Publications

Determining the impact of pinnipeds on the U.S. West Coast ecosystems is a complex assessment involving separating the effects of other predators (including commercial, sport, and tribal fishers), predator and prey population dynamics, disease, and changes in environment. Because California sea lions and harbor seals are opportunistic predators, their food habits change dramatically over areas, seasons, and years in response to changes in abundance and availability of their prey. These ecological interactions are complicated, and at this time there is insufficient information to evaluate whether pinniped predation influences prey populations in most situations. Consumption estimates require information on predators, including an age/sex structured model of seasonal distribution; energetic requirements based on mass and reproductive condition; annual, seasonal, and geographic variation in the percent (by weight) of prey in diet; and average energy density of prey. Statistical models to quantify the impact of pinnipeds on prey have been proposed for the interactions of Cape fur seals and hake in the Benguela Current, gray seals and cod in the North Atlantic, and harp seals and cod and capelin in eastern Canada. The problems encountered in these studies which cause bias in consumption estimates include variation in annual and seasonal proportion of prey in diet and changes in energetic costs. It is also difficult to assess the impact of predation on prey dynamics without understanding the interaction of other predators and other sources of natural mortality. Because of these constraints, the Working Group limited consideration of potential ecosystem impacts to annual biomass consumption estimates for harbor seals and sea lions, socioeconomic implications of pinniped interactions with commercial and sport fisheries, and pinniped interactions with other human activities.

To derive overall annual consumption estimates, the Working Group made the following assumptions: the currently available pinniped population structure and abundance estimates are accurate, average size of different age and sex groups within the population are known, allometric scaling of energy requirements (i.e., consumption rates for large animals are lower than for small animals) from Innis et al. (1987) and Olesiuk (1993) are adequate to estimate biomass consumption, and available data on prey are representative. No assumptions were made regarding caloric density of prey, although it may have important effects on prey selection.

Estimates of annual biomass consumption for California sea lions along the U.S. West Coast are sketchy. Coastwide consumption calculations for sea lions are complicated because different age classes are present on different parts of the coast for varying amounts of time during the year. Adult and subadult males migrate from southern California northward into Oregon, Washington, and British Columbia for 9-10 months of the year, while adult females, juveniles, and pups remain in southern California waters year-round. Additional complexities are differing energy requirements depending on size and reproductive condition and inadequate year-round abundance data for sea lions north of southern California. The Working Group therefore could not calculate a coastwide estimate of annual consumption by California sea lions, but instead estimated biomass consumption for areas where limited data were available. A minimum biomass consumption estimate for California sea lions is 147,191 t coastwide based on the sum of the areas shown in Table 3.

For Puget Sound, the Working Group adopted the National Marine Mammal Laboratory (NMML 1996) estimate of biomass consumption, which used monthly mean population counts of sea lions and a consumption rate based on the average weight of sea lions present and seasonal energetic requirements. NMML (1996) estimated the average biomass consumed each year by California sea lions in Puget Sound between 1986 and 1994 was 830 t (Table 3). Because of an increased number of sea lions present in Puget Sound in 1995, NMML (1996) calculated a separate estimate of annual food consumption by California sea lions in Puget Sound of 2,064 t for 1995. The differences in these estimates for Puget Sound demonstrate the variability in these types of estimates based on annual or seasonal changes in pinniped abundance.

For the Lower Columbia River, the Working Group estimated an annual biomass consumption of 390 t for the sea lions that haul-out seasonally in this area (Table 3). The calculation was based on the average abundance of sea lions between January and June 1991-93.

For the Oregon coast, the Working Group estimated that California sea lions have consumed 5,287 t annually over the past 10 years (Table 3). This estimate was developed using coastwide abundance surveys conducted from 1985 to 1994 (ODFW unpubl. data). The mean of annual peak counts from September of each year was applied to a seasonal abundance profile prepared from monthly surveys conducted in 1984-85. Individual animal weights were estimated to average 180 kg for the months of August through December and 278 kg for the months of January through June, incorporating male weight increases during the winter foraging period (NMFS-AFSC unpubl. data). Monthly consumption estimates were totaled over the 11-month period (August-June) when California sea lions are present in Oregon coastal waters.

