Info: Pacific marine mammals

Michael Williamson (williams@whale.simmons.edu)
Mon, 22 Nov 1995 16:31:47

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From: Michael Williamson <williams@whale.simmons.edu>
Subject: Info: Pacific marine mammals
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http://kingfish.ssp.nmfs.gov/olo/unit23.html> UNIT 23 PACIFIC MARINE
MAMMALS
>
> INTRODUCTION
>
>         In 1791, New England whalers first rounded Cape Horn, and by 1820
> they had pressed on to Hawaii where they began to take on
> provisions and recruit men for their northern summers in
> bowhead-whale-rich Alaskan waters. An average bowhead yielded 100
> barrels of oil, making the fishery attractive to whalers, even
> though over 100 whaling ships were lost between 1826 and 1900 due
> to crude charts and icy Alaskan waters.
>         California's whaling industry is documented back to the mid 1850's
> when shore whaling stations were set up, ranging from the state's
> northernmost border at Crescent City south to San Diego. With a
> hunting range of about 10 miles, shore fisheries harvested only
> whales frequenting the nearshore waters. The northern stations
> targeted humpback whales at first, but included gray whales in
> short order; southern stations took advantage of the natural
> southward migration patterns of the gray whale.
>         Sea lions, reported to be abundant along the California coast and
> offshore islands before 1860, were also exploited for food, oil,
> and clothing. From 1860 to 1870, thousands were harvested for oil.
> In 1915 and 1916, a bounty of $2.00 each was paid on 4,074 sea
> lions. From the late 1920's until passage of the MMPA in 1972,
> commercial and sport fishermen were allowed to kill sea lions that
> interfered with their fishing operations.
>         The Hawaiian monk seal is thought to have been abundant when
> Europeans discovered the Hawaiian Islands. However,
> overexploitation made this seal the endangered species it is today.
> Before passage of the Marine Mammal Protection Act and the
> Endangered Species Act the only protective measures for marine
> mammals were through the International Whaling Commission (IWC),
> and those were for only certain depleted large whales.
>         All marine mammals are now protected by the MMPA and by the ESA.
> Other management responsibilities are addressed in the Magnuson
> Fisheries Conservation and Management Act, which extends the
> jurisdiction of the MMPA throughout the U.S. exclusive economic
> zone, and the Whale Conservation Act, which was intended to further
> aid the recovery of whales.
>
> SPECIES AND STATUS
>
>         At least 50 species of marine mammals occur in U.S. Pacific waters
> (36 whales, dolphins, and porpoises; 11 seals and sea lions;
> walrus; polar bear; and sea otter). Fourteen are commonly seen
> along the coast (gray whale, bottlenose dolphin, harbor seal, and
> others), whereas the 28 others frequent offshore or remote island
> waters (beaked whales, ribbon seal, Hawaiian monk seal, and
> others), or are severely reduced in numbers and thus seldom seen
> (North Pacific right whale and Guadalupe fur seal, for example).
> Table 2<%12>3<%0>-1 summarizes what is known about the status and
> trends of several Pacific marine mammals. Brief discussions below
> for selected species give additional data on distribution, current
> and historical abundance, and population trends.
>
> Eastern Tropical Pacific (ETP) Dolphins
>
>         Four species spotted, spinner, striped, and common dolphin (12
> stocks) are incidentally taken in the international fishery for
> yellowfin tuna in the tropical Pacific waters off Mexico and
> Central America. Until the 1980's, the U.S. maintained the largest
> fleet in the fishery. Although mortality of dolphins was in the
> tens and hundreds of thousands for the first decade of the fishery,
> that mortality has been reduced in recent years (less than 20,000
> were killed in 1992). Because these four species also occur in U.S.
> waters, and because the U.S. was the major market for the fishery,
> NMFS initiated assessments of these populations.
