DOI: 10.5066/f75b01rw
title: Annual Marbled Murrelet Abundance and Productivity Surveys Off Central California (Zone 6), 1999-2021 (ver. 4.0, May 2022)

description: 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, recorded the observation time, angle off of the transect line, and the distance to all groups of Marbled Murrelets detected. A GPS waypoint and view conditions for each murrelet observation were recorded during 1999-2016, and the vessel paused briefly to collect this information. In 2017-present, ocean and view conditions were updated as they changed along the survey and were appended to murrelet observations, along with location from a GPS track, based on matching time; the vessel only paused occasionally to confirm murrelet age-class if necessary. Observers counted Marbled Murrelets as a group when individuals were within 2 m of each other, or if they exhibited behavior indicative of group affiliation (e.g. co-diving, vocalizing with one another; Strong et al. 1995). Observers recorded age-class of each Marbled Murrelet based on three plumage classifications: after-hatch-year (AHY), hatch-year (HY), or unknown and behavior was noted. The vessel occasionally paused or deviated from transect to properly identify Marbled Murrelet age-class; no additional observations were counted during these deviations. The definitions of original behavior codes were confirmed with previous PI's, but were not standardized or consolidated. Flying birds were only counted if they crossed the beam of the vessel; however, these observations were recorded differently over the years. For example, during earlier years, distance to flying birds was supposedly only estimated when flying birds actually crossed the beam (90 degree angle) and this appears to be generally, but not exclusively, true. In later years, flying birds were given a distance and unique angle estimate when they were first detected. In addition to using line-transect methods to count Marbled Murrelets, during 2007-present, observers also used strip-transect methods to count all animal species sighted within a 150-m strip (75-m on each side of the boat), except in 2007 when strip width was 100 m (50-m on each side of the boat). These observations were given a time that could be used to locate the observation using a GPS-track after the survey. Observers recorded all observation data into digital voice recorders; additional data included information on survey start and end times, ocean conditions, viewing conditions, and time periods when effort was paused for any reason (e.g. vessel paused or deviated from transect to identify Marbled Murrelet age-class). The latter effort/conditions observations were consistently recorded in 2017-present, inconsistently from 2007-2016, and infrequently recorded during 1999-2003. Observers reviewed their own recordings and transcribed and tabulated their sighting data into a single spreadsheet that was examined for QAQC and merged into a combined spreadsheet. A GPS track was acquired during most surveys using a handheld GPS unit during 2007-present, but not during 1999-2003. GPS tracks from 2017-present were cleaned to include only on-effort time periods using well-documented effort observations. GPS tracks from 2007-2016 were plotted and cleaned manually using limited effort observations (trimmed to start and end times, off-effort deviations removed) and after visual inspection, obvious deviations from survey routes were manually screened and removed. Some pre-2017 GPS tracks also contained large gaps due to GPS malfunction; these gaps were interpolated when possible by using observer recordings of route waypoint passage times. GPS tracks were used to geo-reference all observations (2017-present) and strip-transect non-murrelet observations and effort/conditions observations (pre-2017) based on nearest matching date/time (waypoints were collected for pre-2017 MAMU observations). Matches were direct for 2017-present data because the GPS track was collected at a 1-s interval; time matches for pre-2017 data typically were within 30 s (equivalent to less than 200 m potential error based on typical survey speeds). To facilitate replication of historical abundance estimates and allow future re-analysis of survey data, we compiled observation and effort information from all 1999-present standardized zig-zag surveys into a single database. Pre-2017 data were provided by previous principal investigators (Henry, Henkel, Peery, and Becker). We identified all completed surveys conducted during this time period and created a final database consisting of four tables linked by a unique SurveyID for each completed survey: 1. Survey Metadata Table: General information for unique surveys, including date, personnel, vessel, general conditions/notes, and what components (2-4, listed below) exist for each survey. 