Atlantic Marine Mammals

Michael Williamson (
Mon, 22 Nov 1995 16:31:45

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From: Michael Williamson <>
Subject: Atlantic Marine Mammals
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>         Marine mammals have been historically important in the United
> States both as targets for commercial harvests and in ecological
> interactions with commercial fisheries. Some scientific attention
> was given to marine mammals as early as 1851 when Matthew F. Maury
> of the U.S. Navy's Depot of Charts and Instruments published his
> whale charts based upon whalers' logs and records of sightings. The
> U.S. Fish Commission, after its creation in 1871, gave more
> attention to marine mammals, commissioning, for example, Starbuck's
> 1878  History of the American Whale Fishery.  The omnibus series
> titled  The Fisheries and Fishery Industries of the United States
> by G. B. Goode and Associates in 1884 described fisheries for the
> great whales as well as smaller whales (e.g. pilot whales,
> bottlenose dolphins, and bottlenose whales) in the North Atlantic.
>         In addition to these direct fisheries, there was also interest in
> the indirect effects of marine mammals on other fisheries. Goode
> also described the destructiveness of marine mammals to fisheries,
> a theme that the U.S. Commissioner of Fisheries used in 1889 in
> supporting a fish meal factory to be built in Woods Hole. The
> commissioner speculated that the 20 tons of predators such as
> porpoises, skates, and dogfish that the proposed factory would
> process annually  should present a marked influence upon the
> sup-ply of edible fishes.   The interest of the U.S. Fish
> Commission was primarily in terms of fisheries, and little
> biological study appears to have been done of marine mammals in
> this region beyond the taxonomic studies of Frederick True starting
> in the 1880's. For example, he provided written instructions to the
> lighthouse keepers on  the best means of collecting and preserving
> specimens of whales and porpoises.
>         With the declining importance of the U.S. harvests of east coast
> species of marine mammals in the late 1800's and early 1900's, the
> incentive for systematic scientific study of the species inhabiting
> northeastern U.S. waters declined. In the 1930's and 1940's,
> Remington Kellogg at the Smithsonian and William Schevill at
> Harvard undertook taxonomic studies, but it wasn't until the late
> 1940's that cetacean biology began to be investigated more
> systematically. Then Schevill began a series of investigations at
> the Woods Hole Oceanographic Institution of cetacean acoustics that
> are still continuing. In the early 1970's, several other
> researchers began studying marine mammals in this region. The
> results of this earlier work was addressed in 1979 when the U.S.
> Marine Mammal Commission sponsored a workshop to help define
> research needed for the study of marine mammals on the U.S. east
> and Gulf coasts and in 1989 at a NMFS-sponsored workshop on Gulf of
> Mexico marine mammal research needs.
>         These workshops set a research agenda that was immediately
> addressed by agencies such as the Minerals Management Service (MMS)
> and the National Marine Fisheries Service. During the 1980's,
> several institutions in the northeast developed active research
> programs which have resulted in a body of knowledge that is being
> drawn upon in developing management approaches for several critical
> marine mammal issues in the region. In the 1990's, increased
> attention has been focused on the characterization of marine mammal
> fauna of the U.S. Gulf of Mexico and the Mid-Atlantic Bight.
>         Thirty-five species of marine mammals range the U.S. Atlantic and
> Gulf of Mexico waters (32 whales, dolphins, and porpoises, two seal
> species, and one manatee). Their status is poorly known, but some,
> like the northern right whale, Atlantic coastal bottlenose dolphin,
> and harbor porpoise, are under stresses that may affect their
> survival. Others, like the harbor seal, are increasing in
> abundance.
>         Table 22-1 summarizes what is known about the status and trends of
> several Atlantic marine mammals. Brief summaries for selected
> species give additional data on distribution, current and
> historical abundance, and population trends.
> Bottlenose Dolphin
>         The number of discrete bottlenose dolphin stocks is unknown. There
> appear to be offshore and coastal types, possibly forming at least
> two distinct populations. There are no comprehensive population
> estimates, but abundance in the Gulf of Mexico is estimated at
> 35,000-45,000<%0> in waters of 100
> fm or less. Aerial surveys between Cape Hatteras and Nova Scotia in
> 1979-82 suggest a northeast U.S. total of 10,000-13,000
> individuals. However, a large die-off of bottlenose dolphins in
> 1987-88 may have resulted in a 50% or greater decline in the
> nearshore or coastal type. As a result of that mortality, the
> population has been classified as depleted under the MMPA. A survey
> of the nearshore environment from New Jersey to Cape Hatteras in
> 1987 resulted in an estimate of abundance of 1,050-7,500 dolphins,
> which were assumed to be of the coastal type.
