NOTE: Project Pacific neither represents nor endorses either position on the harbor seals at Casa Cove/La Jolla Children's Pool in San Diego, CA.  Our own board of directors is so deeply divided on the issue, that we have decided to remain neutral with regard to this controversy.  The purpose of the following  "White Paper" is to educate and inform anyone interested in harbor seals.  The paper also briefly presents a summary of the local San Diego controversy and each position's general perspective on the issue.

White Paper

California's Pacific Harbor Seals       

(with an emphasis on La Jolla, City of San Diego)

by Melissa Studer (May, 2000)

     Figure 1. Pacific harbor seal © 1998 SeaWorld, Inc. All rights reserved.

Table of Contents

I. Introduction

II. Distribution and Identification

III. Behavior

IV. Reproduction

V. General Physiology

VI. Mortality

VII. Population

VIII. La Jolla Seals

IX. Summary and Discussion

X. References

XI. Glossary

XII. Classification

XIII. Related Links

Introduction

This paper provides a general overview of the biology, behavior and population trends of harbor seals (Figure 1). It focuses on the harbor seals of La Jolla, California and the debate over their presence in an area known as the "Children’s Pool." Harbor seals, along with California sea lions and Northern elephant seals, are pinnipeds—all of which are found throughout California, including La Jolla. The harbor seals of La Jolla use the Children’s Pool beach for a "haul-out" site; they are the center of a local controversy. The beach—a man-made structure—has been closed to swimmers for two years, due to bacterial contamination that has been linked to the seals through DNA testing. Though harbor seals are typically "shy" marine mammals when they are ashore, the seals of La Jolla have become accustomed to humans and allow close approaches for a unique view of these marine mammals.

Distribution and Identification

Harbor seals are the most widely distributed among all pinnipeds (seals, sea lions and walruses), inhabiting areas of the North Pacific and North Atlantic oceans. Although there is some debate, scientists generally divide harbor seals into five subspecies (see Appendix for classification; some scientists also recognize Phoca vitulina largha as a subspecies, inhabiting areas of the North Pacific). Each subspecies may be distinguished genetically, behaviorally or geographically. This paper focuses on the P.v. richardsi subspecies, which is distributed from Alaska south to Baja, California (Figure 2).

Harbor seals are often mistaken for California sea lions (and sometimes for young Northern elephant seals—elephant seal pups are about the same size, shape, and may be similar in appearance as adult harbor seals), though there are several differences between the pinnipeds. Some of these differences are outlined in Table 1.

Figure 2. Distribution of harbor seals in the eastern North Pacific (P. v. richardsi)

Table1. Distinguishing characteristics of Pacific pinnipeds.

© 1998 SeaWorld, Inc. All rights reserved.

Behavior

Harbor seals "haul-out" in small to large groups (the average group consists of about 50 animals) for rest, breeding, pupping and molting. They haul-out on sandy beaches (the most popular type of substrate), rocks near shores, sandbars, rocky shorelines, harbors, and piers. Harbor seals prefer haul-out sites that are protected from the wind and waves, and sites that allow for quick access to deep water. Once ashore, they rarely change their location within the haul-out site. Individual seals tend to stay in the same area year round; site fidelity is high, with seals returning to the same haul-out site year after year. Research has also shown that each time seals haul-out, they often occupy the same portion of a rock or beach as their previous haul-out. Also, harbor seals may share their haul-out area with other pinnipeds, such as California sea lions or Northern elephant seals.

Harbor seals are not territorial, though they are considered moderately aggressive when hauled-out. They prefer not to touch each other while ashore, generally keeping about a flipper’s length distance from one another. Young seals tend to stay away from the adults but may interact with one another. Despite the fact that seals congregate in groups while hauled out (and sometimes while in the water), they are considered solitary animals. Seals in the water often behave rather differently than those ashore—swimmers and divers have experienced playful and curious seals. There are accounts of humans being approached by seals and even occasional interaction with them in the water (initiated by the seals), including what appears to be deliberate "touching.

Studies have shown there is a decrease in the numbers of seals hauled-out in the fall and winter (and late summer for the seals in La Jolla). It has also been found that the number of hauled-out seals is affected by human disturbance. Harbor seals are generally considered "shy" animals and avoid human contact. Disturbances (such as noise, being approached by humans, dogs or birds) may cause them to charge into the water with little other provocation. Harbor seals do not migrate, though they are capable of travel over long distances. Occasionally they may move up to 500 km (~300 miles)—this movement is associated with food and breeding activities. In general, they remain close to shore and seldom venture beyond local kelp beds during daylight hours.

