RESIGHT SURVEYS FOR STELLER SEA LIONS IN
CALIFORNIA, WASHINGTON AND BRITISH COLUMBIA, 2002-2008.
Patrick J. Gearin
NOAA, AFSC, National marine Mammal Laboratory
7600 Sand Point Way NE, Seattle, WA 98115
The Steller sea lion, Eumetopias jubatus
, is a listed species under the U.S. Endangered Species Act (ESA). The species is recognized to form two separate genetically isolated stocks; the western stock which is west of Cape Suckling, Alaska at 144˚ W and the eastern stock which is east of 144˚ W (NMFS, 2005). The western stock is listed as endangered under the ESA and the eastern stock is listed as threatened. The Steller Sea Lion Recovery Team recommended in 2000 that researchers begin branding and marking Steller sea lion pups throughout their range as a means to estimate vital population parameters in the future. Population parameters such as survival, age at first reproduction, and natality are important factors to understand population dynamics and gauge the health and stability of populations. Specific rookery sites were chosen to initiate these long term marking studies, both in the western and eastern stocks. For the eastern stock, three rookery sites were chosen in southeast Alaska (Forrester, Hazy and White Sisters) and 2 were chosen further south off southern Oregon and northern California (Rogue Reef and St. George Reef). Steller pup branding and marking in southeast Alaska is conducted by the Alaska Department of Fish and Wildlife. Branding at the southern rookeries in California and Oregon is conducted by the National Marine Mammal Laboratory (NMML) and the Oregon Department of Fish and Wildlife (ODF&W). The marking plan called for branding up to 200 pups every other year at the rookery sites followed by intensive resight surveys to record the presence and distribution of marked pups.
NMML and ODF&W began branding and marking Steller pups at Rogue Reef, Oregon in July 2001. Resight surveys began in Oregon and Washington in 2001. The process of determining survival rates requires frequent surveys for marked Steller sea lions in California, Oregon, Washington and British Columbia, where animals disperse to after the summer breeding season. In Oregon, resight surveys were conducted by ODF&W by vessel, shore and with the use of remote video cameras (Seemore Wildlife) deployed at Rogue Reef. In Washington, NMML conducted Steller resight surveys by vessel, primarily along the northern Washington coast. At St. George Reef, remote video cameras were installed at Southwest Seal Rock to record branded sea lions. In British Columbia, some preliminary surveys in 2002-2004 conducted by DFO and the University of British Columbia recorded a few Steller brands throughout the province and most were observed along the southwest coast of Vancouver Island. In the summer and fall of 2005, Steller sea lion surveys were initiated off SW Vancouver Island, Canada, in cooperation with the Department of Fisheries and Oceans, Canada (DFO). These surveys yielded important information regarding the distribution, relative abundance and frequency of sightings of marked sea lions from the Oregon and California rookery sites. Over 65 different individually branded Steller sea lions were observed and photographed during the 2005 surveys. NMML continued these survey efforts in 2006-2008 and contracted with local Canadian vessel operators and biological observers to conduct Steller sea lion brand resight surveys at selected sites off SW Vancouver Island. Few Steller brands were recorded at Southwest Seal Rock from 2002 – 2005 with the use of remote video cameras because of mechanical failures of the camera system. NMML and ODF&W decided therefore to initiate vessel surveys off St. George Reef in 2006. NMML contracted with Humboldt State University (HSU) in 2006 -2008 to conduct 6-7 Steller sea lion surveys at St. George Reef during the summer months from June – September. In 2007 and 2008, these surveys were extended further south to Patrick’s Point to scan for branded sea lions at Reading Rock and Otter Rock. Shore surveys were also conducted by HSU students in 2007 and 2008 at other coastal haul out sites used by Steller sea lions in northern California.
