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Guadalupe fur seal (Arctocephalus townsendi)
Conservation status
Least Concern (IUCN 3.1)
Threatened (ESA)
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Carnivora
Family:	Otariidae
Genus:	Arctocephalus
Species:	townsendi

Guadalupe fur seal (Arctocephalus Townsendi)

The Guadalupe fur seal (Arctocephalus townsendi) is a threatened species found primarily on Guadalupe Island, Mexico, as well as the San Benito Islands and other areas off the coast of California. The Guadalupe fur seal is an eared seal with thick fur.

The Guadalupe fur seal was first described in 1897, and was thought to be extinct after exploitation by fur sealers in the 19th century. This assumption was corrected in 1928 after discovery of a small group of individuals on Guadalupe Island, two of which were brought to the San Diego Zoo. After the supposed killing of the rest of the discovered population, the species was again considered extinct until identification of a 14-individual herd on Guadalupe Island in 1954.

Since its rediscovery, the Guadalupe fur seal has received numerous federal protections from the U.S. and Mexican governments. The total population has been increasing, with current estimates indicating a minimum of 41,000 individuals in 2017.

Description

The Guadalupe fur seal is a member of the family Otariidae, and possesses long, visible ears. Other members of the Otariidae family that have physical characteristics similar to those of the Guadalupe fur seal include sea lions and fur seals. Guadalupe fur seals have narrow, flat heads, and long and pointed snouts with white vibrissae. The long, pointed snout is more pronounced on males. Guadalupe fur seals have a thick fur coat with fur reaching past the wrists. Fur on the body is dark gray to dark brown in color, while the fur on the head and back of the neck tends to be tan or yellow in color. The fur on females tends to be lighter in color. The fore-flippers are broad and the hind-flippers are long. Adult females can weigh up to 50 kg, while adult males can be up to four times larger than females, weighing up to 180 kg. When mature, males measure approximately 1.8 m and females reach sizes of approximately 1.2 m. The average lifespan of the Guadalupe fur seal is 20 years.

Habitat & Distribution

Guadalupe fur seals are the only species in the Arctocephalus genus to be found north of the equator, inhabiting regions off the coasts of Mexico and southern California, but are most commonly found on Guadalupe Island, Mexico. Other areas occupied by Guadalupe fur seals include Baja California and the San Benito and San Miguel islands. Some individuals have been seen as far north as Washington State. Guadalupe fur seals prefer coastal, rocky habitats at the base of cliffs, and are usually found in caves during breeding season, due to the added protection and lower temperatures such habitat provides. The Guadalupe fur seal is able to travel large distances for breeding and feeding, but does not migrate.

Behavior

Reproduction

Guadalupe fur seals mainly breed on Guadalupe Island, Mexico, though some individuals have been known to breed on the San Benito and San Miguel islands off of California. Males and females will return to breeding colonies at the beginning of June. Breeding season takes place between June and August, with the highest birth rate occurring in late June. Guadalupe fur seals are polygynous, with some males mating with up to twelve females in one breeding season. Females usually give birth between mid-June and early July and breast feed for approximately nine months. Weaning occurs in February and March. Due to pups living in caves and under rocks during the breeding season, very few pups have been observed. The average birth weight for males and females is 4.9 kg and growth is exponential for 145 days. Females undergo estrus about five to ten days after giving birth. Males can be seen acting aggressively and vocally to defend their territories against other males while waiting to breed with females. After mating, females may leave to forage, traveling around 445 km over a two-week period. There is limited information about female foraging behavior and general behavior exhibited at sea.

Feeding and Diet

Guadalupe fur seals mainly feed on coastal and pelagic cephalopods, and small pelagic fish. Most of the details of their diet have been discovered through studies of fecal matter, with over 75% of the undigested material consisting of cephalopod beaks in some cases. The rest of their diet consists of fish, such as the northern anchovy (Engraulis mordax), pacific sardine (Sardinops sagax caerulea), pacific hake (Mercluccius productus), and lanternfish (Myctophidae). Guadalupe fur seals hunt for food by diving to depths up to 85 m, with an average depth of 20 m. Guadalupe fur seals can dive for periods up to 18 minutes, with an average duration of 3 minutes. During foraging, females can complete up to 168 dives per day, with an average of 92 dives per day. In between dives, Guadalupe fur seals are typically found foraging at the ocean surface. The average travel speed is 2 m/s, which is similar to the travel speeds of other fur seals. Due to the limited number of research studies on Guadalupe fur seals, specific feeding habits are not well known.

