The influence of diet on the distribution of nitrogen isotopes in animals was investigated by analyzing animals grown in the laboratory on diets of constant nitrogen isotopic composition. 
The isotopic composition of the nitrogen in an animal reflects the nitrogen isotopic composition of its diet. The δ^(15)N values of the whole bodies of animals are usually more positive than those of their diets. Different individuals of a species raised on the same diet can have significantly different δ^(15)N values. The variability of the relationship between the δ^(15)N values of animals and their diets is greater for different species raised on the same diet than for the same species raised on different diets. Different tissues of mice are also enriched in ^(15)N relative to the diet, with the difference between the δ^(15)N values of a tissue and the diet depending on both the kind of tissue and the diet involved. The δ^(15)N values of collagen and chitin, biochemical components that are often preserved in fossil animal remains, are also related to the δ^(15)N value of the diet. 
The dependence of the δ^(15)N values of whole animals and their tissues and biochemical components on the δ^(15)N value of diet indicates that the isotopic composition of animal nitrogen can be used to obtain information about an animal's diet if its potential food sources had different δ^(15)N values. The nitrogen isotopic method of dietary analysis probably can be used to estimate the relative use of legumes vs non-legumes or of aquatic vs terrestrial organisms as food sources for extant and fossil animals. However, the method probably will not be applicable in those modern ecosystems in which the use of chemical fertilizers has influenced the distribution of nitrogen isotopes in food sources. 
The isotopic method of dietary analysis was used to reconstruct changes in the diet of the human population that occupied the Tehuacan Valley of Mexico over a 7000 yr span. Variations in the δ^(15)C and δ^(15)N values of bone collagen suggest that C_4 and/or CAM plants (presumably mostly corn) and legumes (presumably mostly beans) were introduced into the diet much earlier than suggested by conventional archaeological analysis.

Influence of Diet On the Distribtion of Nitrogen Isotopes in Animals

Stable isotope analysis (SIA) has proven to be a useful tool in reconstructing diets, characterizing trophic relationships, elucidating patterns of resource allocation, and constructing food webs. Consequently, the number of studies using SIA in trophic ecology has increased exponentially over the past decade. Several subdisciplines have developed, including isotope mixing models, incorporation dynamics models, lipid-extraction and correction methods, isotopic routing models, and compound-specific isotopic analysis. As with all tools, there are limitations to SIA. Chief among these are multiple sources of variation in isotopic signatures, unequal taxonomic and ecosystem coverage, over-reliance on literature values for key parameters, lack of canonical models, untested or unrealistic assumptions, low predictive power, and a paucity of experimental studies. We anticipate progress in SIA resulting from standardization of methods and models, calibration of model parameters through experimentation, and continu...

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On the Use of Stable Isotopes in Trophic Ecology

The present paper reviews the effects of water temperature and flow on migrations, embryonic development, hatching, emergence, growth and life-history traits in light of the ongoing climate change with emphasis on anadromous Atlantic salmon Salmo salar and brown trout Salmo trutta. The expected climate change in the Atlantic is for milder and wetter winters, with more precipitation falling as rain and less as snow, decrease in ice-covered periods and frequent periods with extreme weather. Overall, thermal limits for salmonids are species specific. Scope for activity and growth and optimal temperature for growth increase with temperature to an optimal point before constrain by the oxygen content of the water. The optimal temperature for growth decreases with increasing fish size and varies little among populations within species, whereas the growth efficiency may be locally adapted to the temperature conditions of the home stream during the growth season. Indirectly, temperature influences age and size at smolting through its effect on growth. Time of spawning, egg hatching and emergence of the larvae vary with temperature and selective effects on time of first feeding. Traits such as age at first maturity, longevity and fecundity decrease with increasing temperature whilst egg size increases with temperature. Water flow influences the accessibility of rivers for returning adults and speed of both upstream and downstream migration. Extremes in water flow and temperature can decrease recruitment and survival. There is reason to expect a northward movement of the thermal niche of anadromous salmonids with decreased production and population extinction in the southern part of the distribution areas, migrations earlier in the season, later spawning, younger age at smolting and sexual maturity and increased disease susceptibility and mortality. Future research challenges are summarized at the end of the paper.

A review of the likely effects of climate change on anadromous Atlantic salmon Salmo salar and brown trout Salmo trutta, with particular reference to water temperature and flow.