Reproduction

Mating takes place after weaning, usually underwater. Harbor seals do not form harems (unlike many other pinnipeds), though males may mate with several females. The gestation period is 9-11 months, including a two-month period of delayed implantation. Pup mortality is about 21% in the first year. Females become sexually mature at 3-6 years old; males at 3-7 years. Studies have demonstrated that males lose up to 25% of their body weight during the mating season, probably because of the fights that ensue with other males during competition for females as well as decreased feeding activity.

Females give birth to a single pup each year; the pups weigh an average of 10-14 kilos (25-30 lbs), or 13-14% of their mother’s body weight (Figure 3). Rare multiple births have been documented. Females may give birth either on land or in the water. Harbor seal pups are well developed at birth—their eyes are open and they begin swimming shortly after birth. Pups are also born with their adult coat. In southern California, the pupping season generally occurs in late spring or early summer. Female harbor seals recognize their pups primarily through vocalizations and somewhat by smell. Nursing takes place for about four weeks, occurring mostly on land and sometimes in the water.


Figure 3. Female harbor seal and pup © 1998 SeaWorld, Inc. All rights reserved.

General Physiology

Harbor seals have a maximum life span of about 25-30 years; males’ life spans are slightly shorter than females (again, possibly because of competition with other males during the mating season). Their age can be determined by examining a section of a tooth and counting the growth layers. Harbor seals possess acute vision and hearing both on land and in the water. Unlike many other pinnipeds, they are not considered sexually dimorphic, which means males and females are similar in size [weighing 70-90kg (150-200 lbs)] and appearance. They have a blunt snout, v-shaped nostrils, and no protruding ears or ear flaps.

Harbor seals can dive up to 300 meters (1,000 feet) in depth and can stay underwater up to 30 minutes; however, an average dive lasts 3-7 minutes at a depth of 17-87 meters (50-300 feet). Seals have several adaptations for diving—for example, their external ear openings close, their heart rate slows and they have a greater volume of blood than other land mammals of similar size, allowing them to retain more oxygen.

Their flippers are covered with hair, fairly short, and have claws. Harbor seals also have a short, flat tail behind their hind-flippers. While swimming their fore-flippers are used for steering, while their hind-flippers are used for propulsion. They move on land by undulating in a "worm-like" motion. When hauled-out and resting, they often possess a characteristic "banana-shaped" profile.

Molting occurs annually in the spring through summer, when harbor seals shed their coat (or "pelage"). It takes about five weeks for a seal to complete its moult. The pattern on their coats varies between individuals, from a dark gray background with light spots or blotches, to a light background with dark spots or blotches, and all variations in between. Harbor seals can be identified by the combination of pattern and coloration on their coats, which is unique to each individual.

The diet of harbor seals varies with season and region; in general they are considered opportunistic feeders. They feed mostly at night on benthic (bottom-dwelling) organisms. Fish make up their main diet [adult harbor seals eat about 1000-2000 kg (1-2 tons) of fish per year], but they also feed on crustaceans, squid, molluscs, and other invertebrates. Adult harbor seals eat about 5-6% of their body weight daily [for example, a 70 kg seal @ 5½ % would consume 1405 kg of prey per year (150 lb seal @ 5½ % @ 3011 lbs/yr)]; they obtain water from the food they consume.

Mortality

During the 19th and 20th centuries, hunting greatly reduced the population of harbor seals—fur traders hunted seal pups for their coats. Later, salmon fishermen also killed harbor seals presumably because of fishing competition. Today, some hunting still occurs among the indigenous Arctic peoples who legally hunt for food and clothing as part of their culture and tradition. In 1938, the State of California protected pinnipeds from uncontrolled hunting and in 1972, the Marine Mammal Protection Act (MMPA) and its various provisions and amendments further protected marine mammals from being killed or harassed [except under special permit by the National Marine Fisheries Service (NMFS)].

There is evidence that environmental contaminants and pollutants can affect reproductive success and may impair the seals’ immune systems. Disturbances (natural or "unnatural") during pupping season can cause an increase in pup mortality—due to separation or abandonment by their mothers. An El Niño event causes a decrease of their food supply (El Nino results in warmer water temperatures) and therefore affects harbor seal population. Gillnet fisheries accounted for 5-10% mortality of the population of harbor seals in California in the mid-1980’s. Mortality due to gillnets has been decreasing ever since, mostly due to bans on gillnets within three miles of the coast of California. Marine debris is another threat to the seals—nets, plastic materials or debris can be ingested accidentally or can become caught around their necks, strangling the seals as they grow. Natural predators of harbor seals include sharks (their primary predator), killer whales, polar bears, stellar sea lions (minimal predator), eagles and coyotes (preying on pups). Lastly, minimal human-related mortalities have been caused by boat collisions, entrainment in power plants and shootings.

