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Intraspecific variation in stable isotopes provides insight into adfluvial migrations and ecology of brook trout in Lake Superior tributaries
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January 2025
... Identifying habitats which support native fishes as well as advancing population monitoring tools and techniques are critical activities to support management, conservation, and rehabilitation efforts in the Lake Superior basin. For example, Zorn et al. (2025) address the need for inexpensive, non-lethal approaches for confirming the existence of adfluvial life-histories of brook trout (i.e., coaster brook trout) in Lake Superior tributaries. A linear discriminant function (LDF) was developed based on the data and assigned fish to habitat types with over 97 % accuracy; the LDF was subsequently used to identify those tributaries hosting what are likely to be coaster brook trout. ...
Lake Superior and its surrounding watershed support a wide range of species, provide a wealth of ecosystem services, and support a robust economy, much of which is reliant on the health of the ecosystem. Though Lake Superior continues to lead the other Laurentian Great Lakes in condition and quality, it has also undergone significant changes including chemical pollution, invasive species, and harmful algal blooms (HABs). The lake is also sensitive to climate change, with rapidly warming water temperatures, significant nutrient input from extreme storm events, and changes to habitat and food web structure, among other impacts. Understanding the current conditions, trends, and emerging threats to Lake Superior from local to ecosystem scales allows us to better manage the lake now and prepare for the future. This Journal of Great Lakes Research special section features a wide range of research, capturing the status of Lake Superior and providing insight to current and future stressors. Further, this issue includes results from the 2021 Lake Superior Cooperative Science and Monitoring Initiative field season and other collaborative efforts to better understand and protect Lake Superior.
Knowledge of population-level relationships and how these relationships pertain to different life history forms is critical to developing effective management plans for native trout, char, and salmon. In the Lake Superior basin, identifying effective restoration strategies for coaster brook trout (Salvelinus fontinalis), a lake-inhabiting form of brook trout, is hampered by limited information on genetic connectivity and source-sink dynamics among brook trout populations. Here, we infer these relationships by surveying 8,178 single nucleotide polymorphisms in 234 brook trout from seven rivers along the Minnesota shoreline with Lake Superior, including from reaches above and below natural waterfalls that prevent upstream movement. We identified well-differentiated above-barrier populations that supply brook trout to below-barrier reaches. We also compared within-river brook trout to 26 coaster brook trout from Lake Superior. We identified at least four source populations for these coaster brook trout, three of which were located within rivers. Additionally, we estimated N E for within-river populations and detected a decline across recent generations, with the most recent estimates approaching critical thresholds. Finally, comparisons with 94 domestic brook trout representing nine hatchery strains revealed a lack of domestic introgression into wild populations, demonstrating the importance of natural reproduction to population persistence. Our results offer novel insights into sources of coaster brook trout and highlight the role of within-river populations in supporting the coaster life history. Management efforts focused on instream restoration may be more important to rehabilitating coaster brook trout than previously thought and are urgently needed given the population-level conservation status reported here.
Migrations affect the population dynamics, life history, evolution, and connections of animals to natural ecosystems and humans. Many species and populations display partial migration (some individuals migrate and some do not), and differential migration (migration distance varies). Partial migration is widely distributed in fishes but the term differential migration is much less commonly applied, despite the occurrence of this phenomenon. This paper briefly reviews the extent of differential migration in Pacific salmon and trout (genus Oncorhynchus ), a very extensively studied group. Three hypotheses are presented to explain the patterns among species: 1) phylogenetic relationships, 2) the prevalence of partial migration (i.e., variation in anadromy), and 3) life history patterns (iteroparous or semelparous, and duration spent feeding at sea prior to maturation). Each hypothesis has some support but none is consistent with all patterns. The prevalence of differential migration, ranging from essentially non-existent to common within a species, reflects phylogeny and life history, interacting with the geographic features of the region where juvenile salmon enter the ocean. Notwithstanding the uncertain evolution of this behavior, it has very clear implications for salmon conservation, as it strongly affects exposure to predators, patterns of fishery exploitation and also uptake of toxic contaminants.
Understanding resident fish population responses to restored connectivity would enhance decision‐making on dam removal and fish passage. Since such evaluations are limited in the Great Lakes region of North America, we compared abundance, survival, and growth of resident brook trout and brown trout between sets of Michigan streams where populations were or were not interacting with salmonid species that might be present if connectivity existed. We analysed data from 34 electrofishing index sites to compare resident trout populations between streams without versus with Great Lakes access (and migratory Pacific salmonids), and brook trout populations in Great Lakes inaccessible (land‐locked) streams where brown trout were present versus absent. Great Lakes accessibility effects on fish density became increasingly positive for older age groups of brown trout while generally negative for all age classes of brook trout. Brown trout had consistently negative effects on brook trout density in land‐locked streams. Increased connectivity had significant effects on annual survival for only one of seven trout age classes modelled, while intraspecific density‐dependent effects on survival were significant in six models. Significant intraspecific effects on resident trout growth occurred for seven of eleven age classes examined. Negative interspecific effects of Great Lakes access on resident trout growth were most noticeable for age‐0 and age‐1 resident trout, age classes that likely compete with juvenile Pacific salmonids. Our findings provide a more robust understanding of how Great Lakes connectivity affects resident trout populations, highlighting negative influences of brown trout on brook trout and intraspecific density‐dependent effects.
Trout are one of the most culturally, economically, and ecologically important taxonomic groups of freshwater fishes worldwide. Native to all continents in the Northern Hemisphere, trout belong to seven genera, which are distributed across 52 countries. Despite their broad importance as societal icons and as indicators of biodiversity, many of the world’s trout species and lineages are endangered and some require immediate conservation efforts to reverse their precarious decline. Of the 124 recognized species of trout, only 67 (54%) have been assessed by the IUCN as of January 2018. Alarmingly, 73% of these species are currently threatened with global extinction, and four are now extinct. Although some of these species are likely subspecies, lineages, or distinct ecotypes, this level of threat is exceptionally high compared with other vertebrate groups assessed by the IUCN. Widespread imperilment of trout reflects numerous human activities identified in the IUCN assessments, including invasive species, overfishing, pollution, dams, deforestation, agriculture, grazing, and mining. Moreover, climate change is further stressing trout populations by warming water temperatures, shifting streamflow regimes, increasing extreme events (such as floods, drought, and wildfire), and facilitating species invasions – a pattern that will be intensified in coming decades as global temperatures continue to rise. Reversing these declines will require progressive conservation efforts to protect native trout diversity and ameliorate ongoing and future threats at local and global scales. Moreover, comprehensive, coordinated, and comparable approaches are needed immediately to assess conservation status and to delineate conservation units across the globe, particularly for data-poor species. Only by addressing threats at their root causes can we accomplish these conservation goals.
