Robin F. Brown

ASSESSMENT OF HARBOR SEAL PREDATION ON ADULT SALMONIDS IN A PACIFIC NORTHWEST ESTUARY

The populations of many native species have increased or expanded in distribution in recent decades, sometimes with negative consequences to sympatric native species that are rarer or less adaptable to anthropogenic changes to the environment. An example of this phenomenon from the Pacific Northwest is predation by locally abundant pinnipeds (seals and sea lions) on threatened, endangered, or otherwise depleted salmonid (Oncorhynchus spp.) populations. We used survey sampling methodology, acoustic telemetry, and molecular genetics to quantify the amount of harbor seal (Phoca vitulina) predation on a depressed run of coho salmon (O. kisutch) and to determine whether some seals consumed a disproportionately higher number of salmonids than others. Based on a probability sample totaling 759.5 h of observation, we estimated that seals consumed 1161 adult salmonids (95% CI = 503-1818 salmonids) during daylight hours over an 18.9-km estuarine study area in Oregon during an 84-d period in fall 2002. Simultaneous tracking of 56 seals via an acoustic telemetry array indicated that a small proportion of marked seals (12.5%) exhibited behavior that was consistent with specialization on salmonids. These seals spent the majority of their time in the riverine portion of the study area and did so disproportionately more at night than day. Genetic analysis of 116 salmonid structures recovered from 11 seal fecal samples suggested that coho salmon accounted for approximately one-half of total salmonid consumption. Though subject to considerable uncertainty, the combined results lead us to infer that seals consumed 21% (range = 3-63%) of the estimated prespawning population of coho salmon. We speculate that the majority of the predation occurred upriver, at night, and was done by a relatively small proportion of the local seal population. Understanding the extent and nature of pinniped predation can provide important inputs into risk assessments and other modeling efforts designed to aid the conservation and recovery of salmonids in the Pacific Northwest. Such understanding may also help inform management actions designed to reduce the impact of pinniped predation on salmonids, which potentially range from short-term lethal removal programs to long-term ecosystem restoration and protection efforts.

Abundance and Distribution of Harbor Seals (Phoca vitulina) in Oregon, 1975-1983

Harbor seals were observed on 32 haulout sites in Oregon during aerial counts conducted from 1975 to 1983; 90% were seen on 14 sites. The greatest number of seals seen on a haulout was 985 recorded at Cape Arago in July 1982. Counts of harbor seals in 1982 and 1983 were 38.6% greater than counts from 1975 to 1980. These data indicate an increase in numbers of harbor seals in Oregon, an increase corroborated by other information, namely, lower counts made before 1975 and increased use of new haulout sites since 1975. Between 1975 and 1983, numbers within bays increased, whereas numbers on most offshore rocks remained somewhat constant. Decreased harassment and mortality since implementation of the Marine Mammal Protection Act of 1972 doubtless allowed harbor seals to increase in numbers and to reoccupy protected haulout sites in bays. The harbor seal (Phoca vitulina richardsi) is one of five pinniped species common in Oregon. It is the most abundant and ubiquitous pinniped in the state, found in most bays and estuaries, and on many offshore rocks. Harbor seal abundance has been determined at specific haulout sites along the Oregon coast (Graybill 1981; Brown and Mate 1983; Roffe and Mate 1984; Bayer 1985), although there is only one published account of their state-wide distribution and abundance (Pearson and Verts 1970). From 1967 to 1968, Pearson and Verts (1970) conducted four counts from land and one aerial count along the Oregon coast and concluded that there were fewer than 500 harbor seals in the state. More than 3800 harbor seals were killed in Oregon between 1925 and 1972 by statehired and bounty hunters (Pearson 1969). Harbor seals were harassed at inshore areas where they rested and pupped, and their number in Oregon was probably reduced. Harassment and killing of harbor seals were greatly reduced after 1972 when the Marine Mammal Protection Act became effective. Protection probably has resulted in an increase in abundance and redistribution of animals into bays and estuaries. The objectives of this study were to determine the location and use of haulout sites and to document any changes in abundance and distribution of harbor seals in Oregon from 1975 to 1983. METHODS Aerial photographic surveys of seals on land along the entire Oregon coast were performed annually from a high-winged, single-engine aircraft (Cessna 172 or 182) during 1 month in the summer (June, July, or August) from 1975 to 1983 (Fig. 1). Surveys were begun approximately 2 hr before low tide and ended approximately 2 hr after low tide to maximize the number of seals visible on haulout sites (Schneider and Payne 1983; Terhune and Almon 1983). The entire Oregon coastline was scanned during annual surveys to determine locations of harbor seals ashore and to locate new haulout sites. When more than five seals were ashore, the group was photographed from an altitude of 215-305 m using a hand-held 35 mm camera and 300 mm or 70 to 210 mm zoom lens. Photographs were taken within 15° of vertical. Photographic images of seals on land were projected onto a white surface, and each seal was counted. Photographic surveys required 2 days; flights were made from Newport to the north or south on consecutive days. Surveys of some haulout sites were not possible because of inclement weather.