>         Three stocks of spotted dolphin are currently recognized in the
> ETP: the northeastern stock, the west/south stock, and the coastal
> stock. Based on analyses of five years of research vessel data, the
> population size for the northeastern stock is estimated to be
> 731,000 individuals, for the west/south stock, 1,298,000 indi-
> viduals, and for the coastal stock, 36,000 individuals. Eastern
> spinner dolphins number 632,000, whereas the whitebelly spinner
> dolphins number about 1,019,000. Stock specific estimates of common
> dolphin abundance were based on too few sightings and are
> considered unreliable; therefore in 1992, NMFS initiated research
> vessel surveys designed specifically to obtain estimates of
> abundance for common dolphin stocks. A pooled estimate of 3,093,300
> encom- passes the northern, central, and southern stocks of common
> dolphin. Striped dolphin are currently considered to consist of a
> single stock in the ETP with an estimated abundance of 1,918,000
> individuals.
>         Relative abundance estimates have also been generated from dolphin
> sightings obtained using tuna vessel observer data (TVOD). Trends
> in these estimates suggest that most dolphin stocks declined in the
> 1970's, but have been relatively stable since the 1980's. The
> northern stock of common dolphin is an exception. A significant
> decrease in sightings has been observed in the ETP. The cause(s) of
> the decrease in this region is not clear, but it has been suggested
> that if the decline cannot be attributed to fishery mortality, then
> it may have been caused by a shift in distribution in response to
> environmental fluctuations.
>
> Harbor Porpoise
>
>         Harbor porpoise appear to have more restricted movements along the
> western U.S. coast than along the eastern coast. Studies have shown
> some indication that harbor porpoise do not mix freely between
> California, Oregon, and Washington. Regional differences have also
> been seen within California; therefore, it has been recommended
> that animals inhabiting central California be treated as a separate
> stock for management purposes.
>         The current estimate for the central California stock is 3,806. The
> combined estimate for northern California, Oregon, and Washington
> outer coast is 45,713, and for the waters of Puget Sound is 3,352.
> The species was once abundant in Wash-ington's inland waters,
> especially southern Puget Sound, but its abundance is very low
> there now. Harbor porpoise tend to concentrate at the mouth of the
> Columbia River and at many other bays. The kill of harbor porpoise
> is largely limited to set gillnet fisheries for halibut and
> rockfish in central California (coastal setnets are not allowed in
> northern California, and harbor porpoise do not inhabit southern
> California). In recent years, the kill has decreased primarily as
> a result of decreased fishing effort in areas of high harbor
> porpoise concentrations.
>
> Bowhead Whale
>
>         The endangered bowhead whale has ranged as far as the polar ice
> fields of the Northern Hemisphere. Total pre-whaling abundance is
> believed to be 12,000-18,000, but by 1900 it was probably in the
> low thousands. In the U.S. western Arctic, 18,650 bowheads were
> killed by Yankee whalers between 1848 and 1914 from a population
> estimated at less than 20,000. The take by Alaska Eskimos has
> averaged 20-40 whales per year since 1914. The present population,
> 7,500, is about 41% of its 1848 carrying capacity. The stock has
> been increasing since commercial whaling ended and has grown by
> 3.1%/year since 1978 (Fig. 2<%8>3<%0>-1).
>
> Gray Whale
>
>         Still listed under ESA as endangered is the western stock of North
> Pacific gray whales. The eastern North Pacific or  California
> stock was heavily exploited by Yankee whalers in the last half of
> the 19th century. The 1987/88 stock size, 20,869, is believed to be
> equal to or larger than the estimated size of the 1846 population
> of 15,000-20,000, but below estimates for a carrying capacity of
> 24,000. Population growth rate was 3.3%/year between 1967 and 1988,
> despite a subsistence catch of 167 whales per year by the former
> Soviet Union (Fig. 2<%8>3<%0>-2). In light of this recovery, the
> Secretary of Commerce has determined that the eastern Pacific stock
> should be removed from the ESA's list of endangered and threatened
> wildlife.
>
> Humpback Whale
>
>         The endangered humpbacks in the eastern North Pacific Ocean migrate
> between the subtropical waters of Hawaii and coastal Mexico during
> the calving season and the temperate and subarctic waters of
> northern California and Alaska where they feed. Previously,
> humpback whales were estimated to be at 13% of their pre-whaling
> population size estimate of 15,000 (ca. 1850). More recent
> preliminary analysis of photographic identification of individual
> whales in the North Pacific suggests that the total population may
> exceed the current estimate of 1,398-2,040 individuals.  Detailed
> analyses of the available data may provide a better understanding
> of the status of these whales.