The ongoing evolution of tracer mixing models has resulted in a confusing array of software tools that differ in terms of data inputs, model assumptions, and associated analytic products. Here we introduce MixSIAR, an inclusive, rich, and flexible Bayesian tracer (e.g., stable isotope) mixing model framework implemented as an open-source R package. Using MixSIAR as a foundation, we provide guidance for the implementation of mixing model analyses. We begin by outlining the practical differences between mixture data error structure formulations and relate these error structures to common mixing model study designs in ecology. Because Bayesian mixing models afford the option to specify informative priors on source proportion contributions, we outline methods for establishing prior distributions and discuss the influence of prior specification on model outputs. We also discuss the options available for source data inputs (raw data versus summary statistics) and provide guidance for combining sources. We then describe a key advantage of MixSIAR over previous mixing model software-the ability to include fixed and random effects as covariates explaining variability in mixture proportions and calculate relative support for multiple models via information criteria. We present a case study of Alligator mississippiensis diet partitioning to demonstrate the power of this approach. Finally, we conclude with a discussion of limitations to mixing model applications. Through MixSIAR, we have consolidated the disparate array of mixing model tools into a single platform, diversified the set of available parameterizations, and provided developers a platform upon which to continue improving mixing model analyses in the future.
Growing interest in the Alligator Gar Atractosteus spatula among anglers and fishery managers has inspired efforts to better manage populations. Successful management requires identifying population structure and understanding the distribution of stocks and associated differences in life history. This is particularly important in river systems along the coast of the Gulf of Mexico, where transitions from freshwater rivers to saltwater bays provide the potential for life history diversification. We used otolith microchemistry and genetics to assess population structure of Alligator Gars in the Guadalupe River–San Antonio Bay system, Texas. Lifetime Sr:Ca revealed three, distinct life histories that differed in prevalence across the system. River-resident fish (i.e., fish exclusive to freshwater) were present throughout the river but were most common in the uppermost river reach (74% of upper river fish). Transient fish that used both river and bay habitats were also found throughout the river but were most prevalent in the lowermost river reach (66% of lower river fish) and bay (91% of bay fish). Bay residents (i.e., fish exclusive to salt water) were detected but comprised only 9% of bay fish. Haplotype diversity based on mitochondrial DNA was lowest in the upper river, indicating limited gene flow compared with the lower river and bay. Similarly, nuclear DNA analyses indicated nonrandom mating between fish from the upper river, lower river, and bay. The differences in Alligator Gar movement and genetics along the river–bay continuum suggest the presence of a river resident stock that predominates the upper river, and a transient stock that predominates the lower river and bay. Therefore, a local-scale management approach, consistent with the spatial partitioning between stocks, would conserve life history and genetic diversity within the system and provide opportunities to meet the needs of a diverse angling constituency. Understanding how population dynamics differ between stocks is needed to develop appropriate fishery management objectives and corresponding regulations for Alligator Gar.
Received May 20, 2016; accepted December 2, 2016
Adfluvial brook trout in Lake Superior, commonly referred to as coasters, were once widely distributed among tributaries and supported trophy fisheries. The Minnesota Department of Natural Resources recently enhanced efforts to rehabilitate brook trout in Minnesota waters by imposing restrictive harvest regulations intended to produce more large individuals adopting a coaster life-history. The agency evaluated effects of the regulation changes by conducting electrofishing stream surveys concurrently with changes and three additional times over the next 16 years. Catch per unit effort of brook trout across all streams was similar among sampling periods. Generalized linear mixed models indicated a greater proportional size structure (number ≥ 330 mm/number ≥ 200 mm) and proportion of older fish (≥ age 3) after the regulation change. Genetic analyses indicated that individuals from coaster hatchery strains, which were stocked in nearby jurisdictions, made up only 5.6% of all individuals in Minnesota streams and 12% of individuals ≥ 330 mm, although the two largest fish were hatchery strain. Our results indicated that conservative regulations can contribute to rehabilitation of coaster populations and that stocked coasters could not account for the improved size and age structure.
We examined and summarized existing knowledge regarding the distribution and status of self-sustaining populations of brook trout Salvelinus fontinalis at the subwatershed scale (mean subwatershed area = 8,972 ha) across their native range in the eastern USA. This region represents approximately 25% of the species' entire native range and 70% of the U.S. portion of the native range. This assessment resulted in an updated and detailed range map of historical and current brook trout distribution in the Study area. Based on known and predicted brook trout status, each subwatershed was classified according to the percentage of historical brook trout habitat that still maintained self-sustaining populations. We identified 1,660 subwatersheds (31 %) in which over 50% of brook trout habitat was intact; 1,859 subwatersheds (35%) in which less than 50% of brook trout habitat was intact; 1,482 subwatersheds (28%) from which self-sustaining populations were extirpated; and 278 subwatersheds (5%) where brook trout were absent but the explanation for the absence was unknown (i.e., either extirpation from or a lack of historical Occurrence in those subwatersheds), A classification and regression tree using five core subwatershed metrics (percent total forest, sulfate and nitrate deposition, percent mixed forest in the water corridor, percent agriculture, and road density) was a useful predictor of brook trout distribution and status, producing an overall correct classification rate of 7 1 %. Among the intact subwatersheds, 94% had forested lands encompassing over 68% of the land base. Continued habitat loss from land use practices and the presence of naturalized exotic fishes threaten the remaining brook trout populations. The distribution of brook trout subwatershed status and related threshold metrics can be used for risk assessment and prioritization of conservation efforts.
Stable isotopes of carbon, nitrogen, and sulfur are used as ecological tracers for a variety of applications, such as studies of animal migrations, energy sources, and food web pathways. Yet uncertainty relating to the time period integrated by isotopic measurement of animal tissues can confound the interpretation of isotopic data. There have been a large number of experimental isotopic diet shift studies aimed at quantifying animal tissue isotopic turnover rate λ (%·day-1, often expressed as isotopic half-life, ln(2)/λ, days). Yet no studies have evaluated or summarized the many individual half-life estimates in an effort to both seek broad-scale patterns and characterize the degree of variability. Here, we collect previously published half-life estimates, examine how half-life is related to body size, and test for tissue- and taxa-varying allometric relationships. Half-life generally increases with animal body mass, and is longer in muscle and blood compared to plasma and internal organs. Half-life was longest in ecotherms, followed by mammals, and finally birds. For ectotherms, different taxa-tissue combinations had similar allometric slopes that generally matched predictions of metabolic theory. Half-life for ectotherms can be approximated as: ln (half-life) = 0.22*ln (body mass) + group-specific intercept; n = 261, p<0.0001, r2 = 0.63. For endothermic groups, relationships with body mass were weak and model slopes and intercepts were heterogeneous. While isotopic half-life can be approximated using simple allometric relationships for some taxa and tissue types, there is also a high degree of unexplained variation in our models. Our study highlights several strong and general patterns, though accurate prediction of isotopic half-life from readily available variables such as animal body mass remains elusive.
