon carcasses into the terrestrial ecosystem is likely to be a key determinant of terrestrial impact. Bears (Ursus sp.) are responsible for most such transfers in North America but are rare in Norway. The white-tailed eagle (Haliaeetus albicilla) is common however, and a candidate to be a main cause of such transfers. To evaluate this hypothesis, data on the abundance of white-tailed eagles and pink salmon were collected along the river Skallelv in northern Norway in 2021, a year the pink salmon spawned in the river, and in 2022, a year no pink salmon spawned in the river. The abundance of white-tailed eagles along the river was much higher the year pink salmon spawned in the river. Furthermore, white-tailed eagles were observed aggregating and catching pink salmon where and when pink salmon were present at the spawning and post-spawning stages. Based on our observations, we suggest that the white-tailed eagle is the main species involved in the transport of pink salmon from the river into the riparian zone in northern Norway and that other scavengers, in particular the red fox (Vulpes vulpes) and common raven (Corvus corax), play an important role in transporting pink salmon carcasses from the riparian zone to the wider terrestrial ecosystem.

Carrion ecology in inland aquatic ecosystems: a systematic review.

Carrion ecology, i.e. the decomposition and recycling of dead animals, has traditionally been neglected as a key process in ecosystem functioning. Similarly, despite the large threats that inland aquatic ecosystems (hereafter, aquatic ecosystems) face, the scientific literature is still largely biased towards terrestrial ecosystems. However, there has been an increasing number of studies on carrion ecology in aquatic ecosystems in the last two decades, highlighting their key role in nutrient recirculation and disease control. Thus, a global assessment of the ecological role of scavengers and carrion in aquatic ecosystems is timely. Here, we systematically reviewed scientific articles on carrion ecology in aquatic ecosystems to describe current knowledge, identify research gaps, and promote future studies that will deepen our understanding in this field. We found 206 relevant studies, which were highly biased towards North America, especially in lotic ecosystems, covering short time periods, and overlooking seasonality, a crucial factor in scavenging dynamics. Despite the low number of studies on scavenger assemblages, we recorded 55 orders of invertebrates from 179 families, with Diptera and Coleoptera being the most frequent orders. For vertebrates, we recorded 114 species from 40 families, with birds and mammals being the most common. Our results emphasise the significance of scavengers in stabilising food webs and facilitating nutrient cycling within aquatic ecosystems. Studies were strongly biased towards the assessment of the ecosystem effects of carrion, particularly of salmon carcasses in North America. The second most common research topic was the foraging ecology of vertebrates, which was mostly evaluated through sporadic observations of carrion in the diet. Articles assessing scavenger assemblages were scarce, and only a limited number of these studies evaluated carrion consumption patterns, which serve as a proxy for the role of scavengers in the ecosystem. The ecological functions performed by carrion and scavengers in aquatic ecosystems were diverse. The main ecological functions were carrion as food source and the role of scavengers in nutrient cycling, which appeared in 52.4% (N = 108) and 46.1% (N = 95) of publications, respectively. Ecosystem threats associated with carrion ecology were also identified, the most common being water eutrophication and carrion as source of pathogens (2.4%; N = 5 each). Regarding the effects of carrion on ecosystems, we found studies spanning all ecosystem components (N = 85), from soil or the water column to terrestrial vertebrates, with a particular focus on aquatic invertebrates and fish. Most of these articles found positive effects of carrion on ecosystems (e.g. higher species richness, abundance or fitness; 84.7%; N = 72), while a minority found negative effects, changes in community composition, or even no effects. Enhancing our understanding of scavengers and carrion in aquatic ecosystems is crucial to assessing their current and future roles amidst global change, mainly for water-land nutrient transport, due to changes in the amount and speed of nutrient movement, and for disease control and impact mitigation, due to the predicted increase in occurrence and magnitude of mortality events in aquatic ecosystems.