In California, complete seasonal sea lion abundance data are available only for the southern part of the state. The Working Group estimated that the annual biomass consumed by California sea lions in the southern California Bight is 140,684 t (Table 3) based on females, weaned pups, juveniles, and subadult males (adult males were excluded because they do not feed during the short time they are on the rookeries). Consumption rates of lactating females were increased by a factor of 1.6 based on estimates of the increased energetic cost of lactation (Perez and Mooney 1986, Oftedal et al. 1987, Costa and Gentry 1986). Other assumptions included 1) the number of females equals the number of pups (36,184 pups in 1994 (Barlow et al. 1995)) divided by 0.70 (based on natality rates of 70%), 2) lactation period is 6 months following birth (a conservative estimate as some do not wean until as late as 11 months of age), and 3) average mass of females is 95 kg (based upon weights of 17 females captured at San Miguel Island between 1993 and 1995).

Few estimates of harbor seal annual consumption exist in the literature. Harvey (1987) addressed the question of total consumption of fish and of particular prey species by harbor seals in Oregon based on relative abundance of prey species eaten by harbor seals from studies by Graybill (1981), Brown and Mate (1983), Roffe and Mate (1983), and Beach et al. (1985). Based on size (weight) data from live capture of harbor seals in Oregon, daily dietary requirements from Innis et al. (1987), and an estimated harbor seal population in Oregon in 1980 of about 5,000 animals, Harvey (1987) estimated that the total annual biomass consumed by harbor seals was 5,667 t. Harvey (1987) estimated that salmonids comprised less than 1% of the fish consumed, but accounted for 11% (613 t) of the total biomass.

The Working Group estimated annual food consumption by harbor seals using a bioenergetics model integrating data on abundance, sex and age structure, and feeding rates. To derive the consumption estimates, the Working Group assumed the harbor seal population has a stable age distribution and divided it into four age/sex categories: juvenile (0-1 year), subadult (1-4 year), adult female (5+ year), and adult male (5+ year). The proportion of each of these groups in the population was estimated to be 26% juvenile, 17% subadult, 31% adult female, and 26% adult male based on life tables (Bigg 1969, Pitcher and Calkins 1979). Mean weights for each age/sex category were calculated from 627 harbor seals captured in Washington, Oregon, and California (WDFW and ODFW unpubl. data). Population abundance data were from Huber et al. (1993) for Oregon, from Huber (1995) for Washington, and from Hanan (1996) for California. The correction factor for population counts was 1.53 for Washington and Oregon (Huber 1995) and 1.4 for California (Boveng 1988). The Working Group modified the consumption rate equations of Innis et al. (1987) to account for free-ranging seals as proposed by Olesiuk (1993). Table 4 shows the biomass consumption for harbor seals by area in each state. The coastwide estimated total is 70,174 t of biomass consumed annually with 31,495 t in Washington, 8,535 t in Oregon, and 30,142 t in California (Table 4).

The Working Group did not attempt to extrapolate these overall biomass consumption estimates to individual species. However, the Working Group noted that Brown et al. (1989) estimated harbor seal consumption of eulachon, which is the primary prey of harbor seals in the Columbia River during the winter when eulachon are present in large numbers. Brown et al. (1989) examined stomachs of harbor seals killed incidentally in the winter salmon gillnet fishery from 1986 to 1988 and found 97% of the prey eaten during the sampling period was eulachon. Using the age and weight distribution of harbor seals in this area, Brown et al. (1989) estimated that 2,100 harbor seals would consume 335 t of eulachon during January and February in the Columbia River; the pinniped consumption is about 26% of the commercial catch of eulachon in 1988 in the Columbia River and tributaries (WDFW and ODFW 1996). Although Brown et al. (1989) had to make certain assumptions in developing their estimate of prey consumption by seals, the more restrictive time and area of the study and the clear dominance of eulachon in the diet during winter months probably reduces the error in their estimate.