Stable isotope analysis (SIA) has emerged as a common tool in ecology and has proven especially useful in the study of animal diet, habitat use, movement, and physiology. SIA has been vigorously applied to the study of marine mammals, because most species live in habitats or undergo large migrations/movements that make them difficult to observe. Our review supplies a complete list of published SIA contributions to marine mammal science and highlights informative case examples in four general research areas: (1) physiology and fractionation, (2) foraging ecology and habitat use, (3) ecotoxicology, and (4) historic ecology and paleoecology. We also provide a condensed background of isotopic nomenclature, highlight several physiological considerations important for accurate interpretation of isotopic data, and identify research areas ripe for future growth. Because it is impossible to conduct controlled laboratory experiments on most marine mammal species, future studies in marine mammal ecology must draw on isotopic data collected from other organisms and be cognizant of key assumptions often made in the application of SIA to the study of animal ecology. The review is designed to be accessible to all audiences, from students unfamiliar with SIA to those who have utilized it in published studies.

/pdf/using-stable-isotope-biogeochemistry-to-study-marine-mammal-fposok2unj.pdf

Using stable isotope biogeochemistry to study marine mammal ecology

http://digital.csic.es/bitstream/10261/44729/1/Taranger%20et%20al_%2c%20GCE.pdf

Control of puberty in farmed fish

 – Among the species in the family Salmonidae, those represented by the genera Salmo, Salvelinus, and Oncorhynchus (subfamily Salmoninae) are the most studied. Here, various aspects of phenotypic and life-history variation of Atlantic salmon Salmo salar L., brown trout Salmo trutta L., and Arctic charr Salvelinus alpinus (L.) are reviewed. While many strategies and tactics are commonly used by these species, there are also differences in their ecology and population dynamics that result in a variety of interesting and diverse topics that are challenging for future research. Atlantic salmon display considerable phenotypic plasticity and variability in life-history characters ranging from fully freshwater resident forms, where females can mature at approximately 10 cm in length, to anadromous populations characterised by 3–5 sea-winter (5SW) salmon. Even within simple 1SW populations, 20 or more spawning life-history types can be identified. Juveniles in freshwater can use both fluvial and lacustrine habitats for rearing, and while most smolts migrate to sea during the spring, fall migrations occur in some populations. At sea, some salmon undertake extensive oceanic migrations while other populations stay within the geographical confines of areas such as the Baltic Sea. At the other extreme are those that reside in estuaries and return to freshwater to spawn after spending only a few months at sea. The review of information on the diversity of life-history forms is related to conservation aspects associated with Atlantic salmon populations and current trends in abundance and survival. Brown trout is indigenous to Europe, North Africa and western Asia, but was introduced into at least 24 countries outside Europe and now has a world-wide distribution. It exploits both fresh and salt waters for feeding and spawning (brackish), and populations are often partially migratory. One part of the population leaves and feeds elsewhere, while another part stays as residents. In large, complex systems, the species is polymorphic with different size morphs in the various parts of the habitat. Brown trout feed close to the surface and near shore, but large individuals may move far offshore. The species exhibits ontogenetic niche shifts partly related to size and partly to developmental rate. They switch when the amount of surplus energy available for growth becomes small with fast growers being younger and smaller fish than slow growers. Brown trout is an opportunistic carnivore, but individuals specialise at least temporarily on particular food items; insect larvae are important for the young in streams, while littoral epibenthos in lakes and fish are most important for large trout. The sexes differ in resource use and size. Females are more inclined than males to become migratory and feed in pelagic waters. Males exploit running water, near-shore and surface waters more than females. Therefore, females feed more on zooplankton and exhibit a more uniform phenotype than males. The Arctic charr is the northernmost freshwater fish on earth, with a circumpolar distribution in the Holarctic that matches the last glaciation. Recent mtDNA studies indicate that there are five phylogeographic lineages (Atlantic, Arctic, Bering, Siberian and Acadian) that may be of Pleistocene origin. Phenotypic expression and ecology are more variable in charr than in most fish. Weights at maturation range from 3 g to 12 kg. Population differences in morphology and coloration are large and can have some genetic basis. Charr live in streams, at sea and in all habitats of oligotrophic lakes, including very deep areas. Ontogenetic habitat shifts between lacustrine habitats are common. The charr feed on all major prey types of streams, lakes and near-shore marine habitats, but has high niche flexibility in competition. Cannibalism is expressed in several cases, and can be important for developing and maintaining bimodal size distributions. Anadromy is found in the northern part of its range and involves about 40, but sometimes more days in the sea. All charr overwinter in freshwater. Partial migration is common, but the degree of anadromy varies greatly among populations. The food at sea includes zooplankton and pelagic fish, but also epibenthos. Polymorphism and sympatric morphs are much studied. As a prominent fish of glaciated lakes, charr is an important species for studying ecological speciation by the combination of field studies and experiments, particularly in the fields of morphometric heterochrony and comparative behaviour.