Stray compositions of hatchery‐origin Chinook Salmon and steelhead in natural spawning populations of the upper Columbia watershed

AbstractObjectiveOne of the biggest concerns of operating hatchery salmonid programs is high straying of returning adults into nontarget populations and the possible homogenization of genetic diversity among populations caused by spawning of stray fish. The composition of hatchery‐origin stray Chinook Salmon Oncorhynchus tshawytscha and steelhead O. mykiss relative to the natural spawning populations, termed “recipient population stray composition,” was evaluated at three spatial scales in the upper Columbia River basin, where stray target limits were 5–10%.MethodsChinook Salmon carcasses were collected from 1999 to 2018 in spawning areas shortly after spawning, and carcasses were examined to determine origin. Steelhead strays and spawning escapement were evaluated using passive integrated transponder tags between 2013 and 2018. We calculated mean stray compositions for 1999–2018 and for 2014–2018.ResultThe mean recipient population stray compositions ranged between 0.02% and 87.35% and increased with decreasing spatial scale. Recipient stray compositions of all taxa at the basin scale were <3%, and summer and fall Chinook Salmon were <0.5%. Stray compositions in subbasins for all taxa ranged between 0.07% and 33.04%. Spring and summer Chinook Salmon exceeded 5% and 10% (summer Chinook Salmon) in some periods in the Entiat and Methow River subbasins, but stray compositions for all Chinook Salmon were <5% in the Wenatchee, Okanogan, and Hanford Reach subbasins for all periods. All steelhead stray compositions in subbasins exceeded 5%, except for those in the Wenatchee subbasin. Stray compositions of spring Chinook Salmon in tributaries ranged between 0.61% and 87.35%. Only the Chiwawa, Icicle, and Twisp rivers were consistently below 10%.ConclusionIn cases where recipient stray management targets were exceeded, some were the result of single hatchery contributions but others were the result of cumulative contributions from multiple hatcheries. Some solutions to reduce recipient stray compositions will likely involve a combination of changes to hatchery, harvest, and habitat 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.

Ceratonova shasta infection in lower Feather River Chinook juveniles and trends in water-borne spore stages

We performed a five-year (2015–2020) survey of juvenile natural Chinook Salmon (Oncorhynchus tshawytscha), adult salmon carcasses, and river water from the lower Feather River to determine infection prevalence, distribution, and spore quantity of the myxozoan parasite Ceratonova shasta. Average prevalence of infection in juvenile salmon collected from the high flow channel ranged from 45–58% depending on assay method. Initial infection of fry and detection of actinospore stage in river water began in late January or early February. Overt disease occurred in March and was lethal. Infection of the gill was detected weeks ahead of intestinal infection. Water-borne spore measurement and fish infection demonstrate an infectious zone beginning at the outlet of the Thermalito Afterbay. This zone is expanding downriver past the confluence of the Yuba River. Adult carcasses produce billions of myxospores annually that move downriver over the winter. C. shasta infection is one of several factors (predation, limited rearing habitat, elevated water temperature, water withdrawal, etc.) limiting natural Chinook Salmon recruitment in the Feather River.

A win–win between farmers and an apex predator: investigating the relationship between bald eagles and dairy farms

AbstractHuman–wildlife conflicts on farms and ranches are common and well‐documented, particularly with apex predators. Predation of livestock, for example, can result in serious economic burdens for farmers and can become threats to wildlife populations as farmers take action to eliminate or displace populations. Among apex predators, bald eagles (Haliaeetus leucocephalus) have received increased media attention in recent years due to conflicts with farmers across the United States. This raises challenges for both farmers and wildlife managers as eagle abundance continues to increase and natural prey resources decline. Interestingly, a recent study in northwestern Washington State reported high eagle activity on dairy farms in response to declines in salmon carcass availability, an important resource for wintering eagles across western North America. Despite the potential for human–wildlife conflict in these areas, little is known of the relationship between eagles and dairy farms. In this study, we investigated the extent of eagle activity on dairy farms and the relationship between eagles and dairy farmers using semistructured interviews with dairy farmers. We found that (1) eagles were attracted to dairy farms to feed primarily on cow afterbirth and calf carcasses, (2) responding farmers had no issue with the presence of eagles on their farms, and (3) many dairy farmers felt that eagles provided services to their farms. Of these services, the most recognized were scavenging of dairy farm byproducts and removal or deterrence of unwanted pest species. Increased eagle abundance on dairy farms and the subsidy of anthropogenic resources may also influence the ecological role of eagles as top predators in agroecosystems. Ultimately, farmers' decisions to provide anthropogenic resources have apparently mitigated human–eagle conflict while potentially reducing top–down pressures on other wild prey species. Farmers and wildlife managers may each benefit through cooperation in continuing to understand the intricacies of dairy farm–eagle relationships.