Based on the consumption estimates above for harbor seals (70,174 t) and California sea lions (minimum 147,191 t), a minimum total of about 217,000 t is consumed by these two pinniped populations annually. This compares to a total of about 460,100 t harvested in the commercial fisheries off Washington, Oregon, and California in 1995 (NMFS 1996b). These consumption estimates indicate the large quantity of prey removed from the coastal marine food web by California sea lions and harbor seals. Caveats about interpretation remain. Because food habits of pinnipeds vary seasonally and by location, assuming that the consumption patterns derived from studies in a specific area are representative of all areas during all seasons is incorrect. Extrapolating the impact of predation on individual fish species to a larger area is of questionable value because of the errors and biases introduced by too many assumptions.

The Working Group found very few studies that addressed comparative food habits data from both California sea lions and Pacific harbor seals from the same area, same season, and same years. At Everett in northern Puget Sound, Pacific whiting and Pacific herring were the most frequently found prey in samples from both California sea lions and harbor seals (NMML 1996). Both pinnipeds also preyed on market squid (NMML 1996). The major differences between the diets of the two predators appear to be the absence of dogfish in the harbor seal diet and the higher prevalence of salmonids in the diet of sea lions. Salmonid remains occurred in only 2% of harbor seal scats but were found in 15% of sea lion scats. The harbor seal scats contained remains only from adult salmonids, while the sea lion samples contained remains of adult salmonids, jacks, and smolt in nearly equal numbers (NMML 1996). Hanson (1993) found that California sea lions and harbor seals differed in their ability to capture free-swimming salmonids. California sea lions had much better success rates in catching adult salmonids at the mouth of the Russian River (capture rate of 0.52 fish/hour for sea lions compared to 0.27 fish/hour for seals).

Pacific whiting in Puget Sound is an example of a principal prey of both sea lions and harbor seals in the same area. Schmitt et al. (1994) reported declines in all groundfish stocks (including Pacific whiting) in Puget Sound between 1983 and 1993. Pacific whiting aggregate and spawn near Everett (in the Port Susan area) during the winter at the same time that California sea lion males are present. In a recent review, Schmitt et al. (1995) generated estimates of prey consumption by California sea lions in Puget Sound based upon food habits data collected from 1986 through 1988. Pacific whiting was the principal prey species, occurring in 67% of the samples (NMML 1996). The prey samples were analyzed to estimate the total mass of each prey species consumed in the diet, so that a proportion of the biomass consumed could be assigned to each species. Schmitt et al. (1995) estimated that male sea lions consumed 286-573 t of Pacific whiting per year, based on a consumption rate of 5-10% of body mass each day. Gearin et al. (1995) revised this estimate using consumption rates based on allometric relationships of mass to consumption (Innis et al. 1987), arriving at a consumption estimate of 266 t of Pacific whiting. This consumption estimate equates to 5.5% of the average spawning biomass of 4,862 t of Pacific whiting in the Port Susan area. Schmitt et al. (1995) speculated that this level of predation, combined with a commercial harvest utilization rate in excess of 20% of the estimated spawning stock and significant but as yet unquantified levels of harbor seal predation, may have contributed to the decline of the Pacific whiting stock. Due to low abundance, the commercial fishery was closed in 1988. It is unknown whether sea lion and seal predation may now be restricting the recovery of the Pacific whiting stock in Puget Sound or if sea lions in Puget Sound continue to utilize Pacific whiting as winter food to the same extent that they did in the late 1980s.

Harbor seals and California sea lions interact with almost all commercial fisheries on the West Coast. Because pinniped mortalities due to entanglement in fishing gear do not appear to have had any negative effects on the increase in seal or sea lion populations, the principal concerns are damage to catch and gear and potential indirect impacts on the fish stocks. The loss in catch and gear is most severe in salmonid gillnet and salmon troll fisheries (NMFS 1992). Fish caught in gear are removed or damaged by pinnipeds, causing direct loss of income to the fishers. Bait is taken out of traps and off hooks, making the gear ineffective. Fishing gear is damaged, making it "unfishable," especially in the case of California sea lions tearing through salmonid gillnets.

