Steven Kazlowski / Killer WHale / Orca (Orcinus orca) bull and cow in Resurrection Bay, Kenai Fjords National Park, outside Seward, Alaska, May.

Michael Pitts / Bull Elephant seal (Mirounga sp) portrait with penguin walking along beach, St Andrews Bay, South Georgia

Yva Momatiuk & John Eastcott / Pacific Walrus (Odobenus rosmarus divergens) bull portrait on coastal rocks in haul-out cove, summer, Round Island, Bering Sea, Bristol Bay, Alaska

Peter Bassett / Aggressive bull elephant seal and penguins on beach at St Andrews Bay, South Georgia

Steven Kazlowski / Killer Whale / Orca (Orcinus orca) large bull, cow and calf swimming in Resurrection Bay, Kenai Fjords National Park, outside Seward, Alaska, May.

Steven Kazlowski / Killer Whale / Orca (Orcinus orca) large bull swimming in Resurrection Bay, Kenai Fjords National Park, outside Seward, Alaska, May.

Yva Momatiuk & John Eastcott / Pacific Walrus (Odobenus rosmarus divergens) bull swimming in aggressive posture, Round Island, Bristol Bay, Alaska

Ingo Arndt / Southern Elephant Seal (Mirounga leonina) bull swimming, Stromness Bay, South Georgia Island

Yva Momatiuk & John Eastcott / Southern Elephant Seal (Mirounga leonina) bull biting neck of female to restrain her before mating on beach, St. Andrews Bay, South Georgia Island

Yva Momatiuk & John Eastcott / Southern Elephant Seal (Mirounga leonina) bull roaring triumphantly after a successful fight for access to females, St. Andrews Bay, South Georgia Island

Yva Momatiuk & John Eastcott / Southern Elephant Seal (Mirounga leonina) bull chasing his opponent who lost the fight for access to females, St. Andrews Bay, South Georgia Island

Yva Momatiuk & John Eastcott / Southern Elephant Seal (Mirounga leonina) bulls fighting for access to females, St. Andrews Bay, South Georgia Island

Yva Momatiuk & John Eastcott / Southern Elephant Seal (Mirounga leonina) bull roaring and raising his body on beach during breeding season, St. Andrews Bay, South Georgia Island

Yva Momatiuk & John Eastcott / Southern Elephant Seal (Mirounga leonina) bull chasing his opponent who lost a long fight for access to females during spring breeding season, St. Andrews Bay, South Georgia Island

Yva Momatiuk & John Eastcott / Southern Elephant Seal (Mirounga leonina) bull waiting in surf near harem to intercept females during breeding season, St. Andrews Bay, South Georgia Island

Suzi Eszterhas / Antarctic Fur Seal {Arctocephalus gazella} large bull and adult females, Hercules Bay, South Georgia

Suzi Eszterhas / Antarctic Fur Seal {Arctocephalus gazella} large bull and adult females, Hercules Bay, South Georgia

Suzi Eszterhas / Antarctic Fur Seal {Arctocephalus gazella} bull and females with 1-3 week pups, Fortuna Bay, South Georgia

Suzi Eszterhas / Antarctic fur seal {Arctocephalus gazella} bull with King Penguins {Aptenodytes patagonicus} Saint Andrews Bay, South Georgia

Suzi Eszterhas / Antarctic fur seal {Arctocephalus gazella} bull with King Penguins {Aptenodytes patagonicus} Saint Andrews Bay, South Georgia

Yva Momatiuk & John Eastcott / Southern Elephant Seal (Mirounga leonina) bull, cow and pup, during breeding season in spring, St. Andrews Bay, South Georgia Island

Yva Momatiuk & John Eastcott / Southern Elephant Seal (Mirounga leonina) bull approaching cow during breeding season in spring, St. Andrews Bay, South Georgia Island

Yva Momatiuk & John Eastcott / Southern Elephant Seal (Mirounga leonina) bull hind flippers, St. Andrews Bay, South Georgia Island

