Cetaceans

How do whales act as ecosystem engineers?

Consume 65% of productivity in the North Pacific and move nutrients to different ocean basins, promoting productivity in less productive areas

Whale-fall also creates their own deep-sea ecosystem

How did whales evolve?

Evolved from even-hoofed mammals during the Eocene in North India (where a shallow ocean formed).

Earliest whales was likely a tetrapod that spent much time underwater.

Isotope analysis of early “whale” ancestors

More primitive whale species like Pakicetus had oxygen and carbon isotope readings signifying it was a freshwater mammal

Can see as they evolve the species adapts to be more nearshore marine environments

When did the whales split?

Around 36mya Basilosauridae split into baleen and toothed whales

When did baleen whales evolve?

During the Oligocene (30mya), started to see the forming of the Antarctic Circumpolar Current which spreads productivity through the global ocean basins

What is telescoping and how has it occurred in whales?

The movement of nostrils from the top of the snout in terrestrial mammals towards the base of the skull

How did baleen whales lose their teeth/develop baleen?

Ancestral baleen whales show “baleen biters” where species had both teeth and baleen.

Used the suction feeding method - limits the larger prey but opens up options for many smaller prey.

Baleen was a slightly hardened gum growth that grew as suction feeders needed to keep prey in their mouths while expelling water.

What are the two types of baleen feeding types seen in modern mysticetes?

Skim feeding

Gulp feeding

When did many odontocetes disappear from the fossil record?

around 23mya

Why did more primitive tooth baleen whales go extinct?

Likely exploited a very restricted habitat in Australia (has high genetic distributions) which put them at a high risk of extinction

Where did all the whales go?

Coastal primitive mysticetes went extinct allowing for offshore forms to reinvade coastal habitats

What are the two key morphological differences between mysticetes and odontocetes?

Mysticetes - baleen, 2 external blowholes

Odontocetes - teeth, 1 external blowhole

What is the distribution of baleen whales?

Many have a circumpolar distribution although some have more specialised habitats (e.g. Rice’s whale in Gulf of Mexico)

What are the three types of feeding in baleen whales, examples and baleen info (if applicable)

Lunge feeders - rorqual whales long baleen

Skim feeders - right whales short baleen

Suction feeders - grey whale

What are the mechanisms of lunge feeding?

Accelerate rapidly towards dense aggregations of prey, open mouth and inflate the buccal cavity (inversion of the tongue) this causes water to rush into the buccal cavity

Mouth closes, engulfed water is filtered through baleen then whale accelerates onwards

What are the energetic costs associated with lunge feeding?

Lunge feeding is very energetically expensive, but the energy gained from a successful lunge greatly outweighs the costs.

The density of krill is also a determining factor, the more dense the krill is the less lunges a whale will have to perform

What is bubblenetting and how does it help humpbacks forage?

Cooperative behaviour to concentrate small fish into higher densities for efficient mouthfuls of prey.

Migration in humpback whales

Annual migrations from high latitudes in Summer (foraging) to low latitudes in Winter (breeding)

migrate to the tropics for breeding to avoid thermal stress on calve, avoid predation, perhaps and evolutionary tradition?

How might the migration of humpback whales have been an evolutionary tradition?

Whales are very social, the migration from poles to tropics may have evolved early when the distance was shorter, may have continued the behaviour as the distance between poles and tropics increased.

Why do NZ Southern Right Whales choose to calve in the Auckland Islands during winter?

The Auckland Islands are sheltered from the southern ocean but still provide high nutrients for development.

What life history parameters do whales have?

Old age at first reproduction (4-10 years)

Long gestation period (10-11 months) and single births only

Long inter-birth interval

Long lived

How has longevity in mysticetes been measures?

Baleen do not fossilise so it is very hard to age mysticetes, but old whaling fragments have been found embedded into recently caught whales (suggesting they are extreme k-strategists and can live for at least 130 years old).

What is the key foraging difference between odontocetes and mysticetes?

Odontocetes use echolocation to hunt which causes massive differences in morphology and behaviour

What is the most primitive odontocete?

Sperm whales

What are the smaller groups with odontoceti?

Sperm whales (Physteroidea)

Beaked whales (Ziphoidea)

Monodontids, delphinids, porpoises (Delphinoidea)

River dolphins

Sperm whales diversity

Deep divers

Global distribution

Eat squid and fish

Extremely dimorphic

Beaked whales

Deep divers

Squid eaters

Oceanic distributions

Rarely seen alive

Beluga and Narwal

Arctic distributions, costal

High social and vocal

Beluga have 8-10 pairs of conical teeth

Narwhal males have tusks no teeth

What adaptations do beluga and narwhal have for the cold?

Reduced extremities

Thick blubber layer

Vascularised blubber (anatomoses)

Counter current heat exchange in rete mirabile

Dolphins

Most specious group

Highly diverse

Highly social

Porpoises

Small

Spade shaped teeth

Mostly coastal

Not highly social

What are the main features of river dolphins

4 different families (non-monophyletic)

Long, pointed beak

Reduced eyesight

What are the distributions of odontocetes?

Have a wide range of habitats although generally smaller distributions than mysticetes (e.g. Vaquita)

Less migratory than mysticetes

Diet and feeding of odontocetes?

Squids eaters (most)

Fish eaters (oceanic dolphins)

Many odontocetes display feeding patterns follow vertical migration of the deep scattering layer

How does feeding in odontocetes differ from mysticetes?

Hunting individual large prey items

Several species target deep prey

Less seasonal diet

What are the two types of food specialising in killer whales?

Residents: salmon eaters

Transients: marine mammal eaters

What are the life history characteristics of odontocetes?

Long lived

Late maturation

Long gestation periods

Single offspring

Extended maternal care

Long interbirth intervals

k-strategists

How did the introduction of cruise ships into Akaroa Harbour impact the distributions of Hector’s Dolphins?

Following the 2011 earthquakes cruise ships were directed to Akaroa for docking. This caused a long-term shift in Hector’s dolphin distributions towards the mouth of the harbour

Possible mechanisms include increased ambient noise, vessel traffic and benthic habitat degredation.

What are the mating systems in odontoccetes?

Promiscuous mating with varied social organisations

What evidence do we have for social learning in odontocetes?

Diversity of specialised foraging strategies, migration routes and dialects within some species.

Why is culture important in odontocetes?

Enhances the ability of the population to survive and allows knowledge of the environment to be passed along through generations to keep populations stable in times of crisis.