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DEPARTMENT OF THE INTERIOR
Fish and Wildlife Service
CFR Citation: 50 CFR Part 17
RIN ID: RIN 1018-AI44
NOTICE: PROPOSED RULES
ACTION: Endangered and threatened species:
DOCUMENT ACTION: Proposed rule.
SUBJECT CATEGORY: Endangered and Threatened Wildlife and Plants; Listing the Southwest Alaska Distinct Population Segment of the Northern Sea Otter (Enhydra lutris kenyoni) as Threatened
DATES: We will consider comments on this proposed rule received until the close of business on June 10, 2004. Requests for public hearings must be received by us on or before April 12, 2004.
DOCUMENT SUMMARY: We, the Fish and Wildlife Service (Service), propose to list the southwest Alaska distinct population segment of the northern sea otter (Enhydra lutris kenyoni) as threatened under the authority of the Endangered Species Act of 1973, as amended (Act). Once containing more than half of the world's sea otters, this population segment has undergone a precipitous population decline of at least 5668 percent since the mid1980s.
SUMMARY: Northern sea otter; southwest Alaska distinct population,
SUPPLEMENTAL INFORMATION
Background The sea otter (Enhydra lutris) is a mammal in the family Mustelidae
and it is the only species in the genus Enhydra. There are three
recognized subspecies (Wilson et al. 1991): E. l. lutris, known as the
northern sea otter, occurs in the Kuril Islands, Kamchatka Peninsula,
and Commander Islands in Russia; E. l. kenyoni, also known as the
northern sea otter, has a range that extends from the Aleutian Islands
in southwestern Alaska to the coast of the State of Washington; and E.
l. nereis, known as the southern sea otter, occurs in coastal southern
California and is known as the southern sea otter. Figure 1 illustrates the approximate ranges of the three subspecies.
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The two subspecies of northern sea otter are separated by an expanse of open water that measures approximately 320 kilometers (km) (200 miles (mi)) between the Commander Islands in Russia, at the northeastern edge of the range of E. l. lutris, and the Near Islands of the United States, which are the northwestern edge of the range of E. l. kenyoni. Wide, deepwater passes are an effective barrier to sea otter movements (Kenyon 1969) and thus interaction between these two subspecies is considered very unlikely. (See later sections on food habits and animal movements.)
The southernmost extent of the range of E. l. kenyoni is in Washington state and British Columbia, and is the result of translocations of sea otters from Alaska between 1969 and 1972 (Jameson et al. 1982). The Washington and British Columbia population is separated from the nearest sea otters in Alaska by a distance roughly of 483 km (300 mi) to the north, and is separated from the southern sea otter (E. l. nereis) by a distance of more than 965 km (600 mi) to the south.
The sea otter is the smallest species of marine mammal in the world. Adult males average 130 centimeters (cm) (4.3 feet (ft)) in length and 30 kilograms (kg) (66 pounds (lbs)) in weight; adult females average 120 cm (3.9 ft) in length and 20 kg (44 lbs) in weight (Kenyon 1969). The northern sea otter in Russian waters (E. l. lutris) is the largest of the three subspecies, characterized as having a wide skull with short nasal bones (Wilson et al. 1991). The southern sea otter (E. l. nereis) is smaller and has a narrower skull with a long rostrum and small teeth. The northern sea otter in Alaska (E. l. kenyoni) is intermediate in size and has a longer mandible than either of the other two subspecies.
Sea otters lack the blubber layer found in most marine mammals and depend entirely upon their fur for insulation (Riedman and Estes 1990). Their pelage consists of a sparse outer layer of guard hairs and an underfur that is the densest mammalian fur in the world, averaging more than 100,000 hairs per square centimeter (645,000 hairs per square inch) (Kenyon 1969). As compared to pinnipeds (seals and sea lions) that have a distinct molting season, sea otters molt gradually throughout the year (Kenyon 1969).
Sea otters have a much higher rate of metabolism than land mammals of similar size (Costa 1978; Costa and Kooyman 1982, 1984). To maintain the level of heat production required to sustain them, sea otters eat large amounts of food, estimated at 2333 percent of their body weight per day (Riedman and Estes 1990). Sea otters are carnivores that primarily eat a wide variety of benthic (living in or on the sea floor) invertebrates, including sea urchins, clams, mussels, crabs, and octopus. In some parts of Alaska, sea otters also eat epibenthic (living upon the sea floor) fishes (Estes et al. 1982; Estes 1990).
Much of the marine habitat of the sea otter in southwest Alaska is characterized by a rocky substrate. In these areas, sea otters typically are concentrated between the shoreline and the outer limit of the kelp canopy (Riedman and Estes 1990). Sea otters also inhabit marine environments that have soft sediment substrates, such as Bristol Bay and the Kodiak archipelago. As communities of benthic invertebrates differ between rocky and soft sediment substrate areas, so do sea otter diets. In general, prey species in rocky substrate habitats include sea urchins, octopus, and mussels, while in soft substrates, clams dominate the diet.
Sea otters are considered a keystone species, strongly influencing the composition and diversity of the nearshore marine environment they inhabit (Estes et al. 1978). For example, studies of subtidal communities in Alaska have demonstrated that, when sea otters are abundant, epibenthic herbivores such as sea urchins will be present at low densities whereas kelp, which are consumed by sea urchins, will flourish. Conversely, when sea otters are absent, abundant sea urchin populations create areas of low kelp abundance, known as urchin barrens (Estes and Harrold 1988).
Sea otters generally occur in shallow water areas that are near the shoreline. They primarily forage in shallow water areas less than 100 meters (m) (328 feet (ft)) in depth, and the majority of all foraging dives take place in waters less than 40 m (131 ft) in depth. As water depth is generally correlated with distance to shore, sea otters typically inhabit waters within 12 km (0.621.24 mi) of shore (Riedman and Estes 1990). One notable exception occurs along the coast of Bristol Bay, along the north side of the Alaska Peninsula, where a broad shelf of shallow water extends several miles from shore. Prior to the onset of the sea otter population decline (described below), large rafts of sea otters were commonly observed above this shelf of shallow water at distances as far as 40 km (25 mi) from shore (Schneider 1976).
Since the end of the commercial fur harvests, movement patterns of sea otters have been influenced by the processes of natural population recolonization and the translocation of sea otters into former habitat. While sea otters have been known to make long distance movements up to 350 km (217 mi) over a relatively short period of time when translocated to new or vacant habitat (Ralls et al. 1992), the home ranges of sea otters in established populations are relatively small. Once a population has become established and has reached a relatively steady state within the habitat, movement of individual sea otters appears to be largely dictated by social behaviors and by factors in the local environment, including gender, breeding status, age, climatic variables (e.g. weather, tidal state, season), and human disturbance, as described below.