Experimental addition of marine-derived nutrients affects wildflower traits in a coastal meta-ecosystem.

Organismal movement can bring individuals, resources and novel interactions across ecosystem boundaries and into recipient habitats, thereby forming meta-ecosystems. For example, Pacific salmon ecosystems receive large marine-derived nitrogen subsidies during annual spawning events, which can have a wide range of effects on aquatic and terrestrial plant species and communities. In this study, we evaluate the effects of cross-ecosystem nutrient subsidies on terrestrial plant growth and reproduction. We conducted a large-scale field experiment with four treatments: (i) addition of a pink salmon (Oncorhynchus gorbuscha) carcass, (ii) addition of the drift seaweed rockweed (Fucus distichus), (iii) addition of both salmon + rockweed, and (iv) a control. We examined treatment effects on leaf nitrogen and fitness-associated floral traits in four common estuarine wildflower species. We found elevated leaf ∂15N in all plant species and all sampling years in treatments with salmon carcass additions but did not observe any differences in leaf per cent nitrogen. We also observed larger leaf area in two species, a context-dependent increase in floral display area in two species, and a limited increase in plant seed set in response to both salmon carcass treatments. In sum, our study suggests that marine nutrients can affect terrestrial plant growth and reproduction.

Avaliação nutricional e palatabilidade de biscoitos pet para cães

Abstract The study's aim was to evaluate the microbiological, nutritional, textural quality and palatability of pet biscuits made with the inclusion of three flours. The treatments were chicken viscera flour (CVF), commercial Nile tilapia flour (FF) and mixed fish flours of several species (FVF). For the FVF, only the carcasses (backbones) of Nile tilapia, salmon, tuna and sardines were used, and they were washed, whereas FVF as well as the others were cooked for 60 minutes, then pressed, ground and dehydrated for 24 hours at 60° C. After this period, they were crushed and ground for inclusion in the biscuits. The CVF, FF and FVF flours showed 43.82%, 50.48% and 56.70% of crude protein, respectively. CVF had the highest lipid content (10.01%) and FVF had the highest ash content (23.94%) and FVF had the highest caloric value (338.63 kcal 100 g-1). The inclusion of flours in biscuits did not influence the protein and carbohydrate contents, whose average values were 18.48% and 50.23%. However, they influenced the moisture content, lipids, ash and caloric value. Biscuits with the inclusion of viscera (CVF) had the highest lipid content (5.91%) and those with fish had the highest ash content (5.66% and 5.81%) for FF and FVF. Biscuits with FVF had a lower caloric value (318.47 kcal 100 g-1). The microbiological analysis indicated that the biscuits were considered of good quality to feed dogs. Regarding texture and palatability, there was no significant difference between treatments. The inclusion of fish flour, both FF and FVF, is a viable alternative.

Relationship between salmon egg subsidy and the distribution of an avian predator.

As a spatial subsidy, which is the phenomenon of transferring resources from a donor system to a recipient system, anadromous salmonids contribute to the supply of marine-derived nutrients to freshwater and terrestrial systems. Live salmon and salmon carcasses and eggs are utilized by various organisms and affect their abundance and distribution. However, the evaluation of the effect of salmon subsidies on the abundance and distribution of terrestrial animals is biased toward predators or scavengers that utilize spawning adults and carcasses, and few studies have focused on the effect of salmon eggs as a subsidy. To avoid underestimating the function of salmon subsidies, the response to the availability of salmon eggs in various systems should be investigated. Here, we investigated the abundance and feeding behavior of the brown dipper Cinclus pallasii, as a consumer of salmon eggs, based on the hypothesis that the availability of salmon eggs affects the diet composition and stream distribution of this small predator. In addition, to test whether changes in the abundance of brown dippers are determined by salmon spawning, their abundance was compared upstream and downstream of the check dams in three streams during the peak spawning period. Brown dippers used salmon eggs during the spawning season (53.7% of diet composition), and their abundance increased as the number of spawning redds increased. In contrast, this pattern was not observed upstream of the check dam. These results suggested that the abundance and stream distribution of brown dippers vary according to the variation in the spatiotemporal availability of salmon eggs.

