Rapid decreases in water temperature may result in a number of physiological, behavioural and fitness consequences for fishes termed 'cold shock'. Cold-shock stress occurs when a fish has been acclimated to a specific water temperature or range of temperatures and is subsequently exposed to a rapid decrease in temperature, resulting in a cascade of physiological and behavioural responses and, in some cases, death. Rapid temperature decreases may occur from either natural (e.g. thermocline temperature variation, seiches and storm events) or anthropogenic sources (e.g. varied thermal effluents from power generation and production industries). The magnitude, duration and frequency of the temperature change as well as the initial acclimation temperatures of individuals can influence the extent of the consequences of cold shock on fishes. Early research on cold shock focused on documenting mortality events associated with cold shock. However, in recent years, a shift in research has occurred where the focus of cold-shock studies now involves characterizing the sublethal effects of cold shock in terms of the stress response in fishes. This shift has revealed that cold shock can actually be used as a tool for fisheries science (e.g. to induce polyploidy). The cold-shock stress response offers opportunities to develop many exciting research questions, yet to date, cold-shock research has been largely unfocused. Few studies attempt to link laboratory physiology experiments with ecologically relevant field data on behaviour, growth, bioenergetics and fitness. Additional research will allow for the development of more focused and robust management policies and conservation initiatives. This review synthesizes the sublethal physiological and behavioural consequences of cold-shock stress on fishes, identifies natural and anthropogenic sources of cold shock, discusses the benefits of cold shock to fisheries science and describes mitigation and management efforts. Existing knowledge gaps and opportunities for future cold-shock research are presented.

This study examined water temperature patterns and their physical controls for two small, clearing-heated streams in shaded reaches downstream of all forestry activity. Field observations were made during July-August 2000 in the central interior of British Columbia, Canada. For both reaches, downstream cooling of up to 4°C had been observed during daytime over distances of~200 m. Radiative and convective exchanges of energy at heavily shaded sites on both reaches represented a net input of heat during most afternoons and therefore could not explain the observed cooling. In one stream, the greatest downstream cooling occurred when streamflow at the upstream site dropped below about 5 L·s -1 . At those times, temperatures at the downstream site were controlled mainly by local inflow of groundwater, because the warmer water from upstream was lost by infiltration in the upper 150 m of the reach. Warming often occurred in the upper subreach, where cool groundwater did not interact with the channel. At the second stream, creek temperature patterns were comparatively stable. Energy balance estimates from one afternoon suggested that groundwater inflow caused about 40% of the~3°C gross cooling effect in the daily maximum temperature, whereas bed heat conduction and hyporheic exchange caused about 60%.Résumé : Cette étude examine les patrons et les contrôles physiques de la température de l'eau, pour deux petits cours d'eau réchauffés en clairière, dans des sections ombragées en aval de toute activité forestière. Les observations de terrain ont été effectuées durant les mois de juillet et août 2000 dans le centre intérieur de la Colombie-Britannique, Canada. Pour les deux sections, un refroidissement vers l'aval allant jusqu'à 4°C a été observé durant le jour sur des distances de~200 m. Les échanges d'énergie par radiation et convection aux sites fortement ombragés dans les deux sections représentent un apport net de chaleur durant la plupart des après-midi et, par conséquent, ne peuvent pas expliquer le refroidissement observé. Dans un des cours d'eau, le plus grand refroidissement s'est produit lorsque le débit au site en amont diminuait en deçà de 5 L·s -1 . Les températures au site en aval étaient alors principalement contrôlées par l'entrée locale d'eau souterraine parce que l'eau plus chaude provenant de l'amont se perdait par infiltration dans les premiers 150 m en amont de la section. Un réchauffement s'est souvent produit dans la sous-section en amont, où l'eau froide souterraine n'interagissait pas avec le lit. Dans le second cours d'eau, les patrons de température du ruisseau étaient comparativement stables. Les estimations du bilan énergétique durant un après-midi suggèrent que les entrées d'eau souterraine causent environ 40 % du refroidissement global de~3°C de la température maximale journalière tandis que la conduction du lit et les échanges hyporhéiques en causent environ 60 %.[Traduit par la Rédaction] Story et al. 1396