West Coast Salmon Troll Fishery

Miller et al. (1983) conducted a comprehensive study of marine mammal-fishery interactions in California waters in 1979-80 and reported that the commercial-salmon troll fishery had the highest rate of salmon depredation by pinnipeds, with an estimated loss of 12,459 legal-sized salmon (about 1% of the catch) to California sea lions in 1980. Beeson and Hanan (1996) reported a much greater incidence of California sea lion predation in the 1995 commercial-salmon troll fisheries; an estimated 86,700 salmon (legal- and sub-legal-sized salmon) were removed from troll gear during the fishery, which caught an estimated 734,800 (legal- and sub-legal-sized) salmon off California. Beeson and Hanan (1996) determined that this predation is about 12% of what the troll fishery caught, and estimated the commercial value of the sea lion removals at $1.73 million. Increased losses of troll-caught salmon to sea lions have also been reported off the Oregon coast.

Washington Salmonid Gillnet Fisheries

Harbor seals and California sea lions interact with salmonid gillnet fisheries throughout Puget Sound (NMFS 1992). Tribal biologists have noted considerable loss of catch to pinnipeds in the Green River, Duwamish River, and lower Nisqually River. Pinnipeds have damaged up to 12% of yearly catches from the tribal set-net fishery in the Neah Bay area (Gearin et al. 1989). California sea lions interact with tribal set-net fisheries for coho and steelhead in the Lake Washington Ship Canal, and substantial losses of steelhead from gillnets have been observed (Gearin et al. 1988a, 1988b, Pfeifer et al. 1989).

Columbia River/Grays Harbor/Willapa Bay Salmon Gillnet Fisheries

Damage to salmon in the gillnet fisheries in the Columbia River, Grays Harbor, and Willapa Bay was recorded during observer programs in 1980-82 and 1991-93. In the Columbia River, the incidence of damage was comparable between the two studies except for a high damage rate in winter 1993, which may have been due to a record-low catch (Scordino 1993). In Grays Harbor, approximately 7-23% of chinook salmon caught each season had been damaged by pinnipeds. In Willapa Bay, the range was about 4-14% per season. The variation in rates is attributable to the annual variation in catch; as the catch decreases, the proportion of damaged fish increases.

California Tribal Salmon Gillnet Fishery

In the Klamath River in 1981 and 1982, Herder (1983) monitored the tribal-subsistence salmon gillnet fishery and estimated a depredation rate on salmonids of 13.2% due to harbor seals. Harbor seals were found to consume 3.6% and 7.9% of the chinook salmon, coho salmon, and steelhead released from a seining-tagging operation in 1981 and 1982 respectively. Herder (1983) found that even though the nearby harbor seal population was 150-200 animals, only 7 harbor seals per day were responsible for the salmonid gillnet fishery depredation. All depredation during more than 700 hours of gillnet fishing observations were by harbor seals; no California sea lions were observed taking salmonids from the nets even though salmonids were present in California sea lion scat samples from this area.

California Set-Net and Drift Gillnet Fisheries for Halibut, Seabass, and Swordfish/Sharks

In 1980, Miller et al. (1983) reported the highest pinniped depredation rate in the California gillnet fisheries occurred in the California halibut and white seabass set-net fisheries off southern California, where pinnipeds depredated 10% of the catch. In contrast, the white croaker, Pacific bonito, and flying fish gillnet fisheries experienced a depredation rate of less than 2%. Data collected in 1995 by CDFG show nearly the same situation of sea lions and harbor seals primarily depredating catch in the California halibut, white seabass, and barracuda gillnet fisheries (Beeson and Hanan 1996). There are also reports of pinniped depredation in gillnet fisheries that target mackerel, Pacific bonito, rockfish, shark, and swordfish.

From July 1990 to July 1994, NMFS observers monitored 60,967 set-net sets (mostly targeting on California halibut). Pinniped depredation was reported in 19% of the observed sets. During the 1993-94 white seabass season, fisher logbooks indicated 20% of the fishing days had "fish lost to pinnipeds" (Beeson and Hanan 1996). In the 1994-95 season, there was a reported loss in this fishery in 12% of the fishing days. Commercial fishers report that pinnipeds can damage 10-30% of the catch daily, a monetary loss of approximately $50-75 per day, or $3,000-4,000 for a season (Beeson and Hanan 1996). Because of the implementation of restrictions on the use of set-nets in California waters, fishing effort in the halibut set-net fishery has declined substantially over the past 5 years, from more than 7,000 days of effort and more than 200 boats in 1990 to less than 2,000 days of effort and 40 boats in 1994 (Beeson and Hanan 1996). According to commercial gillnet fishers, depredation rates and gear damage have increased over the past 5 years for boats that remain in the fishery. Many fishers have reported to CDFG that they are being "put out of business" by continual pinniped depredations and related loss of income. Commercial fishers also report that pinniped depredation is more intense during El Niño periods.