Home range and movement patterns of sea otters vary depending on the gender and breeding status of the otter. In the Aleutian Islands, breeding males remain for all or part of the year within the bounds of their breeding territory, which constitutes a length of coastline anywhere from 100 m (328 ft) to approximately 1 km (0.62 mi). Sexually mature females have home ranges of approximately 816 km (510 mi), which may include one or more male territories. Male sea otters that are not part of the breeding population do not hold territories and may move greater distances between resting and foraging areas than breeding males (Lensink 1962, Kenyon 1969, Riedman and Estes 1990, Estes and Tinker 1996).
Studies of movement patterns of juvenile sea otters found that juvenile males (12 years of age) were found to disperse later and for greater distances, up to 120 km (75 mi), from their natal (birth) area than 1yearold females, for which the greatest distance traveled was 38 km (23.6 mi) (Garshelis and Garshelis 1984, Monnett and Rotterman 1988, Riedman and Estes 1990). Intraspecific aggression between breeding males and juvenile sea otters may cause juvenile otters to move from their natal areas to lower quality habitat (Ralls et al. 1996), and survival of juvenile sea otters, though highly variable, is influenced by intraspecific aggression and dispersal (Ballachey et al. in litt.).
Sea otter movements are also influenced by local climatic
conditions such as storm events, prevailing winds, and in some areas,
tidal state. Sea otters tend to move to protected or sheltered waters
(bays, inlets, or lees) during storm events or high winds. In calm
weather conditions, sea otters may be encountered further from shore
(Lensink 1962, Kenyon 1969). In the Commander Islands, Russia ,
weather, season, time of day, and human disturbance have been cited as factors that induce sea
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otter movement (BarabashNikiforov 1947, BarabashNikiforov et al. 1968).
Due to their dependence on shallow water feeding areas, most sea otters in Alaska occur within 12 km (0.621.24 mi) from shore. Thus, most sea otters are within Stateowned waters, which include the area from mean high tide to 4.8 km (3 miles) offshore, and any that go further offshore are within the U.S. Exclusive Economic Zone, which extends 370.4 km (200 nautical miles) seaward from the coast of the United States.
While sea otters typically sleep in the water, they also haul out and sleep on shore (Kenyon 1969). Female sea otters have also been observed to give birth while on shore (BarabashNikiforov et al. 1968, Jameson 1983). Although they typically haul out and remain close to the water's edge, sea otters have been observed on land at distances up to several hundred meters from the water (Riedman and Estes 1990). The majority of coastal lands within the range of the southwest Alaska population of the northern sea otter are part of our National Wildlife Refuge (NWR) system, including Alaska Maritime NWR, Izembek NWR, Alaska Peninsula/Becharof NWR, and Kodiak NWR. The National Park Service also has large parcels of coastal lands in southwest Alaska, including Katmai National Park and Aniakchak National Monument and Preserve. The vast majority of remaining coastal lands in southwest Alaska are owned by the State of Alaska and Alaska Native Corporations. Privately owned lands constitute a very minor proportion of coastal lands in southwest Alaska.
Female sea otters in Alaska live an estimated 1520 years, while male lifespan appears to be about 1015 years (Calkins and Schneider 1985). Firstyear survival of sea otter pups is generally substantially lower than that for prime age (210 years old) animals (Monson and DeGange 1995, Monson et al. 2000). Male sea otters appear to reach sexual maturity at 56 years of age (Schneider 1978, Garshelis 1983). The average age of sexual maturity for female sea otters is 34 years, but some appear to reach sexual maturity as early as 2 years of age. The presence of pups and fetuses at different stages of development throughout the year suggests that reproduction occurs at all times of the year. Some areas show evidence of one or more seasonal peaks in pupping (Rotterman and SimonJackson 1988).
Similar to other mustelids, sea otters can have delayed implantation of the blastocyst (developing embryo) (Sinha et al. 1966). As a result, pregnancy can have two phases: from fertilization to implantation, and from implantation to birth (Rotterman and Simon Jackson 1988). The average time between copulation and birth is around 67 months. Female sea otters typically will not mate while accompanied by a pup (Lensink 1962; Kenyon 1969; Schneider 1978; Garshelis et al. 1984). Although females are physically capable of producing pups annually, the length of pup dependency may be the primary factor determining pupping interval.
Maximum productivity rates have not been measured through much of the sea otter's range in Alaska. Estes (1990) estimated a population growth rate of 1720 percent per year for four northern sea otter populations expanding into unoccupied habitat. In areas where resources are limiting or where populations are approaching equilibrium density, slower rates of growth are expected. Equilibrium density is defined as the average density, relatively stable over time, that can be supported by the habitat (Estes 1990).
Distribution and Status
Historically, sea otters occurred throughout the coastal waters of
the north Pacific Ocean, from the northern Japanese archipelago around
the north Pacific rim to central Baja California, Mexico. The historic distribution of sea otters is depicted in Figure 2.
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Prior to commercial exploitation, the rangewide estimate for the species was 150,000300,000 individuals (Kenyon 1969, Johnson 1982). Commercial hunting of sea otters began shortly after the Bering/ Chirikof expedition to Alaska in 1741. Over the next 170 years, sea otters were hunted to the brink of extinction first by Russian, and later by American fur hunters.
Sea otters became protected from commercial harvests under the International Fur Seal Treaty of 1911, when only 13 small remnant populations were known to still exist (Figure 2). The entire species at that time may have been reduced to only 1,0002,000 animals. Two of the 13 remnant populations (Queen Charlotte Island and San Benito Islands) subsequently became extinct (Kenyon 1969, Estes 1980). The remaining 11 populations began to grow in number, and expanded to recolonize much of the former range. Six of the remnant populations (Rat Islands, Delarof Islands, False Pass, Sandman Reefs, Shumagin Islands, and Kodiak Island) were located within the bounds of what we now recognize as the southwest Alaska population of the northern sea otter (see Distinct Vertebrate Population Segment, below). These remnant populations grew rapidly during the first 50 years following protection from further commercial hunting. At several locations in the Aleutian Islands, the rapid growth of sea otter populations appears to have initially exceeded the carrying capacity of the local environment, as sea otter abundance at these islands then declined, either by starvation or emigration, eventually reaching what has been described as ``relative equilibrium'' (Kenyon 1969).