Population

To determine harbor seal populations, scientists typically survey their haul-out sites during the molting season and count the number of seals ashore. Because there are always a number of seals that are away from their haul-out site, scientists must arrive at an estimate—usually the number of seals hauled-out is then multiplied by a factor of at least 1.2 to reach the total population estimate. There has been an increase in the Pacific harbor seal population since 1940, but improvements in census techniques may be responsible for some of the increase in numbers.

Eastern Pacific harbor seal populations are divided among three "stocks" by the NMFS: Oregon/Washington, inland waters of Washington, and California (seals off Baja, California are not included among the three stocks). In 1996, the NMFS estimated there were about 30,000 harbor seals in California; the total population of eastern Pacific harbor seals from Alaska south to Baja is estimated to be approximately 300,000. In 1995 it was estimated there were 5,500 harbor seals in southern California, mostly at the offshore islands. Counts have increased steadily over the years, with the exception of El Niño years. Between 1985 and 1995, it was found that the average annual growth rate of harbor seals in California was 3.5% (southern CA had a relatively lower growth rate). Also between 1985 and 1995, the growth rate was found to be slowing (but still remaining positive). Declines in numbers at particular sites are thought to be from competition between harbor seals and thus displacement to other haul-out sites; it has also been suggested that the number of harbor seals hauled-out may be limited by available space.

A 1993 analysis indicated that harbor seals might be close, but not at OSP (optimum sustainable population). Bringing marine mammal populations to its OSP level is the main goal of the Marine Mammal Protection Act (MMPA). This level is defined as "with respect to any population, the number of animals which will result in the maximum productivity of the population, keeping in mind the carrying capacity of the habitat and the health of the ecosystem of which they form a constituent element." (Carrying capacity is further defined as "the largest average number of individuals of a species that can be supported over a long period.") Therefore, a population is considered at the OSP level if it is "above the point where the growth rate has slowed." Pacific harbor seals are not considered "endangered" or "threatened" under the Endangered Species Act; they are not considered "depleted" under the MMPA. However, the NMFS concluded that fishery mortality (mainly due to gillnets) cannot be considered "insignificant and approaching zero mortality and serious injury rate." The Pacific harbor seal population is increasing (though, again, the increase is slowing), and fishery mortality is decreasing. It is difficult to determine if the increase in population is due to "recovery" from the decrease that occurred when they were hunted and killed, or if the increase is the result of an increase in the carrying capacity. Also, an increase in the number of haul-out sites was found, as well as an increase in the number of animals at each site. It has been speculated that the increase in the number of haul-out sites (and also the number of animals at each site) is the result of seals using sites that may not have been suitable in the past, but are now used as seal populations increase. (NOTE: A haul-out site is generally considered a "rookery" if there are pups present at the site—the general term "haul-out site" is usually used for population counts). The next survey by the California Department of Fish and Game is due in May or June of 2000.

The California Department of Fish and Game conducted a count of Pacific harbor seals of California throughout 1982-1994. Aerial surveys were conducted during the molting season, when maximum numbers of harbor seals were ashore. Peak numbers of seals hauled-out typically occur within 1½ hours after low tide. The survey was conducted during weekdays, when there was less human disturbance. The 1982-1994 counts included about 30-50 mainland haul-out sites throughout California. Photographic records of each haul-out site were used to obtain the most accurate counts possible. It is important to note, again, that these counts include only seals that are hauled-out, and therefore are lower than the entire population. The results are shown in Figure 4:

Figure 4. Counts of Pacific harbor seals ashore in California (including the mainland and the Channel Islands) for 1982-1995. (The numbers for 1982 and 1983 include only mainland haul-out sites).

La Jolla Seals

Over the years, more and more harbor seals have chosen an area of San Diego (La Jolla), California known as the "Children’s Pool" as a haul-out site. Harbor seals (and sometimes California sea lions) have traditionally hauled-out onto a nearby rock known as "Seal Rock" (Figure 5). In 1994, the City of San Diego established a five-year temporary marine mammal reserve at Seal Rock (known as SRMMR/Seal Rock Marine Mammal Reserve).

Figure 5. Seals on Seal Rock © 1998 SeaWorld, Inc. All rights reserved.