ANTIBODIES TO MARINE CALICIVIRUSES IN THE STELLER SEA LION (EUMETOPIAS JUBATUS SCHREBER)

Sera from 145 Steller sea lions (76 adults, three subadults, 37 pups, and 29 fetuses) were tested for neutralizing antibodies to nine marine calicivirus serotypes. Antibodies were found to San Miguel sea lion virus (SMSV) types 1, 5, 6, 7, 8, 10 and 13, and to Tillamook (bovine) calicivirus, but no antibodies were found to the walrus calicivirus. Titers (microtiter neutralization assay) ranged from 1:20 to 1:320, with many positive reactions at the higher dilutions (≥1:80). Antibodies to SMSVs 5 and 10 were most common among animals sampled in Alaskan waters, while antibodies to SMSV-6 were most common among pups from the southern Oregon coast. These data provide evidence that Steller sea lions, like their California sea lion (Zalophus c. californianus Lesson) counterparts, have experienced widespread exposure to multiple serotypes of marine caliciviruses.

Movements of Male California Sea Lions Captured in the Columbia River

Abstract There is growing concern in the Pacific Northwest over predation by migratory male California sea lions (Zalophus californianus) on threatened and endangered salmonid (Onchorynchus spp.) stocks. We compared movements of 14 male California sea lions known to have previously consumed salmonids at Bonneville Dam on the Columbia River or Willamette Falls on the Willamette River (“river”-types), with 12 animals of unknown foraging history (“unknown”-types). We captured sea lions in the Columbia River and instrumented them with satellite-linked transmitters during 2003–2004, 2004–2005, and 2006–2007. Transmitters operated for an average of 87.9 d (range 23-200 d) resulting in 14,539 location fixes. All 14 river-type animals returned to either Bonneville Dam or Willamette Falls whereas none of the 12 unknown-types exhibited this behavior. Minimum upstream and downstream transit times between the mouth of the Columbia River and Bonneville Dam (210 rkm) were 1.9 d and 1 d. Duration at the dam ranged from 2 d to 43 d. The median start dates of the southbound migration from the Columbia River to the breeding grounds for river-type and unknown-type sea lions were 20 May and 15 June, respectively. The maximum travel speed during migration was approximately 130 km d-1 (5.4 km h-1). Our results clearly show that not all California sea lions in the Columbia River prey on salmonids at Bonneville Dam or Willamette Falls. However, factors influencing recruitment into the upriver salmonid-foraging subpopulation are unknown.

Isolation of reptilian calicivirus Crotalus type 1 from feral pinnipeds.

