MEPS 481:211-223 (2013)  -  DOI: https://doi.org/10.3354/meps10190

ABSTRACT: A suite of adaptive traits allows Pacific salmon to exploit diverse habitats during their lives, facilitating their persistence in highly variable and heterogeneous environments. We investigated how juvenile sockeye salmon Oncorhynchus nerka, which typically rear in lakes before migrating rapidly to sea, make use of riverine and estuarine habitats in the Chignik Lake system (Alaska, USA) where lacustrine rearing capacity limits sockeye salmon productivity. Their distribution, growth, and genetic stock composition were examined during June to August, 2007 to 2009. Sockeye salmon inhabited the estuary for up to 3 mo each summer, representing 2 distinct age classes: Age-0 fry and parr, and Age 1+ smolts. The fry and parr grew rapidly in the estuary, attaining sizes comparable to the lake-reared smolts. Smolts also grew in the estuary in all years, although they occupied the estuary for a briefer period in years when they entered at a larger size. Using genetic mixture analyses, fry and parr in the estuary were assigned to a population that spawns in Chignik River immediately upstream of the estuary, whereas the smolts were assigned to 2 genetically distinct population groups associated with separate nursery lakes farther up in the basin. Our findings highlight the role of estuaries for juvenile sockeye salmon in systems with limited freshwater rearing capacity and high salmon density. The persistence of such populations depends in part on preserving a continuum of habitat types, especially in the southern range of the species where a shifting climate and human activities are expected to most greatly impact populations.

KEY WORDS: Oncorhynchus nerka · Life history variation · Estuary · Rearing habitat · Juvenile growth · Genetic stock composition · Single nucleotide polymorphism · Climate