Wildlife Research and Management - Wildlife Research
Date Published: January 2008
Number of Pages: 24
Author(s): Monique M. Lance, Scott F. Pearson (WDFW) and Martin G. Raphael (USDA Forest Service)
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 five monitoring zones throughout this range, two of which are 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. Washington Department of Fish and Wildlife has been responsible for monitoring the outer Washington coast (Zone 2). Within Zone 2 there are two geographic strata based on marbled murrelet density: Stratum 1 (north of Pt. Grenville ¡V high density) and Stratum 2 (south of Pt. Grenville ¡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 2007, at-sea surveys began 15 May and ended 26 July, and PSUs were accessed from four ports along the Washington coast. By design, all PSUs in Stratum 1 were sampled three times, except that PSU 8 was sampled twice. All PSUs in Stratum 2 were sampled once. Only half of PSU 12, which is located at the mouth of Willapa Bay, was sampled due to sustained adverse wind and tide conditions. Because of the difficulty associated with sampling this PSU, the sampling area was reduced to exclude the mouth of Willapa Bay from our 2007 estimate and all past population estimates were also adjusted to account for the reduced area sampled. A second survey of PSU 9 and 11 was conducted to investigate late season marbled murrelet distribution and abundance.
In Zone 2, highest concentrations of marbled murrelets were observed in PSU 7 on 14 June (n = 145), which spans the region between Kalaloch and the Raft River. In previous years, PSU 6 located to the north near Destruction Island contained high counts of marbled murrelets: 2004 (n = 215), 2005 (n = 90), and 2006 (n = 72). There were no juvenile (Hatch Year) marbled murrelets observed in 2007; however, this study was designed to monitor breeding birds and not to estimate juvenile recruitment, which would require extending the sampling period into August.
The marbled murrelet population estimate for all zones in the Northwest Forest Plan area 2007 was 17,400 (95% confidence interval 12,800 ¡V 21,909). The population estimate has ranged from 17,400 ¡V 23,700 over the 8 years of monitoring. Trend analyses indicate that for the 2000-2007 period, the estimated annual rate of population change over the entire sample area was -2.2%, with 95% confidence interval of -5.6% to +1.3% (P = 0.19 for a downward trend). When all zones are combined, we have ƒna ƒn95% percent power of detecting a 5 percent annual change within a 9-year sampling period (Miller et al. 2006), but only 8 years of monitoring have been completed. For the Washington outer coast (Zone 2), density and population size estimates for 2007 suggest overall marbled murrelet density was slightly higher in 2007 than in the previous two years, but lower than 2002 ¡V 2004 estimates. The population estimate for the Washington coast for 2007 was 2,525 birds (95% confidence interval = 1,271 - 3,811 birds). For the inland Washington waters (Zone 1), population size estimates have fluctuated over the sampling period and do not exhibit an increasing or decreasing trend. The population estimate for inland Washington waters for 2007 was 6,985 birds (95% confidence interval = 4,105 - 10,382 birds).
Lance, M.M., S.F. Pearson, and M.G. Raphael. 2008. 2007 at-sea marbled murrelet population monitoring: Research Progress Report. Washington Department of Fish and Wildlife, Wildlife Science Division, Olympia, WA. 24 pp.