Yva Momatiuk & John Eastcott / Southern Elephant Seal (Mirounga leonina) bull, St. Andrews Bay, South Georgia Island

Kevin Schafer / Northern Elephant Seal (Mirounga angustirostris) researcher marking large bull, Farallon Islands, California

Graham Eaton / Bull Huss / Larger Spotted Dogfish (Scyliorhinus stellaris) caught on a fishing line, Cardigan Bay, Wales, UK, May

Yva Momatiuk & John Eastcott / Antarctic Fur Seal (Arctocephalus gazella) bull flipper, Right Whale Bay, South Georgia Island

Yva Momatiuk & John Eastcott / Antarctic Fur Seal (Arctocephalus gazella) bull with moulted penguin feathers stuck to its wet fur, Right Whale Bay, South Georgia Island

Yva Momatiuk & John Eastcott / Southern Elephant Seal (Mirounga leonina) bull resting on sandy beach, Right Whale Bay, South Georgia Island

Yva Momatiuk & John Eastcott / Antarctic Fur Seal (Arctocephalus gazella) bull on beach, Right Whale Bay, South Georgia Island

Yva Momatiuk & John Eastcott / Antarctic Fur Seal (Arctocephalus gazella) bull with moulted penguin feathers stuck to its wet fur, Right Whale Bay, South Georgia Island

Yva Momatiuk & John Eastcott / Antarctic Fur Seal (Arctocephalus gazella) bull with moulted penguin feathers stuck to its wet fur, Right Whale Bay, South Georgia Island

Yva Momatiuk & John Eastcott / Southern Elephant Seal (Mirounga leonina) bull on gravel beach, Antarctic Bay, South Georgia Island

Yva Momatiuk & John Eastcott / Antarctic Fur Seal (Arctocephalus gazella) bull, blond morph, sitting on gravel beach, Antarctic Bay, South Georgia Island

Yva Momatiuk & John Eastcott / Antarctic Fur Seal (Arctocephalus gazella) bulls with one blond morph sitting on gravel beach, Antarctic Bay, South Georgia Island

Yva Momatiuk & John Eastcott / King Penguin (Aptenodytes patagonicus) trio standing around Southern Elephant Seal (Mirounga leonina) bull on gravel beach, St. Andrews Bay, South Georgia Island

Yva Momatiuk & John Eastcott / Southern Elephant Seal (Mirounga leonina) bull mating with female on beach outside harem, St. Andrews Bay, South Georgia Island

Yva Momatiuk & John Eastcott / Southern Elephant Seal (Mirounga leonina) bull mating with female after a successful fight, St. Andrews Bay, South Georgia Island

Yva Momatiuk & John Eastcott / Antarctic Skua (Catharacta antarctica) pecking torn flesh on bloody nose of Southern Elephant Seal (Mirounga leonina) bull wounded during fight for access to females, St. Andrews Bay, South Georgia Is...

Yva Momatiuk & John Eastcott / Southern Elephant Seal (Mirounga leonina) bulls fighting for access to females, St. Andrews Bay, South Georgia Island

Yva Momatiuk & John Eastcott / Southern Elephant Seal (Mirounga leonina) bulls fighting for access to females, St. Andrews Bay, South Georgia Island

Yva Momatiuk & John Eastcott / Southern Elephant Seal (Mirounga leonina) bulls fighting for access to females, St. Andrews Bay, South Georgia Island

Yva Momatiuk & John Eastcott / Southern Elephant Seal (Mirounga leonina) bulls fighting for access to females, St. Andrews Bay, South Georgia Island

Yva Momatiuk & John Eastcott / Southern Elephant Seal (Mirounga leonina) bulls fighting for access to females, St. Andrews Bay, South Georgia Island

Yva Momatiuk & John Eastcott / Southern Elephant Seal (Mirounga leonina) bull roaring in tussock grass, Cooper Bay, South Georgia Island

Yva Momatiuk & John Eastcott / Southern Elephant Seal (Mirounga leonina) bull and female copulating on beach during breeding season with pup nearby, St. Andrews Bay, South Georgia Island

