Marbled Murrelets prefer stratified waters close to freshwater inputs in Haida Gwaii, British Columbia, Canada

Abstract

The Marbled Murrelet (Brachyramphus marmoratus) is a small seabird that is currently listed as threatened in Canada. Understanding this species’ marine habitat preferences plays a vital role in our ability to focus conservation planning. We used the longest-running at-sea survey dataset available in British Columbia to examine hotspot persistence and habitat use at Laskeek Bay, Haida Gwaii, BC. The Laskeek Bay Conservation Society has been conducting spring and summer surveys along fixed transect routes in open and shoreline waters from 1997 to 2018. Along with analyzing this long-term dataset, we conducted surveys to measure oceanographic variables (2018–2019) and tested whether Marbled Murrelets in the same area used prey and oceanographic information to select marine habitat in conjunction with physical habitat features. Our hotspot persistence map, defined as areas that repeatedly had counts above a 75% threshold relative to other areas during a given survey, showed that murrelets consistently preferred shoreline transects. Murrelets also preferred shallow marine areas closer to streams, above higher proportions of sandy substrate and closer proximity to abundant nesting habitat. Modeling weather and time variables contributed little additional predictive power. Nonetheless, models that included physical environmental, oceanographic, and prey variables outperformed those with only physical environmental variables. Stratified water was the oceanographic variable most strongly related to higher counts. Our study suggests that stratified waters could work with stream systems to create productive zones for foraging murrelets, and highlights the importance of murrelets having access to marine areas with the preferred physical features.

Considerations for a threatened seabird: The impact of shoreline avian predators on at‐sea marbled murrelets

“…We video‐recorded sonar output, which was subsequently processed using Reefmaster 2.0 software (Reefmaster Software Ltd, West Sussex, United Kingdom). We defined a fish school as a free‐floating cloud composed of 10 or more individuals located within 100 meters of one another (Pastran et al 2021).…”

“…The shoreline has long stretches of rocky cliffs interspersed with beaches. The nearshore waters ranged from 2‒52 m in depth, with a bottom containing a mix of fine and coarse grain sand and rocky sediments (Pastran et al 2021). Murrelets have consistently been reported in these nearshore waters, during summer months, since 1997 (Pastran et al 2021).…”

“…In a habitat suitability model study conducted along the Washington and California coast,Lorenz et al 2016 found murrelets up to 2.9 km from shore, with an average distance of ~840 m. Another study byHébert and Golightly (2008), also based in California, found the average distance from shore was around 1.4 km. Murrelets at Laskeek Bay have consistently been observed at high frequencies within 200 m from shore(Pastran et al 2021).F I G U R E 6 A. Conditional relationships between real eagle counts, kite status, and the predicted marbled murrelet counts along the coastal waters of Louise Island, Haida Gwaii, BC, Canada.…”