Teleost fishes are prominent vertebrate models of evolution, illustrated among old world radiations by the Cichlidae of East African Great Lakes and new-world radiations by the circumpolar Arctic charr Salvelinus alpinus. Herein, we describe variation in lake charr S. namaycush morphology, life history, physiology and ecology, as another example of radiation. The lake charr is restricted to northern North America, where it originated from glacial refugia and diversified in large lakes. Shallow and deepwater morphs arose in multiple lakes, with a large-bodied shallow-water ‘lean’ morph in shallow inshore depths, a small-bodied mid-water ‘humper’ morph on offshore shoals or banks, a robust, large-bodied moderate to deep-water ‘redfin’; morph and a large-bodied deep-water ‘siscowet’ morph at depths > 100 m. Eye position, gape size, and gillraker length and spacing adapted for feeding on different-sized prey, with piscivorous morphs (leans, siscowets and presumably redfins) reaching larger asymptotic size than invertivorous morphs (humpers). Lean morphs are light in colour, whereas deepwater morphs are drab and dark, although the pattern is reversed in dark tannic lakes. Morphs shift from benthic to pelagic feeding at a length of 400–490 mm. Phenotypic differences in locomotion, buoyancy and lipid metabolism evolved into different mechanisms for buoyancy regulation, with lean morphs relying on hydrodynamic lift and siscowet morphs relying on hydrostatic lift. We suggest that the Salvelinus genus, rather than the species S. alpinus, is a diverse genus that should be the subject of comparative studies of processes causing divergence and adaptation among member species that may lead to a more complete evolutionary conceptual model.
Considerable progress has been made in the development of statistical tools to quantify trophic relationships using stable isotope ratios, including tools that address size and overlap of isotopic niches. We build upon recent progress and propose a new probabilistic method for determining niche region and pairwise niche overlap that can be extended beyond two dimensions, provides directional estimates of niche overlap, accounts for species-specific distributions in niche space, and, unlike geometric methods, produces consistent and unique bivariate projections of multivariate data. We define the niche region (N R) as a given 95% (or user-defined a) probability region in multivariate space. Overlap is calculated as the probability that an individual from species A is found in the N R of species B. Uncertainty is accounted for in a Bayesian framework, and is the only aspect of the methodology that depends on sample size. Application is illustrated with three-dimensional stable isotope data, but practitioners could use any continuous indicator of ecological niche in any number of dimensions. We suggest that this represents an advance in our ability to quantify and compare ecological niches in a way that is more consistent with Hutchinson's concept of an ''n-dimensional hypervolume.''
Hard-part microchemistry offers a powerful tool for inferring the environmental history and stock assignment of individual fishes. However, despite the applicability of this technique to a wide range of fisheries conservation and management issues, its use has been restricted to only a small fraction of North American species and inland waters. In this article, we provide freshwater fisheries professionals with an accessible review of methods and applications of hard-part microchemistry techniques. Our objectives are to (1) summarize the science of hard-part microchemistry; (2) provide guidelines for designing hard-part microchemistry studies, including sample sizes, laboratory analyses, statistical techniques, and inferential limitations; and (3) identify conservation and management applications where these techniques may be particularly useful. We argue that strategic use of hard-part microchemistry methods (specifically when they are used in concert with other indirect tracer techniques such as stable isotope chemistry and genetics) can advance fish management and conservation across all stages of fish life history.
RESUMEN
la microquímica de partes duras representa una herramienta poderosa para inferir la historia ambiental y la asignación de stocks en peces. No obstante, a pesar de la aplicabilidad de esta técnica a un amplio rango de aspectos de conservación y manejo de pesquerías, su utilización se ha restringido a sólo una pequeña fracción de especies de aguas continentales en Norte América. En este trabajo, se presenta una revisión accesible de los métodos y aplicaciones de técnicas de microquímica de partes duras, dirigida a los profesionales en pesquerías de aguas interiores. Los objetivos son: (1) resumir la ciencia de la microquímica de partes duras, (2) proporcionar guías para el diseño de estudios de microquímica de partes duras, incluyendo tamaños de muestra, análisis de laboratorio, técnicas estadísticas y limitaciones de orden inferencial, y (3) identificar aplicaciones para la conservación y manejo en las cuales estas técnicas puedan ser particularmente útiles. Se argumenta que la utilización estratégica de métodos de microquímica de partes duras (específicamente cuando éstos son usados en conjunto con otras técnicas de rastreo indirecto como química de isótopos estables y genética) puede abonar a la conservación y manejo de los peces durante todos los estadios de vida.
Two distinct types of brook trout Salvelinus fontinalis have been hypothesized to occur in Lake Superior: large fish that inhabit Lake Superior for much of the year but spawn in tributary streams, and small fish that are resident in tributary streams. The lake type has declined markedly in range and abundance, and a greater understanding of the behavior and ecology of these populations is needed to support conservation efforts. Comparisons of stable isotope (δC and δN) signatures between fish caught in the lake and those captured in streams supported the hypothesis of relatively distinct types differing in habitat use and trophic ecology. Comparisons of δC values for brook trout, other fishes, and aquatic invertebrates collected from stream, stream-mouth, and lake habitats suggested that large-type brook trout are lake specialists, whereas small-type brook trout are stream specialists, stream–lake generalists, or some mixture of the two. Delineating the diversity in habitat use and trophic ecology of Lake Superior brook trout represents a crucial initial step toward understanding the mechanisms responsible for the observed phenotypic diversity and for developing science-based plans to conserve or restore this diversity.Received March 9, 2010; accepted February 7, 2011
Brook trout Salvelinus fontinalis are one of two salmonine species native to Lake Superior. Abundant and widely distributed a century ago, Lake Superior's brook trout (coasters) have been reduced to a few remnant stocks, probably as a result of exploitation and habitat loss. Twenty brook trout captured in Nipigon Bay, Lake Superior, were surgically implanted with radio transmitters and were located from June 1999 to October 2000. Brook trout locations were used to determine the characteristics of utilized lake habitat and to identify streams used for spawning and the spawning areas within them. These locations were also used to establish daily and seasonal movement patterns. A total of 638 locations were obtained during the tracking period, 483 occurring within Nipigon Bay and the remaining 155 within tributaries. Brook trout were located almost exclusively within the shallow nearshore areas of Nipigon Bay; 92% of the locations were less than 7 m deep and 94% were less than 400 m from shore. Brook trout occupied deeper areas with steeper shoreline slopes during July and August, when the water temperatures of shallow nearshore areas were at their highest. Following selected individuals for 24-h periods revealed that brook trout often used deeper areas during daylight hours and moved to extremely shallow nearshore areas during the night. Radio-tagged brook trout began ascending tributaries during late summer in both years of this study. The mean residency time for brook trout in tributaries was 46 d. Spawning occurred in early October, and most radio-tagged brook trout returned to Lake Superior by mid-October. Four different streams were used during the spawning period. Brook trout entering streams exhibited strong spawning site fidelity between years.