Miller et al. (1983) found that sea lions depredated more than 1% of the swordfish catch in the shark-swordfish gillnet fishery in 1981. From July 1990 to July 1994, NMFS observers in this fishery documented that 250 (2.5%) of the total observed drift gillnet sets (9,892 sets) sustained pinniped depredation. In addition to depredation of catch, sea lions and harbor seals damage gillnet gear. Miller et al. (1983) estimated the total value of fish removed by pinnipeds and gear loss in California gillnet fisheries was $121,000 in 1980. Today, fishers claim that individual gear damage and catch loss in gillnet fisheries range from $1,000 to $20,000 annually.

In addition to commercial gillnets, sea lions also depredated CDFG gillnets used for a striped bass tagging study in the Bay-Delta (Dave Kohlhorst, CDFG, 1416 9th St., Sacramento, CA 95814. Pers. commun., April 1996). Sea lions removed 100 striped bass from the gillnets over a 10-day period, as far as 60 miles inland from the San Francisco Bay Bridge.

California Herring Gillnet Fishery

Pacific herring are fished during the winter spawning season (November to March) in San Francisco Bay, Tomales Bay, Humboldt Bay, and Crescent City. Both California sea lions and Pacific harbor seals interact and depredate catch in this fishery. Miller et al. (1983) reported that foraging activities by sea lions and harbor seals in San Francisco Bay usually involved only one to four animals per net. Total depredation of catch was less than 1% for both the 1979-80 and 1980-81 seasons. In recent years, according to one Humboldt Bay herring fisher, depredation has increased because of increased numbers of both harbor seals and sea lions. Sea lions are the main cause of gear damage (Beeson and Hanan 1996).

Puget Sound Salmon Net-Pen Facilities

NMFS has received many reports of both harbor seals and California sea lions damaging salmonids in net-pens. Although pinnipeds normally cannot access whole fish through the net-pen webbing, they can bite and kill fish through the webbing and then consume the parts of the fish. In some instances, net-pens have been ripped open by California sea lions, allowing salmon in the pen to escape. The extent of predation problems in this fishery depends upon the type of pens used and the size of fish in the pen. Net-pens made of flexible materials allow predation by pinnipeds, while solid net-pens prevent pinnipeds from catching the fish (P. Dorn, Suquamish Tribe, P.O. Box 498, Suquamish, WA 98392. Pers. commun., July 1995). Net-pens that contain larger fish are reportedly more likely to be the target of pinniped predation (M. Huff, Port Gamble S'Klallam Tribe, 31974 Little Boston Road, Kingston, WA 98346. Pers. commun., July 1995). One net-pen facility in Puget Sound recorded 71,449 salmon damaged by California sea lions from October 1995 to June 1996 (R. Safford, Global Aqua, 9507 NE South Beach Drive, Bainbridge Island, WA 98110. Pers. commun., February 1997). In spite of an investment of more than $200,000 in predator nets, California sea lions were still finding access to the net-pens. The salmon lost to sea lions during this period accounted for 4-5% of production at harvest, with a value of $1.67 million based on a weight of 3.6-4.5 kg per salmon at production and a sales price of about $5.72/kg. The facility reports that it is incurring additional costs of $60,000-$70,000 per year due to the sea lions for divers to repair nets and remove killed fish from pens, and firecrackers used in attempt to deter sea lions from pens (S. McKnight, Global Aqua, 9507 NE South Beach Drive, Bainbridge Island, WA 98110. Pers. commun., February 1997).

