MARINE MAMMAL DISTRIBUTION

Zoogeography

Zoogeography

• Study of the distribution of extant species

• Water temperature critical for marine mammals

– Directly on animals physiology

– Indirectly on prey

– Species often occur in latitudinal bands

• Shape of nearby land/shelf

• History is Critical

– When did lineages arise and diversify?

– Continental Drift and Climate Change

– The early and middle Miocene

Basic Climatic Zones

• Polar

• Subpolar/Cold Temperate

• Temperate

• Subtropical

• Tropical

Basic Types of Distribution

• Cosmopolitan

• Pan Tropical

• Temperate/Subpolar

• Circumpolar

• Anti-tropical

• Regional (Endemic)

• still unknown for many species

Horizontal Habitats

• Nearshore

– Lakes and Rivers

– Estuaries

– Freshwater and saltwater mix, high productivity and low visibility

– Bays

– Relatively protected waters

– Coastal

– Shallow waters, often high energy (wave action)

• Offshore

– Continental Shelf

• Relatively shallow but deeper than nearshore habitats

• Light usually penetrates to bottom over much of this habitat

– Continental Slope

• Depth changes rapidly, light penetration begins to diminish

• Often associated with high productivity

– Pelagic

• Extremely deep, no light at depth

• Generally low productivity except in areas of relief (seamounts, etc)

• Frontal dynamics and current features may be very important

Vertical Marine Habitats

• Vertical Distribution of Habitats

– Light, temperature, pressure, salinity, and water density change considerably as depth increases

– Deep-water habitats can be divided into photic and aphotic zones

– Depth where these start varies considerably with water visibility

Ice Habitats

• Many pinnipeds rely on ice as habitat

– Haul outs

– Breeding

• Polar bears use the ice to stalk seals

• Cetaceans must navigate the ice to access many polar habitats

– Fast ice

– Ice attached to shore that does not move

– Pack ice

– Ice that forms at sea and moves with currents

– Covers central Arctic, surrounds Antarctica

– Largely melts in summer, especially in Antarctica

– Ice floes

– Large pieces of sea ice broken by wind or waves

– Leads

– Open water formed when floes move apart

Current Distributions: Mysticetes

• Typified by seasonal shifts from high latitudes (feeding in summer) to low latitudes (breeding in winter)

• Bowhead: arctic

• Right whales: temperate

• Gray whale: warm temperate

• Rorquals: cosmopolitan

– B. edeni, B. brydei pantropical (<40°)

Current Distributions: Odontocetes

• Not limited by temperature in general

• Sperm whales – pelagic, cosmopolitan

– 2 smaller species more tropical

• Narwhal and Beluga – coastal, arctic

– Move with sea ice

• Beaked whales – pelagic, regional or antitropical

– In general, very poorly known

• Delphinidae – coastal and pelagic forms; tropical, anti-tropical, cosmopolitan, regional all found

• Porpoises – coastal, sometimes freshwater, regional/endemic

• “River Dolphins” – large tropical river drainages; one coastal species in SA

– Indus, Ganges, Yangtze, Orinoco, Amazon

Current Distributions: Sirenians

• Tropical/Subtropical; Regional

– Recently extinct Stellar’s Sea Cow was cold temperate

• Dugongs: fully marine

– Limited by marine plant distributions

– Prefer >18°C, <6m depth

• Manatees (Trichechids): tend towards freshwater sources

– Amazon manatee: obligate fresh water

Current Distributions: Pinnipeds

• Cetaceans more successful in low latitudes, pinnipeds more successful at high latitudes

• Odobenids

– disjunct circumpolar

• Otariids

– cool temperate/subpolar (except N. Atlantic)

– lower latitudes where cold currents occur

•– Arctopcephalus (fur seals) have 6 species only in southern ocean

– Distributions highly influenced by sealing

– Some species highly endemic, but others widespread

– Zalophus (sea lions) mainly in north with California sea lion most widespread

• Phocids

– Most widespread pinnipeds

– Northern group Phocinae

• Many give birth on ice or in ice lairs

• Temperate, Arctic, subarctic, some landlocked lake seals

– Monachinae

• Warm water seals, elephant seals, Antarctic ice seals

– Some ice seals can maintain holes (Ringed seal) in ice, others must stay near ice edge (Bearded seal)

– Monk seals only true warm water seals

Current Distributions: Sea otters and Polar Bear

• Sea Otter

– North Pacific

– Tied to shallow waters

– Poor dispersal ability

• Polar Bear

– Circumpolar

– Track seal distribution (mainly ringed seals)

Current and historical distributions

• May have been modified greatly by human activities both ancient and modern

• Pinnipeds in central and northern California are a perfect example

Pinnipeds of central California

• Currently dominated by CA sea lions and N elephant seals with northern fur seals (NFS) rare and only

breeding in recent and small colonies on offshore islands

• Most NFS breeding is in Alaska and may forage in pelagic waters as far south as Baja

• A strange observation: remains of NFS extremely common in archeological sites in California.

Explanations of NFS abundance in ancient times

• Always had northern rookeries and foraged closer to shore where they were available or were hunted

more commonly

• More abundant on offshore rookeries of California

• Were historically more abundant and had mainland rookeries

Burton et al (2001)

• Used archeological data, stable isotopes to address these hypotheses: what did they find?

– Differences in hunting or foraging location did not explain remains

– NFS were mainland breeders in CA during mid-late Holocene

– NFS were extremely abundant historically compared to other pinnipeds and may have limited the

abundance of other pinnipeds