Wildlife Research and Management - Wildlife Research
Date Published: January 2007
Number of Pages: 24
Author(s): Monique M. Lance and Scott F. Pearson
The Marbled Murrelet was listed as a Threatened species in California, Oregon and Washington in 1992. A recovery plan was published in 1997 that outlined recovery strategies including developing and conducting standardized at-sea surveys. Along with federal and state researchers, Washington Department of Fish and Wildlife has participated in a program to estimate marbled murrelet population size and trends since 2000. This monitoring program uses at-sea line transects within 8 km of the Washington, Oregon, and northern California coastline in the area of the Northwest Forest Plan. There are two zones in Washington. Zone 1 includes the Strait of Juan de Fuca, Hood Canal and the San Juan Islands and is monitored by U.S. Forest Service Pacific Northwest Research Station. Washington Department of Fish and Wildlife has been responsible for monitoring the outer Washington coast (Zone 2), which is one of five designated Conservation Zones. Within Zone 2 there are two geographic strata based on marbled murrelet density: Stratum 1 (north coast ¡V high density) and Statum 2 (south coast ¡V low density). Each stratum is divided into primary sampling units (PSUs), which is a roughly rectangular area along approximately 20 km of coastline. In 2006, at-sea surveys began 16 May and ended 27 July and PSUs were accessed from four ports along the Washington coast. By design, all PSUs in Stratum 1 were sampled three times and PSUs in Stratum 2 were sampled once, except PSU 12, which is located at the mouth of Willapa Bay and was not sampled due to sustained adverse wind and tide conditions.
In Zone 2, highest concentrations of marbled murrelets were observed in PSU 6 located near Destruction Island for the third year in a row; however, high counts were far lower in 2006 (n = 72) than were observed in 2004 (n = 215) and 2005 (n = 90). Numbers of marbled murrelets observed in PSU 7 were lower in 2006, but there were more birds observed in PSU 4 (near the Quileute River in LaPush) than seen in previous years. There were no juvenile (Hatch Year) marbled murrelets observed in 2006; however, this study was designed to monitor breeding birds and not to estimate juvenile recruitment.
For all west coast zones combined, there has been no detectable decrease in the breeding at-sea murrelet population over 7 years of monitoring. When all zones are combined, we have ƒn. 95% percent power of detecting a 5 percent annual decrease within a 9-year sampling period (Miller et al. 2006), but only 7 years of monitoring have been completed. For the Washington outer coast (Zone 2), density and population size estimates for 2006 suggest overall marbled murrelet density was slightly lower in 2006 than in the previous two years, but not as low as the 2000 and 2001 estimates. The population estimate for the Washington coast for 2006 was 2,381 birds (95% confidence interval = 1,672- 3,430 birds). For inland Washington waters, (Zone 1), there is currently no indication of a population decline, but additional years of sampling are needed to have a high power to detect a population decline should one occur (Miller et al. 2006). The population estimate for Zone 1 for 2006 was 5,899 birds (95% confidence interval = 4,013 - 8,208 birds).
Lance, M.M. and S.F. Pearson. 2007. 2006 at-sea Marbled Murrelet population monitoring: Research Progress Report. Washington Department of Fish and Wildlife, Wildlife Science Division, Olympia, WA. 14 pp.