https://onlinelibrary.wiley.com/doi/pdf/10.1034/j.1600-0633.2003.00010.x

Atlantic salmon Salmo salar L., brown trout Salmo trutta L. and Arctic charr Salvelinus alpinus (L.): a review of aspects of their life histories

The effects of formalin and ethanol preservation on the δ 13 C and δ 15 N isotope signatures of Arctic charr Salvelinus alpinus muscle tissue were examined. The lipid content of the tissue samples studied ranged from 3·6 to 6·1 % and was not correlated with the magnitude of observed isotopic shifts in preserved samples. Ethanol and formalin significantly depleted and enriched, respectively, the δ 13 C isotope signatures of preserved tissues when compared to control samples. Ethanol did not significantly enrich δ 15 N signatures in comparison to controls, whereas formalin did. A meta-analysis of multiple species effects further demonstrated significant preservation effects in fish tissue. Statistical analysis of data obtained by correcting preserved tissue isotope signatures with literature, bootstrapped or meta-analysis derived correction factors demonstrated significant differences between corrected and control sample isotope signatures or failure to produce a unity slope when the data sets were regressed against one another. Species-specific, bootstrapped linear correction models resulted in no such errors. Results suggest that species-specific correction methods should be used for fishes because of the known wide variation in fish tissue lipid content and composition. Accordingly, the use of pilot studies will be required to develop correction factors that properly adjust for preservation effects when interpreting temporal patterns in historic analyses of food webs.

The effects of preservation on fish tissue stable isotope signatures

– Stable isotopes of carbon and nitrogen (δ13C and δ15N) were examined in wild and aquaculture origin Atlantic salmon, Salmo salar, to evaluate their utility to identify escaped farmed fish. Samples of muscle tissue obtained from wild Conne River, Newfoundland, salmon were significantly more enriched in nitrogen (δ15N: mean = 12.75; SD ± 0.38‰) but depleted in lipid corrected carbon (δ13C′: mean = −20.51; SD ± 0.23‰) by comparison with aquaculture specimens obtained from Bay d'Espoir, Newfoundland (δ15N = 10.96 ± 0.19‰; δ13C′ = −19.25 ± 0.17‰) resulting in a complete separation of the two groups. Aquaculture specimens differed in δ13C′ from analyses of commercial salmon diet by 0.24‰, within the enrichment range associated with trophic transfers, while the δ15N values in salmon muscle were enriched by 5.01‰. Although differences occurred in direct comparisons of white muscle and adipose tissue (N = 49), the average δ13C′ and δ15N signatures varied in absolute amounts by only 0.5‰, supporting the use of adipose tissue as a nonlethal means to determine isotopic signatures of Atlantic salmon.

Resumen

1. Examinamos isotopos estables de carbono y nitrogeno (δ13C y δ15N) de ejemplares de Salmo salar procedentes de una poblacion natural y de acuicultura para evaluar su utilizacion en la identificacion de individuos que se escapan de granjas.



2. Muestreos de tejido muscular obtenidos de ejemplares del Rio Conne (Terranova, Canada) mostraron estar significativamente enriquecidos en nitrogeno (δ15N: media = 12.75; SD ± 0.380/00) pero no contuvieron carbono lipidico (δ13C′: media = −20.51; SD ± 0.230/00) en comparacion con individuos de acuicultura procedentes de Bay d'Espoir, Terranova (δ15N = 10.96 ± 0.19; δ13C′ = −19.25 ± 0.170/00), resultando en una separacion completa de ambos grupos de ejemplares.



3. Los ejemplares de acuicultura difirieron en δ13C′ de analisis de dietas comerciales para salmon en un 0.240/00, dentro del rango de enriquecimiento asociado a trasferencias troficas mientras que los valores de δ15N en musculo aparecieron enriquecidos en un 5.010/00.



4. Aunque aparecieron diferencias en comparaciones directas de musculo blanco y tejido adiposo (N = 49), el promedio de senales de δ13C y δ15N vario en cantidades absolutas por solo 0.50/00, hecho que apoya el uso de tejido adiposo como un medio no letal para determinar senales isotopicas en Salmo salar.

