Fisheries Behavioral Ecology - Abstracts
Ryer, C.H., A.W. Stoner, and R.H. Titgen. 2004. Behavioral mechanisms underlying the refuge value of benthic habitat structure for two flatfishes with differing anti-predator strategies. Marine Ecology Progress Series 268:231-243.
Abstract
Juvenile flatfish habitat is usually modeled on the basis of sediment grain-size, depth
and temperature. Recent evidence indicates that some juvenile flatfishes associate with emergent
structures such as sponge, shell and other biogenic and bed-form features of otherwise low-relief
shelf habitats. In laboratory experiments we examined the habitat preference and effects of habitat
structure upon predation vulnerability of sub-yearling (Age-0) Pacific halibut Hippoglossus
stenolepis and northern rock sole Lepidopsetta polyxystra. When given the choice between bare
sand or sand with 16% sponge coverage, halibut demonstrated strong preference for sponge, while
rock sole showed no preference. Larger Age-2 halibut (used as predators in the subsequent experiment)
also preferred sponge, but this preference declined with increasing hunger. When allowed to
forage for Age-0 flatfishes in either bare sand or sponge, predators consumed more prey in sand and
consumed more Age-0 halibut than rock sole. We were able to determine which behavioral processes
in the predator–prey interaction were modified by the presence of habitat structure. Predator–prey encounter rates decreased in the sponge habitat as predator search was impeded: predators paused
more frequently and swam more slowly to maneuver through the sponges. Sponges also tended to
hinder the pursuit of prey. Rock sole utilized stereotypic flatfish defense-mechanisms, relying upon
immobility, burial and crypsis, and were less likely to flush at a predator’s approach than halibut.
Halibut have a less developed ability to mimic sediments, but a deeper/narrower body that confers
greater swimming speed, and were more likely to flush as a predator approached. Once they had
flushed and were pursued by a predator, halibut were more likely to escape than were rock sole.
These experiments support an accumulating body of evidence that emergent structure, in otherwise
low-relief benthic habitats, may play an important role in the ecology of some juvenile flatfishes.
Removal of emergent structure by towed fishing gear and other anthropogenic and/or natural disturbance
may influence patterns of distribution for juvenile halibut, as fish redistribute to less preferred
habitat, and may decrease survival rates through increased losses to predation.
Last updated
26 April, 2007
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