RESEARCH ARTICLE


Density-Dependent Growth in Juvenile Sockeye Salmon (Oncorhynchus Nerka)



Kim D. Hyatt1, Donald J. McQueen2, *, D. Paul Rankin1, Eric Demers 3
1 Fisheries and Oceans Canada, Pacific Biological Station, 3190 Hammond Bay Road, Nanaimo, B.C. V9R 6N7
2 125 Pirates Lane, Nanaimo, B.C. V9R 6R1
3 Biology Department, Vancouver Island University, 900 Fifth Street, Nanaimo, B.C. V9R 5S5


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© 2011 Hyatt et al.

open-access license: This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International Public License (CC-BY 4.0), a copy of which is available at: (https://creativecommons.org/licenses/by/4.0/legalcode). This license permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

* Address correspondence to this author at the 125 Pirates Lane, Nanaimo, BC, V9R 6R1, Canada; Tel: 250 754 0639; Fax: 250 754 0679; E-mail: don_mcqueen@telus.net


Abstract

Data gathered over 77 lake-years from 4 coastal British Columbia sockeye salmon nursery lakes suggest that density-dependent growth reductions are only possible at exceptionally high fry densities. In Great Central Lake (n=33 years) and Sproat Lakes (n=30 years) there was no relationship between smolt weight and mean summer fry densities ranging from 760-3800 fry ha-1. However, in two years when Sproat Lake fry densities were unusually high (1983=5183 ha-1, 1996=4801 ha-1) smolt weights were among the lowest recorded. In Woss and Vernon lakes (n=14 lake-years), there were significant bottom-up relationships between fall-fry weights and zooplankton biomass, but no relationships between December-fry weights and average fry densities (range 331-1361 ha-1), nor were there significant top-down relationships between fry densities and average zooplankton biomass. Comparisons of zooplankton production with bioenergetic-based fry consumption, suggested that the carrying capacity for Vernon Lake which had the highest rate of zooplankton production, was 12,700 fry ha-1, and for Sproat Lake which had the lowest zooplankton production, was 5200 fry ha-1. We conclude that fry densities in the range commonly observed for British Columbia coastal lakes (i.e. 500-4000 ha-1) cannot cause density-dependent reductions in prey biomass or fry growth rates. Further research is necessary.

Keywords: juvenile sockeye salmon, density dependence, aquatic food web, bioenergetics, zooplankton production, consumption by sockeye fry.