Ten virus isolates were obtained from three species of marine mammals sampled on San Miguel Island (California, USA) and 1,200 km north on Rogue Reef (Oregon, USA) during tagging operations in 1986–87. Seven of these 10 were derived from 30 sampled Steller sea lion (Eumetopias jubatus pups, while two of 10 were isolated from one of 19 sampled California sea lion (Zalophus californianus californianus pups, and the remaining isolate was derived from 30 sampled northern fur seal (Callorhinus ursinus) pups. All 10 isolates were identified as belonging to a single serotype, reptilian calicivirus Crotalus type 1 (RCV Cro-1), previously isolated from both healthy and diseased snakes and frogs in a California zoologie collection. The marine samples also showed that nine of 30 Steller sea lion pups, one of 19 California sea lion pups and zero of 30 fur seal pups were producing type specific neutralizing antibodies to RCV Cro-1. This represents the first reported instance of the isolation from marine sources of a calicivirus originally isolated from a terrestrial species.

An Outbreak of Probable Leptospirosis in California Sea Lions along the Oregon Coast during Fall 1984

California sea lions (Zalophus californianus) experience periodic outbreaks of the bacterial disease leptospirosis causing death and debilitation. In fall 1984, an outbreak of presumed leptospirosis occurred during the northward migration of male California sea lions. The assumption that Leptospira bacterium was present was strengthened by positive serology and demonstration of organisms using silver staining techniques in the kidneys of three animals from Oregon. Systematic beach surveys and reports of dead and debilitated sea lions on beaches were used to estimate the mortality of Zalophus during their northward migration off Oregon. From August 1984 to February 1985, 252 male Zalophus ranging in age from 2 to 13 years were found dead on the beaches of Oregon. The number of animals found dead represent approximately 15% of the total animals seen on haul-out sites during peak northern migration off Oregon. California sea lions, Zalophus californianus, breed annually during June and July off Mexico and southern California (Odell 1981). After the breeding season, males migrate north along the coasts of California, Oregon, Washington, and British Columbia (Mate 1975; Antonelis and Fiscus 1980; Bigg 1985). Off Oregon, peak numbers of male California sea lions occur in September, and decline throughout winter as animals move farther north (Mate 1975; Graybill 1981; Brown 1988). In fall 1984, unusually large numbers of dead and sick California sea lions were reported along the coasts of northern California, Oregon and Washington. A report from northern California indicated many California sea lions were dying of an infection of the bacterium Leptospira serovar pomona (Dierauf et al. 1985). A similar die-off of Z. californianus during the 1970 northern migration was attributed to Leptospira interrogans pomona (Vedros et al. 1971). Animals infected with Leptospira bacteria display clinical signs, including reluctance to use hind limbs and rear quarters due to pain from interstitial nephritis, and a tendency, because of thirst, to seek fresh water sources such as streams and sloughs (Vedros et al. 1971). This latter symptom causes animals to come ashore at pasturelands, upstream areas, and at stream outlets on sandy beach areas where they are not normally seen. This paper confirms the presence of Leptospira-like bacteria in sick and dead Z. californianus collected in Oregon. We report the numbers of dead Z. californianus found in Oregon during fall-winter 1984-1985 and ages of 43 of these individuals.

Survival rates of Steller sea lions from Oregon and California

Due to significant population declines in the 1970s and 1980s, Steller sea lions (Eumetopias jubatus) were listed as threatened under the U.S. Endangered Species Act in 1990, and subsequently partitioned in 1997 into an endangered western stock and a threatened eastern stock. We estimated survival rates from a mark-recapture study of 7 eastern stock cohorts marked as pups in California and Oregon from 2001 to 2009 (n = 1,154 pups) and resighted range-wide from 2002 to 2013. First-year survival rates were among the lowest found for Steller sea lions thus far, averaging 0.46 (range 0.21–0.72) for females and 0.44 (0.21–0.68) for males; yearling survival rates, however, were among the highest, averaging 0.85 for females and 0.81 for males. Low pup and high yearling rates offset each other, however, so that cumulative survival rates to age 4, averaging 0.33 for females and 0.27 for males, were similar to those found in studies from Alaska and Russia. While range-limit effects and environmental variation may be related to the low and variable pup survival rates we found, populations in Oregon and California nonetheless continued to grow, which contributed to delisting of the eastern stock in 2013. Continued monitoring and incorporation of new information on vital rates into regional population models will help inform post-delisting monitoring for the eastern stock of Steller sea lions.