William R. C. Beaumont

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.

Development of schooling behaviour during the downstream migration of Atlantic salmon Salmo salar smolts in a chalk stream

The downstream migratory behaviour of wild Atlantic salmon Salmo salar smolts was monitored using passive integrated transponder (PIT) antennae systems over 10 years in the lower reaches of a small chalk stream in southern England, U.K. The timing of smolt movements and the likely occurrence of schooling were investigated and compared to previous studies. In nine of the 10 consecutive years of study, the observed diel downstream patterns of S. salar smolt migration appeared to be synchronized with the onset of darkness. The distribution of time intervals between successive nocturnal detections of PIT-tagged smolts was as expected if generated randomly from observed hourly rates. There were, however, significantly more short intervals than expected for smolts detected migrating during the day. For each year from 2006 to 2011, the observed 10th percentile of the daytime intervals was <4 s, compared to ≥55 s for the simulated random times, indicating greater incidence of groups of smolts. Groups with the shortest time intervals between successive PIT tag detections originated from numerous parr tagging sites (used as a proxy for relatedness). The results suggest that the ecological drivers influencing daily smolt movements in the lower reaches of chalk stream catchments are similar to those previously reported at the onset of migration for smolts leaving their natal tributaries; that smolts detected migrating during the night are moving independently following initiation by a common environmental factor (presumably darkness), whereas those detected migrating during the day often move in groups, and that such schools may not be site (kin)-structured. The importance of understanding smolt migratory behaviour is considered with reference to stock monitoring programmes and enhancing downstream passage past barriers.

The effects of a small hydropower scheme on the migratory behaviour of Atlantic salmon Salmo salar smolts

The potential effects of a hydropower scheme on the migratory behaviour of Atlantic salmon Salmo salar smolts was studied on the River Frome, southern England. The potential delay to migration at the intake of the hydropower scheme was assessed, together with the effects of passage through the turbine on the temporal and spatial migration of the fish in the river and estuary. The migratory behaviour of the emigrating S. salar smolts was monitored using miniature acoustic transmitters and an array of acoustic receivers positioned at the hydropower scheme and in the river and estuary. The majority of the smolts bypassed the hydropower scheme with only 8.1% of the fish moving downstream through the turbine. Movement was nocturnal and occurred during elevated river flows. There was no apparent delay at the turbine intake or at the adjacent weir. The subsequent migration of all smolts through the estuary of the River Frome occurred during both day and night and there was a distinct ebb-tide migration through the estuary and into the coastal zone. There was no difference in the rate of migration between smolts that moved through the turbine or over the weir. The detection of smolts during both the freshwater migration and the transition from the freshwater to the marine environments was high (91.8 and 73.3%, respectively). A laboratory investigation on the de-scaling of smolts indicated that removal of 1, 5 and 10% of scales had no significant effect on saltwater survival or the measured physiological parameters (gill Na+ -K+ -ATPase activity, plasma osmolality and chloride concentrations). Smolt passage through the turbine was assessed and resulted in either no damage to the integument or scale loss or between 20 and 80% of total body area of recaptured smolts. It is estimated that 1.53% of the smolt population would suffer significant damage after passage through the turbine. The implications of the hydropower scheme on the population of salmon in the River Frome are discussed.

Under what circumstances does the capture and tagging of wild Atlantic salmon Salmo salar smolts affect probability of return as adults

Adult return rates for wild Atlantic salmon Salmo salar smolts captured in a rotary screw trap and tagged with coded wire (CW) tags were compared with a control group, using detections from passive integrated transponder (PIT) antennae systems over 7 years in a small chalk stream in southern England, U.K. Compared with control smolts, capture and CW-tagging of experimental smolts affected detected return rates only under certain conditions, with a decreased return probability for smolts caught and tagged following mild winter river temperature anomalies and during the night. Similarly, analysis of the experimental smolts revealed that capture and CW-tagging following mild winters decreased their probability of return as adults. There were also marginal positive effects of length at PIT-tagging as parr and length at CW-tagging as smolts, on individual probability of return as adult. The results support the hypothesis that the effect of procedures involving the capture and tagging of migrating wild S. salar smolts will vary with the circumstances under which they are performed. The implications of the findings are considered in the context of ongoing investigations to derive and report marine return rates for S. salar in support of national and international stock assessments and in developing best practice.

FishMORPH - An agent-based model to predict salmonid growth and distribution responses under natural and low flows

Predicting fish responses to modified flow regimes is becoming central to fisheries management. In this study we present an agent-based model (ABM) to predict the growth and distribution of young-of-the-year (YOY) and one-year-old (1+) Atlantic salmon and brown trout in response to flow change during summer. A field study of a real population during both natural and low flow conditions provided the simulation environment and validation patterns. Virtual fish were realistic both in terms of bioenergetics and feeding. We tested alternative movement rules to replicate observed patterns of body mass, growth rates, stretch distribution and patch occupancy patterns. Notably, there was no calibration of the model. Virtual fish prioritising consumption rates before predator avoidance replicated observed growth and distribution patterns better than a purely maximising consumption rule. Stream conditions of low predation and harsh winters provide ecological justification for the selection of this behaviour during summer months. Overall, the model was able to predict distribution and growth patterns well across both natural and low flow regimes. The model can be used to support management of salmonids by predicting population responses to predicted flow impacts and associated habitat change.