Gerking (1959. Biol. Rev. 34: 221-242) proposed a theory about the restricted movement of stream fishes that may be considered a paradigm in salmonid biology. The restricted movement paradigm (our term) hold that resident stream salmonids are sedentary. Numerous studies have supported the restricted movement paradigm, but nearly all have relied on the recapture of marked fish from the same areas in which they were released, an approach we believe is biased against detecting movement. We round substantial movement of trout in streams in Colorado and Wyoming using two-way weirs' and radio telemetry. A review of the research on Lawrence Creek, Wisconsin, also showed that movement was important in the response of the trout population to habitat enhancement. Movement of resident stream fish has profound implications for research (e.g., measuring production and habitat models) and management (e.g., habitat enhancement, special regulations, and stocking hatchery fish). Methods capable of detecting fish movement could be incorporated into many studies to assess its importance in systems of interest. New theories and experiments are needed to understand the mechanisms that cause stream salmonids to move.
The brook trout Salvelinus fontinalis is an important species across North America, being the focus of restoration and conservation efforts in the eastern United States and considered a threat to native salmonids in the western part of the country. Bioenergetics models have emerged as useful tools for studying the ecology and management of fish species, but these models should be critically evaluated prior to widespread application. We conducted laboratory experiments to refine model parameters (metabolism and the activity multiplier) and to test a model for brook trout. Brook trout metabolic rates increased with temperature up to 20°C, then declined sharply. Specific metabolism declined with increasing fish size. Validation experiments conducted for 7, 21, and 31 d at 12-16°C showed that the model predicted consumption within 1.6 ± 3.6%, growth within 2.3 ± 12.5%, and final weight within 1.7 ± 5.1% of measured values. The results of this study will allow biologists to better use bioenergetics models to study the trophic dynamics of brook trout throughout their range.
Quantifying nutritional sources for Mysis diluviana will help to clarify the basis for production in lakes with Mysis and improve models of migration-driven nutrient and contaminant transport. We sampled Mysis, plankton, and benthos across Lake Superior using a stratified-random design that provided a statistically valid representation of the lake across depths. We then estimated nutritional contributions to Mysis using stable isotope ratios of Mysis, zooplankton, Bythotrephes, Diporeia, oligochaetes, and detritus in a multiple-source, dual-isotope mixing model. Lake-wide, small (<1.0 cm) mysids relied almost exclusively upon plankton, whereas large mysids occupied a higher trophic position and obtained nutrition among sources. Model estimates of mean benthic contributions to large Mysis ranged from 27% to 58%. We predicted the importance of benthos to Mysis to track declining benthic biomass with depth. Model results indicated that if Diporeia were the only benthic food eaten, benthic contributions would decline to 40% with depth, but inclusion of detritus in the model resulted in consistent importance of benthic food across depths. The importance of benthos to mysid nutrition suggests strong benthic–pelagic coupling at all lake depths and might limit the ability of Mysis to support fisheries in systems that have lost Diporeia.
Lake Superior once supported abundant lake-dwelling brook trout Salvelinus fontinalis called coasters; however, only scattered remnant populations remained by the early 20th century. Owing to their early decline, there is little information about their ecology and life history, yet such information is vital for the ecologically based rehabilitation and management of coasters. This study reviews the ecology of coaster brook trout from a life history perspective and presents quantitative data on the biology and status of the few populations that have been studied. Within the Lake Superior basin, some brook trout are stream residents while others are lacustrine or adfluvial. Although the variation in migratory behavior may be related to individual energetics, the role of evolution and the proximate factors triggering specific life histories remain uncertain. Comparisons of recent biological data from populations in the Lake Superior basin show that the northern populations have longer lengths at age and length frequency distributions skewed toward longer individuals. The degrees to which this difference is driven by variation in individual growth rates and size-selective mortality are unknown. All known populations around the Lake Superior basin appear to have a small number of individuals and are thus of conservation concern. We believe that biotic interactions such as competition with introduced salmonines (in particular coho salmon Oncorhynchus kisutch) have a strong negative influence on the individual and population performance of coasters. Coupled with high past and recent mortality from fisheries, these factors may create bottlenecks limiting the growth and rehabilitation of the remnant populations. Lake Superior coaster brook trout are persisting, albeit uncertainly, under conditions different from those in which they once thrived. Management focused on native ecosystem rehabilitation may foster the return of these fish as abundant members of Great Lakes food webs, and recent basinwide restrictions on length and catch limits are a positive step toward enhancing their rehabilitation and evolution.
Brook trout (Salvelinus fontinalis) are found throughout Lake Superior, Lake Nipigon, and their tributaries. Lacustrine and adfluvial life history variants were historically popular with anglers and were called coasters; coaster brook trout populations are now severely reduced and are of conservation concern. Coasters were known to grow larger and mature later than their stream resident counterparts. This study compared movement patterns, age, size, condition, and relative weight of wild coaster and resident brook trout from the Hurricane River, Pictured Rocks National Lakeshore, Michigan. Wild brook trout ≥ 100 mm from the Hurricane River downstream from Hurricane Falls were tagged with passive integrated transponder tags and monitored for stream-lake movement behavior from May 2003 to November 2007. During 2006 and 2007, brook trout were scale sampled and aged to construct a regression that was then used to calculate the age of all brook trout tagged from 2003 to 2007. Most brook trout movement took place in the fall with October the peak month of emigration with a secondary peak in late spring/early summer and some activity nearly year round. There were no differences found in age structure, size or condition between coasters and residents while in the stream. Our data suggest that a priori growth differences are not determining the expression of coaster outmigration and that stream-lake movements made by coasters, likely driven by habitat requirements, may be highly flexible and facultative.
