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Divergent foraging strategies of three co-occurring north Pacific flatfishes
Hurst, T.P.; Ryer, C.H.; Ramsey, J.M.; Haines, S.A. (2007). Divergent foraging strategies of three co-occurring north Pacific flatfishes. Mar. Biol. (Berl.) 151(3): 1087-1098.
In: Marine Biology. Springer: Heidelberg; Berlin. ISSN 0025-3162; e-ISSN 1432-1793, more
Peer reviewed article  

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  • Hurst, T.P.
  • Ryer, C.H.
  • Ramsey, J.M.
  • Haines, S.A.

    Despite facing similar constraints imposed by the environment, significant variation in life history traits frequently exists among species generally considered to comprise a single ecological guild. For juvenile flatfishes, constraints on foraging activity include variation in light and prey availability, as well as predation risk. This paper describes the visual constraints on, and divergent foraging strategies of three co-occurring north Pacific flatfish species, northern rock sole (Lepidopsetta polyxystra), Pacific halibut (Hippoglossus stenolepis), and English sole (Pleuronectes vetulus). Visual foraging abilities measured in the laboratory decreased rapidly below 10-4 µmol photons·m-2 s-1, and were similar among species. Despite similar sensory constraints, field sampling in August 2004 at a Kodiak Island nursery site (Holiday Beach, 57o41.2' N, 152o27.7' W) identified species differences in diets, diel foraging patterns, and within-nursery depth distributions. Northern rock sole and English sole fed primarily on bivalve siphons and polychaetes, whereas mysids dominated the diets of Pacific halibut. Northern rock sole were geographically the most widespread but feeding activity was temporally restricted to the dusk period. Pacific halibut were rare in shallow depths (<5 m) and fed most intensively prior to dusk. English sole fed throughout the daylight hours and were abundant only in the shallowest (<5 m) habitats. These differences in diets, foraging times, and habitat use appear related to previously documented species-specific behavioral characteristics as well as general spatial (increasing with depth) and temporal (increasing during foraging activity) variations in predation risk. At one extreme, the conservative behavioral strategy of northern rock sole may permit use of a broader range of foraging habitats, whereas English sole may be restricted to shallow water by limited behavioral responses to predation threat. These observations demonstrate that the appearance of habitat partitioning is not due to differences in sensory ability, but reflects multi-faceted, species-specific responses to the ecological tradeoffs between foraging and predation risks.

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