>
> Northern (Steller) Sea Lion
>
>         The northern or Steller sea lion, classified as threatened under
> the ESA, ranges in coastal waters of the North Pacific Ocean from
> California to Japan. The species has declined sharply throughout
> its range in just the last 20 years, and it is now well below its
> optimum level. The number of adults and juveniles in U.S. waters
> crashed from 154,000 in 1960 to 40,000 in 1992. Most of this 73%
> decline occurred in Alaska waters between Kenai and Kiska, where
> sea lion trend site counts declined from 105,289 in 1959 to about
> 21,000 in 1992 (Fig. 2<%6>3<%0>-3). The decline in Alaska is
> believed to be due to a combination of incidental kills in
> fisheries, illegal shooting, changes in the numbers and/or quality
> of prey, and possibly unidentified factors. The Steller sea lion
> population off Washington and Oregon is low but stable at about
> 3,000. In California, they have slowly declined since the 1950's to
> about 2,000. The 1992 range-wide estimate for this species is
> 116,000.
>
> Northern Fur Seal
>
>         The northern fur seal of the North Pacific Ocean, considered
> depleted under the MMPA, ranges across subarctic Pacific Rim waters
> from California to Japan. It numbers 982,000 in U.S. waters. The
> major U.S. breeding population is on Alaska's Pribilof Islands of
> St. Paul and St. George. Production on the Pribilof Islands dropped
> more than 60% between 1955 and 1980, but has since been stable. On
> St. George Island, production has continued to decline about
> 6%/year since 1970 (Fig. 2<%12>3-<%0>4). Small U.S. breeding
> populations are also found on Alaska's Bogoslof Island (1,500), and
> California's San Miguel Island (6,000).
>
> California Sea Lion
>
>         There are three subspecies of California sea lion found on the U.S.
> west coast and British Columbia, in the Galapagos Islands, and in
> Japan (probably extinct). The breeding range of California sea
> lions extends from the Channel Islands off the coast of southern
> California, U.S., to Isla Santa Margarita, on the Pacific coast of
> Baja California, Mexico, and at various islands located in the Gulf
> of California, Mexico. Annual U.S. pup production during 1990
> exceeded 26,700 pups. The U.S. population is currently increasing
> at a rate of 10.2% annually (since 1983). In 1990, the U.S. stock
> had a population size of 111,000. The total population size of the
> western Baja California stock was estimated at 74,500.
>         A number of human-related interactions, such as incidental take
> during fishing operations, entanglement, illegal killing, and
> pollutants, result in deaths of sea lions. Estimates of California
> sea lions killed incidentally by commercial setnet and driftnet
> fishing vessels operating off California were obtained from data
> collected by scientific observers on fishing vessels, fishing log
> books, and fish landing receipts. Those estimates ranged from 1,865
> sea lions killed in 1991 to 4,288 killed in the fishing year
> 1986-87. Sea lions have also been observed entangled with
> monofilament line, gillnet and trawlnet fragments, packing bands,
> rubber bands, polyfilament rope and line, and other manufactured
> items. Studies of entanglement rates indicate that entangled
> animals make up a small proportion of the population. There is also
> evidence of sea lion mortality resulting from gunshot wounds. These
> interactions appear to be a result of fishermen shooting the
> animals when either their gear or their catch was in danger.
>         Studies have been initiated to look at rates of premature births in
> relation to the level of environmental contaminants and disease
> agents.
>
> Harbor Seal
>
>         The Pacific harbor seal ranges along the west coast of North
> America from Cedros Island, Baja California, Mexico, northward to
> western Alaska. In a recent count of harbor seals during their
> molting period (which is considered to be the time of peak
> abundance on shore), approximately 23,000 harbor seals were
> estimated to reside in the Channel Islands and along the California
> mainland (Fig. 23-6). The population sizes of harbor seals in
> Oregon and Washington have been estimated at 45,700 seals. Harbor
> seals in the Gulf of Alaska have declined significantly during the
> past two decades.
>
> Hawaiian Monk Seal
>
>         The Hawaiian monk seal is limited to the small islands and atolls
> of the 1,100-mile northwest portion of the Hawaiian Archipelago.