Coaster brook trout are a migratory form of brook trout Salvelinus fontinalis that spend part of their lives in the Great Lakes. Over the last century the abundance of coaster brook trout in Lake Superior has declined dramatically, and only remnant stocks remain. Recently, the rehabilitation of coaster brook trout in Lake Superior has become a goal of fish management agencies. The specific goal agreed upon by all of the agencies involved is to maintain widely distributed, self-sustaining populations in as many of the historical habitats as practical. We discuss realistic expectations for rehabilitation and emphasize the need for management agencies, academia, and angling organizations to work cooperatively. We first present a brief history of coaster brook trout in Lake Superior, then discuss habitat requirements and protection, the regulations required for rehabilitation, stocking, species interactions, and the role that human dimensions play in rehabilitation. The management issues that must be addressed are implementation of a basinwide survey to identify remnant stocks and critical habitat, restrictive harvest regulations, watershed rehabilitation, critical biological review, and the formulation of expectations before experimental stocking programs are initiated, along with coordinated, basinwide information sharing and cooperative management among agencies similar to that undertaken during the rehabilitation of lake trout Salvelinus namaycush in Lake Superior. Future research needs include basic coaster biology and life history, habitat use in streams and the lake, interaction with other species in the Lake Superior fish community, and interaction between stream-resident and coaster brook trout. Successful rehabilitation will require a shift from a harvest fishery to one with minimal or no harvest of coaster brook trout in the Lake Superior basin. Coaster brook trout rehabilitation will take time and will proceed at different rates at different locations, depending on the presence of remnant stocks, quality of habitat, angling pressure, and political will.
The dynamics of ecological systems include a bewildering number of biotic interactions that unfold over a vast range of spatial scales. Here, employing simple and general empirical arguments concerning the nature of movement, trophic position and behaviour we outline a general theory concerning the role of space and food web structure on food web stability. We argue that consumers link food webs in space and that this spatial structure combined with relatively rapid behavioural responses by consumers can strongly influence the dynamics of food webs. Employing simple spatially implicit food web models, we show that large mobile consumers are inordinately important in determining the stability, or lack of it, in ecosystems. More specifically, this theory suggests that mobile higher order organisms are potent stabilizers when embedded in a variable, and expansive spatial structure. However, when space is compressed and higher order consumers strongly couple local habitats then mobile consumers can have an inordinate destabilizing effect. Preliminary empirical arguments show consistency with this general theory.
Migrations between spawning, growth and refuge habitats are critical for many fish species. Partially migratory populations of brook charr Salvelinus fontinalis (known as brook trout in the United States), in which a portion of the population migrates, were once widespread in the Great Lakes region of North America, but are now scarce and a rehabilitation priority. Great Lakes fishery managers lack a simple, non-lethal means to determine whether a large brook charr caught in a Great Lakes accessible stream reach represents a stream-resident fish or migrant that previously spent time foraging and growing in Great Lakes waters. We explored a relatively inexpensive and non-lethal stable isotope approach for documenting lake to stream movements of brook charr, using fin clips from brook charr captured in streams in fall prior to spawning. Using fin tissue from juvenile and adult coho salmon captured in Michigan tributaries to Lake Superior, we confirmed distinct stable isotope signatures indicative of prior stream and Lake Superior foraging. We identified brook charr from tributaries accessible to Lake Superior whose stable isotope signatures were similar to those of lake-captured brook charr, lake charr and splake (a brook charr–lake charr hybrid) and distinct from stable isotope signatures of brook charr in streams inaccessible to Lake Superior fishes, suggestive of an adfluvial migratory pattern. Brook charr from two streams had elevated δ15N values, indicative of previous residency in a downstream lake receiving water from a sewage treatment facility. Our findings demonstrate the utility of stable isotope analysis as a non-lethal technique for confirming adfluvial movements of brook charr from Lake Superior to streams.
Adfluvial brook trout Salvelinus fontinalis populations in the Lake Superior basin have suffered declines over the last century due to habitat degradation and exploitation. Natural resources agencies throughout the basin have restored habitat and implemented restrictive angling regulations as tools to protect remnant coaster brook trout populations, but the success of these practices is unknown in some locations. We used electrofishing and passive integrated transponder (PIT) tag movement data from 2008 to 2020 to
describe population characteristics, temporal trends, and adfluvial life history of coaster brook trout in Washington Harbor, Isle Royale National Park, Lake Superior after implementation of catch-and-release regulations in 2004. Our results document the presence of an adfluvial coaster brook trout population in Washington Harbor, Isle Royale. Temporal trends indicate that brook trout abundance and distribution in Washington Harbor increased since earlier observations in the late 1990s and early 2000s likely due to enactment of protective regulations, and increased stream flows and water levels observed in recent years in both Washington Creek and Lake Superior, respectively. Annual tag detection of Washington Harbor brook trout in Washington Creek at the antenna arrays varied from 25% in 2009 to 100% in 2011 and 2013, and averaged 60.7% throughout the study. Peak in adfluvial brook trout use of Washington Creek was from August – October with few detections occurring outside of the presumed spawning period. This study provides valuable insight into the population characteristics, movement patterns, and temporal increase in abundance of an adfluvial brook trout population in Lake Superior.
Over the last 150 years, many of the native migratory salmonid populations in North America have declined or been extirpated, and their native habitats have been significantly altered. Life history variation within and among migratory fish populations plays an important role in their persistence when faced with changing habitat conditions. One of the most extreme life history events in salmonids is the movement from lotic to lentic habitats, a migration that can span long distances and different habitat types. Understanding the factors affecting migratory life histories expressed by individuals within a population play an important role in dynamics and habitat requirements of the whole population. Here, I investigate three primary factors that contribute to an individual fishes’ “decision” to migrate: genetics, environmental conditions, and individual body condition. In rainbow trout Oncorhynchus mykiss of the Shasta River, California we found distinct genetic structure among subpopulations in spatially separate habitats. Within one of those population segments we detected partial migration in which some individuals migrate, but others do not. We found that increased in daily mean water temperature were associated with upriver migration of adult coaster brook trout Salvelinus fontinalis in the Salmon Trout River, Michigan. In the Pilgrim River, Michigan we documented a previously unrecognized population of migratory brook trout. These results provide information critical to understanding the ecology of these at-risk populations and broaden our understanding of migratory behavior in general. The methodologies we developed to quantify movement data in the context of migratory life histories are applicable to other systems where further understanding of the drivers of migratory life history variation is needed.
