Predator-prey interactions of common murres (Uria aagle) and fish in the northwest Atlantic : foraging strategies on multiple scales

Davoren, Gail K. (2001) Predator-prey interactions of common murres (Uria aagle) and fish in the northwest Atlantic : foraging strategies on multiple scales. Doctoral (PhD) thesis, Memorial University of Newfoundland.

[English] PDF (Migrated (PDF/A Conversion) from original format: (application/pdf)) - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (31MB) [English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. (Original Version)

Abstract

The Northwest Atlantic ecosystem is currently undergoing changes in species interactions and ocean climate. Capelin (Mallotus villosus ), the dominant forage fish in the ecosystem, is the main prey item of marine birds, mammals and piscivorous fish. In the 1990s, spawning capelin were small, spawned later, shifted their distribution southerly to non-traditional areas compared to historical accounts, and abundance estimates have varied widely. During these changes and divergent biomass estimates, this research was initiated. The focus of this thesis is the multi-scale behavioural interactions of marine predators and prey: a marine diving bird, the common murre ( Uria aalge ), and its main prey species, capelin. This study integrates both colony-based and vessel-based techniques. I showed that some aggregations of capelin are stable in space and time on a number of scales: fine- (1-100 m; minute-hour), coarse- (1-100 km; day-week) meso-scale (100-1000 km; annual), allowing murres to use memory to locate prey at sea during different periods during their annual cycle. Social foraging techniques appeared to be important on fine- and coarse-scales (local enhancement, network foraging) while no evidence was found for social foraging techniques over larger spatial scales (Information Center Hypothesis). Spatial scales at which murres tracked capelin were highly variable, as found in other studies examining predator-prey interactions of mobile organisms. The tracking scales of murres to capelin were smallest during the breeding (0.8-5.1 km) and pre-breeding periods (3.1-8 km), compared to post-breeding (6.0-50.0 km). This variability in spatial associations between predators and their prey was likely due to different energetic requirements, locomotory constraints and search strategies used among these periods. Inter-colony comparisons of provisioning behaviour by murres revealed low feeding rates of chicks at the largest murre colony in eastern Canada relative to a smaller colony, which resulted in the lowest average mass and condition of fledgling murres (191.6 ± 4.0 g) reported in the literature. Density-dependence, both while foraging at sea and rearing chicks at the colony, and prey distribution around the largest colony resulted in additional provisioning constraints relative to a smaller colony and divergent life history strategies at the two colonies. Poorer chick condition, and presumably lower recruitment, may have resulted in a lack of population growth at the larger colony, which contains 85% of the common murres in the Northwest Atlantic. Clearly, common murres interact with their prey over multiple temporal and spatial scales and these behavioural interactions are manifested in demographic parameters.

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