Inter‐stage survival of wild juvenile Atlantic salmon, Salmo salar L.

TLDR: Density-dependent factors related to a beaver dam, which limited spawning distribution, may have contributed to poor survival and increased fry emigration in one year and environmental factors, particularly winter conditions, in streams such as Catamaran Brook may act as bottlenecks to natural production of Atlantic salmon.

Abstract: A biological model was developed to calculate annual survival between life stages of juvenile Atlantic salmon, Salmo salar L, in Catamaran Brook, a small stream basin (52 km2) in the Miramichi River catchment in New Brunswick, Canada Seven years’ data (1990–1996) were used in the model Input variables included: daily fish counts and measurements of parr (3–4 age classes), smolts, and adult salmon at a fish-counting fence near the stream mouth; biennial quantification of all habitat types along the watercourse; fish density estimated by electric fishing at 30 sites; and estimates of young-of-the-year emigration via stream drift Continuous recording of stream discharge provided data to assist in interpretation of survival estimates Annual survival for juvenile salmon in their first 3 years of life in the stream averaged between 31% and 34% The greatest annual variation (CV = 0699) occurred at the egg to 0+ (summer) stage with a low of 92% survival recorded for a winter with an atypical midwinter flood event; parr and pre-smolt survival were similarly affected Survival from egg deposition (after correction for losses caused by predation and retention/non-fertilization) to smolt emigration was between 016% and 052%, which is low relative to estimates from many other studies Survival of smolts to returning 1-sea-winter adults (grilse) averaged 85% Potential errors in the computation of the model are discussed, eg inaccurate counts of spawning adults during high autumn stream flow A possible explanation for the low egg to smolt survival was the environmental conditions experienced during various winters Mean egg survival was 13 times higher (393%) and egg to smolt survival increased to 103% when the two winters characterized by extremely low discharge or midwinter freshets were excluded from the calculation Density-dependent factors related to a beaver dam, which limited spawning distribution, may also have contributed to poor survival and increased fry emigration in one year Environmental factors, particularly winter conditions, in streams such as Catamaran Brook may act as bottlenecks to natural production of Atlantic salmon