> This species is listed as endangered under the ESA, due to a
> decline of approximately 50-60% between the late 1950's and the
> late 1970's. The largest population is located at French Frigate
> Shoals, and since 1989 this population has declined by 25-40%. At
> present, the total population is approximately 1,550. Since 1985,
> average counts (including pups) at the five main breeding sites
> peaked at 656 in 1986, but have generally declined since then to a
> low of 480 in 1991. Pup production during the same period has been
> highly variable, increasing from 1985 to 1988, declining 35% in
> 1990, and increasing again in 1991 and 1992 (Fig. 23-7).
>
> ISSUES
>
>         Studies of marine mammal populations have focused on four primary
> questions: 1) Have fisheries interactions and other human-related
> activities directly harmed marine mammals or significantly altered
> the carrying capacity of the marine ecosystem for them; 2) Are the
> depleted marine mammals recovering, and have the best steps been
> taken to speed their recovery; 3) What actions are necessary to
> minimize potential conflicts between the ESA, MMPA, MFCMA, and
> other Federal laws on marine resources and fisheries management;
> and 4) How can marine mammal populations be monitored in the face
> of environmental variability?
>         Specific concerns in light of these research issues are discussed
> below.
>
> Bycatch and Multispecies Interactions
>
>         El Nio events in California are often associated with increased
> interactions between California sea lions and fisheries. This seems
> to be related to a change in forage conditions for sea lions during
> El Nio events, where sea lions tend to feed more heavily on fish
> caught by commercial and recreational fishermen. Given the
> increased number of California sea lions at this time, the most
> recent El Nio could result in major problems for west coast
> fishermen unless methods for minimizing this interaction are
> developed in the near future.
>         Another issue involves competition for food. U.S. and foreign
> commercial fisheries have been operating in the eastern North
> Pacific for more than 100 years, and fish catches have been
> sustained there for many decades. Some fish populations, however,
> have collapsed and are no longer commercially viable, such as the
> California sardine. The impact of removing millions of fish and
> shellfish from the marine ecosystem each year on the marine mammals
> that also depend on them is unknown.
>         Marine mammals are also incidentally killed in many fisheries. In
> recent years, the fishery-caused mortality of spotted, spinner, and
> common dolphins has been reduced dramatically relative to mortality
> levels in 1986. In 1991, the kill of dolphins in the ETP, expressed
> as a percentage of population size, was less than 2% for all the
> stocks. The current population is thought to be able to withstand
> this level of mortality. Still, incidental mortality in 1991 likely
> exceeded 20,000 animals. An in- ternational regime is currently
> being developed by nations that purse seine for tunas in the ETP
> with the goal of eliminating dolphin mortality entirely over the
> next few years.
>         The harbor porpoise kill in California's fisheries declined from
> 200-300/year in the mid-1980's to less than 100/year after gillnet
> fishing ceased. The harbor porpoise kill by the Makah Indian tribal
> setnet salmon fishery off the north coast of Washington declined
> from over 100 in 1987-88 to 13 in 1990 when the fishing effort was
> reduced.
>         The known kill of Steller sea lions in Alaska fisheries has
> declined from over 1,400 in 1982 to 23 in 1990. The numbers killed
> in other fisheries is believed to be even smaller.
>
> Recovery of Protected Species
>
>         Eleven U.S. west coast marine mammal species are listed as
> endangered or threatened under the ESA. Though the data are
> limited, right whales in the eastern North Pacific Ocean are
> believed to be near extinction: only <%8>5<%0>-7 sightings have
> been made in the past 25 years. There are far too few data on other
> species, such as blue and humpback whales, to judge whether any
> recovery is taking place. Gray whales have recovered to levels near
> those estimated for the mid-1800's. California sea lions, northern
> elephant seals, and harbor seal populations along the west coast
> are also increasing. Some human activities may, however, be
> affecting the recovery of some species. For example, adult female
> humpback whales with calves have apparently been abandoning
> traditional nearshore calving and calf rearing habitat near Maui,
> Hawaii, possibly in response to repeated human interference or
> contact.