Although the future timber supply in the northern hemisphere is expected to come from boreal and subboreal forests, little research has been conducted in these regions that examines the temperature responses of small, lakeheaded streams to streamside timber harvesting. We examined the temperature patterns of two subboreal outlet streams in north-central British Columbia for 1 year before and 3 years after clearcut logging and found only modest changes (averaging 0.05-1.1°C) with respect to summer daily maximum and minimum temperatures, diurnal fluctuations, and stream cooling. A multistream comparative survey conducted in the same geographic region revealed that streams headed by small lakes or swamps tended to cool as they flowed downstream, and headwater streams warmed, regardless of whether or not timber harvesting took place. Stream cooling was attributed to a combination of warm outlet temperatures (promoted by the presence of the lakes) and cold groundwater inflows. A regression model revealed that summertime downstream warming or cooling in headwater and outlet streams could be predicted by upstream maximum summer temperatures and canopy cover. Lentic water bodies and groundwater inflows are important determinants of stream temperature patterns in subboreal forests and may subsequently moderate their responses to streamside harvesting.Résumé : Bien que les sources futures de bois dans l'hémisphère nord doivent, pense-t-on, provenir surtout des forêts boréales et subboréales, les réactions thermiques des petits cours d'eau qui prennent naissance dans les lacs à la récolte du bois dans la zone riparienne restent mal connues. Nous avons examiné les patterns de température dans deux petits émissaires de lacs dans la région subboréale du centre-nord de la Colombie-Britannique pendant une année précédant une coupe à blanc et durant les trois années qui ont suivi; nous n'avons trouvé que de faibles changements (en moyenne 0,05-1,1°C) dans les températures journalières maximales et minimales en été, ainsi que dans les fluctuations journalières et le refroidissement des cours d'eau. Un inventaire comparatif de plusieurs ruisseaux dans la même région géographique montre que les ruisseaux qui prennent naissance dans un lac ou un marécage tendent à se refroidir vers l'aval, alors que les ruisseaux de tête de bassin se réchauffent, qu'il y ait eu ou non récolte du bois. Le refroidissement des ruisseaux s'explique par la combinaison de températures chaudes à l'origine de l'émissaire (à cause de la présence du lac) et l'influx d'eau souterraine froide. Un modèle de régression indique que le réchauffement et le refroidissement en aval pendant l'été dans les ruisseaux de tête et les émissaires peuvent être prédits à partir des températures maximales d'été de l'amont et de la couverture de la canopée. La présence de masses d'eau lenitiques et celle d'influx d'eaux souterraines sont d'importants facteurs déterminants des patterns de température des ruisseaux dans les forêts subboréa-les et elles peuvent ensuite mitiger leur ...

The impact of freshwater environmental factors on spawning migration mortality was modeled to provide a predictive tool for fisheries management of four run timing groups of Fraser River sockeye salmon Oncorhynchus nerka: early Stuart (Stuart Lake), early summer, summer, and late. We tested the significance of different measures of water temperature, discharge, fish abundance, and entry timing for forecasting discrepancies between lower-river and upriver escapement estimates using multiple regressions of principal component scores. Descriptive discrepancy models (i.e., ''management adjustment'' models) identified using Akaike's information criterion were consistent with the known biology of each group. For example, temperature and discharge thresholds were selected for early Stuart run discrepancy models, reflecting the extremes in both variables experienced by these early migrants. Predictive discrepancy models were also generated for each run timing group by using the limited number of environmental variables that are available in-season to fisheries managers. Even predictive discrepancy models using simple environmental metrics of average river temperature, flow, and river entry timing provide a valuable tool for forecasting relative indices of spawning migration mortality. This study provides an example of how environmentally based predictive tools can be used to inform fisheries management decisions and improve the probability of achieving spawning escapement targets.