Wildlife Research and Management - Wildlife Research
Date Published: March 10, 2009
Number of Pages: 24
Author(s): Monique M. Lance, Scott F. Pearson (WDFW) and Martin G. Raphael, Thomas D. Bloxton, Jr. (USDA Forest Service)
The Marbled Murrelet was listed as a Threatened species in California, Oregon and Washington in 1992 by U.S. Fish and Wildlife Service. 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 and the information derived from this effort is the only information available to assess population size and trends in this geographic area. This monitoring program uses at-sea line transects within 8 km of the Washington, Oregon, and northern California coastline in the area covered by 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 the Pacific Northwest Research Station, U.S.D.A. Forest Service; Zone 2 includes the Washington outer cost and is monitored by Washington Department of Fish and Wildlife. Within Zone 2 there are two geographic strata based on marbled murrelet density: Stratum 1 (north of Pt. Grenville – high density) and Stratum 2 (south of Pt. Grenville – low density). Each stratum is divided into primary sampling units (PSUs), which is a roughly rectangular area along approximately 20 km of coastline. In 2008, at-sea survey effort began 19 May and ended 28 July, and PSUs were accessed from four ports along the Washington coast. By design, all PSUs in Stratum 1 were sampled three times. All PSUs in Stratum 2 were sampled once. A fourth survey of PSU 3 and a second survey of PSU 10 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 1 July (n = 114), which spans the region between Kalaloch and the Raft River. This is consistent with 2007 when we observed 145 marbled murrelets in PSU 7 on 14 June. 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 2008; 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 in 2008 was 17,791 (95% confidence interval 14,631 – 20,952). The population estimate has ranged from 17,354 – 23,673 over the 9 years of monitoring. The population estimate for the Washington coast for 2008 (Zone 2) was 1,944 birds (95% confidence interval = 1,187 - 2,843 birds). In Zone 2, density and population size estimates for 2008 appeared to decline relative to the previous 6 years of monitoring with the most notable apparent declines occurring in Stratum 2. However, Zone 2 population estimates were even lower in 2000 and 2001. 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 2008 was 4,699 birds (95% confidence interval = 3,132 - 6,201 birds).
Lance, M.M., S.F. Pearson, M.G. Raphael, and T. D. Bloxton, Jr. 2009. 2008 at-sea marbled murrelet population monitoring: Research Progress Report. Washington Department of Fish and Wildlife, Wildlife Science Division, Olympia, WA. 17 pp.