Population Trends of Sea Otters in Southwest Alaska
The following discussion of population trends is related to the
southwest Alaska distinct population segment of sea otters addressed in
this proposed rule. The southwest Alaska population ranges from Attu
Island at the western end of Near Islands in the Aleutians, east to
Kamishak Bay on the western side of lower Cook Inlet, and includes
waters adjacent to the Aleutian Islands, the Alaska Peninsula, the Kodiak archipelago, and the Barren Islands (Figure 3).
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Survey procedures vary in different locations. In some parts of southwest Alaska, sea otters have been counted in a narrow band of water adjacent to the shoreline; in others, transects by boat or plane have been used to sample an area, and the resulting sea otter density is extrapolated to generate a population estimate for the entire study area. Like survey efforts of most species, detection of all the individuals present is not always possible. Sea otters spend considerable time under water, and it is not possible to detect individuals that are below the surface at the time a survey is conducted. Also, observers do not always detect every individual present on the surface. Only a few surveys have been conducted using methods that allow for calculation of a correction factor to adjust for the estimated proportion of otters not detected by observers. Making such an adjustment entails having an independent estimate of the number of otters present in an area, also known as ``groundtruth,'' and combining it with the regular survey data in order to calculate a correction factor to adjust for sea otters not detected during the survey. Thus, survey results can be of several types: They can be direct counts or estimates, and in either case they may be adjusted or unadjusted for sea otters not detected by observers.
In the following discussion of population trends, results are
presented separately for surveys conducted in the Aleutian Islands, the
Alaska Peninsula, the Kodiak Archipelago, and Kamishak Bay. For the
Alaska Peninsula, results are presented for the separate surveys that
have been conducted for north Peninsula offshore areas, south Peninsula
offshore areas, south Alaska Peninsula Islands, and the South Alaska
Peninsula shoreline. The general locations of the survey areas are depicted in Figure 4 AD.
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Unless otherwise specified, the survey results are unadjusted for
otters not detected by observers. Within each study area, recent
surveys were conducted using methods similar to those used in the past,
so that counts or estimates would be as comparable as possible with
baseline information for that area. Although there may be slight
differences in the time of year that surveys were conducted, we do not
believe these timing differences hinder comparisons of survey results
because otters are likely to remain in the same general area, as they
are not migratory. A summary of sea otter survey data from each survey
area within the southwest Alaska population is presented in Table 1,
followed by a narrative description of the results for each area.
Table 1.Summary of Sea Otter Population Surveys in Southwest Alaska
[Estimates include 95% confidence intervals where available. Estimates for the Kodiak archipelago and Kamishak
Bay are the only values adjusted for sea otters not detected.]
Survey Area Year Count or estimate Source
Aleutian Islands..................... 1965 9,700 Kenyon (1969).
1992 8,048 Evans et al. (1997).
2000 2,442 Doroff et al. (2003).
North Alaska Peninsula Offshore Areas 1976 11,681 Schneider (1976).
*1986 6,474
7,539
South Alaska Peninsula Offshore Areas *1986 13,900
17,500
2001 1,005
Aleutian Islands
The first systematic, largescale population surveys of sea otters in the Aleutian Islands (Figure 4A) were conducted from 1957 to 1965 by Kenyon (1969). The descendants of two remnant colonies had expanded throughout the Rat, Delarof, and western Andreanof Island groups. The total unadjusted count for the entire Aleutian archipelago during the 1965 survey was 9,700 sea otters. In 1965, sea otters were believed to have reached equilibrium densities at roughly onethird of the Aleutian archipelago, ranging from Adak Island in the east to Buldir Island in the west (Estes 1990). Islands in the other twothirds of the archipelago had few sea otters, and researchers expected additional population growth in the Aleutian to occur through range expansion.
From the mid1960's to the mid1980's, otters expanded their range, and presumably their numbers as well, until they had recolonized all the major island groups in the Aleutian. Although the exact size of the sea otter population at the onset of the decline is unknown, a habitat based computer model estimates the predecline population in the late 1980s may have numbered approximately 74,000 individuals (Burn et al. 2003).
In a 1992 aerial survey of the entire Aleutian archipelago we counted a total of 8,048 otters (Evans et al. 1997), approximately 1,650 (19 percent) fewer than the total reported for the 1965 survey. Although sea otters had recolonized all major island groups, they had unexpectedly declined in number by roughly 50 percent in portions of the western and central Aleutian since 1965, based on a comparison of the 1965 and 1992 survey results. Sea otter surveys conducted from skiffs during the mid1990s at several islands also indicated substantial declines in the western and central Aleutians (Estes et al. 1998). It was not known at the time if these observed declines were due to an actual reduction in numbers of sea otters or a redistribution of otters between Aleutian Islands.
In April 2000, we conducted another complete aerial survey of the Aleutian archipelago. We counted 2,442 sea otters, which is a 70 percent decline from the count eight years previously (Doroff et al. 2003). Along the more than 5,000 km (3,107 miles) of shoreline surveyed, sea otter density was at a uniformly low level. this result showed clearly that a decline in abundance of sea otters in the archipelago had occurred, as opposed to redistribution among islands.
The aerial and skiff survey data both indicate that the onset of the decline began in the latter half of the 1980s or early 1990s. Doroff et al. (2003) have calculated that the decline proceeded at an average rate of 17.5 percent per year in the Aleutians. Although otters had declined in all island groups within the archipelago, the greatest declines were observed in the Rat, Delarof, and Andreanof Island groups. this result was unexpected, as the remnant colonies in these island groups were the first to recover from the effects of commercial harvests, and sea otters were believed to have been at equilibrium density at most of these islands in the mid1960s.
The current estimate of the population in the Aleutian Islands is 8,742 sea otters. This estimate is based on results of the survey conducted in April of 2000, adjusted for otters not detected. Alaska Peninsula
Three remnant colonies (at False Pass, Sandman Reefs, and Shumagin
Islands) were believed to have existed near the western end of the Alaska Peninsula
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after commercial fur harvests ended in 1911 (Kenyon 1969). During
surveys in the late 1950s and early 1960s, substantial numbers of sea
otters were observed between Unimak Island and Amak Island (2,892 in
1965) on the north side of the Peninsula, and around Sanak Island and
the Sandman reefs (1,186 in 1962), and the Shumagin Islands on the south side (1,352 in 1962) (Kenyon 1969).
