- Year-round habitat use of marine predators provides knowledge of important marine areas throughout different life stages. Large-scale, environmental variability, both in space and time, causes changes in the behavior and distribution of marine predators that are important to quantify for conservation. In the Northern California Current System (NCCS), common murres (Uria aalge) are widely distributed, however, regional gaps exist in information of seasonal movements and individual foraging behavior. My goal was to use individual tracking devices to relate distribution and behavior of common murres to conditions in the environment. I used satellite transmitters on non-breeding common murres captured at the Yaquina Head colony in Newport, Oregon and in the Columbia River plume over multiple years (2012- 2013, 2015-2017), which included the progression of a marine heatwave. I developed behavior-specific habitat models for three different movement groups: central-place foraging, non-central-place foraging, and dispersing during the non-breeding period. In addition, I quantified behavioral and distribution responses to increasing ocean variability between the summers of 2013 and 2015 using dive activity linear mixed models to determine the environmental influence on dive frequency and dive duration.
I found habitat use was dependent on large-scale movement patterns of individual murres. During the breeding season, murres that engaged in central-place foraging had extremely large foraging ranges and non-linear, bimodal trends with ocean depth and salinity. Non-central-place foragers during the breeding period, engaged in more restricted foraging activity with decreasing ocean depths, during daylight hours, and spent more time foraging in 2015 than in any other year. During the non-breeding period, murres often foraged nearshore in waters masses associated with warm sea surface temperature, upwelling, and low salinity levels. These conditions were associated with productive bays and river mouths.
Dive activity and dive locations revealed selectivity in spatial-use under warmer temperatures. Foraging activity was high in the Columbia River plume and murres spent more time diving in this area during a warm year. Dive frequency decreased and dive durations were longer also during the warm year suggesting deeper and more dispersed prey. In addition to foraging in the Columbia River plume, murres sought out other low saline water masses in the Salish Sea and waters with cooler ocean temperatures along continental slope habitat.
Results from this study advance the current understanding of murre space-use in the NCCS and provide insight into the flexible movement patterns of non-breeding murres associated with a large breeding colony on the central Oregon coast. Use of the waters off Vancouver Island, the Salish Sea, and the central and south coast of Washington was important throughout seasons and over several years. These regions served multiple purposes for murres such as foraging during their flightless, molting period and refuge during poor ocean conditions. These findings provide marine spatial planners with important information on regional habitat use of a marine predator during contrasting years of average and anomalously warm ocean conditions.