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Abstract

The Marbled Murrelet Brachyramphus marmoratus breeds and overwinters along the coast of British Columbia, Canada, and is listed as Threatened under the Canadian Species at Risk Act. Understanding population trends for this seabird species is important for management and recovery, yet long-term time-series data for Marbled Murrelet abundance are rare. We update trends and annual fluctuations of Marbled Murrelet numbers derived from at-sea counts in Laskeek Bay, Haida Gwaii, on the north coast of British Columbia, 1990–2020. We found a non-significant negative trend (−1.55% per year). Counts varied seasonally and peaked in early June; counts also varied with distance from shore, with the highest numbers occurring within 1 km of shore. Importantly, a change in survey protocol after 1996, which reduced the transect width from 400 m to 100 m, resulted in lower counts, and we found that counts were 2.7 times greater when wider transects were surveyed. Inter-annual fluctuations in counts were high, but we found no significant relationships between bird counts and either large-scale oceanographic cycles or more localized indicators of ocean productivity. Compared to previous analyses of this dataset, which showed strong declines, the absence of a trend in at-sea counts is more in line with trends derived from systematic radar counts conducted within the Haida Gwaii conservation region over a similar period (−2.8% per year). Our study emphasizes the need to investigate fluctuations in at-sea counts more closely to understand what may be driving peaks in at-sea counts, including possible movement of birds between regions.

DOI

http://doi.org/10.5038/2074-1235.52.1.1568

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52_1_141-147_Appendix1.pdf (320 kB)
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