The two sites chosen to mark Steller pups were Pyramid Rock at Rogue Reef, Oregon and Southwest Seal Rock at St. George Reef in northern California. These sites are the largest Steller sea lion rookeries in the lower forty eight states. Steller sea lion pups were branded along the left flank. Sea lions branded at Rogue Reef, Oregon have a letter R following the numbered digit (i.e. 25R). Sea lions branded at St. George Reef in California have a letter Y following the brand number. All Steller pups were tagged on both front flippers with white plastic all-flex tags. The tag numbers match the brand numbers. In 2005, a special study was conducted at Rogue Reef to investigate branding mortality (Scordino, 2005). As part of this study, only 100 Steller pups were branded at Rogue Reef in 2005 and 80 more were tagged but not branded. The 80 tagged pups were used as a control group to compare survival to 80 branded pups which were marked on the same day. Although these tagged pups are more difficult to identify than the branded pups, many of them have subsequently been observed throughout the Pacific Northwest from 2005-2007. These resights will also be reported in this report. A total of 955 Steller pups have been branded and tagged at Rogue Reef and St. George Reef from 2001-2007, and 80 pups were tagged only on both front flippers at Rogue Reef in 2005 (Table 1).
Table 1. Steller pup cohorts branded at Rogue Reef and St. George Reef from 2001-2007.
General survey protocols and data collection
|| Brand sequence
|| Rogue Reef
|| 1R– 179R
|| St. George Reef
|| 1Y – 140 Y
|| Rogue Reef
|| 180R – 370R
|| St. George Reef
|| 141Y – 291Y
|| Rogue Reef
|| 371R – 470R
|| Plus tags 1-80
|| No permit
|| Rogue Reef
|| 471R – 663R
Brand resight vessel surveys require at least two people to conduct, one to operate the vessel and one to photograph and record data. Sea lions are counted from a distance of 100 m when the haul out site is first approached. The sea lions are then scanned carefully before closer approach with binoculars to note branded and tagged animals. Each site may take several hours to survey depending on sea lion abundance and location. Branded and or tagged Steller sea lions with R or Y letter designations were recorded and photographed whenever possible. Photographs were taken with a digital camera so that images could be stored for later evaluation and transmission. Resight data collected for each tagged/branded sea lion include; date, time, location, observer(s) photo record, general behavior/association with other animals and a brand quality index for each digit. Females with pups are noted.
Survey effort in Northern California
NMML contracted with Humboldt State University in the summers of 2006 – 2008 to conduct surveys for Steller sea lions in northern California. In 2006, NMML contracted HSU to conduct 5 vessel surveys at St. George Reef from July through September at three selected sites including; Southwest Seal Rock, North Seal Rock, and Castle Rock. In 2007, NMML contracted HSU to conduct 7 vessel surveys off St. George Reef and 10 shore surveys at several offshore haul outs north of Arcata, California. The shore surveys focused at haul out sites near Patrick’s Point including Reading Rock, Otter Rock, and Palmer’s Point.
Survey effort in British Columbia
The earliest Steller resights for the Rogue Reef or St. George Reef cohorts in British Columbia were in 2003 from a joint survey cruise by DFO and UBC which surveyed most of the known Steller rookery and haul out sites in the province. These survey cruises were continued from 2004-2006 and these resight data were sent to NMML by Peter Olesiuk of DFO and Andrew Trites of UBC.
NMML contracted with Canadian biologists and observers to conduct surveys off southwest Vancouver Island from 2005-2008. Six primary sites were surveyed during the studies including (from south to north) Carmanah Point, Pachena Point, Folger Island, Wouwer/Batley Islands, Mara Rocks, and Long Beach Rocks. The survey areas are not rookery sites but are only seasonal haul out sites. Some of these sites are seasonal in nature so the sampling regime attempted to survey during periods of maximum sea lion abundance. The plan was to survey each site five times between July 1 and November 30, each year. Surveys were spaced at intervals of at least two weeks. Pachena Point, Folger Island, and Wouwer Island are seasonal sites which have low abundance until at least September so they were not surveyed during July and August unless local information indicated they were present.
Additional sites surveyed less frequently in 2006 -2008 included Juan Perez Island (Estevan Point) and Berryman Point in Clayoquot Sound. In addition to the contracted surveys in 2005-2008, additional survey effort was conducted opportunistically by observers around Vancouver Island. The opportunistic effort includes surveys near Norris Rocks on the east side of Vancouver Island in the winters of 2004 -2006. A few brand resights were also collected from Race Rocks, an ecological reserve to the southwest of Victoria B.C. Sightings from Race Rocks were collected by whale watch vessel operators or refuge rangers and reported to NMML.
NMML received additional resight data in February 2009 from Rod Palm who operates the Strawberry Isle Research group in Clayoquot Sound near Tofino. These resights and confirming photographs were collected near coastal haul out sites around Clayoquot Sound.