Wetland,
Thanks for a really great question, and for your great name as well.
It just so happens that I am a marine biologist who studied wetlands
in his heyday, so I appreciate being able to respond to your question
about marine mammals.
Most surveys of large marine animals are conducted from the air.
Vessel-based (shipboard) surveys are also used, and make use of
detection equipment such as sonar, along with visible sitings. Survey
efforts may also make use of listening devices that can detect
identifiable sounds such as the well known songs of whales, which are
specific to individual species. For some animals that emerge from the
water (e.g. walruses, seals), land-based surveys are also useful.
When specific large-scale activities are planned in an area of ocean
(drilling, military exercises, and so on) surveys are often conducted
in advance (and may be required in some circumstances) to assist in
protecting marine mammals. Surveys are also conducted to understand
general population dynamics, and to provide information for
establishing the health of a population, or conversely, to determine
if a population is endangered and in need of protective measures.
As a result of these survey efforts, some areas of the ocean are
fairly well characterized in terms of large marine mammal populations,
and the seasonal variability of these populations, as animals move
between feeding grounds, head to breeding/birthing areas, or otherwise
migrate in well-established patterns. The gray whales that migrate
to San Ignacio lagoon in Baja California every year (to the amazement
and delight of thousands of tourists) is a prime example of a
population whose movement patterns are well characterized:
http://www.mexonline.com/sanignacio.htm
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A fairly typical description of a marine mammal survey effort can be
found here:
http://www.mms.gov/eppd/sciences/esp/profiles/pc/PC-BRD-2.htm
U.S.Geological Survey/Biological Resources Division
Marine Mammal and Seabird Surveys of the Southern California Planning
Area
Objectives
"The purpose of the study is to determine the relative abundance,
seasonal occurrence, and distribution of marine mammals and seabirds
occupying the offshore waters of the Southern California Planning
Area."
Methods
"Marine mammal and seabird population surveys are being conducted by
aircraft at regular intervals over a 3-year period in an area
extending from just south of Monterey County to the Mexican border and
out to approximately 40 to 100 nautical miles from the shoreline."
Importance to MMS
"Post-lease construction schedules, development of active leases, and
operation of offshore support activities from onshore facilities are
all potentially affected by the presence of marine mammals and
endangered or threatened seabirds. Old data do not adequately support
MMS decisions on post-lease development or operation plans."
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The U.S National Oceanographic and Atmospheric Administration (NOAA)
has a helpful description of key survey techniques, along with some of
the strengths and shortcomings of each, here:
http://nmml.afsc.noaa.gov/education/science/studymm3many.htm
The site covers the uses of ground counts (observing marine mammals
such as seals on land), shore based counts (observing, e.g., migrating
gray whales from shore), aerial surveys, and vessel-based surveys.
The site includes a brief description of scaling-up estimation
techniques (how to estimate full population from a limited survey) and
some of the difficulties in actually getting good counts.
Clicking on the "learn more" buttons will take you to additional
topics, including:
--surveying marine mammal feeding habits;
–instruments used in surveying, including: Radio Transmitters,
Time-depth Recorders, Geographic Location Recorders, Satellite-linked
Transmitters, Hydrophones, and underwater video cameras.
--specific survey and research projects
The use of telemetry – instruments that use radio, wireless and
satellite technology to transmit data from animals to survey teams
miles, or thousands of miles, away, has greatly improved our ability
to survey marine mammal populations. These sophisticated instruments
can provide a wealth of detail about animal movements and habits, even
when they cannot be studied through direct visual observation.
An example of a Steller sea lion equipped with a transmitter
‘backpack" can be seen here:
http://nmml.afsc.noaa.gov/AlaskaEcosystems/sslhome/Satellite/Default.htm
If you have a broadband connection, the site also has some a movie
about the sea lion population.
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A very good overview of regional survey efforts off the coast of
Massachusetts for whales, dolphins and other mammals, is the "Summary
of marine mammal observations during 2001 surveys" which is found
here:
www.mwra.state.ma.us/harbor/enquad/pdf/2002-01.pdf
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The results of all this survey activity lead to overall assessments of
the population under observation, often referred to as "stock
assessments". These assessments are specific to certain areas of the
oceans, and are the first place someone would turn to in order to
understand population densities and geographic distributions.