As summarized in Table 1 and described below, surveys of sea otters along the Alaska Peninsula have covered four areas, with the same method being used in a given area. For the north Alaska Peninsula offshore area (Figure 4B), shoreline counts are not an appropriate survey method due to the broad, shallow shelf in Bristol Bay, a condition under which sea otters occur further from the shore than elsewhere. Consequently, the north Alaska Peninsula offshore area has been surveyed from aircraft using northsouth transects extending from the shoreline out over the shelf. Using this method, Schneider (1976) calculated an unadjusted population estimate of 11,681 sea otters on the north side of the Alaska Peninsula in 1976, which he believed to have been within the carrying capacity for that area. Brueggeman et al. (1988) conducted replicate surveys of the same area during three time periods in 1986. We reanalyzed the original 1986 survey data to address computational errors in the survey report; our recalculated estimates range from 6,4749,215 sea otters for this area for the three surveys in 1986 (Burn and Doroff in prep.). In May 2000, we replicated the survey design of Brueggeman et al. (1988) using identical survey methods. The 2000 survey estimate of 4,728 sea otters indicates abundance on the north side of the Alaska Peninsula had fallen by 2749 percent in comparison with the minimum and maximum point estimates of the 1986 survey (Burn and Doroff in prep.).
We believe the decline in this particular area may have been even greater than these results indicate, as the severity of sea ice in Bristol Bay makes the North Alaska Peninsula the only area where seasonal differences in the distribution of otters are likely to occur. Substantially more otters were counted in transects of the Port Moller area in the May 2000 survey than in the 1986 surveys, which occurred later in the year. Large aggregations of sea otters in Port Moller may be a seasonal phenomenon related to sea ice; overflights in July and August, when the sea ice has left, have not recorded large numbers of sea otters in this area (B. Murphy, Alaska Department of Fish and Game, in litt. 2002). Consequently, had the May 2000 survey been conduced later (e.g. July or August) when the sea ice and the otters were more dispersed, it seems likely that fewer would have been in the Port Moller transect areas, which would have resulted in a lower count in the 2000 survey.
Offshore areas on the south side of the Alaska Peninsula (Figure 4B) were surveyed at three different time periods in 1986 (Brueggeman et al. 1988). Noting computational errors in the survey report, we re analyzed the original 1986 survey data, resulting in estimates of 13,90017,500 sea otters for the three surveys conducted in 1986 (Burn and Doroff in prep.). We replicated the survey in April 2001, when our estimate of 1,005 otters for the south Alaska Peninsula offshore area indicated a decline in abundance of at least 93 percent when compared with the minimum and maximum point estimates in this area from the 1986 surveys. Specific areas of high sea otter concentrations in 1986, such as Sandman Reefs, were almost devoid of sea otters in 2001 (Burn and Doroff in prep.).
Several island groups along the south side of the Alaska Peninsula (Figure 4C; Pavlof and Shumagin Islands, as well as Sanak, Caton, and Deer Islands) are another survey area. In 1962, Kenyon (1969) counted 1,900 otters along these islands. Twentyfour years later, in 1986, Brueggeman et al. (1988) counted 2,122 otters in the same survey area. In 1989, DeGange et al. (1995) counted 1,589 otters along the shorelines of the islands that had been surveyed in 1962 and 1986, which was approximately 1628 percent fewer sea otters than were reported in the earlier counts. This decrease was the first indication of a sea otter population decline in the area of the Alaska Peninsula. When we counted sea otters in these island groups in 2001 we recorded only 405 individuals (Burn and Doroff in prep.), which is an 81percent decline from the 1986 count reported by Brueggeman et al. (1988).
The shoreline of the Alaska Peninsula from False Pass to Cape Douglas (Figure 4D) is another survey area. In 1989, DeGange et al. (1995) counted 2,632 sea otters along this stretch of shoreline. In 2001 we counted 2,651 sea otters (Burn and Doroff in prep.), nearly the same as the 1989 count. When we subdivided and compared the results for the eastern and western components of the survey areas, we found that the count along the eastern end of the Peninsula, from Cape Douglas to Castle Cape, increased approximately 20 percent, from 1,766 in 1989 to 2,115 in 2001. For the western end of the Peninsula from False Pass to Castle Cape, however, there was evidence of a population decline, with 866 counted in 1989 as compared to 536 in 2001, a drop of almost 40 percent. (We also counted 42 sea otters along the shoreline of Unimak Island in 2001, but there is no suitable baseline data for comparison.) Based on what is known about sea otter movements and the distance between the eastern and western ends of the Peninsula, we believe that it is unlikely that these observations represent a change in distribution.
The results from the different survey areas along the Alaska Peninsula indicate various rates of change. Overall, the combined counts for the Peninsula have declined by 6572 percent since the mid 1980s, based on the data presented in Table 1.
We have calculated an estimate of the current population for the entire Alaska Peninsula, including an adjustment for otters not detected by observers. In making this calculation, we first revised the combined total number of sea otters observed during the most recent surveys (8,789), to account for potential doublecounting in an area of overlap between two of the study areas along the Peninsula. We then multiplied this revised number of otters (8,328) by the correction factor of 2.38 provided by Evans et al. (1997) for the type of aircraft used, to account for otters not detected by observers. The result is an adjusted estimate of 19,821 sea otters along the Alaska Peninsula as of 2001 (Burn and Doroff in prep.).
Kodiak Archipelago
One of the remnant sea otter colonies in southwest Alaska is
thought to have occurred at the northern end of the Kodiak archipelago
(Figure 4D), near Shuyak Island. In 1959, Kenyon (1969) counted 395 sea
otters in the Shuyak Island area. Over the next 30 years, the sea otter
population in the Kodiak archipelago grew in numbers, and its range
expanded southward around Afognak and Kodiak Islands (Schneider 1976,
SimonJackson et al. 1984, SimonJackson et al. 1985). DeGange et al.
(1995) surveyed the Kodiak archipelago in 1989 and calculated an
adjusted population estimate of 13,526 sea otters. In July and August
1994, we conducted an aerial survey using the methods of Bodkin and
Udevitz (1999) and calculated an adjusted population estimate of 9,817,
approximately 27 percent lower than the estimate for 1989 (Doroff et
al. in prep.). Although both surveys corrected for animals not detected
by observers, differences in survey methods led to questions about [[Page 6610]]
the ability to compare results between the two surveys. In June 2001,
we surveyed the Kodiak archipelago using the same observer, pilot, and
methods as in 1994. The result was an adjusted population estimate of
5,893 sea otters for the archipelago in 2001 (Doroff et al. in prep.),
which is a 40percent decline in comparison to the 1994 estimate and a 56percent decline from the 1989 estimate.