Statistical Rethinking: A Bayesian Course with Examples in R and Stan builds readers’ knowledge of and confidence in statistical modeling. Reflecting the need for even minor programming in today’s model-based statistics, the book pushes readers to perform step-by-step calculations that are usually automated. This unique computational approach ensures that readers understand enough of the details to make reasonable choices and interpretations in their own modeling work. The text presents generalized linear multilevel models from a Bayesian perspective, relying on a simple logical interpretation of Bayesian probability and maximum entropy. It covers from the basics of regression to multilevel models. The author also discusses measurement error, missing data, and Gaussian process models for spatial and network autocorrelation. By using complete R code examples throughout, this book provides a practical foundation for performing statistical inference. Designed for both PhD students and seasoned professionals in the natural and social sciences, it prepares them for more advanced or specialized statistical modeling. Web Resource The book is accompanied by an R package (rethinking) that is available on the author’s website and GitHub. The two core functions (map and map2stan) of this package allow a variety of statistical models to be constructed from standard model formulas.
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 δ ¹⁵ N. 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 δ ¹⁵ N.
Based on AIC c , 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.
Anadromous fishes are well known to shape the structure and function of recipient ecosystems by introducing nutrients and rich organic matter from the ocean. In contrast, the importance of potamodromous migrations, confined to freshwater, and the subsidies they provide to stream ecosystems has received much less attention.
Our objective was to determine the importance of excretion, eggs, milt, and carcasses as nutrient and energy sources from a large population (82 449 suckers) of migrating longnose ( Catostomus catostomus ) and common white ( Catostomus commersonii ) suckers into a small (wetted width c . 10 m) oligotrophic river system. We hypothesise that the adfluvial suckers provide a large material subsidy that increased the productivity of the Cypress River and that this resource subsidy rivals or exceeds those delivered by other native and non‐native fishes (e.g. Pacific salmonids).
In total there was an estimated 5635 kg of eggs, 2025 kg of milt, and 1 kg of carcasses from suckers that spawn in the Cypress River. Relative to other mainly non‐native fishes, suckers provided 92% of the annual egg biomass and 95% of the milt. Suckers, however, only provided <1% (1 kg) of the annual carcass biomass, whereas, pink salmon provided 50% (600 kg). Overall, suckers provided 84% and 78% of the annual subsidies of N and P, or 212 and 14 kg respectively. Ambient NH 4 concentrations in the river were consistently below that predicted from excretion equations suggesting that microorganisms may have rapidly taken up much of the released ammonium.
Downstream of the falls, epilithon biomass was over nine times more abundant, benthic invertebrate densities were approximately two times higher, and fish biomass was eight times greater compared to upstream. There were no upstream–downstream differences in substrate organic matter biomass. Fishes downstream of the falls had higher δ ¹³ C and δ ¹⁵ N values than biota upstream of the falls consistent with the anticipated effect of lake derived subsidies. Using stable isotopes values and a mixing model, we estimated that sucker eggs comprised 25–58% of the diet of stream fishes during the growing season.
Suckers provided a large subsidy, greater than all other fishes, without mass mortality and significantly enhanced the productivity of the recipient river system. Stable isotopes revealed that subsidies were incorporated into the stream food web. Differences between salmon and sucker subsidies related to the type, magnitude, timing, and the life history of the donor highlight the potential importance of spawning migrations of adfluvial suckers, and other potamodromous fishes, in streams and rivers around the world.
RationaleNormalizing δ13C values of animal tissue for lipid content is necessary to accurately interpret food-web relationships from stable isotope analysis. To reduce the effort and expense associated with chemical extraction of lipids, various studies have tested arithmetic mass balance to mathematically normalize δ13C values for lipid content; however, the approach assumes that lipid content is related to the tissue C:N ratio.Methods
We evaluated two commonly used models for estimating tissue lipid content based on C:N ratio (a mass balance model and a stoichiometric model) by comparing model predictions to measure the lipid content of white muscle tissue. We then determined the effect of lipid model choice on δ13C values normalized using arithmetic mass balance. To do so, we used a collection of fish from Lake Superior spanning a wide range in lipid content (5% to 73% lipid).ResultsWe found that the lipid content was positively related to the bulk muscle tissue C:N ratio. The two different lipid models produced similar estimates of lipid content based on tissue C:N, within 6% for tissue C:N values <7. Normalizing δ13C values using an arithmetic mass-balance equation based on either model yielded similar results, with a small bias (<1‰) compared with results based on chemical extraction.Conclusions
Among-species consistency in the relationship between fish muscle tissue C:N ratio and lipid content supports the application of arithmetic mass balance to normalize δ13C values for lipid content. The uncertainty associated with both lipid extraction quality and choice of model parameters constrains the achievable precision of normalized δ13C values to about ±1.0‰. Published in 2015. This article is a U.S. Government work and is in the public domain in the U.S.A.
We offer suggestions to avoid misuse of information-theoretic methods in wildlife laboratory and field studies. Our suggestions relate to basic science issues and the need to ask deeper questions (4 problems are noted), errors in the way that analytical methods are used (7 problems), and outright mistakes seen commonly in the published literature (5 problems). We assume that readers are familiar with the information-theoretic approaches and provide several examples of misuse. Any method can be misused-our purpose here is to suggest constructive ways to avoid misuse.
Genetic differentiation among brook trout (Salvelinus fontinalis) of different life history forms and populations can result from reproductive isolation imposed by natural or anthropogenically derived barriers to gene flow, behavioral incompatibilities, or differential exposure to environmental cues. We used multi-locus microsatellite genotypes and likelihood and Bayesian-based analyses to characterize the degree of genetic differentiation and evidence of introgression among stream resident brook trout above a natural barrier, and putative stream residents and adfluvial (coaster) brook trout from below the barrier in the Salmon Trout River (STR); the sole tributary along the southern shore of Lake Superior known to be inhabited by a viable remnant population of coaster brook trout. Two genetically differentiated populations were identified, generally associated with individuals inhabiting sections of the STR above and below the falls. No evidence of differentiation was found between a priori classified resident and coaster brook trout from below the falls. Gene flow from individuals above the falls was detected based on evidence of interbreeding between upper river individuals and coasters below the falls. We collected only a relatively small number of individuals that we a priori classified as being stream residents below the falls, and these individuals had a high probability of having ancestry originating from the population above the barrier, which suggests that the stream-resident life history may be exceptionally rare or absent in the lower Salmon Trout River.