The Hubbs-SeaWorld Research Institute (H-SWRI) conducted a study from October 1995 to September 1997 to determine the extent of which harbor seals (and sea lions) use the reserve. The study (including harbor seals on Seal Rock and those hauled-out at the Children’s Pool Beach) was used in the decision as to whether or not to make the reserve permanent. Reports show the highest number of seals on Seal Rock was 62 in April of 1996 and 65 of May, 1997. The peak numbers for the La Jolla area, in general, were 166 in June, 1996 and 172 in July, 1997. This is the peak of breeding and molting, the typical time of maximum haul-out. The numbers of seals that were hauled-out varied with the time of day and the tide. Larger numbers were hauled-out on SRMMR within two hours of low tide; for the La Jolla area, a greater number of animals were seen hauled-out in the later afternoon or evening, regardless of the tide. Also, the number of seals hauled-out generally decreased during the first few calm days after a storm.

Part of the H-SWRI study included releasing ten rehabilitated (restored to health by SeaWorld) and tagged seals at Seal Rock; they remained in the area throughout the study. During this study all of them were seen near the SRMMR. The study also found that more seals were hauled-out during the late spring and early summer. Disturbance was primarily from humans approaching the seals and gulls nipping at their flippers; occasionally loud noises would cause the seals to charge into the water. The study also indicated that when docents (or volunteers) were present, the seals seemed to be disturbed less often and not approached as closely by humans. However, this "docent program" existed only for a brief period of time, which did not allow for conclusive results. The results of the H-SWRI study are shown in Figure 6:

Figure 6. Peak monthly counts of harbor seals observed in the La Jolla area (including Seal Rock and Children’s Pool Beach) in 1996 and 1997 (counts for Oct-Dec, 1997 were unavailable).

In November of 1999, the San Diego City Council voted to make the reserve permanent, subject to review after five years. This protects the seals hauled-out on the rock from being harassed or approached by swimmers and divers. And, it reinforces existing protection by Federal and State statutes from "walkers" at low tide, however anyone fishing may enter the reserve under state law.

There is (and has been) considerable debate concerning the seals that haul-out onto the beach at the Children’s Pool (Figure 7). Recently, the number of seals that use the beach to haul-out has been increasing, though there is some debate over when they started using the beach as well as the number of seals there in the past. Since 1997, the beach has been closed due to contamination of the water—DNA evidence indicated the pollution is the result of the harbor seals’ fecal matter. Tests for total coliform bacteria and fecal coliform bacteria (Eschericia coli) generally show levels exceeding state standards for swimming. 

There are some people that believe the seals should be left undisturbed and allowed to continue using the beach as a haul-out site (and rookery)—and that they should be protected. During the months of February and March, 2000 ten pups were born on the Children's Pool Beach. Some consider the seals a benefit to the community, attracting visitors who are able to get a rare close-up view of these marine mammals (on the only beach in California where the seals can be viewed up close). With regard to the rise in eco-tourism, they could potentially benefit the local economy.

There are others who would like the beach re-opened for use by the public, regardless of how that could affect the seals. The Children’s Pool is a man-made structure that was given to the City of San Diego by Ellen B. Scripps in 1931 and has since accumulated sand and created a larger and larger beach area. Some believe the pool should be restored to its original 1930’s condition and "given back" to the people for whom it was originally intended. Although it is referred to as the "Children’s Pool Beach", before being closed due to contamination it was used frequently by divers as well as swimmers. It provides a convenient and sheltered site for divers to access deeper nearby locations.

Several options for reducing pollution at the Children’s Pool have been discussed. These range from physically removing the seals, using underwater barriers to prevent them from entering the Children’s Pool, to restoring the site to its original 1931 condition. The latter option would include dredging the beach, which would not only "scare" the seals away temporarily, but also may prevent them from returning due to less sand (or space) for them to "haul-out". Some wish to come up with some kind of a solution that would allow for co-existence, hopefully allowing both the seals and people to be able to use the beach—e.g., by reconfiguring the beach and sea wall for better water circulation, which would lead to fewer seals hauled-out. On the other hand, some maintain that potential co-existence is unlikely given the "shy" nature of the harbor seals and the likelihood of greater disturbances that would create an unsuitable haul-out location. Still, others suggest that prior to the beach closure, seals and people successfully co-existed on the beach and in the water—it is also believed by some that the seals actually became more accustomed to the presence of humans, which is not typical seal behavior.

Table 2 gives the results of the survey conducted by the California Department of Fish and Game in conjunction with the National Marine Fisheries Service, specifically with regard to the seals of La Jolla. The La Jolla haul-out site is the only site in mainland San Diego County. Harbor seals also inhabit San Clemente Island 104 km (65 miles) to the west of San Diego and the nearby Coronado Islands in Mexico.

Figure 7. Children's Pool Beach, La Jolla (Photo courtesy of R.D. Glenn)

Table 2. Yearly counts of harbor seals from aerial surveys conducted during molting season for Seal Rock (SR) and the La Jolla Children’s Pool Beach (CPB). Surveys were conducted near low tide and during the week, when numbers of seals hauled-out are generally highest.