>         In the case of the Hawaiian monk seal, progress in managing the
> recovery of this species varies among the main breeding
> populations. At Kure Atoll, with a high level of management
> intervention, excellent progress is apparent in the increase in
> number of births from one in 1986 to 14 in 1992. In addition, the
> management programs have bolstered the immature size classes, and
> recruitment of females into reproductive age classes is expected to
> further enhance recovery at this site. The Pearl and Hermes Reef
> population also appears to be growing and is expected to continue
> its recovery in the near future.
>         The largest monk seal population, at French Frigate Shoals, may be
> near its environmental carrying capacity, in which case further
> growth would not be expected. Indeed, in the past three years, this
> population has declined, due to poor juvenile survival and low
> birth rates triggered by reduced prey availability. Management
> efforts have been directed toward rehabilitation of juvenile
> females to enhance their survival and reproductive potential. In
> addition, the foraging ecology of seals at French Frigate Shoals is
> being assessed through studies of relative prey abundance over
> time, as well as seal movement and diving patterns using
> satellite-linked telemetry.
>         Populations at Laysan and Lisianski Islands have not grown as
> expected, and appear to be limited by high mortality of females due
> to male mobbing behavior, where multiple males simultaneously
> attempt to mate with a single female.  Management has focused on
> monitoring the occurrence of such behavior and conducting research
> into mitigation methods. Currently, efforts aim to disassociate
> offending males from the breeding process by chemically suppressing
> their testosterone level and aggressive reproductive behavior.
> The status of the species as a whole is indicated by the annual
> mean beach counts of seals and the number of pups born. The total
> number of births has been highly variable, but without trend since
> the early 1980's. However, mean counts have fallen since 1985,
> largely as a result of declines at French Frigate Shoals. Efforts
> to reverse this trend will continue, through rehabilitation of
> seals at French Frigate Shoals and elimination of mobbing-related
> mortality at Laysan and Lisianski Islands.
>         Recovery plan action will provide a way to gauge progress in the
> restoration of endangered and threatened resources.
>
> Scientific Advice and Adequacy of Assessments
>
>         Some northern pinniped populations, such as Steller sea lion,
> northern fur seal, and harbor seal, have declined in the last 20
> years. During the same period, other pinniped populations farther
> south along the west coast have increased, such as harbor seal,
> California sea lion, northern fur seal, and northern elephant seal.
> Growing marine mammal populations will raise different fishery
> management concerns. The biological information needed to assess
> and manage these problems is generally lacking.
>         Marine mammal populations need to be monitored on a regular basis.
> However, annual changes in environmental conditions make accurate
> monitoring difficult. For example, large-scale
> oceanographic changes associated with El Nio conditions
> affect the distributions of whales. Because of the expense
> involved, many of the marine mammal populations are moni-tored only
> once every 2-5 years. Generally, precision of marine mammal
> population estimates are such that changes in population size must
> be on the order of 20-50% to be detectable, but management advice
> is often needed before such large changes occur.
>
> Progress
>
>         International Dolphin Conservation Act of 1992: Bill H.R. 5419
> amended the MMPA to establish a global moratorium to prohibit
> harvesting of tuna through the use of purse seine nets deployed on
> or to encircle dolphins or other marine mammals.  Proposed
> Management Regime for Marine Mammals: The Marine Mammal Protection
> Act governs the management of marine mammals in the United States.
> Prior to the 1988 amendments to the MMPA, fisheries could only be
> granted permits to take marine mammals incidentally if there was
> scientific evidence to prove that all stocks of marine mammals
> involved in the fisheries were at or above their optimum
> sustainable population (OSP) level. However, sufficient evidence
> regarding the status relative to OSP only exists for a few stocks.
>         Due to problems and economic losses associated with this system of
> management, the Act was amended in 1988 to allow a 5-year interim
> exemption period, during which time the incidental taking of marine
> mammals was permitted in commercial fishing operations.  During
> this time, it was expected that additional information would be
> gathered on the species involved and on the nature and extent of
> their interactions with different fisheries.  This period ended on
> 1 October 1993 and a decision will have to be made between the old
> system or development of a new management scheme for all marine
> mammals. NMFS is currently collaborating with a number of
> scientists, conservation organizations, and fisheries experts in
> order to formulate this new regime which will require the best
> available information on marine mammal stocks.