A typical stock assessment begins like this:
ATLANTIC SPOTTED DOLPHIN (Stenella frontalis):
Northern Gulf of Mexico Stock
STOCK DEFINITION AND GEOGRAPHIC RANGE
"The Atlantic spotted dolphin is endemic to the Atlantic Ocean in warm
temperate to tropical waters. Sightings of this species are
concentrated along the continental shelf edge and also occur over the
continental shelf in the northern Gulf of Mexico; Southeast Fisheries
Science Center, but they have been reported as occurring around
oceanic islands and far offshore in other areas . The island and
offshore animals may be a different stock than those occurring on the
continental shelf. Atlantic spotted dolphins were seen in all seasons
during seasonal recent GulfCet aerial surveys of the northern Gulf of
Mexico during 1993-1995. Atlantic spotted dolphins were seen in 1992
during regional aerial surveys conducted in the autumn of 1992-1994
over the U.S. continental shelf. These surveys were designed to
estimate abundance of bottlenose dolphins and spotted dolphin
abundance was not estimated. It has been suggested that there may be a
seasonal movement of this species onto the continental shelf in the
spring, but data supporting this hypothesis are limited."
[NOTE: I removed the many references in the text above to make it
easier to read].
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The full list of NOAA's stock assessments (and the years for which an
assessment is available) is available here:
http://www.nmfs.noaa.gov/prot_res/PR2/Stock_Assessment_Program/individual_sars.html
and includes a lengthy list which I'm including here as it directly
addresses your question about the sources that are availble regarding
population distributions and densities:
Atlantic Spotted Dolphin (N. Gulf of Mexico) 1995
Atlantic Spotted Dolphin (Western North Atlantic) 2000 1999 1998
1997 1995
Bairds Beaked Whale (Alaska) 1999 1997
Baird's Beaked Whale (CA-OR-WA) 2000
Beluga Whale (Beaufort Sea) 1999 1997
Beluga Whale (Bristol Bay) 1999 1997
Beluga Whale (Cook Inlet) 2000 1999 1998
Beluga Whale (E. Bering Sea) 1999 1997
Beluga Whale (E. Chukchi Sea) 1999 1997
Blainville's Beaked Whale (Hawaii) 2000
Blainville's Beaked Whale (Western N. Atlantic) 1995
Blainville's Beaked Whale (N. Gulf of Mexico) 1995
Blue Whale (Hawaii) 2000
Blue Whale (Eastern N. Pacific, formerly CA/Mexico) 2000
Blue Whale (Western N. Atlantic) 2001 2000
Bottlenose Dolphin (CA Coastal) 2001 2000
Bottlenose Dolphin (CA-OR-WA Offshore) 2000
Bottlenose Dolphin (E. Gulf of Mexico Coastal) 1997 1995
Bottlenose Dolphin (Gulf of Mexico Bay Sound and Estuarine) 1999
1995
Bottlenose Dolphin (Gulf of Mexico Continental Shelf and Slope) 1995
Bottlenose Dolphin (Gulf of Mexico Outer Continental Shelf) 1995
Bottlenose Dolphin (Hawaii) 2000
Bottlenose Dolphin (N. Gulf of Mexico Coastal) 1997 1995
Bottlenose Dolphin (Western Gulf of Mexico Coastal) 1997 1995
Bottlenose Dolphin (Western N. Atlantic Coastal) 2001 2000 1999
1997 1995
Bottlenose Dolphin (Western N. Atlantic Offshore) 2000 1999 1998
1997 1995
Bowhead Whale (Western Arctic) 2000 1998
Bryde's Whale (Eastern Tropical Pacific) 2000
Bryde's Whale (Hawaii) 2000
Bryde's Whale (N. Gulf of Mexico) 1995
Clymene Dolphin (N. Gulf of Mexico) 1995
Common Dolphin (Western N. Atlantic) 2001 2000 1999 1998 1997
1995
Cuvier's Beaked Whale (Alaska) 1999 1997
Cuvier's Beaked Whale (CA-OR-WA) 2000
Cuvier's Beaked Whale (Hawaii) 2000
Cuvier's Beaked Whale (N. Gulf of Mexico) 1995