Use of stable isotopes to distinguish farmed from wild Atlantic salmon, Salmo salar

– A model based on proximate considerations of life histories of Atlantic salmon, Salmo salar, was examined for its applicability to fit the variation in life-history of wild Arctic charr, Salvelinus alpinus, based on a qualitative assessment of information related to growth and lipid dynamics of Arctic charr. The original salmon model is discussed in context of modifications required to account for added complexities in the life history of Arctic charr in relation to anadromy versus residency. A study from North Norway shows that individual charr that emigrate from the lakes to the sea, maintain a high growth rate in the lake in late summer and early autumn compared with resident fish. Their relatively low lipid level in autumn combined with a high rate of change of lipid during winter was associated with postponement of maturation in the anadromous individuals. Individuals that remain resident in the lake arrested growth in autumn. Their high lipid level in autumn combined with a low rate of change of lipid during winter was associated with maturation the following summer, without emigration from freshwater. Results from this and other related studies show similarities with the model derived from lipid and growth dynamics of Atlantic salmon. The adjusted charr model illustrates possible proximate explanations for the high variation in life-history strategies of Arctic charr. However, the model does not account for the characteristic return migration of immature charr into freshwater several weeks after their entry to the sea. The proximate physiological stimulus for this movement of immature fish is not entirely clear.

Resumen

1. Examinamos un modelo basado en consideraciones proximas sobre la biologia de Salmo salar para su aplicabilidad a la biologia de Salvelinus alpinus, basado en evaluaciones cualitativas de informacion relacionadas con la dinamica del crecimiento y de lipidos en S. alpinus. Discutimos el modelo original de S. salar en el contexto de las modificaciones necesarias para incluir la complejidad anadida de la biologia de S. alpinus con relacion a la anadromia versus residencia.



2. Un estudio hecho en el norte de Noruega mostro que, en comparacion a los individuos residentes de S. alpinus, los individuos que emigran desde los lagos hasta el mar mantienen una alta tasa de crecimiento en el lago durante el final del verano e inicio de otono. Niveles relativamente bajos de lipidos en otono combinados con una alta de intercambio de lipidos durante el invierno parecieron asociado a una maduracion pospuesta en los individuos anadromos. Los individuos que permanecen residentes en el lago reducen el crecimiento en otono. Su alto nivel de lipidos en otono combinado con una menor tasa de intercambio de lipidos parecio asociada a la maduracion, el verano siguiente, sin emigracion desde aguas dulces.



3. Los resultados de este y otros estudios relacionados muestran similitud con el modelo derivado de la dinamica de lipidos y de crecimiento en S. salar. El modelo para S. alpinus ilustra posibles explicaciones proximas para la alta variacion en las estrategias biologicas de S. alpinus. Sin embargo, no explica la migraciones de vuelta a aguas dulces varias semanas despues de entrar en el mar, caracteristicas de juveniles de S. alpinus. Los estimulos fisiologicos proximos que expliquen estos movimientos en individuos inmaduros no estan claros.

Modelling the life-history variation of Arctic charr

Spawning migration timing of maiden Atlantic salmon Salmo salar and previous spawners was analysed in the catches in 1989-2004 in the large subarctic River Teno in the northernmost parts of Finland and Norway. The hypothesis was that the migration timing of previous spawners and their maiden counterparts is similar, with the migration timing similar between sexes. In most cases, however, previous spawners were observed to migrate into the River Teno and its tributaries earlier than their maiden counterparts. The difference in run timing was especially evident between maiden one-sea-winter (1SW) Atlantic salmon and the corresponding group of previous spawners [1S1, 1 year at sea (1) followed by first spawning (S) and reconditioning period of 1 year (1) at sea and second spawning run] for both sexes in the River Teno and in its two tributaries. The same was also evident between 2SW maiden and 2S1 previous spawning female Atlantic salmon in the River Teno. Females showed earlier spawning migration than males both in previous spawners and maiden Atlantic salmon. Different maiden sea-age classes also showed differences in run timing as multi-sea-winter fish (2-4SW) ascended earlier than 1SW fish but the timing of 1S1 and 2S1 previous spawning females coincided. The results suggest that run timing of Atlantic salmon may not be strictly genetically fixed as previous spawners ascend earlier than they did on their first spawning migration as maiden fish, and indicated that the closeness of the reconditioning area of postspawners to the river of origin resulted in an early ascent. Run timing of different sea-age groups has major management implications if the populations are heavily exploited with numerous fishing methods in different periods of the fishing season, as in the River Teno system.

J. B. Dempson

Papers

Atlantic salmon Salmo salar L., brown trout Salmo trutta L. and Arctic charr Salvelinus alpinus (L.): a review of aspects of their life histories

The effects of preservation on fish tissue stable isotope signatures

Use of stable isotopes to distinguish farmed from wild Atlantic salmon, Salmo salar

Modelling the life-history variation of Arctic charr

Previously spawned Atlantic salmon ascend a large subarctic river earlier than their maiden counterparts