Spatiotemporal Responses of Wintering Bald Eagles to Changes in Salmon Carcass Availability in the Pacific Northwest

Each winter, thousands of bald eagles (Haliaeetus leucocephalus) from across western North America migrate to Pacific Northwest rivers to feed on the carcasses of post-spawning chum salmon (Oncorhynchus keta). However, declining salmon populations and impacts of climate change are reducing the availability of salmon carcasses as a wintering food source for eagles. The ability of eagles to adjust to these impacts is crucial to their survival, and their responses are currently unknown. I hypothesized that eagles are responding by redistributing to non-river habitat in search of alternative food sources. Specifically, I examined the redistribution of over-wintering eagles from river habitat to nearby agricultural areas in response to seasonal declines in carcass availability. Over two consecutive winters, I conducted weekly eagle surveys on a 30-km stretch of the Nooksack River and a 22.5-km stretch of farmland northwest of the river. I examined the association between salmon carcass distribution and eagle abundance on the Nooksack River, and evaluated the temporal relationship between eagle abundance on the Nooksack River versus neighboring farmland. I found a strong negative association between eagle abundance on the river versus adjacent farmland, and observed eagles primarily concentrated near dairy farms and waterfowl rafts. My results suggest that eagles are responding to declining carcass availability by redistributing to non-river habitat in search of alternative food sources, and that a substantial fraction may migrate to agricultural areas.

Emergent trophic interactions following the Chinook salmon invasion of Patagonia

AbstractIn 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.

Evaluation of high oil residue camelina meal (HORM) on Atlantic salmon ( Salmo salar ) growth performance, carcass composition, intestinal morphology and inflammatory biomarker gene expression

High oil residue camelina meal (HORM) was included in low fish meal, low fish oil diets for juvenile Atlantic salmon at a dietary inclusion level of 0, 20, 40, 60, 80 or 100 g/kg to determine the effect of diet on growth performance, carcass composition, morphology and inflammatory biomarker gene expression in the distal intestine. Diets were fed to Atlantic salmon (mean weight ± standard deviation: 2.3 ± 0.1 g/fish; 50 fish/40 L tank; 3 tanks/treatment) for 16 weeks. Salmon fed 0, 20 and 40 g/kg HORM had significantly higher weight gain, growth rate, protein efficiency, and lower feed conversion ratio, than salmon fed 60, 80 and 100 g/kg HORM. Distal intestinal morphology showed lamina propria were wider in salmon fed 60 g/kg HORM, compared with salmon fed the other dietary treatments. Transcript expression of the distal intestine showed significant differential expression across treatments, as determined by qPCR. IL17Ar and GILT1 were down-regulated 1.3- to 1.5-fold in salmon fed 80 and 100 g/kg HORM, compared with 0 g/kg HORM. Nfkb2 was also down-regulated in salmon fed 40, 80 and 100 g/kg HORM, compared with the control treatment. The transcript encoding thioredoxin was 1.9-fold upregulated in salmon fed 100 g/kg HORM compared with 0, 20 and 40 g/kg HORM-fed groups. This study finds that inclusion of dietary HORM at 20 and 40 g/kg results in acceptable growth. In general, transcript expression of some inflammation-relevant genes responded to dietary HORM; however, further research is needed to determine whether the higher levels of HORM (≥60 g/kg) are associated with inflammation and detrimental to fish health.

