The Northwest Forest Plan (NWFP) is an ecosystem management plan for federal lands in the U.S. Pacific Northwest. To evaluate the NWFP’s effectiveness at conserving the marbled murrelet (Brachyramphus marmoratus), we estimated murrelet abundance at sea annually from 2000 to 2018 in inshore marine waters associated with the NWFP area. We divided this area of coastal waters into five geographic subareas corresponding with conservation zones established in the U.S. Fish and Wildlife Service’s recovery plan for the marbled murrelet. We used line transect distance estimation methods to account for detectability. Our abundance estimate for the planwide area in 2017 was about 23,000 murrelets. We did not find evidence for a linear trend for the overall NWFP area (0.3 percent per year). At the state scale, we found strong evidence for a declining linear trend in Washington (-3.9 percent per year). For Oregon, we found strong evidence for an increasing linear trend (2.0 percent per year). In California, we found strong evidence for an increasing linear trend (4.5 percent per year). At the individual conservation zone scale, we found strong evidence for a linear decline in Conservation Zone 1 (-4.9 percent per year), some evidence for a negative trend in Conservation Zone 2 (-3.0 percent per year, some evidence for positive linear trend in Conservation Zone 3 (1.4 percent per year), and strong evidence for a linear increase in Conservation Zone 4 (3.7 percent per year). Because of the extreme variability associated with the trend in Conservation Zone 5 (7.3 percent annual rate of change; 95 percent confidence interval: -4.4 to 20.3 percent, years 2000 to 2017), we concluded that there was no evidence for a trend in that conservation zone. These results indicate a pattern of decreasing at-sea abundance in the northern part of the plan area and increasing abundance to the south. We have no definitive explanation for this north-south pattern; however, one potential explanation might be the emigration of birds from other areas of the species’ range. A large-scale “marine heatwave” influenced the California Current during 2014–2016, which may have influenced distribution of murrelets, though the mechanism for this change in distribution is not yet clear. These at-sea population monitoring results indicate that the NWFP goal to stabilize and increase marbled murrelet population sizes has not yet been achieved.
McIver, William R.; Pearson, Scott F.; Strong, Craig; Lance, Monique M.; Baldwin, Jim; Lynch, Deanna; Raphael, Martin G.; Young, Richard D.; Johnson, Nels. 2021. Status and trend of marbled murrelet populations in the Northwest Forest Plan area, 2000 to 2018. Gen. Tech. Rep. PNW-GTR-996. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 37 p.