2. Observations Table: MAMU sightings, non-MAMU sightings, and Effort/Conditions changes recorded by observers were combined in a single table. These data all represent time-based information recorded while surveying. Observation locations are derived from the MAMU observation waypoints (pre-2017) or from GPS tracks (non-MAMU observations pre-2017 and all observations in 2017-present). 3. Survey Routes Table: Existing Survey Routes for all surveys were compiled into a single table consisting of ordered waypoint locations. Routes were spatially cross-referenced with murrelet observations to verify correct route identification. 4. Survey Tracks Table: Existing Survey Tracks for all surveys were compiled into a single table of time and location information. Tracks were cleaned for 2017-present using effort observations (trimmed to start and end times, off-effort deviations removed) and conditions were annotated to all track points. GPS tracks from 2007-2016 were cleaned manually using limited effort observations (trimmed to start and end times, off-effort deviations removed), and after visual inspection, obvious deviations from survey routes were removed. Some pre-2017 GPS tracks also contained large gaps due to GPS malfunction; these gaps were interpolated when possible using observer recordings of route waypoint passage times. Infrequent view conditions observations (viewing conditions, beaufort) were not appended to pre-2017 tracks. The 2017 data in this database support the following U.S. Geological Survey Data Series: Felis, J.J., Adams, J., and Kelsey, E.C., 2018, Abundance and productivity of marbled murrelets (Brachyramphus marmoratus) off central California during the 2017 breeding season: U.S. Geological Survey Data Series 1093, 12 p., https://doi.org/10.3133/ds1093. The 2018 data in this database support the following U.S. Geological Survey Data Series: Felis, J.J., Kelsey, E.C., and Adams, J., 2019, Abundance and productivity of marbled murrelets (Brachyramphus marmoratus) off central California during the 2018 breeding season: U.S. Geological Survey Data Series 1107, 10 p., https://doi.org/10.3133/ds1107. The 2019 data in this database support the following U.S. Geological Survey Data Series: Felis, J.J., Kelsey, E.C., Adams, J., Horton, C., and White, L., 2020, Abundance and productivity of marbled murrelets (Brachyramphus marmoratus) off central California during the 2019 breeding season: U.S. Geological Survey Data Series 1123, 13 p., https://doi.org/10.3133/ds1123. The 2020 and 2021 data in this database support the following U.S. Geological Survey Data Series: Felis, J.J., Adams, J., Horton, C.A., Kelsey, E.C., and White, L.M., 2022, Abundance and productivity of Marbled Murrelets (Brachyramphus marmoratus) off central California during the 2020 and 2021 breeding seasons: U.S. Geological Data Report 1157, 12 p., https://doi.org/10.3133/dr1157. In addition, the data in this database support reports and publications that used pre-2017 data (Becker and Beissinger 2003, Henkel and Peery 2008, Henry et al. 2012, Henry 2017, Henry and Tyler 2017, Peery et al. 2006, Peery et al. 2008, Peery and Henry 2010). References: Becker, B.H., Beissinger, S.R. and Carter, H.R. 1997. At sea density monitoring of Marbled Murrelets in central California: Methodological considerations. Condor: 743-755. Becker, B.H., and S.R. Beissinger. 2003. Scale-dependent habitat selection by a nearshore seabird, the Marbled Murrelet, in a highly dynamic upwelling system. Marine Ecology Progress Series 256: 243-255. Buckland, S.T., E.A. Rexstad, T.A. Marques, C.S. Oedekoven. 2015. Distance Sampling: Methods and Applications. Springer International Publishing, Cham, Switzerland. Henkel, L.A. and M.Z. Peery. 2008. Abundance and productivity of Marbled Murrelets off central California during the 2007 breeding season. Moss Landing Marine Laboratories, Moss Landing, CA. Henry, R.W. 2017.Murrelet at-sea abundance, productivity, and prey resources in Zone 6. In P. Halbert and S.W. Singer [Eds.] Marbled Murrelet Landscape Management Plan for Zone 6. Felton, CA: California Department of Parks and Recreation, 235 pp. Henry, R.W., W.B. Tyler, and M.Z. Peery. 2012. Abundance and productivity of Marbled Murrelets off Central California during the 2010 and 2011 breeding seasons. California State Parks, Half Moon Bay, CA. Henry, R.W., and W.B. Tyler. 2017. Abundance and productivity of Marbled Murrelets off central California during the 2013-2016 breeding seasons. University of California Santa Cruz, Santa Cruz, CA. Peery, M.Z., B.H. Becker, and S.R. Beissinger. 2006. Combining demographic and count-based approaches to identify source-sink dynamics of a threatened seabird. Ecological Applications 16: 1516-1528. Peery, M.Z., L.A. Hall, J.T. Harvey, and L.A. Henkel. 2008. Abundance and productivity of Marbled Murrelets off central California during the 2008 breeding season. Moss Landing Marine Laboratories, Moss Landing, CA. Peery, M.Z., and R.W. Henry. 2010. Abundance and productivity of Marbled Murrelets off central California during the 2009 breeding season. Moss Landing Marine Laboratories, Moss Landing, CA.