ISSN:
1095-8649
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Biology
Notes:
We tested two biologically based predictions that potentially influence scales of spatial association between Atlantic cod, Gadus morhua, and prey populations of capelin, Mallotus vilhsus. If cod aggregate in response to concentrations of prey, then spatial association (coherence) between capelin and cod was predicted to peak at the scale of maximum capelin spatial variance. If capelin-cod coherence did not match the scale of maximum prey spatial variability, then capelin-cod coherence was predicted to peak at the spatial scale that maximizes net energetic benefit to the predator. Contrary to predictions, we found no evidence of aggregative responses of cod to capelin over resolution scales of 20 m to 10 km. This result was observed consistently at the temporal scale of a single transect (c. 1 h duration) and at the scale of averaged transects (c. 2 weeks duration). Estimates of cod foraging energetics showed that they were not constrained by physiology to aggregate relative to capelin at any scale less than 10 km. A net energetic gain of 478 to 784 kJ would result if a 44 cm, 752 g cod consumed a ration of eight to 12 capelin over a period of 58 h. Energetic calculations included costs of egestion and excretion (317 to 476 kJ), maintenance (58 kJ), digestion (125 to 188 kJ), and continuous swimming during ration assimilation (79 kJ). During this period, a 44 cm cod could travel over 38 km swimming at 1 b.l. s−1. Foraging cod are virtually certain to encounter capelin over this distance based on the abundance of pre-spawning capelin present in coastal bays during the spawning season. This study illustrates that aggregative responses of predators do no occur at all scales and possibly occur over a very limited range of scales.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1095-8649.1994.tb01093.x
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