Status and Conservation

The Guadalupe fur seal was listed as threatened under the Endangered Species Act in December 1985. The Marine Mammal Protection Act (MMPA) and the National Marine Fisheries Service (NMFS) classify the Guadalupe fur seal as depleted (strategic stock).

Life History

The IUCN states that information regarding age structure is lacking, but describes Guadalupe fur seals as reaching sexual maturity around 4-5 years of age, and as having a maximum life span of around 20 years. Rates of recruitment and survival have not yet been determined as of 2018.

Historical & Present Range

The NMFS states that little data exists regarding the range of the species before commercial exploitation took place. Historical accounts and studies of skeletal remains indicate a distribution from the Revillagigedo Islands to Monterey Bay, CA (around 18˚N to 37˚N). Historically, breeding may have taken place within the California Channel Islands. The specific pre-exploitation breeding range described by the NMFS is from Guadalupe, the San Benitos and Cedros islands, and potentially Socorro Island, north to San Miguel Island. At the time of the listing, the NMFS concluded that breeding was only occurring on Guadalupe Island, Mexico. Throughout the 1900s, the only colony of Guadalupe fur seals was on Guadalupe Island, but a colony was found to be developing in the southeast on San Benitos Este in 1999.

Sightings have occurred in the Gulf of California and along the California coast, but the most recent data show that the only locations where Guadalupe fur seals spend time on land throughout the entire year are the Guadalupe and San Benito islands. The majority of the individuals residing in the San Benito islands are sexually immature, meaning that this population is not currently self-sustaining. The colony on Guadalupe Island is considered to be the only breeding population, and the colony on the San Benito islands is not regarded as reproductive but instead as an expansion of the population on Guadalupe Island.

Critical Habitat

In the 1985 listing decision, the NMFS did not designate any critical habitat for the Guadalupe Fur Seal. The NMFS found that all regions that met the necessary requirements for being critical to species conservation or requiring active preservation were outside of U.S. jurisdiction. The NMFS states that a reevaluation of the establishment of critical habitat will occur if areas within the U.S. are found to meet the necessary criteria.

Historical & Present Population Size

Historical population size is suggested to have ranged from 20,000-200,000. The NMFS concluded that the population prior to 19th-century harvesting was at least 30,000 individuals. The NMFS stated in 1985 that a 1984 census of Guadalupe Island totaling 1,597 individuals is the most accurate approximation, and concluded that at this time, the Guadalupe fur seal was not abundant within its pre-exploitation habitat.

Population recovery was observed in the 20th and 21st centuries, with discrete growth occurring from 1950-1980 and exponential growth occurring in the 1980s. In the 1990s, the total population size was not greater than 10,000 individuals. The per-year rate of population increase from 1955 to 1993 was 13.7%. In 1993, the population on Guadalupe Island was underestimated at 7,408 individuals because pups that were not dependent on their mothers were not included in the population count. Surveys in 2009 and 2010 produced a total population size of approximately 20,000, based on an estimate of 17,581 individuals on Guadalupe Island and 2,503 individuals on the San Benito Islands. A 2018 analysis of counts taken between 1984 and 2013 determined an average population growth rate of 5.9% per year within this period, and estimated the 2013 population size as consisting of 34,000-44,000 animals. Due to a lack of data, this estimate was made using standard pinniped population ratios and the assumption that the period within which births occur has not changed over time. Determination of life-history information would increase the accuracy of this assessment. A more recent modeling study conducted in 2018 still considers the species to be recovering, and predicts a mean population size of at least 41,000 individuals in 2017.

It has been stated that the total population size is likely not portrayed accurately by any census due to the tendency of the species to use boulders as shelter or reside within caves, making counts difficult.

History of ESA & IUCN

ESA

Federal Notice

The Guadalupe Fur Seal was declared at risk of extinction in a notice issued by the U.S. Fish and Wildlife Service (FWS) on March 11, 1967. A notice published on July 30, 1970, describes a proposal to alter the Endangered Species List after the removal of all species listed without using the proper protocol. This notice, in which the FWS declares the intent of rebuilding and adding to the list with both removed and new species, does not include the Guadalupe Fur Seal.

Proposed Rule

On January 3, 1985, the NMFS acknowledged in a proposed rule that the Guadalupe fur seal was excluded from the lists made in 1970 and onwards. This document proposes to officially classify the Guadalupe fur seal as threatened under the Endangered Species Act (ESA). This proposal was influenced by a petition by the Center for Environmental Education/Seal Rescue Fund (CEE/SRF) to list the Guadalupe fur seal as endangered. The CEE/SRF provided a list of reasons to support their recommendation, first describing obstacles to the recovery of the species. They cited the dramatic reduction in population size due to 19th-century commercial harvesting, the slow population growth observed on Guadalupe Island, and the increased vulnerability of the species to anthropogenic disturbance due to its small distribution and singular breeding colony. Additionally, they made mention of existing protections for the Guadalupe fur seal. The CEE/SRF discusses the banning of commercial trade of the species and its products by Appendix I of the Convention on International Trade in Endangered Species (CITES), which also classifies the species as at risk of extinction. The Center also recorded the listing of the species by the IUCN as vulnerable, and the initial labeling of the species as “threatened with extinction” by the FWS in 1967.

