교육데이터 활용•지원 서비스

Since 2017, U.S. Geological Survey, Western Ecological Research Center (USGS WERC) partnered with California State Parks to continue long-term, annual at-sea surveys to estimate at-sea abundance and juvenile (i.e. hatch-year) productivity of Marbled Murrelets (Brachyramphus marmoratus) in U.S. Fish and Wildlife Service Conservation Zone 6 (central California: San Francisco Bay to Monterey Bay). Marbled Murrelets have been listed as Endangered by the State of California and Threatened by the U.S. Fish and Wildlife Service since 1992. Marbled Murrelets have been surveyed at sea off central California since 1995 (Becker et al. 1997), and standardized surveys to estimate abundance and productivity have been conducted since 1999 (excluding 2004-2006; Henkel and Peery 2008, Peery et al. 2009, Peery and Henry 2010, Henry et al. 2012, Henry et al. 2013, Henry 2017, Henry et al. 2017). In addition to continuing annual surveys, USGS WERC worked with collaborators to compile a single database that included all survey effort and observation data to facilitate future analysis. All existing standardized survey observations and effort information from 1999-present are included in this database. Survey methods and database creation are summarized herein. More detailed information is available in the metadata for each data table in the database. Historically, survey routes were designed as continuous, approximately 100 kilometer (km) zig-zag transect lines to sample nearshore (200-1350 meter [m] from coast) and offshore (1350-2500 m from coast) strata, with approximately three-times greater survey effort within the nearshore stratum to accommodate greater Marbled Murrelet densities known to occur nearshore (see Henry 2017 and references therein). Survey routes originally were drawn starting at a random distance (up to 2500 m) from shore, and an equal number of routes were drawn using starting points at the north and south ends of the survey area. Even though surveys (with very few exceptions) were conducted from north to south, survey routes drawn from the south resulted in a greater amount of habitat surveyed in south-facing, leeward bays which often had greater relative abundances of Marbled Murrelets. In contrast, survey routes drawn from the north resulted in a greater amount of habitat surveyed in more exposed, west- or north-facing stretches of the coast (Henry 2017). A pool of randomly drawn routes, drawn from both the north and the south, were originally created between 1999 and 2003. All subsequent annual survey routes have been randomly selected from this pool, mostly without intra-annual replication; therefore, annual survey routes included approximately half drawn from the south and half drawn from the north. Almost all surveys were conducted by following the selected route from north (Pillar Point Harbor, Half Moon Bay) to south (Soquel Point, Monterey Bay) using a GPS. Most surveys were completed in a single day, although several surveys during 1999-2001 were conducted during two consecutive days. When the survey route intersected land or crossed hazardous areas (e.g. extreme nearshore areas or the passage between Ano Nuevo Island and the mainland), effort was maintained while safely navigating to the next transect segment. Surveys were almost exclusively conducted during the morning through early afternoon when view conditions were excellent or good. Surveys were conducted from a small boat using line-transect methods (Becker et al. 1997, Peery et al. 2006, Buckland et al. 2015, Henry 2017). Vessels used included a 4-m inflatable skiff (1999-2003) and several similar 6-m skiffs (2007-present). Prior to each survey, observers calibrated distance estimation using a laser rangefinder on buoys in the harbor or with buoys towed at known distances. In 2017-2019, marks were placed along the bow of the boat in 10-degree increments to facilitate estimations of sighting angles. Two observers, standing on either side of an open skiff,