Kamishak Bay
Kamishak Bay is located on the west side of lower Cook Inlet, north of Cape Douglas (Figure 4D). In 1994, Kamishak Bay was included as part of a survey for marine birds and marine mammals in lower Cook Inlet (Agler et al. 1995). The unadjusted population estimate of 5,914 sea otters from the 1994 survey included sea otters from both the southwest Alaska and the southcentral Alaska stocks (see section on Distinct Vertebrate Population Segment, below), therefore an estimate for only the Kamishak Bay area is not available. In the summer of 2002, the U.S. Geological Survey (USGS), Biological Resources Division conducted an aerial survey of lower Cook Inlet and the Kenai Fiords area. This survey was designed, in part, to estimate sea otter abundance in Kamishak Bay. The method used was identical to that of the 2001 aerial survey of the Kodiak archipelago, which includes a correction factor for sea otters not detected by the observer (Bodkin and Udevitz 1999). Sea otters were relatively abundant within Kamishak Bay during the 2002 survey, with numerous large rafts of sea otters observed. The adjusted estimate for the current sea otter population size in Kamishak Bay is 6,918 (USGS in litt. 2002). As no previous estimates for Kamishak Bay exist, the population trend for this area is unknown.
Overall Comparison
The history of sea otters in southwest Alaska is one of commercial exploitation to near extinction (1742 to 1911), protection under the International Fur Seal Treaty (1911), and population recovery (post 1911). By the mid to late1980s, sea otters in southwest Alaska had grown in numbers and recolonized much of their former range. The surveys conducted in various areas, described above, provide information about the extent of declines within those areas. However, due to differences in the years of the various baseline surveys for different areas (1962, 1965, 1976, 1989), it is difficult to combine those surveys as a basis for estimating the overall size of the sea otter population throughout southwest Alaska at the onset of the decline. Therefore, as part of our effort to evaluate information reflecting the overall magnitude of the decline, we also have considered information provided by Calkins and Schneider (1985), who summarized sea otter population estimates worldwide based on data collected through 1976. Much of the information they present is from unpublished Alaska Department of Fish and Game survey results, and we include this information as it is the only comprehensive reference for estimating the overall magnitude of the sea otter decline in southwest Alaska.
Calkins and Schneider (1985) provided estimates as of 1976, adjusted for animals not detected by observers, for the Aleutian Islands (55,10073,700), north Alaska Peninsula (11,70017,200), south Alaska Peninsula (22,00030,000) and Kodiak archipelago (4,0006,000). They did not report a specific estimate for the Kamishak Bay area, which presumably was included within their estimate for the Kenai Peninsula and Cook Inlet area (2,5003,500 otters), and we are assuming that half of the sea otters estimated for Kenai Peninsula and Cook Inlet occurred in Kamishak Bay (1,2501,750). Combining these estimates, the sea otter population in the area encompassing the range of the southwest Alaska population was believed to have numbered between 94,050128,650 animals as of 1976. As sea otters had not yet fully recolonized southwest Alaska or reached equilibrium density in all areas in 1976, additional population growth was expected. Therefore, the overall population prior to the onset of the decline in the 1980's probably was higher than the population estimate for 1976.
Our estimate for the current size of the southwest Alaska
population of the northern sea otter is 41,474 animals (Table 2). This
estimate is based on recent survey information, adjusted for animals not detected.
Table 2.Current Population Estimates for the Sea Otter in Southwest Alaska
[Alaska Peninsula and Unimak Island counts are adjusted using a correction factor of 2.38 for twinengine
aircraft surveys of sea otters according to Evans et al. (1997). Aleutian Islands, Kodiak Archipelago, and
Kamishak Bay surveys are adjusted using surveyspecific correction factors.]
Unadjusted Adjusted
Survey area Year count or count or Reference
estimate estimate
Aleutian Islands................ 2000 2,442 8,742 Doroff et al. (2003).
North Alaska Penninsula Offshore 2000 4,728 11,253 Burn and Doroff (in prep.). Areas.
South Alaska Peninsula Offshore 2001 1,005 2,392 Burn and Doroff (in prep.). Areas.
South Alaska Peninsula Shoreline 2001 \a\ 2,190 5,212 Burn and Doroff (in prep.).
South Alaska Peninsula Islands.. 2001 405 964 Burn and Doroff (in prep.).
Unimak Island................... 2001 42 100 Burn and Doroff (in prep.).
Kodiak Archipelago.............. 2001 ........... 5,893 Doroff et al. (in prep.).
Kamishak Bay.................... 2002 ........... 6,918 USGS Unpublished data.
Total....................... ........... ........... 41,474 ....................................... \a\ Does not include a count of 461 sea otters from False Pass to Seal Cape, which was also surveyed as part of the south Alaska Peninsula Offshore Areas survey.
The 1976 population estimate based on the work of Calkins and
Schneider (1985) is not directly comparable to our current estimate
because of somewhat different survey approaches and estimation
techniques. Nevertheless, the results provide a basis for at least a
rough comparison of the overall extent of the decline of sea otters in
southwest Alaska. When compared to the estimate of 94,050128,650 from
Calkins and Schneider (1985), our current estimate of approximately
41,500 sea otters is 53,00087,000 lower, which is 5668 percent lower than the estimate for 1976.
[[Page 6611]]
Translocated Sea Otter Populations
As part of efforts to reestablish sea otters in portions of their historical range, otters from Amchitka Island (part of the Aleutian Islands) were translocated to other areas outside the range of what we now recognize as the southwest Alaska distinct population segment, but within the range of E. l. kenyoni (Jameson et al. 1982). These translocation efforts met with varying degrees of success. From 1965 to 1969, 412 otters (89 percent from Amchitka Island, and 11 percent from Prince William Sound, which is in southcentral Alaska, outside the range of the southwest Alaska DPS) were translocated to six sites in southeast Alaska (Jameson et al. 1982). Since that time, these translocated populations have grown rapidly in numbers and expanded their range. The most recent surveys conducted between 1994 and 1996 estimated 12,632 otters in southeast Alaska (USFWS 2002b).
Sea otters from Amchitka Island also were translocated to Washington and Oregon, and to British Columbia, Canada, between 1969 and 1972 (Jameson et al. 1982). Sea otters translocated to British Columbia were captured at Amchitka Island and Prince William Sound; the otters translocated to Washington and Oregon were captured at Amchitka Island only. The British Columbia and Washington populations have grown in number and expanded their range, while the Oregon population disappeared. The most recent estimates of population size are 550 in Washington and 2,000 in British Columbia (Jameson and Jeffries 2001; Watson et al. 1997). Although these populations, as well as sea otters in southeast Alaska, are descended from sea otters at Amchitka Island, they are geographically isolated from the southwest Alaska population and their parent population by hundreds of kilometers (see section entitled Distinct Vertebrate Population Segment, below) and are not included in this proposed listing action.