Cuvier's Beaked Whales (Western N. Atlantic) 2001 2000 1999
1998 1997 1995
Dalls Popoise (Alaska) 2000 1997
Dall's Porpoise (CA-OR-WA) 2000
Dwarf Sperm Whale (Hawaii) 2000
Dwarf Sperm Whale (N. Gulf of Mexico) 2000 1999 1995
Dwarf Sperm Whale (Western N. Atlantic) 2000 1999 1998 1997
1995
False Killer Whale (Hawaii) 2001 2000
False Killer Whale (N. Gulf of Mexico) 1995
Fin Whale (CA-OR-WA) 2001 2000
Fin Whale (Hawaii) 2000
Fin Whale (Northeast Pacific) 2001 1998
Fin Whale (Western N. Atlantic) 2001 2000 1999 1998 1997
1995
Frasers Dolphin (N. Gulf of Mexico) 1995
Gervais Beaked Whale (N. Gulf of Mexico) 1995
Gervais Beaked Whale (Western N. Atlantic) 1995
Gray Whale (Eastern N. Pacific) 2000 1997
Harbor Porpoise (Bering Sea) 2000 1997
Harbor Porpoise (Central CA) 2001 2000 1999
Harbor Porpoise (Gulf of Alaska) 2000 1997
Harbor Porpoise (Gulf of Maine-Bay of Fundy) 2001 2000 1999
1998 1997 1995
Harbor Porpoise (Inland WA) 2000 1999 1998
Harbor Porpoise (Northern CA) 2001 2000 1999
Harbor Porpoise (OR-WA Coastal) 2000 1999 1998
Harbor Porpoise (Southeast Alaska) 2000 1997
Humpback Whale (CA-OR-WA-Mexico) 2001 2000 1999
Humpback Whale (Central N. Pacific) 2001 2000 1999 1998
Humpback Whale (Gulf of Maine, formally Western N. Atlantic) 2001
2000 1999 1998 1997 1995
Humpback Whale (Western N. Pacific) 2001 2000 1999 1998
Killer Whale (E. North Pacific Resident) 2001 1998
Killer Whale (E. North Pacific Transient) 2000 1999 1998
Killer Whale (Easten N. Pacific Offshore) 2000 1999
Killer Whale (Easten N. Pacific Southern Resident) 2001 1999
Killer Whale (Hawaii) 2000
Killer Whale (N. Gulf of Mexico) 1995
Killer Whale (Western N. Atlantic) 1995
Long-Beaked Common Dolphin (CA) 2000
Long-Finned Pilot Whale (Western N. Atlantic) 2001 2000 1999
1998 1997 1995
Melon-Headed Whale (Hawaii) 2000
Melon-Headed Whale (N. Gulf of Mexico) 1995
Mesoplodont Beaked Whale (Western N. Atlantic) 2001 2000 1999
1998 1997
Mesoplodont Beaked Whales (CA-OR-WA) 2000 1998
Minke Whale (Alaska) 2001 1997
Minke Whale (Canadian E. Coastal) 2001 2000 1999 1998 1997
1995
Minke Whale (CA-OR-WA) 2000 1998
Northern Bottlenose Whale (Western N. Atlantic) 1998 1995
Northern Right Whale (Eastern N. Pacific, formally N. Pacific) 2001
2000 1998
Northern Right Whale (Western N. Atlantic) 2001 2000 1999 1998
1997 1995
Northern Right Whale Dolphin (CA-OR-WA) 2000
Pacific White Sided Dolphin (CA-OR-WA, N and S) 2000
Pacific White Sided Dolphin (N. Pacific, formerly Central N. Pacific)
2000 1997
Pantropical Spotted Dolphin (Hawaii) 2000
Pantropical Spotted Dolphin (N. Gulf of Mexico) 1995
Pantropical Spotted Dolphin (Western N. Atlantic) 2000 1999 1998
1997 1995
Pygmy Killer Whale (Hawaii) 2000
Pygmy Sperm Whale (CA-OR-WA) 2000
Pygmy Sperm Whale (Hawaii) 2000
Pygmy Sperm Whale (N. Gulf of Mexico) 1999 1995
Pygmy Sperm Whale (Western N. Atlantic) 2000 1999 1998 1995
Risso's Dolphin (Hawaii) 2000
Risso's Dolphin (CA-OR-WA) 2000
Risso's Dolphin (N. Gulf of Mexico) 1995
Risso's Dolphin (Western N. Atlantic) 2001 2000 1999 1998
1995
Rough Toothed Dolphin (Hawaii) 2000
Rough Toothed Dolphin (N. Gulf of Mexico) 1995
Sei Whale (E. North Pacific) 2000
Sei Whale (Nova Scotia) 2000 1999
Sei Whale (Western N. Atlantic) 1998 1995
Short-Beaked Common Dolphin (CA-OR-WA) 2000
Short-Finned Pilot Whale (CA-OR-WA) 2000 1999
Short-Finned Pilot Whale (Hawaii) 2000
Short-Finned Pilot Whale (N. Gulf of Mexico) 1995
Short-FInned Pilot Whale (Western N. Atlantic) 2001 2000 1999
1998 1997 1995
Sowerbys Beaked Whale (Western N. Atlantic) 1995
