Reddin et a\ : Diurnal and nocturnal temperatures for Salmo salar 



423 



8 10 12 



16 18 20 



16 18 -2 2 4 

 Water temperature (°C) 



Figure 5 



Difference between night and day temperatures recorded hourly by data storage 

 tags and expressed as cumulative counts for weeks 24 to 29 from Campbellton 

 River, 2002. Water temperatures are shown for six periods and for all day and 

 night temperatures. Thin solid line is for daytime temperatures and thick line is 

 for night time temperatures. In the multi-line graphs labelled "day" and "night," 

 the square=week 24, the circle=week 25, triangle = week 26, polygon=week 27, 

 dark pentagon=week 28 and the star=week 29. 



temperature profiles collected by these data storage tags 

 provide detailed information on the thermal habitat 

 experienced by 15 Atlantic salmon postsmolts for periods 

 ranging from a few days to about two months at sea. 

 Temperatures recorded ranged from below 0° to nearly 

 20°C, although most of the time was spent in water from 

 8° to 15°C, probably near the surface. 



Sigholt and Finstad (1990) and Handeland et al. 

 (2003) reported that lethal sea water temperatures for 

 both wild and farmed salmon smolts adapting to seawa- 

 ter occurred at very low and very high temperatures. At 

 the lower end of the range in temperatures, some mor- 

 talities occurred at sea temperatures of 6-7°C, whereas 

 at the higher end, mortalities occurred at temperatures 