The total number of otters removed from Amchitka as part of this translocation program was just over 600 animals (Jameson et al. 1982). Estes (1990) estimated that the sea otter population at Amchitka Island remained essentially stable at more than 5,000 otters between 1972 and 1986, and consequently there is no evidence that removals for the translocation program have been a contributing factor in the current population decline.
Previous Federal Action
Based on the results of the April 2000 sea otter survey in the Aleutian Islands, we added sea otters in the Aleutians to our list of candidate species in August of 2000 (65 FR 67343). On October 25, 2000, we received a petition from the Center for Biological Diversity (Center) in Berkeley, California, requesting that we list the Aleutian population of the northern sea otter as endangered. As we already had identified sea otters in the Aleutians as a candidate species, we considered the petition to be a second, redundant petition, and in accordance with our petition management guidance (61 FR 36075) did not make an additional 90day or 12month finding on this petition. On November 14, 2000, we received a Notice of Intent to sue from the Center challenging our decision not to propose to list sea otters in the Aleutians under the Act. We responded to the Center that funds were not available during Fiscal Year 2001 to prepare a proposed listing rule.
On August 21, 2001, we received a petition from the Center to
designate the Alaska stock of sea otters (Statewide) as depleted under
the Marine Mammal Protection Act (MMPA; 16 U.S.C. 1361 et seq.). Under
the MMPA, a marine mammal species or population stock is considered to
be depleted when it is below its Optimum Sustainable Population (OSP)
level. The OSP is defined in the MMPA as: ``the number of animals which
will result in the maximum productivity of the population or the
species, keeping in mind the carrying capacity of the habitat and the
health of the ecosystem of which they form a constituent element.'' In
accordance with the MMPA, we published a notice in the Federal Register
on September 6, 2001, announcing the receipt of this petition (66 FR
4661). On November 2, 2001, we published our finding on the petition in
the Federal Register (66 FR 55693). While we acknowledged the evidence
of a population decline in the southwest Alaska stock, the best
available information suggested that the southeast Alaska stock was
increasing, and the southcentral Alaska stock was either stable or
increasing. We found that the petitioned action was not warranted under
the MMPA for the following reasons: (1) The best estimate of the
population size for the entire state of Alaska was greater than the
value presented in the petition; (2) based on the best estimate of
population size, the Alaska stock of sea otters was above OSP level;
and (3) recent information had identified the existence of three stocks
of sea otters in Alaska: southwest, southcentral, and southeast
(Gorbics and Bodkin 2001). The boundaries of these three stocks are depicted in Figure 5.
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We recently revised the MMPA stock assessment reports for sea otters in Alaska. Draft stock assessment reports identifying the three stocks of sea otters were made available for public review and comment from March 28 to June 26, 2002 (67 FR 14959). The sea otter stock assessment reports were finalized on August 20, 2002, and notice of their availability was published on October 9, 2002 (67 FR 62979).
On January 11, 2002, we received a petition from the Sea Otter Defense Initiative (SODI), a project of the Earth Island Institute, in Deer Isle, Maine. The petition requested that we emergency and permanently list the southwest Alaska stock of sea otters as endangered. We responded to SODI that, based on the best available population estimate that we prepared in response to the Center's petition to list the Alaska stock of sea otters as depleted under the MMPA, an emergency listing of the southwest Alaska stock was not warranted. We also notified SODI that we had begun the preparation of this proposed rule during Fiscal Year 2002.
Based on additional sea otter surveys along the Alaska Peninsula and Kodiak archipelago, and the identification of multiple stocks of sea otters in Alaska, we expanded the candidate species designation on June 3, 2002, to include the geographic range of the southwest Alaska stock of the northern sea otter. Notification of this change was included in our June 13, 2002, notice of review of candidate species (67 FR 40657).
Distinct Vertebrate Population Segment
Pursuant to the Act, we must consider for listing any species,
subspecies, or, for vertebrates, any distinct population segment (DPS)
of these taxa if there is sufficient information to indicate that such
action may be warranted. To interpret and implement the DPS provision
of the Act and Congressional guidance, the Service and the National
Marine Fisheries Service published, on December 21, 1994, a draft
Policy Regarding the Recognition of Distinct Vertebrate Population
Segments Under the Endangered Species Act and invited public comments on it (59 FR 65885). After review of comments and further
consideration, the Services adopted the interagency policy as issued in
draft form, and published it in the Federal Register on February 7,
1996 (61 FR 4722). This policy addresses the recognition of DPSs for
potential listing actions. The policy allows for more refined
application of the Act that better reflects the biological needs of the
taxon being considered, and avoids the inclusion of entities that do not require its protective measures.
Under our DPS policy, three elements are considered in a decision regarding the status of a possible DPS as endangered or threatened under the Act. These are applied similarly for additions to the list of endangered and threatened species, reclassification, and removal from the list. They are: (1) Discreteness of the population segment in relation to the remainder of the taxon; (2) the significance of the population segment to the taxon to which it belongs; and (3) the population segment's conservation status in relation to the Act's standards for listing (i.e., is the population segment, when treated as if it were a species, endangered or threatened?). A systematic application of the above elements is appropriate, with discreteness criteria applied first, followed by significance analysis. Discreteness refers to the isolation of a population from other members of the species and we evaluate this based on specific criteria. We determine significance by using the available scientific information to determine the DPS's importance to the taxon to which it belongs. If we determine that a population segment is discrete and significant, we then evaluate it for endangered or threatened status based on the Act's standards. Discreteness
Under our Policy Regarding the Recognition of Distinct Vertebrate Population Segments, a population segment of a vertebrate species may be considered discrete if it satisfies either one of the following conditions:
1. It is markedly separated from other populations of the same taxon as a consequence of physical, physiological, ecological, or behavioral factors. Quantitative measures of genetic or morphological discontinuity may provide evidence of this separation.
2. It is delimited by international governmental boundaries within which differences in control of exploitation, management of habitat, conservation status, or regulatory mechanisms exist that are significant in light of section 4(a)(1)(D) of the Act.
