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Marine Ecology Progress Series

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MEPS 251:245-254 (2003)  -  doi:10.3354/meps251245

Predator distribution and habitat patch area determine predation rates on Age-0 juvenile cod Gadus spp.

B. J. Laurel1,*, R. S. Gregory2, J. A. Brown1

1Ocean Sciences Centre, Memorial University of Newfoundland, St. John¹s, Newfoundland A1C 5S7, Canada
2Department of Fisheries and Oceans, Science Branch, PO Box 5667, St. John¹s, Newfoundland A1C 5X1, Canada

ABSTRACT: Eelgrass Zostera marina provides refuge to numerous fish species but is vulnerable to fragmentation through natural and anthropogenic disturbance. In Bonavista Bay, Newfoundland, eelgrass patch size was altered to measure changes in predation risk in Age-0 juvenile cod, Gadus morhua. Artificial eelgrass mats of 5 sizes (0.32, 1.1, 5.5, 11 and 22 m2) were deployed in duplicate at each of 2 sites in Newman Sound in Terra Nova National Park during summer/autumn in 1999 and 2000. Predator distribution was determined using a combination of weekly underwater transect surveys and biweekly seining. Relative predation rates were measured by tethering Age-0 cod at the center of each patch and recording the incidence of predation (n = 1116 tether sets). Predation rates were negatively correlated with patch size during both years, suggesting that larger patches reduce predator foraging ability. However, high predator densities in the largest eelgrass patch resulted in higher than expected rates of predation. Therefore, habitat dimension affected predation risk in juvenile cod via 2 opposing mechanisms. Our results stress the importance of considering both habitat areal extent and predator distribution when estimating the effects of habitat fragmentation on predation rates.

KEY WORDS: Predator-prey interactions · Edge effects · Eelgrass · Juvenile cod · Predator distribution · Habitat fragmentation

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