W. D. Riley

Using novel methodologies to examine the impact of artificial light at night on the cortisol stress response in dispersing Atlantic salmon (Salmo salar L.) fry

Artificial light at night (ALAN) is known to disrupt the nocturnal dispersal behaviour of Atlantic salmon fry, yet the underlying physiological mechanism is unknown. Here novel methodologies are utilised to examine whether behavioural disruption seen in dispersing fry is mediated via a cortisol stress response. Fry showed the capacity to mount a stress response, however, the two methods for sampling cortisol provide conflicting results as to whether ALAN acts as a stressor to dispersing fry.

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.

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.

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.

Small Water Bodies in Great Britain and Ireland: Ecosystem function, human-generated degradation, and options for restorative action

Small, 1st and 2nd-order, headwater streams and ponds play essential roles in providing natural flood control, trapping sediments and contaminants, retaining nutrients, and maintaining biological diversity, which extend into downstream reaches, lakes and estuaries. However, the large geographic extent and high connectivity of these small water bodies with the surrounding terrestrial ecosystem makes them particularly vulnerable to growing land-use pressures and environmental change. The greatest pressure on the physical processes in these waters has been their extension and modification for agricultural and forestry drainage, resulting in highly modified discharge and temperature regimes that have implications for flood and drought control further downstream. The extensive length of the small stream network exposes rivers to a wide range of inputs, including nutrients, pesticides, heavy metals, sediment and emerging contaminants. Small water bodies have also been affected by invasions of non-native species, which along with the physical and chemical pressures, have affected most groups of organisms with consequent implications for the wider biodiversity within the catchment. Reducing the impacts and restoring the natural ecosystem function of these water bodies requires a three-tiered approach based on: restoration of channel hydromorphological dynamics; restoration and management of the riparian zone; and management of activities in the wider catchment that have both point-source and diffuse impacts. Such activities are expensive and so emphasis must be placed on integrated programmes that provide multiple benefits. Practical options need to be promoted through legislative regulation, financial incentives, markets for resource services and voluntary codes and actions.