Tillapaugh et al. (1991) reported that seal attacks on salmonid farms in British Columbia annually cost fish farmers an estimated $4 million (Canadian) in lost revenues due to fish kill and escapes. In addition, from 1989 to the summer of 1991, B.C. fish farmers spent an estimated $2 million in direct costs for anti-seal nets and technology (Tillapaugh et al. 1991). Rueggeberg and Booth (1989) also surveyed salmonid farmers in British Columbia to estimate the impact of pinnipeds on the net-pen fishery. About 25% of the farmers surveyed reported losing fish to harbor seal and sea lion predation, totaling 61,000 salmonids. They also reported losing approximately 44,000 fish to holes in net-pens created by harbor seals, sea lions, or river otters. If this is representative of the entire industry, Rueggeberg and Booth (1989) estimate that the fishery lost 101,700 fish per year to harbor seal and sea lion predation and 61,600 fish to net damage by pinnipeds or river otters, or approximately 1% of total production.

California Live Bait Operations

California sea lions have been known to haul-out on bait barges, where they prey on the bait, scare the bait, and block the operator's access to the barge. One bait barge operator reported losing 50% of the bait overnight to sea lions (Beeson and Hannan 1996). Some bait-pen operators have installed chain-link fences on top of the barges and nets around the outside of the pens to keep sea lions from accessing the barge or the pens.

California Round-Haul Fisheries

California sea lions and harbor seals interact with the round-haul herring fishery and the purse seine fisheries for squid, sardine, and mackerel by foraging in the nets and frightening fish out of the net (Miller et al. 1983). Round-haul nets currently cost about $30,000 each, and sea lions have been observed "chewing" portions of the net. In the round-haul herring fishery, only sea lions were involved in depredations (Miller et al.1983).

Trap Fisheries

Lobster, crab, and live-fish trap fishers report that California sea lions frequently destroy their traps. Miller et al. (1983) did not report any pinniped interaction or depredation in the trap fisheries. However, sea lions are now reported to open traps to remove the bait (sea lions do not prey on the trapped lobsters or crab) and destroy the traps (Beeson and Hanan 1996). These interactions are most prominent in the San Diego area, although there are also reports from Ventura and Santa Barbara fishers. California sea lions also have been reported to remove bait and damage Dungeness crab pots in Puget Sound in recent years.

Other Commercial Fisheries

Other commercial fisheries with pinniped interactions and depredations include the non-salmon hook-and-line and trawl fisheries. Miller et al. (1983) reported that 517 kg of rockfish, about 1% of the total catch, were depredated by sea lions in the southern California hook-and-line fishery. There is little current information on sea lions depredating hook-and-line fisheries. One fisher described sea lions depredating mackerel used to bait a shark set-line, while another mentioned sea lions depredating mackerel caught for the fresh-fish market (Beeson and Hannan 1996). Miller et al. (1983) reported sea lions removing fish in the cod end of trawl nets, although no current data exist. In Elkhorn Slough, Oxman (1995) found that harbor seals competed with commercial fisheries for four species: white croaker, sanddab, lingcod, and English sole.

Interactions between pinnipeds and sport fishers have been reported coastwide. In Washington and Oregon, both harbor seals and sea lions are known to remove salmonids from sport hook-and-line gear (NMFS 1992). In the Columbia River, most of the interactions occur during the spring chinook fisheries in the lower mainstem, at the mouths of tributaries, and in the Willamette River when California sea lions are most abundant. There is little documentation of the extent of this interaction and no estimates of economic losses attributable to pinnipeds. However, in recent years, state fisheries agencies have received increased reports of pinnipeds removing salmonids from fishing gear in coastal waters, inshore bays and estuaries, and inriver fisheries. Sport fishers in some areas have reported that if California sea lions are within 100 m of a fish when hooked, a sea lion will take the fish before it can be landed (Chuck Tracy, WDFW, Columbia River Anadromous Fisheries Division, 16118 NE 219th St., P.O. Box 999, Battleground, WA 98604. Pers. commun., October 1995). In the spring of 1994, interviews of sport anglers by Huber et al. (1995a) in the Lewis River (tributary of the Columbia River) indicated that fishers experienced frequent predation of hooked fish by California sea lions, although only a small number of sea lions were present.

In many bays in Oregon, successful sport crabbing from boats or docks, using crab rings or pots, has been severely impacted or eliminated because California sea lions steal crab bait and destroy gear. Harbor seals also occasionally steal bait from crab rings.