The focus of our DPS evaluation is the subspecies E. l. kenyoni, which occurs from the west end of the Aleutian Islands in Alaska, to the coast of the State of Washington (Wilson et al. 1991), as depicted in Figure 1. To the west of the Aleutian Islands, the sea otters in Russia are recognized as a separate subspecies, E. l. lutris. To the east of the Aleutians, a discontinuity in sea otter distribution occurs at Cook Inlet. This discontinuity also was specifically recognized during the process of identifying marine mammal stocks under the MMPA, and is reflected by the boundary separating the southwest Alaska stock of sea otters from the southcentral stock, as shown in Figure 4. Although sea otters inhabit both the eastern and western shores of lower Cook Inlet, their distribution around the Inlet is not contiguous because the presence of winter sea ice in upper Cook Inlet forms a natural break in sea otter distribution. This break in sea otter distribution in the upper portion of the Inlet persists throughout the icefree portions of the year as well (Rotterman and SimonJackson 1988).
In the lower portion of Cook Inlet, a different type of barrier exists in the form of an expanse of deep water. The distance across lower Cook Inlet ranges from 5090 km (3156 miles). While sea otters are physically capable of swimming these distances, the water depths of up to 260 m (142 fathoms) and lack of food resources for sea otters in deep water areas makes such movements across this open water area quite unlikely.
Surveys conducted for sea otters and other species in the area of Lower Cook Inlet confirm the discontinuity of sea otters in this area. In the summer of 1993, Agler et al. (1995) conducted boatbased surveys of marine birds and mammals, including sea otters, in Lower Cook Inlet. During approximately 1,574 km (978 miles) of survey effort, only one sea otter was observed in the center of the Inlet. More recently, during an aerial survey of sea otters conducted in the summer of 2002, no otters were observed on 324 km (201 miles) of transects flown across the center of Cook Inlet (USGS in litt. 2002).
Information gathered incidental to surveys of other species also
indicates that sea otters rarely occur in the offshore areas of lower
Cook Inlet, further confirming the discontinuity of sea otters in this area. NMFS has conducted aerial surveys of beluga whales,
Delphinapterus leucas, in Cook Inlet since 1993. In addition to beluga
whales, observers recorded observations of other marine mammals,
including sea otters. During these surveys, which covered a combined
total of 11,583 km (7,197 miles) of systematic transects flown across
the inlet over several years, no sea otters were observed in the
deeper, offshore areas of Cook Inlet (Rugh et al. 2000). The NMFS also
conducted a marine mammal observer program during the Cook Inlet salmon
drift and set gillnet fisheries in 1999 and 2000 (Fadely and Merklein
2001). During this period with several thousand hours of observations, no sea otters were recorded in the offshore
[[Page 6614]]
areas of Cook Inlet. Given the amount of survey effort that has been
expended, the almost complete lack of observations in deeper offshore
waters indicates that there is little exchange of sea otters between the eastern and western shores of lower Cook Inlet.
The population of sea otters represented by the southwest Alaska stock is genetically different from both the southcentral and southeast Alaska stocks. Studies using mitochondrial DNA analysis identified ten different genotypes within the range of sea otters; six of these ten different genotypes are found in Alaska (Sanchez 1992, Bodkin et al. 1992, Cronin et al. 1996). Gorbics and Bodkin (2001) demonstrated that mitochondrial DNA haplotype frequencies (a descriptive genetic characteristic) differ significantly among sea otters from southwest Alaska (west of Cook Inlet) compared to those from southcentral Alaska (east of Cook Inlet) and southeast Alaska.
Additional genetic analysis of both mitochondrial and nuclear
(microsatellite) DNA (these are two different approaches for examining genetic diversity) has shown similar patterns of genetic
differentiation and supports the identification of multiple populations
of sea otters in Alaska. As mitochondrial DNA is maternally inherited,
it can only be used to assess gene flow in females. Analysis of nuclear
genetic markers, such as microsatellite DNA, can be used to assess gene
flow by both males and females and provide a better quantification of
genetic differentiation than mitochondrial DNA alone (Cronin et al.
2002). Pairwise comparisons of both mitochondrial and nuclear DNA
between individual sampling locations from southwest and southcentral
Alaska had 40 significant differences out of 60 comparisons (67%). In
addition, tests of heterogeneity between pooled sampling locations
showed significant differences between sea otters in southwest and
southcentral Alaska in three out of three tests (Cronin et al. 2002).
These genetic differences are most likely the result of little or no
movement of animals across stock boundaries (Gorbics and Bodkin 2001).
The boundary between the southwest and southcentral stocks of sea
otters is in the area of Cook Inlet, and the aforementioned genetic
differences and lack of observations from the center of Cook Inlet
indicate that sea ice and deep water constitute physical barriers that
effectively limit animal movements between the southwest and southcentral Alaska stocks of sea otters.
Sea otters in southwest and southcentral Alaska also differ morphologically. Comparison of 10 skull characteristics between 26 adult sea otters from Amchitka Island and 42 sea otters from Prince William Sound showed numerous statistically significant differences, with the Amchitka otters being the larger of the two (Gorbics and Bodkin 2001).
These genetic and morphological differences were part of the basis for identification of sea otter population stocks under the MMPA (USFWS 2002a, USFWS 2002b, USFWS 2002c). The Service and NMFS have adopted the methods of Dizon et al. (1992), who outlined four criteria for consideration when identifying marine mammal population stocks: (1) Distribution; (2) population response; (3) morphology; and (4) genetics. Applying these criteria to the best available scientific information, Gorbics and Bodkin (2001) identified three stocks of sea otters in Alaska, the southwest, southcentral, and southeast stocks, with ranges as depicted in Figure 5.
In summary, sea otters from the Aleutians Islands to the middle of Cook Inlet are a population that differs from other sea otters in several respects. Sea otters to the west of the Aleutians are recognized as belonging to a different taxon, the subspecies E. l. lutris. Within the taxon E. l. kenyoni, there are physical barriers to movement across the upper and the lower portions of Cook Inlet, and there are morphological and genetic differences between sea otters that correspond to the southwest and southcentral Alaska stocks that we identified under the MMPA, with Cook Inlet being the boundary separating these stocks. The geographic separation between the southwest and southeast Alaska stocks is even greater than between the southwest and southcentral Alaska stocks. In addition, Bodkin et al. (1999) note that haplotype frequencies in southeast Alaska (a translocated population) differed significantly from both ``parent'' stocks.