Yva Momatiuk & John Eastcott / Southern Elephant Seal (Mirounga leonina) pair copulating on beach, St. Andrews Bay, South Georgia Island

Yva Momatiuk & John Eastcott / Southern Elephant Seal (Mirounga leonina) bull chasing away another male from females, St. Andrews Bay, South Georgia Island

Yva Momatiuk & John Eastcott / Southern Elephant Seal (Mirounga leonina) bull chasing away another male from females, St. Andrews Bay, South Georgia Island

Yva Momatiuk & John Eastcott / Southern Elephant Seal (Mirounga leonina) bull chasing away another male from females, St. Andrews Bay, South Georgia Island

Yva Momatiuk & John Eastcott / Southern Elephant Seal (Mirounga leonina) bulls fighting for females on beach during breeding season in spring, St. Andrews Bay, South Georgia Island

Yva Momatiuk & John Eastcott / Southern Elephant Seal (Mirounga leonina) bull with King Penguins (Aptenodytes patagonicus), St. Andrews Bay, South Georgia Island

Yva Momatiuk & John Eastcott / Southern Elephant Seal (Mirounga leonina) bull moving fast toward another bull on beach where he waits to intercept females during breeding season, St. Andrews Bay, South Georgia Island

Yva Momatiuk & John Eastcott / Southern Elephant Seal (Mirounga leonina) bull on beach during breeding season, St. Andrews Bay, South Georgia Island

Yva Momatiuk & John Eastcott / Southern Elephant Seal (Mirounga leonina) bulls fighting in surf during breeding season, St. Andrews Bay, South Georgia Island

Yva Momatiuk & John Eastcott / Southern Elephant Seal (Mirounga leonina) bulls fight for access to females during breeding season, St. Andrews Bay, South Georgia Island

Yva Momatiuk & John Eastcott / Southern Elephant Seal (Mirounga leonina) female and bull on beach during breeding season, St. Andrews Bay; South Georgia Island

Yva Momatiuk & John Eastcott / Southern Elephant Seal (Mirounga leonina) bulls challenge each other on beach during breeding season, St. Andrews Bay; South Georgia Island

Yva Momatiuk & John Eastcott / King Penguin (Aptenodytes patagonicus) group approaching Southern Elephant Seal (Mirounga leonina) female and bull, St. Andrews Bay, South Georgia Island

Yva Momatiuk & John Eastcott / Southern Elephant Seal (Mirounga leonina) bull emerging from surf, St. Andrews Bay, South Georgia Island

Yva Momatiuk & John Eastcott / Southern Elephant Seal (Mirounga leonina) bull waiting in surf to intercept females during breeding season, St. Andrews Bay, South Georgia Island

Yva Momatiuk & John Eastcott / Southern Elephant Seal (Mirounga leonina) bull resting, Fortuna Bay, South Georgia Island

Yva Momatiuk & John Eastcott / Southern Elephant Seal (Mirounga leonina) bull resting, Fortuna Bay, South Georgia Island

Yva Momatiuk & John Eastcott / Southern Elephant Seal (Mirounga leonina) bull attempting to copulate with female, Right Whale Bay, South Georgia Island

Ingo Arndt / Pacific Walrus (Odobenus rosmarus divergens) juvenile bull resting, Bristol Bay, Round Island, Alaska

Ingo Arndt / Pacific Walrus (Odobenus rosmarus divergens) bull, Bristol Bay, Round Island, Alaska

Ingo Arndt / Pacific Walrus (Odobenus rosmarus divergens) bull, Bristol Bay, Round Island, Alaska

Ingo Arndt / Pacific Walrus (Odobenus rosmarus divergens) bulls, Bristol Bay, Round Island, Alaska

Suzi Eszterhas / Antarctic Fur Seal (Arctocephalus gazella) bull on shore, Hercules Bay, South Georgia

Suzi Eszterhas / Antarctic Fur Seal (Arctocephalus gazella) colony, Hercules Bay, South Georgia

Suzi Eszterhas / Antarctic Fur Seal (Arctocephalus gazella) bull, Fortuna Bay, South Georgia

Tom Hugh-Jones / Presenter Steve Leonard with Jerome Poncet next to Southern elephant seal bull (Mirounga leonina) on location for Extreme Animals programme, St Andrews Bay, South Georgia, 2001

Peter Bassett / Southern elephant seal {Mirounga leonina} wounded bull trying to mate, St. Andrews Bay, South Georgia, Antarctica.