Interactions between sport fisheries and pinnipeds have been documented extensively in California, where pinniped depredation of salmonids caught by sport fishers occurs both in rivers and in the ocean. Pinniped feeding rates on hooked salmonids in the Klamath River in the 1960s, 1970s, and 1980s were less than 1% (Herder 1983). In the ocean fisheries in the Monterey Bay area in 1969, sea lions removed about 4% of the fish caught by commercial and sport fishing vessels (Briggs and Davis 1972). The overall loss rate for ocean sport anglers was less than 1% in 1980, but large numbers of juvenile California sea lions removed as much as 17% of the hooked salmonids in Monterey Bay between February and April (Miller et al. 1983).

Studies conducted by CDFG show increased rates of predation by pinnipeds on salmonids caught in the charterboat and private skiff fishery in 1994 and 1995 (Beeson and Hanan 1996). In 1995, ocean salmonid sport landings were greatest in Monterey and San Francisco. Monterey also had the highest depredation rates (number of sea lion takes relative to total angler landings) during March (21%), April (27%), and September (19%), coinciding with the male sea lion spring and fall migrations. In the Monterey area during April, sea lions took an estimated 11,900 salmonids from angler lines, 43% of the total number of salmonids taken in the Monterey sport fishery for the 1995 season (charterboat and private skiff combined). Statewide, anglers landed an estimated 498,600 salmonids, while an estimated total of 27,900 salmonids were lost to sea lions (5.3% of total hooked).

In southern California, sport fishing is a $536-million business (Thompson and Crooke 1991). Since at least 1979, more pinniped interactions in the non-salmonid sport fishery occurred in southern California, especially near San Diego, than any other area (Miller et al. 1983, Hanan et al. 1989). Sea lions directly affect charterboat fishing by consuming bait and chum and depredating hooked fish. Miller et al. (1983) found that fewer fish were caught by charterboats when a sea lion was present. Consequently, when sea lions are present, skippers frequently move the boats to other fishing areas, resulting in additional fuel costs and loss of fishing time.

Sea lion interactions with charterboat fisheries and depredation of catch occur throughout the year in southern California (Beeson and Hanan 1996). For the first seven months of 1995, 14% of all non-salmonid trips were depredated by sea lions (1,414 depredated trips out of 10,042 total trips). A depredated trip was defined as a charterboat trip with at least one fish reported taken by sea lions. In comparison, in central/northern California, less than 2% of the non-salmonid trips were depredated by sea lions (55 depredated trips out of 2,939 total trips). The majority of depredations involved California barracuda in nearshore coastal waters in the Los Angeles and San Diego areas.

In 1979 and 1980, Miller et al. (1983) reported that there were no pinniped interactions with charterboat trips in California north of Avila (San Luis Obispo County), and depredation was rare except in the San Diego area. In 1980, the total annual loss from depredation by California sea lions in southern California was estimated at 15,141 non-salmonids that had a fresh-fish market value of $28,100; Pacific bonito comprised 78% of this loss. Beeson and Hanan (1996) analyzed the charterboat fishing logs, statewide, for January through July 1995, and found that 26,138 non-salmonids were taken by pinnipeds. Of this total, 97% were taken in southern California and had a fresh-fish market value exceeding $145,200; California barracuda comprised 59% of this loss.

In 1994, the San Diego charterboat fleet experienced sea lion depredations throughout the year, ranging from 7% in February to a high of 38% in April (number of depredated trips relative to the total number of trips). The highest percentage of depredated trips occurred in March through May. California barracuda were taken most often by sea lions, although rockfish, mackerel, kelp, and barred sand bass were also taken (Beeson and Hanan 1996).

Hanan et al. (1989) found interaction and depredation rates for charterboat fisheries in the San Diego area decreased in spring and early summer, and increased in mid-summer. They attributed this seasonal trend to sea lions congregating in the Channel Islands for the breeding season. Hanan et al. (1989) found that the interaction and depredation rates declined following an El Niño event, and suggested that the reason was a reduced number of available fish.