Elaboração de patê utilizando resíduos de pescado

Knowing the potential of fish waste for the preparation of pâtés, there is the possibility of adding greater sustainability to the aquaculture sector. The aim was to prepare pâtés from fish processing residues with the inclusion of smoked fishmeal and evaluate their sensory, microbiological, physicochemical, and shelf-life characteristics. Three treatments were used: pâté without fishmeal inclusion (PSF), with smoked salmon carcass meal inclusion (PFSD), and smoked tilapia carcass meal (PFTD). The inclusion of the flours reduced the moisture, carbohydrate, and water activity. However, they increased the ash, salt, and collagen content. The lipid content was higher for the PFSD. The PSF showed peak oxidation at 15 days and the PFSD and PFTD around 45 days over the course of the 90-day shelf-life. The luminosity and b* coordinate were lower for PFTD, while the a* coordinate was higher for PFSD. Only the b* coordinate showed changes in PSF and PFSD throughout the 30 days of shelf-life, and its color tended to yellow at 15 days. The sensory analysis did not differ statistically between treatments (p > 0.05) for all attributes, except color, where the highest score was attributed to PSF. As for the overall impression, PSF also obtained the highest score, which may be associated with its color. By including fish flours, the nutritional composition and color of the tilapia-trimmed pâtés are changed, achieving an average acceptance level of 67%.

Links between fluctuations in sockeye salmon abundance and riparian forest productivity identified by remote sensing

AbstractPacific 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.

Salmon subsidies predict territory size and habitat selection of an avian insectivore.

The annual migration and spawning event of Pacific salmon (Oncorhynchus spp.) can lead to cross-boundary delivery of marine-derived nutrients from their carcasses into adjacent terrestrial ecosystems. The densities of some passerine species, including Pacific wrens (Troglodytes pacificus), have been shown to be positively correlated with salmon abundance along streams in Alaska and British Columbia, but mechanisms maintaining these densities remain poorly understood. Riparian areas near salmon streams could provide higher quality habitat for birds through greater food availability and more suitable vegetation structure for foraging and breeding, resulting in wrens maintaining smaller territories. We examined relationships between salmon biomass and Pacific wren territory size, competition, and habitat selection along 11 streams on the coast of British Columbia, Canada. We show that male wren densities increase and territory sizes decrease as salmon-spawning biomass increases. Higher densities result in higher rates of competition as male wrens countersing more frequently to defend their territories along streams with more salmon. Wrens were also more selective of the habitats they defended along streams with higher salmon biomass; they were 68% less likely to select low-quality habitat on streams with salmon compared with 46% less likely at streams without salmon. This suggests a potential trade-off between available high-quality habitat and the cost of competition that structures habitat selection. Thus, the marine-nutrient subsidies provided by salmon carcasses to forests lead to higher densities of wrens while shifting the economics of territorial defence toward smaller territories being defended more vigorously in higher quality habitats.

Temporal and Age‐Based Variation in Juvenile Sablefish Diet Composition and Quality: Inferences from Stomach Contents and Stable Isotopes

AbstractPrey communities in the North Pacific Ocean have been disrupted by marine heatwaves, and reductions in forage fishes have had notable impacts on upper‐trophic‐level consumers. Little is known about the potential effects of a changing prey base for some commercially valuable fishes, such as Sablefish Anoplopoma fimbria. The objectives of this study were to evaluate temporal and age‐based shifts in diets of juvenile Sablefish, with a focus on understanding their reliance on high‐quality forage fishes. We collected Sablefish from a bay in Southeast Alaska over 2 years (2017–2019) during their first autumn (September–October; age 0), in late winter (March; age 1), and during their second summer (July; age 1). Pacific Herring Clupea pallasii constituted the majority of the Sablefish diet by weight (82.1%) and by frequency of occurrence (40.7%), with variation among months, years, and age‐classes. Stable isotopes corroborated our interpretation of diet composition from stomach contents and indicated that age‐0 Sablefish sampled in October 2017 relied on more depleted carbon sources than other groups, potentially explained by consumption of adult salmon carcasses. Significant relationships between stable isotope ratios and Sablefish length indicated that size‐based diet composition differences were most prevalent during March and July. Sablefish exploited prey taxa of variable quality (0.02–5.3 kJ/g), but mean energy density of consumed prey differed little among years or months (3.62–4.48 kJ/g). Overall, 21% of stomachs sampled were empty, with the percentage of empty stomachs peaking in late winter (46%). Stomach content weights expressed as a percentage of body weight were highest in autumn 2018, when Pacific Herring comprised over 80% of the diets by weight. Consumption of high‐energy prey, such as Pacific Herring, may contribute to rapid growth of Sablefish during the critical prewinter period. If strong Sablefish year‐classes become more frequent with a warming ocean, they will require substantial prey resources to support their growth to adulthood.