Yva Momatiuk & John Eastcott / Pacific Walrus (Odobenus rosmarus divergens) bull with pale skin hauling-out after many hours in cold sea, after warming on land skin turns reddish-brown, summer, Round Island, Bering Sea, Bristol Bay...

Yva Momatiuk & John Eastcott / Pacific Walrus (Odobenus rosmarus divergens) bull with pale skin hauling-out after many hours in cold sea, after warming on land skin turns reddish-brown, summer, Round Island, Bering Sea, Bristol Bay...

Yva Momatiuk & John Eastcott / Pacific Walrus (Odobenus rosmarus divergens) bulls resting in haul-out showing small claws on hind-flipper, Round Island, Bering Sea, Bristol Bay, Alaska

Yva Momatiuk & John Eastcott / Pacific Walrus (Odobenus rosmarus divergens) males with large tusks resting on coastal rocks, summer, Round Island, Bering Sea, Bristol Bay, Alaska

Yva Momatiuk & John Eastcott / Pacific Walrus (Odobenus rosmarus divergens) bulls hauled-out in cove protected by rocky outcrop, summer, Round Island, Bering Sea, Bristol Bay, Alaska

Yva Momatiuk & John Eastcott / Pacific Walrus (Odobenus rosmarus divergens) two bulls fighting in shallow waters off-shore, summer, Round Island, Bering Sea, Bristol Bay, Alaska

Yva Momatiuk & John Eastcott / Pacific Walrus (Odobenus rosmarus divergens) bull portrait on coastal rocks in haul-out cove, summer, Round Island, Bering Sea, Bristol Bay, Alaska

Yva Momatiuk & John Eastcott / Pacific Walrus (Odobenus rosmarus divergens) bull portrait on coastal rocks in haul-out cove, summer, Round Island, Bering Sea, Bristol Bay, Alaska

Yva Momatiuk & John Eastcott / Pacific Walrus (Odobenus rosmarus divergens) bull portrait on coastal rocks in haul-out cove, summer, Round Island, Bering Sea, Bristol Bay, Alaska

Yva Momatiuk & John Eastcott / Pacific Walrus (Odobenus rosmarus divergens) bull portrait on coastal rocks in haul-out cove, summer, Round Island, Bering Sea, Bristol Bay, Alaska

Yva Momatiuk & John Eastcott / Pacific Walrus (Odobenus rosmarus divergens) bull portrait, summer, Round Island, Bering Sea, Bristol Bay, Alaska

Yva Momatiuk & John Eastcott / Pacific Walrus (Odobenus rosmarus divergens) bulls interacting in crowded haul-out cove, summer, Round Island, Bering Sea, Bristol Bay, Alaska

Yva Momatiuk & John Eastcott / Pacific Walrus (Odobenus rosmarus divergens) bull resting in haul-out cove and waving front flippers, summer, Round Island, Bering Sea, Bristol Bay, Alaska

Yva Momatiuk & John Eastcott / Pacific Walrus (Odobenus rosmarus divergens) bull dozing in haul-out cove, covering head with front flipper, summer, Round Island, Bering Sea, Bristol Bay, Alaska

Tui De Roy / Galapagos Sea Lion (Zalophus wollebaeki) subadult bulls sparring, Darwin Bay, Genovesa Tower Island, Galapagos Islands, Ecuador

Larry Minden / California Sea Lion (Zalophus californianus) bull in water, Monterey Bay, California

Peter Bassett / Southern elephant seals (Mirounga leonina) fighting. South Georgia St Andrews Bay Antarctica

Peter Bassett / Southern elephant seal bull and King penguin rookery. Antarctica, St Andrews Bay