Another potential impact of expanding pinniped populations on the coastal ecosystems is contamination of shellfish beds. In the 1980s, high concentrations of fecal coliform at the Dosewallips River in Hood Canal, Washington, resulted in the closure of commercially and recreationally harvested shellfish beds to protect the health of the public. The contamination was determined to be caused by the feces of large numbers of harbor seals that used the area as a haul-out (Calambokidis et al. 1989, Calambokidis and McLaughlin 1988). To alleviate the contamination problem, a fence was built to prevent seals from hauling-out near shellfish beds, and a raft was built in deeper water as an alternative haul-out site for the seals. At present, the Dosewallips shellfish beds are partially open to commercial and recreational use (K. Anderson, Puget Sound Water Quality Action Team, P.O. Box 40900, Olympia, WA 98504-0900. Pers. commun., July 1995). The partial closure remaining at Dosewallips River is due to contamination from both agriculture and seals.

The Working Group found that only 1 site of the 77 commercial shellfish beds in Washington was closed because of high coliform counts caused by seals. In Quilcene Bay, Henderson Inlet, Belfair State Park, Port Gamble Bay, and other Hood Canal areas, human and domestic animal sewage appears to be a more widespread cause of contamination than harbor seals (Anderson, pers. commun., July 1995). Nevertheless, oyster growers in Grays Harbor, Willapa Bay, and Hood Canal have expressed concern that fecal coliform contamination from increasing pinniped populations may cause future shellfish closures in Washington. Similar pinniped contamination concerns have been raised at commercial oyster aquaculture sites in Tillamook and Yaquina Bays in Oregon, but no studies have addressed the concern.

Since passage of the MMPA, seals and sea lions have been afforded protection from disturbance, harassment, and killing, thereby allowing them to occupy areas from which they would have been removed in the past. The result has been direct conflict between pinniped and human use at public and private beaches, public marinas, and private docks, and involves landowners, vessel operators, and beachgoers.

Pinniped interactions with humans also have expanded into the freshwater environment as pinniped occurrence in bays and upriver has increased. California sea lions have been observed more than 145 miles up the Columbia River at the Bonneville Dam and have interacted with sport fishers throughout the river. In the Willamette River, California sea lions haul-out on docks in the Portland, Oregon metropolitan area and prey on spring chinook and steelhead at the fishway at the Willamette Falls. Reports of California sea lions occurring far inland from the ocean are increasing in other areas such as the Nisqually River and Chehalis River in Washington and up the San Francisco Bay Delta as far inland as Antioch.

The Working Group found that the most frequently reported pinniped conflicts with humans are encounters on docks, marinas, and public beaches. In California, reports of problems with sea lions and harbor seals have been received from harbors in Humboldt Bay, Noyo River, San Francisco Bay, Santa Cruz, Monterey Bay, Redondo Beach, and San Diego. In Washington and Oregon, problems with California sea lions are commonly reported in harbors in Puget Sound, Washington, and in Astoria and Yaquina Bay, Oregon. Most problems reported are caused by California sea lions hauling-out on docks and boats. California sea lions have prevented owners from accessing their boats, boats have been fouled, and the weight of animals has damaged docks and small boats. Some small boats reportedly have sunk from the weight of the animals. Fishers at Cape Arago in Oregon frequently report California sea lions jumping onto their vessels and stealing bait. Sea lions also have been reported to have bitten people carrying fish and taken fish laid out on docks. The number of California sea lions hauled-out on Pier 39 in San Francisco increased from 6 to nearly 500 between 1990 and 1994, with a high of 627 in 1991. The City of San Francisco finally "gave up" the pier to the sea lions, as animals reacted aggressively when humans attempted to remove them, and it is now a tourist attraction.

Another indirect effect of increasing pinniped populations on human safety is the possibility of an increase in the number of large sharks that prey on pinnipeds . Although there have been a number of media reports that increased attacks on humans by the great white shark (Carcharodon carcharias) are related to an increase in the shark populations caused by increased numbers of pinnipeds in coastal areas, the Working Group found little scientific information on this issue. McCosker and Lea (1996) report that the majority of shark attacks on humans have occurred at or near the surface, near shore, and in the vicinity of pinniped colonies and/or river mouths. Recent information on changes in shark abundance and distribution resulting from the increased populations of pinnipeds comes from studies by Pyle et al. (1996) at the Farallon Islands. At the Farallon Islands, increased attacks on pinnipeds between 1987 and 1993 are attributed to increased numbers of white sharks in the area; prior to that, increased numbers of attacks were attributed to increased populations of elephant seals and sea lions (Pyle et al. 1996).

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