Locations of marine animals revealed by carbon isotopes

Knowing the distribution of marine animals is central to understanding climatic and other environmental influences on population ecology. This information has proven difficult to gain through capture-based methods biased by capture location. Here we show that marine location can be inferred from animal tissues. As the carbon isotope composition of animal tissues varies with sea surface temperature, marine location can be identified by matching time series of carbon isotopes measured in tissues to sea surface temperature records. Applying this technique to populations of Atlantic salmon (Salmo salar L.) produces isotopically-derived maps of oceanic feeding grounds, consistent with the current understanding of salmon migrations, that additionally reveal geographic segregation in feeding grounds between individual philopatric populations and age-classes. Carbon isotope ratios can be used to identify the location of open ocean feeding grounds for any pelagic animals for which tissue archives and matching records of sea surface temperature are available

Does relatedness influence migratory timing and behaviour in Atlantic salmon smolts?

Aggregating and moving with relatives may enable animals to increase opportunities for kin selection to occur. To gain group-living benefits, animals must coordinate their behaviour. Atlantic salmon, Salmo salar, demonstrate both territoriality and schooling: the two key social behaviours performed by fish. In this investigation we compared the migratory timing and behaviour of six distinct full-sibling groups of tagged S. salar smolts with a large control sample from the same wild population. The results clearly demonstrate that the incidence of schooling and diel migratory timing is not significantly influenced by relatedness, and this adds further support to the hypothesis that S. salar smolt migration is primarily an adaptive response to environmental conditions, rather than a behaviour based solely on genetics or kin-biased behaviour. Used in conjunction with the results of two previous investigations, this is the first study to illustrate that kin discrimination among full-sibling groups of parr does not lead to kin-biased schooling in smolts. Thus, even within the same full-sibling groups, the extent of kin-biased behaviour in fish can both differ within a life history stage under varying ecological conditions and shift from one life history stage to the next

Modelling human choices: MADeM and decision‑making

Research supported by FAPESP 2015/50122-0 and DFG-GRTK 1740/2. RP and AR are also part of the Research, Innovation and Dissemination Center for Neuromathematics FAPESP grant (2013/07699-0). RP is supported by a FAPESP scholarship (2013/25667-8). ACR is partially supported by a CNPq fellowship (grant 306251/2014-0)

26th Annual Computational Neuroscience Meeting (CNS*2017): Part 3 - Meeting Abstracts - Antwerp, Belgium. 15–20 July 2017

This work was produced as part of the activities of FAPESP Research,\ud Disseminations and Innovation Center for Neuromathematics (grant\ud 2013/07699-0, S. Paulo Research Foundation). NLK is supported by a\ud FAPESP postdoctoral fellowship (grant 2016/03855-5). ACR is partially\ud supported by a CNPq fellowship (grant 306251/2014-0)

Consumer-resource elemental imbalances in a nutrient rich stream

Pronounced stoichiometric imbalances (CNP) between consumers and resources reported from nutrient-poor systems potentially constrain key ecological processes, but such imbalances should be less marked when more nutrients are available. In a headwater stream rich in nutrients (total P  =  208 µg/L; total oxidizable N  =  7 mg/L), we determined the elemental composition and standing stock of the consumer species and basal resources in relation to taxonomic identity, feeding mode, and season (spring and autumn). Compared with previous studies, basal resources had low elemental ratios (CN and CP), reflecting the high concentrations of inorganic nutrients in the water. Nevertheless, elemental imbalances were still evident between consumers and these basal resources, particularly for organisms feeding on detritus. Some of the variation in elemental ratios among consumers could be attributed to taxonomic identity. Furthermore, detritivores typically were depleted in N and P compared to taxonomically related species with different feeding modes. Elemental ratios of primary consumers differed between the 2 sampling occasions. Collector-gatherers and scrapers had lower CP and NP and shredders had higher CN in October than in May. Basal resources (fine and coarse particulate organic matter and periphyton) made up most of the standing stock of organic N and P, but quantities varied between May and October. The elemental composition of consumers of basal resources appeared to track changes in resource availability. Even with a plentiful supply of inorganic N and P available to primary producers, the availability of elements from food (a combination of quality and quantity) may influence the elemental composition of consumers