We used fish traps and electrofishing surveys to characterize the biology, life history traits, and potential biotic interactors important to the rehabilitation of native, adfluvial coaster brook trout Salvelinus fontinalis in Lake Superior. This study focused on the Salmon Trout River, Michigan, which is the site of the last known remnant population of adfluvial brook trout on the south shore of Lake Superior. The brook trout captured in passive traps (weirs) in the river ranged from 56 to 554 mm in total length (TL) and from 0 (young of the year) to 6 years of age. This population displayed a protracted 5-month migration into the river but one that included relatively few fish. Coaster brook trout in this population appear to initiate adfluvial migrations near age 3 and 300 mm TL. Relative weight values increased with fish length and therefore reproductive life stage, possibly indicating the shift from river to lake habitats. This population of coaster brook trout is small and subject to potential biotic interactions with exotic species and population limitation because of an active fishery in the lake and river. Migratory runs of brook trout coincided with large runs of coho salmon Oncorhynchus kisutch, and the instream juvenile salmonid composition included proportionately high densities of coho salmon and rainbow trout O. mykiss. In addition, Floy tag return data indicated that exploitation of reproductive-age Salmon Trout River coaster brook trout was at least 12% and may have been as high as 50% in the open waters of Lake Superior. A recent increase in the legal minimum length limit and reduction of the daily bag limit for recreational harvest may slow or reverse this trend.
We investigated bioenergetics modeling of growth as an approach for assessing the effects of temperature changes on stream dwelling rainbow trout Oncorhynchus mykiss. Study objectives were (1) to determine the relative effect of temperature versus food consumption on model-predicted growth and (2) to identify relationships between model-predicted food consumption and commonly measured environmental variables. A bioenergetics model for rainbow trout was calibrated to apparent age-1 growth in summer and fall–spring periods for 10 years at eight Sierra Nevada, California, study sites. Model analyses showed that the observed year-to-year variation in summer growth was related to food consumption but not to temperature and that temperature was more important, but still of secondary importance, to observed variation in fall–spring growth. Growth at all sampling sites appeared lower and more variable in summer than in other seasons, and variation among sites and years in the food consumption parameter P (determined by fitting the model to observed apparent growth) was highly related to environmental variables during fall–spring but not during summer. During fall–spring, 80% of the variation in P was explained by a linear regression model that included temperature, flow, and trout density. Summer P-values were only weakly related to stream gradient. Our data and analysis indicate that (1) when not extreme, temperatures in summer may have less effect on growth than during other seasons and (2) growth is more affected by factors controlling food consumption (including indirect effects of temperature) than by the direct effects of temperature.
Abstract – Metapopulation theory has attracted considerable interest with reference to the salmonids. There has been little empirical evidence, however, to guide the evaluation or application of metapopulation concepts. From knowledge of salmonid life histories and our own work with bull trout (Salvelinus confluentus), Lahontan cutthroat trout (Oncorhynchus clarki henshawi) and westslope cutthroat trout (Oncorhynchus clarki lewisi), we suggest that simple generalizations of salmonid metapopulations are inappropriate. Although spatial structuring and dispersal mechanisms are evident, the relevance of extinction and colonization processes are likely to vary with life history, species, scale, and landscape. Understanding dispersal, the role of suitable but unoccupied habitats, and the potential for extinction debts in non-equilibrium metapopulations are key issues. With regard to conservation of salmonids, we suggest that efforts to understand and conserve key processes likely to influence the persistence of populations or metapopulations will be more successful than efforts to design minimal habitat reserves based on metapopulation theory.
Stable isotopes can illuminate resource usage by organisms, but effective interpretation is predicated on laboratory validation. Here we develop stable isotope clocks to track resource shifts in anadromous rainbow trout (Oncorhynchus mykiss). We used a diet-switch experiment and model fitting to quantify N stable isotope (δ(15)N) turnover rates and discrimination factors for seven tissues: plasma, liver, fin, mucus, red blood cells, muscle, and scales. Among tissues, diet-tissue δ(15)N discrimination factors ranged from 1.3 to 3.4 ‰. Model-supported tissue turnover half-lives ranged from 9.0 (fin) to 27.7 (scale) days. We evaluated six tissue turnover models using Akaike's information criterion corrected for small sample sizes. The use of equilibrium tissue values was supported in all tissues and two-compartment models were supported in plasma, liver, and mucus. Using parameter estimates and their uncertainty we developed stable isotope clocks to estimate the time since resource shifts. Longer turnover tissues provided accurate estimates of time since resource switch for durations approximately twice their half-life. Faster turnover tissues provided even higher precision estimates, but only within their half-life post-switch. Averaging estimates of time since resource shift from multiple tissues provided the highest precision estimates of time since resource shift for the longest duration (up to 64 days). This study therefore provides insight into physiological processes that underpin stable isotope patterns, explicitly tests alternative models, and quantifies key parameters that are the foundation of field-based stable isotope analysis.
1. Modelling the effects of climate change on freshwater fishes requires robust field-based estimates accounting for interactions among multiple factors.
2. We used data from an 8-year individual-based study of a wild brook trout (Salvelinus fontinalis) population to test the influence of water temperature on season-specific growth in the context of variation in other environmental (i.e. season, stream flow) or biotic factors (local brook trout biomass density and fish age and size) in West Brook, a third-order stream in western Massachusetts, U.S.A.
3. Changes in ambient temperature influenced individual growth rates. In general, higher temperatures were associated with higher growth rates in winter and spring and lower growth rates in summer and autumn. However, the effect of temperature on growth was strongly context-dependent, differing in both magnitude and direction as a function of season, stream flow and fish biomass density.
4. We found that stream flow and temperature had strong and complex interactive effects on trout growth. At the coldest temperatures (in winter), high stream flows were associated with reduced trout growth rates. During spring and autumn and in typical summers (when water temperatures were close to growth optima), higher flows were associated with increased growth rates. In addition, the effect of flow at a given temperature (the flow-temperature interaction) differed among seasons.
5. Trout density negatively affected growth rate and had strong interactions with temperature in two of four seasons (i.e. spring and summer) with greater negative effects at high temperatures.
6. Our study provided robust, integrative field-based estimates of the effects of temperature on growth rates for a species which serves as a model organism for cold-water adapted ectotherms facing the consequences of environmental change. Results of the study strongly suggest that failure to derive season-specific estimates, or to explicitly consider interactions with flow regime and fish density, will seriously compromise our ability to predict the effects of climate change on stream fish growth rates. Further, the concordance we found between empirical observations and likely energetic mechanisms suggests that our general results should be relevant at broader spatial and temporal scales.