> Pilot Whale
>         Two species of pilot whales occur in the North Atlantic, the
> shortfin pilot whale in the south and the longfin in the north. The
> range of the two species overlaps seasonally in the Mid-Atlantic
> region of the western North Atlantic. The longfin pilot whale
> occurs northward into Canadian and Greenland waters and eastward to
> Europe; it is subject to an ongoing harvest around the Faroe
> Islands and incidental capture in several fisheries in U.S. and
> Canadian waters. The shortfin pilot whale may be subject to a low
> level of bycatch in several U.S. fisheries. Population structure
> and general life history of both species is very poorly known.
> Abundance has been estimated for the longfin pilot whale in the
> eastern North Atlantic (750,000) and for the continental shelf
> region of the western North Atlantic (roughly 11,000).
> Fin Whale
>         Fin whales, listed as endangered under the ESA, are probably the
> most numerous large cetaceans in temperate waters of the western
> North Atlantic Ocean. They range widely throughout the continental
> shelf in all seasons, but most sightings occur from the Great South
> Channel on Cape Cod, north throughout the southwest Gulf of
> Maine. Stock structure and total abundance are unknown. An estimate
> of abundance off the northeast coast in 1979-82 was 5,200 in spring
> and 1,500 in winter.
>         Important research and management questions are whether separate
> stocks exist, the location of calving grounds and annual calf
> production, and the location of the wintering grounds for the
> northwest Atlantic population.
> Humpback Whale
>         The humpback whale is listed as endangered. Reasonably discrete
> summer stocks occur in the Gulf of Maine, Gulf of St. Lawrence, and
> the waters of Newfoundland-Labrador, west Greenland, Iceland, and
> Norway. The estimated total population is about 5,100 whales. Along
> the northeast coast, humpbacks frequent the Great South Channel,
> Georges Bank, Stellwagen Bank, and Jeffreys Ledge during summer.
> A minimum estimate of the population prior to commercial whaling
> (about 1865) was 4,400-4,700 humpbacks.
>         Entanglement with fishing gear and sporadic toxin-induced die-offs
> are prob-lems for the species. In recent years the number of
> sightings of young humpbacks in the Mid-Atlantic region has
> increased, generally in the areas of the Chesapeake and Delaware
> bays.
> Right Whale
> Northern right whales occur on the continental shelf from Florida
> to Nova Scotia. The endangered western North Atlantic stock is the
> only northern hemisphere right whale population with a significant
> number of individuals (300-350) the other stocks being virtually
> extinct. The pre-eighteenth century population may have been as
> high as 10,000, and, if so, the current population is more than 95%
> depleted.
>         Individual identification, satellite tagging, genetic analysis, and
> the use of video cameras to document behavior are new research
> methods that have been applied in recent years. Many questions,
> however, remain. Among them are the location of summering grounds
> for 30% of the population and wintering grounds for 80% of the
> population. Human impacts (net entanglement and ship strikes) are
> affecting some 60% of the population and may be inhibiting
> recovery. Two areas important to the northern right whale, the
> summer feeding grounds off the New England coast and the winter
> calving area along the Georgia and northern Florida coast, have
> recently been proposed as critical habitat.
> Harbor Porpoise
>         The northwestern Atlantic harbor porpoise is found from
> Newfoundland, Canada, to Florida. It is hypothesized that there are
> three populations: Newfoundland, Gulf of St. Lawrence, and Gulf of
> Maine-Bay of Fundy. However, there is not enough evidence to test
> this hypothesis against the alternative of a single population.
> Summer aggregations occur in the Gulf of Maine, Gulf of St.
> Lawrence, and the east coast of Newfoundland. The winter
> distribution is poorly understood. The 1991-92 population estimate
> of the Gulf of Maine population is 47,200 (95% CI:
> 32,800-68,000). No useful estimates of abundance for the other
> populations exist. The average estimate of annual mortality by the
> U.S. Gulf of Maine sink gillnet fishery from 1990 and 1992 is about
> 1,700 (range 900-2,400). These estimates do not include bycatch
> from fisheries south of Cape Cod or north of the U.S. border. The
> estimated bycatch of the other two populations is largely unknown,
> though some new data do exist for the Bay of Fundy, which are
> currently being analyzed.
> Harbor Seal
>         Harbor seals, year-round residents of Maine and eastern Canada, are
> seasonal-winter residents in southern New England (SNE). Harbor
> seal numbers have apparently increased in recent years, due
> primarily to protection under the MMPA. Recent surveys suggest that
> 26,000 harbor seals occur in the Gulf of Maine, and they are
> increasing. Bycatch levels are relatively low, and major concerns
> are competition with fisheries and periodic disease outbreaks.