Based on our consideration of the best scientific information available, we find that the southwest Alaska population of the northern sea otter that occurs from the Aleutian Islands to Cook Inlet, corresponding to the southwest Alaska stock as identified by us previously under the MMPA (Figure 5), is markedly separated from other populations of the same taxon as a consequence of physical factors, and there is genetic and morphological discontinuity that is evidence of this separation. Therefore, the southwest Alaska population of the northern sea otter meets the criterion of discreteness under our Policy Regarding the Recognition of Distinct Vertebrate Population Segments. Significance
If we determine a population segment is discrete, we next consider available scientific evidence of its significance to the taxon to which it belongs. Our policy states that this consideration may include, but is not limited to, the following:
1. Persistence of the discrete population segment in an ecological setting unusual or unique for the taxon,
2. Evidence that loss of the discrete population segment would result in a significant gap in the range of the taxon,
3. Evidence that the discrete population segment represents the only surviving natural occurrence of a taxon that may be more abundant elsewhere as an introduced population outside its historic range, or
4. Evidence that the discrete population segment differs markedly from other populations of the species in its genetic characteristics.
The sea otter population that corresponds to the southwest Alaska stock contains over 60 percent of the range for the subspecies E. l. kenyoni. Following protection from commercial exploitation in 1911, sea otters recovered quickly in southwest Alaska, which is a remote part of the State. In the mid1980s, biologists believed that 94 percent of the subspecies E. l. kenyoni, and 84 percent of the world population, existed in southwest Alaska (Calkins and Schneider 1985). Despite the recent population decline, current information indicates that roughly half of all sea otters in the subspecies E. l. kenyoni exist in the southwest Alaska population. Thus, the loss of this population segment would result in a significant gap in the range of the taxon because it comprises 60 percent of the range and approximately half of the population of the subspecies. In addition, the best scientific information available demonstrates the southwest Alaska population differs significantly from the southcentral and southeast Alaska stocks in terms of genetic characteristics (Gorbics and Bodkin 2001). Therefore, we find that the southwest Alaska population segment is significant to the taxon to which it belongs because the loss of this segment would result in a significant gap in the range of the taxon, and because there is evidence that it differs markedly from other populations of the taxon in its genetic characteristics.
Summary of Discreteness and Significance Evaluations
Based on the above consideration of the southwest Alaska population of the northern sea otter's discreteness and its
[[Page 6615]]
significance to the remainder of the taxon, we find that it is a
distinct population segment, or DPS, as described under our Policy
Regarding the Recognition of Distinct Vertebrate Population Segments.
The population's discreteness is due to its separation from other
populations of the same taxon as a consequence of physical factors, and
there are morphological and genetic differences from the remainder of
the taxon that are evidence of this separation. The population
segment's significance to the remainder of the taxon is due principally
to the significant gap that its loss would represent in the range of
the taxon, and also to the fact that it differs markedly from other
populations of the species in its genetic characteristics. We refer to
this population segment as the southwest Alaska DPS for the remainder of this proposed rule.
Conservation Status
Pursuant to the Act, we must consider for listing any species, subspecies, or, for vertebrates, any distinct population segment of these taxa, if there is sufficient information to indicate that such action may be warranted. We have evaluated the conservation status of the southwest Alaska DPS of the northern sea otter in order to make a determination relative to whether it meets the Act's standards for listing the DPS as endangered or threatened. Based on the definitions provided in section 3 of the Act, endangered means the DPS is in danger of extinction throughout all or a significant portion of its range, and threatened means the DPS is likely to become endangered within the foreseeable future throughout all or a significant portion of its range.
Summary of Factors Affecting the Species
Section 4 of the Act and regulations (50 CFR part 424) promulgated
to implement the listing provisions of the Act set forth the procedures
for adding species to the Federal list. As defined in section 3 of the
Act, the term ``species'' includes any subspecies of fish or wildlife
or plants, and any distinct population segment of any species or
vertebrate fish or wildlife which interbreeds when mature. We may
determine a species to be an endangered or threatened species due to
one or more of the five factors described in section 4(a)(1) of the
Act. These factors, and their application to the southwest Alaska DPS of the northern sea otter, are as follows:
A. The Present or Threatened Destruction, Modification, or Curtailment of Its Habitat or Range
Habitat destruction or modification are not known to be major factors in the decline of the southwest Alaska DPS of the northern sea otter. At present, no curtailment of range has occurred, as sea otters still persist throughout the range of the DPS, albeit at markedly reduced densities. However, as there is no evidence to suggest that the decline has abated, it is possible that additional losses may occur that would curtail the range of sea otters in southwest Alaska.
Humaninduced habitat effects occur primarily in the form of removal of some of the prey species used by sea otters as a result of resource use such as commercial fishing, which occurs throughout southwest Alaska. While there are some fisheries for benthic invertebrates in southwest Alaska, there is little competition for prey resources due to the limited overlap between the geographic distribution of sea otters and fishing effort. In addition, the total commercial catch of prey species used by sea otters is relatively small (Funk 2003).
In studies of sea otters in the Aleutians, there was no evidence that sea otters are nutritionally stressed in that area, and foraging behavior, measured as percent feeding success, has increased during the 1990's (Estes et al. 1998).
Development of harbors and channels by dredging may affect sea otter habitat on a local scale by disturbing the sea floor and benthic invertebrates that sea otters eat. Typically, the number and size of these activities are small relative to the overall range of the DPS. B. Overutilization for Commercial, Recreational, Scientific, or Educational Purposes
Following 170 years of commercial exploitation, sea otters were protected in 1911 under the International Fur Sea Treaty, which prohibited further hunting. In 1972, the Marine Mammal Protection Act (MMPA) established a moratorium on the take of all marine mammals in U.S. waters. Section 101(b) of the MMPA provides an exemption for Alaska Natives to take marine mammals for subsistence purposes. Although the Native exemption was established in 1972, subsistence harvest of sea otters did not begin in earnest until the mid1980s (SimonJackson 1988). In October 1988, we initiated the marine mammal Marking, Tagging, and Reporting Program (MTRP) to monitor the harvest of sea otter, polar bear (Ursus maritimus), and Pacific walrus (Odobenus rosmarus divergens) in Alaska (50 CFR 18.23(f)). The majority of the sea otter harvest occurs in southeast and southcentral Alaska. Information from the MTRP estimates the subsistence harvest of sea otters from the southwest Alaska DPS averaged less than 100 sea otters per year during the 1990s (Burn and Doroff in prep.). Based on the magnitude of the current decline, the impact of the subsistence harvest is negligible.
Scientific research on sea otters occurs primarily as aerial and skiff surveys of abundance, and such surveys are conducted infrequently (once every few years) and when they occur, they last for very short durations of time. During the
FOR FURTHER INFORMATION CONTACT Douglas Burn, (see ADDRESSES) (telephone 907/7863800; facsimile 907/7863816).
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