Document Type

Article

Journal/Book Title/Conference

Transactions of the American Fisheries Society

Volume

128

Issue

6

Publisher

American Fisheries Society

Publication Date

1999

Keywords

ontogenetic, habitat shifts, juvenile, Bear Lake, sculpin

First Page

1201

Last Page

1212

Abstract

Bear lake sculpin Cottus extensus exhibit ontogenetic habitat shifts during their initial year of life. Distribution and habitat switching was measured with bimonthly bottom-trawl surveys repeated throughout the summer. Patterns of daily growth increments on otoliths were used to measure the history of habitat residence, individual size at the time of the habitat switch, and habitat-specific growth rates. Laboratory experiments and known-age fish confirmed daily increment formation of otoliths. After dispersing during an initial pelagic larval stage, postlarval juveniles settled in both the warm, food-rich littoral zone and the cold, unproductive profundal zone. During summer, initial profundal-zone inhabitants underwent a unidirectional habitat shift to the more productive littoral zone. Fish that moved to the littoral zone grew twice as fast as those in the profundal zone and encountered little apparent predation mortality risk there. Habitat shifts were therefore consistent with both growth optimization and predatory avoidance. However, shifts occurred at a wide range of body sizes throughout the summer. The large spatial scale of the lake, limited swimming ability of juvenile fish, diel migratory behavior, and lack of complex habitat structure may preclude shifts at discrete body sizes for this species.

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