> Beaked Whales
>         There are four species of beaked whales in the northwest Atlantic,
> however little is known on their distribution, biology, and
> population structure. Based on cetacean surveys conducted during
> the early 1980's and 1990's, these species are distributed along
> the shelf edge (2,000 m), principally along the southern edge of
> Georges Bank and associated with oceanographic fronts and Gulf
> Stream meanders. Population estimates for these species are not
> available. Determination of minimum abundance estimates will
> require substantial survey effort in shelf-edge waters and waters
> seaward to at least the Gulf Stream off the northeast U.S. and
> eastern Canada coasts.
> Bycatch and Multispecies Interactions
>         Studies of marine mammal populations have focused on three primary
> questions: 1) Have fisheries interactions and other human-related
> activities directly harmed marine mammals or adversely altered
> their environment; 2) Are the depleted and endangered marine
> mammals recovering, and have the best steps been taken to speed
> their recovery; and 3) What actions are necessary to minimize
> potential conflicts between the ESA, MMPA, MFCMA, and other Federal
> laws on marine resources and fisheries management?
>         Much attention has been focused on the first of the three
> questions, in monitoring the numbers of marine mammals killed due
> to human-related causes and in attempting to determine the size of
> marine mammal populations. Current methods for estimating
> abundances, and thus, trends of marine mammal populations, require
> a significant effort and expense and take many years to obtain
> desired levels of precision. These surveys are continuing and will
> need to be repeated at regular intervals to provide the best advice
> for management of marine mammal populations.
>         In the meantime, there are some populations thought to be at risk
> or otherwise of significant management concern. For example, the
> bycatch of harbor porpoise in sink gillnet fisheries in U.S. and
> Canadian waters appears to be large relative to likely levels of
> natural production for this species. The magnitude of this bycatch
> and the abundance of this species were reviewed in an international
> scientific workshop in May 1992, and it was recommended that the
> bycatch should be reduced. Three methods for accomplishing this
> have been identified: Setting maximum catch limits annually,
> setting time and area closures, and modification of the sink
> gillnet fishing gear. Evaluation of these options and research
> necessary to actually implement one or more of them are of high
> priority.
>         Bycatch of other species in this region is lower than that for
> harbor porpoise, but its significance is not known because of
> uncertainties about abundance of those species. Of special concern
> is the bycatch of several species of beaked whales in the U.S.
> drift gillnet fishery for swordfish.
>         Human activity may have a profound influence on the recovery of
> northern right whales in the Atlantic. The population was depleted
> by over exploitation to such an extent that net gains in population
> size have been extremely slow. The annual loss of even a single
> right whale incidental to human activity, such as being struck by
> a merchant ship or entangled in fishing gear, may prohibit or
> significantly prolong their recovery to the point where northern
> right whales are no longer fully functional members of their marine
> ecosystems.
>         Increasing populations of pinnipeds, particularly harbor seals and
> grey seals, present a different management issue. Commercial
> activity, such as fishing and coastal development, has become a
> major source of income for many people inhabiting U.S. coastal
> areas. This growth of commercial activity occurred during a period
> when marine mammals were severely depleted due to over exploitation
> by humans, whether for direct commercial purposes or to reduce
> human-perceived competition for resources. Now that some species
> are beginning to recover toward pre-exploitation levels, conflicts
> between the increasing populations of marine mammals and human
> activity are beginning to surface. For example, harbor and grey
> seals may prey upon Atlantic salmon being raised in commercial net
> pen operations. The resolution of these conflicts presents a
> management problem that did not exist while marine mammal
> populations were severely depleted.
> Recovery of Protected Species
>         Over the past year Endangered Species Recovery Plans have been
> completed for the humpback and right whales in this region. These
> plans outline comprehensive management and research agendas that
> would take initial steps toward ensuring the recovery of these
> species. Critical issues for both species are entanglement and
> mortality in fishing gear. For the humpback whale, entanglement
> occurs especially in Canadian waters, making it important to
> determine the genetic relationship between animals in U.S. and
> Canadian waters to assess the effects of this bycatch.
>         In addition to entanglement, the right whale appears to be prone to
> collisions with ships, which may kill or seriously injure
> individuals. The mitigation of these human impacts on right whales
> is listed as a Priority One Item in the Implementation Schedule of
> the national Right Whale Recovery Plan. This topic was also seen as
> a top priority by participants in the Right Whale Workshop convened
> by NOAA/NMFS in Silver Spring, Maryland, in  April 1992.
>         Over the past few years, there have been several instances of
> unusual mortality events which have affected marine mammal
> populations. Such events have been detected in harbor seals,
> humpback whales, and bottlenose dolphins along the Atlantic and
> Gulf of Mexico coasts. About 350 dead harbor seals were recovered
> along the New England coast during an influenza outbreak in
> 1979-80. A smaller outbreak of the same disease occurred in 1982.