After reviewing the petition and determining its credibility, the NMFS was required to complete its own evaluation of the species. The five factors defined by the ESA to classify the magnitude of the threats to a species are as follows:

"(1) Present or threatened destruction, modification, or curtailment of its habitat or range

(2) Overutilization for commercial, recreational, scientific or education purposes

(3) Disease or predation

(4) Inadequacy of existing regulatory mechanisms

(5) Other natural or man-made factors affecting its continued existence".

The NMFS decided that the listing of the Guadalupe fur seal was most warranted by the factor of overutilization. The NMFS found that the existing protections against harvesting under U.S. and Mexican law, and the observed survival and population growth of the species, did not warrant the species to be declared as “in danger of extinction throughout all or a significant portion of its range,” or "endangered." A listing of "threatened" was proposed instead, as the current population levels indicated the Guadalupe fur seal to be at risk of endangerment within some or all of its range.

Final Rule

A final ruling on the decision was published on December 16, 1985, which would go into effect January 15, 1986, officially listing the Guadalupe fur seal as threatened under the ESA. Specific criteria are provided that would result in the initiation of a status review, with the potential for delisting if the review shows the species to no longer be threatened or endangered. These criteria include:

“(1) growth to a population size of 30,000 animals

(2) establishment of one or more additional rookeries within the historical range

(3) growth to the level at which maximum net productivity of the population occurs”.

IUCN

The Guadalupe fur seal was first assessed by the IUCN in 1965 and described as: “Very rare but believed to be stable or increasing.” Assessments in 1982, 1986, 1988, 1990, 1994, and 1996 list the species as “Vulnerable,” with an evaluation in 2008 lowering the species’ risk level to “Near Threatened.” Currently, the IUCN lists A. townsendi as being of “Least Concern”.

Human Impact

The 1985 listing decision by the NMFS states that the human activity occurring near Guadalupe island has not had adverse effects on the observed population increase, and that no data exists predicting that the magnitude of this activity is approaching a point where it would undermine the ongoing recovery. The NMFS cites several sources of human impact that could affect A. townsendi. It is suggested that oil spills that could potentially result from offshore oil and gas drilling, as well as sonic booms from Air Force testing programs, could prove harmful to individual animals. Tourism and fishing activity may cause disturbance to the species on land, and the latter may result in depletion of food sources and entanglement in fishing gear if fisheries operations move into feeding grounds or waters around Guadalupe Island.

Major Threats

Current threats listed by the IUCN are water pollution from industrial and military waste, ecosystem modifications, shipping routes, oil and gas drilling, and fishing and other activities harvesting marine life. The NMFS has documented and is researching an ongoing Unusual Mortality Event (UME) impacting the Guadalupe fur seal, as evidenced by a higher-than-average frequency of strandings occurring since 2015 off the coast of California and since 2019 off the coasts of Washington and Oregon. These strandings are attributed to increases in water temperature in the Pacific Ocean brought about by the El Niño event that took place in 2015, indicating that the increasing number of drastic changes in oceanic climate may impact the recovery of the Guadalupe fur seal. A 2004 study of mitochondrial DNA of historic and current populations revealed a decrease in genetic variability (and thus potential impacts on fitness) due to the bottleneck event caused by commercial exploitation. Overall, the existence of a singular breeding colony on Guadalupe Island increases the vulnerability of the species and may impact its ongoing recovery.

Current Conservation Efforts

In addition to being listed in the ESA, by the IUCN, and in CITES, the Guadalupe fur seal is protected by the MMPA (since December 21, 1972), and by California's Fish and Game Code. The 1985 NMFS listing states that Guadalupe Island was designated in 1928 as a wildlife refuge by the Mexican government, which outlawed the hunting of A. townsendi in 1967. The same document also describes collaboration between the NMFS and the Mexican government on programs studying marine mammals. Satellite tracking is currently used to evaluate the feeding and migration of Guadalupe fur seals, as well as the potential effects of fishing activity and oil spills. The Marine Mammal Center, located in Sausalito, CA, and the Seaworld location in San Diego, are cited as rehabilitating stranded individuals affected by the UME.