Final results of a transfer experiment to help evaluate juvenile

Final results of a transfer experiment to help evaluate juvenile Chinook salmon
survival in an estuary
C. D. Levings1 and J.S. Macdonald
Fisheries and Oceans Canada, Science Branch, Pacific, Centre for Aquaculture and
Environmental Research, 4160 Marine Drive, West Vancouver BC Canada V7V 1N6
We examined the smolt to adult survival of juvenile Chinook salmon (Oncorhynchus
tshawytscha) in the Campbell River estuary in British Columbia, Canada, where smolts were
denied access to their natural estuarine ecosystem during their outmigration to the open
ocean. We present the final results of an extensive set of transfer experiments conducted in
1983, 1984, and 1985. Smolts were transferred from a hatchery on the Campbell River by
helicopter in late April. They were released to four locations, two that ensured an estuarine
experience (the river and the estuary), and two beyond the estuary in a transition ecosystem
and a marine ecosystem. Each year, in a single day approximately 35000 marked fish in three
replicate batches were released at each location. The dispersal of each of the four groups was
documented by recovery of the smolts in an extensive beach seining program. Their survival as
adults was documented from recoveries in the fishery, and upon their return to the spawning
grounds and at the hatchery. Results were essentially the same as those we reported earlier,
based on 34 % of adult returns. The data showed strong interaction between year and release
site. Chinook salmon released to the river and estuary survived better than those deprived of
an estuarine experience in 1983 and 1984 but release site had no effect on survival in 1985.
However when data were summarized over years, fish deprived of the estuary showed a
decrease in survival relative to those that had estuary access. We discuss the differences in
survival in the context of smolt dispersal and conditions in the ecosystems, ocean survival,
habitat restoration efforts in the estuary, and comment on process-oriented habitat studies
relative to efforts to directly assess estuarine juvenile to adult survival.
1 Retired/Scientist