Sperm Whale (CA-OR-WA) 2001 2000 1999
Sperm Whale (Hawaii) 2000
Sperm Whale (North Pacific) 1998
Sperm Whale (N. Atlantic) 2001 2000 1999 1998 1997 1995
Sperm Whale (N. Gulf of Mexico) 1995
Spinner Dolphin ( Western N. Atlantic) 1998 1995
Spinner Dolphin (Hawaii) 2000
Spinner Dolphin (N. Gulf of Mexico) 1995
Stejnegers Beaked Whale (Alaska) 1999 1997
Striped Dolphin (CA-OR-WA) 2000
Striped Dolphin (Hawaii) 2000
Striped Dolphin (N. Gulf of Mexico) 1995
Striped Dolphin (Western N. Atlantic) 2000 1998 1997 1995
Tures Beaked Whale (Western N. Atlantic) 1995
White-Beaked Dolphin (Western N. Atlantic) 1997 1995
White-Sided Dolphin (Western N. Atlantic) 2001 2000 1999 1998
1997 1995
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Pinnipeds (Seals and Sea Lions)
Bearded Seal 2001 1997
CA Sea Lion (U.S.) 2000
Gray Seal (Western N. Atlantic) 2001 2000 1999 1998 1995
Guadalupe Fur Seal 2000
Harbor Seal (Bering Sea) 1998
Harbor Seal (CA) 2001 2000
Harbor Seal (Gulf of Alaska) 1998
Harbor Seal (OR-WA Coastal) 2000 1998
Harbor Seal (SE AK) 1998
Harbor Seal (WA Inland) 2000 1998
Harbor Seal (Western N. Atlantic) 2001 2000 1999 1998 1995
Harp Seal (Western N. Atlantic) 2001 2000 1999 1998 1995
Hawaiian Monk Seal 2001 2000 1999
Hooded Seals (Western N. Atlantic) 1999 1998 1995
Northern Elephant Seal (CA Breeding) 2000
Northern Fur Seal (Eastern Pacific) 2001 2000 1998
Northern Fur Seal (San Miguel Island) 2000 1998
Ribbon Seal 2001 1997
Ringed Seal 2001 1997
Spotted Seal 2001 1997
Steller Sea Lion (Eastern) 2001 2000 1999 1998
Steller Sea Lion (Western) 2001 2000 1999 1998
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Marine Mammals Under the Jurisdiction of the U.S. Fish and Wildlife
Service
West Indian Manatee (Antillean)
West Indian Manatee (Florida)
Polar Bear (AK Chukchi/Bering Seas)
Polar Bear (AK S. Beaufort Sea)
Pacific Walrus (AK)
Sea Otter (AK)
Sea Otter (CA)
Sea Otter (WA)
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For all the effort that goes into these surveys, I don't want to give
a false impression. There is still a great deal that is not known
about the distribution of marine mammal populations around the globe.
Although it is hard to generalize, a basic rule of thumb is that we
know much more – for obvious reasons – about animals that spend time
near the surface and close to shore. In a way, this is lucky, since a
good deal of human activity of significance also tends to keep to the
same near-shore, shallow areas of the ocean. The surveys make it
possible to understand the marine mammal populations, and take steps
to minimize disruption to them, if we have the collective will to do
so.
For those animals that keep to the deep, off shore waters, the
statement in one of the above-mentioned stock assessment reports best
sums up the situation: "Little is known about the population size of
blue whales". In my own estimate, this situation is not likely to
change much in the immediate future.
I have given you an overview of the survey techniques to gather
population information on marine mammals. I haven't gone into a great
deal of technical information, because it wasn't my impression that
that's what you were looking for.
However, I don't consider this answer complete until you are satisfied
with the results. If you would like any additional information,
please post a "Request for Clarification" before rating this answer.
I'd be happy to provide some more details.
search strategy: marine mammal population surveys |