> Although there were not high levels of mortality, stranding network
> members were responsible for isolating phocine distemper in harbor
> seals in 1992. The same disease was responsible for the death of
> over 17,000 seals in Europe in 1988. In late 1987, 14 humpback
> whales apparently died due to the presence in prey species of a
> biotoxin associated with algal blooms.
>         Three different mortality events affected bottlenose dolphins in
> the last few years. A major mortality event affected the coastal
> migratory stock on the east coast in 1987-88. It was estimated that
> the population declined over 50% and, as a result, this stock has
> been designated as depleted. In the winter and spring of 1990,
> mortality levels of bottlenose dolphins along a portion of the Gulf
> coast were much higher than usual. In 1992, over 100 dead
> bottlenose dolphins were recovered from a two-county area of Texas
> within a two-month period. Large numbers of fish were also killed.
> Survey results suggest that it is unlikely that these mortalities
> had a significant impact on the population.
>         The stranding network is an important source of information on the
> biology of marine mammals. Data on vital rates, condition of the
> populations, and importantly, sources of mortality, can be acquired
> from stranded animals. For example, stranded animals with remnants
> of fishing gear indicate fishery interactions in areas or fisheries
> not participating in observer programs. Furthermore, examinations
> of stranded animals can indicate other causes of death from human
> interactions; for example, ship collisions are known to be a
> significant source of right whale mortality because of such
> evidence. Increased efforts to examine fully every stranded marine
> mammal are necessary to give a broader-based information base on
> causes of mortality and basic biology.
> Progress
>         The NMFS research program on marine mammals in the U.S. Atlantic
> Ocean and Gulf of Mexico has resulted in significant improvements
> in our knowledge of these species. Most recent research has focused
> on three areas: Estimates of distribution and abundance, estimates
> of total bycatch, and estimates of vital rates.
>         Surveys conducted since 1990 have established the relationship of
> the distribution of several species of toothed whales to the Gulf
> Stream wall and warm core rings, and have confirmed the strong
> relationship to the continental shelf break. Revised estimates of
> abundance for these species are being developed. Surveys of harbor
> porpoise conducted since 1987 have mapped their summer distribution
> pattern, and have allowed development and testing of sighting
> survey methods for estimates of absolute abundance.
>         A coordinated international multi-investigator study, Years of the
> North Atlantic Humpback Whale (YONAH), is underway for 1992-95. At
> the conclusion of the project, the geographic distribution,
> abundance, behavior, and genetic structure of North Atlantic
> humpback whales will be known more precisely and reliably than has
> ever been possible for any pelagic whale species in an entire ocean
> basin. The project will be a model for the foundation of studies
> required for comprehensive understanding, conservation, and
> management of a cetacean species.
>         A multi-agency, multi-investigator effort to study
> right whales on their wintering and calving grounds off the
> southeastern United States and to develop a program to mitigate the
> impact of human interference with right whales has been underway
> since 1988. The results are expected to provide a model for efforts
> aimed at assisting the recovery of this endangered species.
>         A program of placing observers aboard commercial fishing vessels
> has resulted in new estimates of bycatch rates of harbor porpoise
> and other species. By combining these with estimates of total
> fishing effort in several fisheries based on a previously existing
> port sampling program, estimates of total bycatch have been made.
> These have been completed for harbor porpoise for three years and
> are being developed for other species. These data collection
> programs are also enabling development of an understanding of
> seasonal bycatch patterns which may provide a basis for seasonal
> and area controls on fisheries to reduce the bycatch.
>         Biological sampling of the marine mammals killed in commercial
> fishing operations has been conducted with a very high degree of
> cooperation from fishermen. These samples are being analyzed in
> conjunction with samples from other regions to determine population
> structure and net reproductive rates. For example, recent results
> suggest that harbor porpoise from across the North Atlantic are
> more closely related than those in other regions, and that the
> natural mortality rates of pilot whales are high for younger and
> older ani-mals but very low for middle-aged animals.
>         In an effort to establish baseline data on contaminants in marine
> mammals, NMFS has established a National Marine Mammal Tissue Bank.
> Ultimately, the Bank will contain tissues of the highest quality
> maintained in a manner that allows their accurate use for
> retrospective analysis. A pilot project has been completed using
> tissues from stranded pilot whales and from harbor porpoises caught
> incidentally in fisheries. The Tissue Bank project also has
> recognized the need to establish consistency in tissue analysis and
> has set up a quality assurance program available to any laboratory
> analyzing contaminant levels in marine mammals. As part of this
> effort, standard reference materials with known contaminant levels
> are being developed for use in calibration.