Re-introduction of Atlantic salmon, Salmo salar L., to the Tadnoll Brook, Dorset

Atlantic salmon had become extinct in Tadnoll Brook, Dorset, a tributary of the Frome. Fry were reared from River Frome native stock and introduced to Tadnoll Brook. Dispersal downstream of the introduction site was high initially, through at least 1 km; despite dispersal a density of salmon parr of 8 per 100 m2 was achieved in the introduction reach. Survival was 71 % egg – fry in egg boxes, 4.1 % fry – smolt and 2.9 % egg – smolt. There were two migratory periods, in the autumn following the introduction, and in the following spring. Approximately 45 % of the surviving population remained in Tadnoll Brook for a second summer. Observed patterns were consistent with suggestions that fry and parr distribution is constrained by habitat limitation

Seeing double: size-based versus taxonomic views of food web structure

Here, we investigate patterns in the size structure of one marine and six freshwater foodwebs: that is, how the trophic structure of such ecological networks is governed by the body size of its interacting entities. The data for these food webs are interactions between individuals, including the taxonomic identity and body mass of the prey and the predator. Using these detailed data, we describe how patterns grouped into three sets of response variables: (i) trophic orderings; (ii) diet variation; and (iii) predator variation, scales with the body mass of predators or prey, using both a species- and a size-class-based approach. We also compare patterns of size structure derived from analysis of individual-based data with those patterns that result when data are ‘‘aggregated’’ into species (or size class-based) averages.This comparison shows that analysis based on species averaging can obscure interesting patterns in the size structure of ecological communities. Specifically, we found that the slope of prey body mass as a function of predator body mass was consistently underestimated and the slope of predator–prey bodymass ratio (PPMR) as a function of predator bodymass was overestimated, when species averages were used instead of the individuallevel data. In some cases, no relationship was found when species averageswere used, but when individual-level data were used instead, clear and significant patterns were revealed. Further, when data were grouped into size classes, the slope of the prey bodymass as a function of predator bodymasswas smaller and the slope of the PPMR relationship was greater compared to what was found using species-aggregated data.Wealso discuss potential sampling effects arising from size-class-based approaches, which are not always seen in taxonomical approaches. These results have potentially important implications for parameterisation of models of ecological communities and hence for predictions concerning the dynamics of ecological communities and their response to different kinds of disturbances

The influence of the freshwater environment and the biological characteristics of Atlantic salmon smolts on their subsequent marine survival

Atlantic salmon have declined markedly in the past 20-30 years throughout their range. Much of the focus for this decline has been on increased mortality during the marine phase of the life cycle. However, marine mortality does not operate independently of factors acting in freshwater and the biological characteristics of smolts migrating to sea. Over recent decades, juvenile salmon in many rivers have grown faster and migrated to sea at a younger age, and thus typically smaller. This has shortened the generation time for many individuals, and may dampen the impact of increased marine mortality, assuming expected higher in-river survival prior to smolting is not outweighed by increased mortality of smaller smolts at sea. Over the same period, smolt run-timing across the geographic range has been occurring earlier, at a rate of almost three days per decade, on average. This has given rise to growing concerns about smolts potentially missing the optimum environmental migration “window”, the timing of which may also be changing. Contaminants and other factors operating in freshwater also impact on smolt quality with adverse consequences for their physiological readiness for life at sea. Given that managers have very limited ability to influence the broad scale factors limiting salmon survival at sea, it is vital that freshwater habitats are managed to both maximise smolt output and to minimise the impact of factors acting in freshwater which may compromise salmon once they migrate to sea.Publisher PDFPeer reviewe

Stable isotopes reveal age-dependent trophic level and spatial segregation during adult marine feeding in populations of salmon

Locating and differentiating the marine feeding areas used by adult salmon (Salmo salar) is essential to stock-based management and conservation, but traditional tagging studies are limited and influenced by the uneven distribution of the fisheries or research vessel surveys. Here, a novel approach is used, based on the observation that the isotopic composition of animal tissues is intrinsically linked to the environmental conditions during tissue growth, which allows for the distinction of pelagic fish feeding in different locations. This isotopic approach is applied using archived collections of salmon scales and shows that (i) salmon act as size-structured pelagic predators, (ii) adult salmon from different natal origins within the UK (and hence components of the southern European stock complex) feed in different oceanic regions before their return, (iii) one-sea-winter (1SW) and multi-sea-winter salmon returning to some rivers in the UK are separated in their marine feeding areas, whereas those from others are not, and (iv) salmon from the rivers sampled are not feeding in regions of the Northwest Atlantic used by 1SW salmon returning to rivers in Newfoundland. Therefore, the stable isotope approach allows for retrospective investigations of marine diet, location, and migration at stock- and cohort-specific levels