Spawning distribution of Atlantic salmon (Salmo Salar L.) in controlled flow channels.

The spawning distribution of Atlantic salmon in specially designed controlled flow channels was studied in relation to spawning density, water temperature, water velocity, water depth, test egg plant mounds, rock weirs, and floating shelters in an attempt to devise management procedures which would reduce egg mortality on the spawning beds arising from egg nest overlap and egg predation. -- Behavior observations included daily counts of spawners occupying beds in various sections, daily positioning of tagged fish in some sections and continuous surveillance of pairs spawning in the channels or in a specially built observation chamber. Spawning area placed into egg nests was plotted daily and the patterns of redd locations were examine by comparison to theoretical probability distributions. Test egg plant mounds, weirs and shelters were installed in the channel and current patterns noted about the former two. Daily water temperature fluctuations and daily fluctuations in fish frequenting spawning beds were correlated. -- Adults spawned successfully free of serious predation, disease or egg retention. Territorialism and mating were observed in established pairs. The territory often changed in locale and rate especially amongst the males. Females did not always place their spawnings in one redd and one redd was often composed of eggs from several different females. Resident salmon parr and trout were discovered as potential salmon egg predators. Analysis indicated randomness in the redd patterns but contagion was isolated on one channel section containing a rock weir. As the spawning density was raised in channel sections, the redd area diminished but redd superimposition still continued to increase. At the highest spawning density imposed of 1 female per 6.4 square yards 25 per cent of the bed area was in redds with 13 per cent of this superimposed. The correlation of daily water temperature fluctuations with spawning activity was significant in one year but insignificant the following year. Salmon were flexible in their water velocity and water depth preferences at redd sites and selections were largely a reflection of the water profiles available. The test egg plant mounds affected the redd distribution; current patterns about the mounds indicated an area of maximum subterranean current on the forward slope of the mounds where adults places redds. Spawners congregated notably under shelter in holding pools but not under shelter over spawning bed