As concerns for losses of migratory species heighten globally, scientists are being challenged to characterize diversity in the migratory behaviors to support scientifically defensible conservation programs. Anecdotal observations of brook trout (Salvelinus fontinalis) inhabiting Lake Superior and its tributaries suggest the occurrence of two forms: a large lake form hypothesized to originate in streams and reside in Lake Superior for significant parts of the year and a small stream form hypothesized to be stream resident. Declines in the lake form are a conservation concern and understanding of the variation in migratory behavior is needed to assist conservation efforts. We used analyses of vertebrae and otoliths to test whether the growth histories of lake and stream caught fish differed as expected for adult and juvenile stages from a migratory population (migration), individuals differing in the age of outmigration to the lake (staggered migration), or a combination of residents and migrants (partial migration). Lake caught fish grew faster and lived longer than stream caught fish and differences in length-at-age were apparent by the end of the first year of life. There was no evidence of individuals abruptly changing growth history in a way that would suggest habitat switches later in life. Growth histories of lake and stream caught brook trout were also similar to those of migrants and residents from other brook trout populations or sub-populations. Our findings support the hypothesis of partial migration as an explanation for the diversity observed in Lake Superior brook trout and demonstrate how analyses of growth histories can help clarify migratory systems in species whose movements are challenging to track.
The isotopic composition of many elements varies across both land and ocean surfaces in a predictable fashion. These stable-isotope ratios are transferred into animal tissues, potentially providing a powerful natural geospatial tag. To date, most studies using stable isotopes as geolocators in marine settings have focussed on mammals and seabirds conducting large ocean-basin scale migrations. An increasing understanding of isotopic variation in the marine environment, and improved sampling and analytical techniques, however, means that stable isotopes now hold genuine promise as a natural geolocation tag in marine fishes. Here, the theoretical background underpinning the use of stable isotopes of C, N and O in otolith, scale and muscle tissues as geolocation tools in the marine environment is reviewed, and examples of their applications are provided.
There is still much to do in developing informed policy on the issue of migratory ("coaster") brook trout Salvelinus fontinalis. My purpose in this paper is to provide a summary of research from other programs that may be useful for understanding the dichotomy between coaster and stream-resident brook trout. Great Lakes glacial history, population structure at the watershed level, landscape-scale habitat patterns, the energetics of resident and migratory brook trout, and dichotomous movements of young of year all provide important context for coaster brook trout. I apply a new growth model to literature sources on brook trout life history to scope the potential range of coaster-resident life histories. The results indicate that juvenile growth falls largely into two groups, depending on whether the adult prey field incorporates fish in the diet. Combining ideas on variation in the standard metabolic rate and habitat productivity with a new theory of food web structure from other authors leads to an interesting working hypothesis for coaster brook trout that builds on W. E. Ricker's original observations on brook trout diet over 75 years ago.
Many Salmo trutta populations consist of non-anadromous (freshwater-resident) brown trout and anadromous (sea-run migratory) sea trout. Although adult brown trout and sea trout can usually be identified using differences in size and body colouration, it is not possible to easily identify eggs/alevins as the progeny of brown trout or sea trout. In this study we show that δ13C and δ15N, measured using a continuous flow isotope ratio mass spectrometer (CF-IRMS), can accurately identify fish eggs as the progeny of freshwater-resident (δ13C(egg) = −25.7 ± 1.9‰,δ15N(egg) = 9.2 ± 1.8‰) or migratory (δ13C(egg) = −19.9 ± 1.1‰, δ15N(egg) = 14.3 ± 1.5‰) adult female Salmo trutta. Case studies show that stable isotope analysis is a more reliable technique for distinguishing anadromous adult fish than differentiation using morphological characteristics. For example, stable isotope analysis of brown trout from Loch Eck, Scotland, revealed that some individuals possessed δ13C and δ15N signatures indicative of marine feeding despite visual identification as freshwater-resident fish. It is most likely that these fish are misidentified sea trout although it possible that these fish may be brown trout that have adopted an estuarine feeding strategy to avoid interspecific competition for food within Loch Eck with salmon, powan and Arctic charr. Most stable isotope studies of fish ecology use terminal tissue sampling to provide sufficient biological material for isotopic analysis; however, our study suggests that adipose fin tissue could provide a comparable measure of δ13C and δ15N. Such a strategy would be invaluable when studying the trophic ecology or migration patterns of fish of high conservation value. Copyright © 2000 John Wiley & Sons, Ltd.
Fisheries management plan for the Minnesota waters of Lake Superior
- C A Goldsworthy
- K A Reeves
- J E Blankenheim
- N R Peterson
Goldsworthy, C.A., Reeves, K.A, Blankenheim, J.E., Peterson, N.R., 2017. Fisheries
management plan for the Minnesota waters of Lake Superior. Special Publication
181, Minnesota Department of Natural Resources, St. Paul, Minnesota.
Global status of trout and char: Conservation challenges in the twenty-first century
- C C Muhlfeld
- D C Dauwalter
- V S Angelo
- A Ferguson
- J J Giersch
- D Impson
- I Koizumi
- R Kovach
- P Mcginnity
- J Schöffmann
- L A Vøllestad
A brook trout rehabilitation plan for Lake Superior. Miscellaneous Publication 2003-03. Great Lakes Fishery Commission
- L E Newman
- R B Dubois
- T N Halpern
Newman, L.E., DuBois, R.B., Halpern, T.N., 2003. A brook trout rehabilitation plan for
Lake Superior. Miscellaneous Publication 2003-03. Great Lakes Fishery Commission.
Status of brook trout rehabilitation in Lake Superior in 2017
- H R Quinlan
Quinlan, H.R., 2021. Status of brook trout rehabilitation in Lake Superior in 2017. In:
The state of Lake Superior in 2017. Edited by M.P. Ebener and T.C. Pratt [online].
Superior Fishing-The Striped Bass, Trout, and Black Bass of the Northern States
- R B Roosevelt
Roosevelt, R.B., 1865. Superior Fishing-The Striped Bass, Trout, and Black Bass of the
Northern States. G.W. Carleton, Minnesota Historical Society Press, St. Paul,
Minnesota.
Management Plan for Inland Trout in Michigan. Michigan Department of Natural Resources Fisheries Report
- T G Zorn
- T A Cwalinski
- N A Godby
- B J Gunderman
- M A Tonello
Zorn, T.G., Cwalinski, T.A., Godby Jr., N.A., Gunderman, B.J., Tonello, M.A., 2018.
Management Plan for Inland Trout in Michigan. Michigan Department of Natural
Resources Fisheries Report 30, Lansing.