Ideal free eagles: Bald Eagle (Haliaeetus leucocephalus) distribution in relation to Pacific salmon (Oncorhynchus spp.) availability on four spawning rivers

The movement of individuals according to the availability of resources has a fundamental effect on animal distributions. In the Pacific Northwest, Bald Eagles (Haliaeetus leucocephalus (Linnaeus, 1766)) rely heavily on scavenging opportunities during the non-breeding period, and their distribution and movements are thought to be strongly influenced by the availability of post-spawning Pacific salmon (genus Oncorhynchus Suckley, 1861) carcasses. We surveyed the abundance of eagles and salmon on four adjacent rivers on Vancouver Island, British Columbia, Canada, during the 2017 fall spawning season. Salmon began to arrive in late September, peaked in abundance in mid-November, and were absent after early December. The seasonal progression of Bald Eagle abundance matched that of salmon carcass availability. The slope of proportional eagle–salmon relationship was significantly positive, though lower than the 1:1 match predicted by Ideal Free Distribution theory. The numerical response of Bald Eagles to salmon abundance was elevated on one of the rivers, potentially due to physical features such as sandbars and mudflats that increased the availability of carcasses and provided access points for eagles.

Barras de cereais salgadas feitas com sementes, cascas de frutas e farinha de peixe

Cereal bars are practical, popular, and represent a multicomponent food with market potential. This work aimed to develop tasty cereal bars with kabocha seeds (Cucurbita moschata), kabochapeels, pineapple peel (Ananassp.), and passion fruit peel (Passiflorasp.) with different levels of fishmeal, as nutritional enrichment. To this purpose, the fish meal was prepared with tilapia and salmon carcasses added to the basic ingredients of the bar. The fish concentrate levels used were 0% (control), 5%, 10% and 15%, amounting to four treatments, with five replications. The elaborated bars were analyzed for proximate compositional, sensory properties, and microbiological contamination. The resultsindicated high levels of protein (49.65%) and lipid (32.40%) for fishmeal. The inclusion of this concentrate in cereal bars interfered with their composition by increasing protein content and reducing the content of carbohydrates and caloric value. As forsensory properties, the average scores were around 6, which indicates that the panelists slightly liked the product. It can be concluded that the addition of up to 15% of tilapia fishmeal with salmon in savory cereal bars containing seed and fruit peel, improve their nutritional composition without adversely affecting their sensory quality.

Terrestrial and semi-aquatic scavengers on invasive Pacific pink salmon (Oncorhynchus gorbuscha) carcasses in a riparian ecosystem in northern Norway

Pacific pink salmon (Oncorhynchus gorbuscha) invasions, thought to originate from populations introduced and established in Russia, occurred along the Norwegian coast in 2017 and 2019. Despite several thousand pink salmon entering and establishing in northern Norwegian rivers, current understanding of the ecological effect of the species in northern Europe is limited. Scavengers feeding on pacific salmon carcasses are important vectors for the transport of marine derived energy and nutrients to terrestrial ecosystems in the Pacific Northwest, North America, where the salmon naturally occur. However the role of terrestrial and aquatic scavengers in the consumption and removal of pink salmon beyond the salmon’s native range is unknown. This study has identified terrestrial and sub-aquatic vertebrate scavengers on pink salmon carcasses in a sub-arctic river in northern Norway. Avian scavengers filmed by a camera placed near sites baited with pink salmon carcasses included the Eurasian magpie (Pica pica), hooded crow (Corvus cornix), common raven (Corvus corax), the European herring gull (Larus argentatus), redwing (Turdus iliacus) and goosander (Mergus merganser). However, the largest carcass weight was removed by red foxes (Vulpes vulpes). Carcasses entering Vesterelv River in 2019 were estimated to provide energy and nutrients to the river ecosystem an order of magnitude lower than in the Pacific Northwest. This study provides some of the first information in northern Europe on the mechanisms and quantification of energy and nutrient transfer from the ocean to riparian environments via introduced Pacific pink salmon. Results help to begin to determine the ecological effect of pink salmon and the development of appropriate management strategies.