Mark Carwardine / Pacific white-sided dolphin / Lag (Lagenorhynchus obliquidens) swimming fast, showing dorsal fin, Johnstone Strait, Vancouver Island, British Columbia, western Canada

Alex Mustard / Basking shark (Cetorhinus maximus) rear view of shark feeding at the surface on plankton, Cairns Of Coll, Isle of Coll, Inner Hebrides, Scotland, UK, North East Atlantic Ocean, June

Alex Mustard / 2020VISION / Dorsal fin of a Basking shark (Cetorhinus maximus) at the surface, Cairns of Coll, Inner Hebrides, Scotland. UK, June.

Kathryn Jeffs / Southern Type B Killer whale (Orcinus orca) hunting Weddell seal (Leptonychotes weddelli), Antarctica. Taken on location for BBC Frozen Planet series, January

Martin Camm / Carwardine / Illustration of Striped dolphin (Stenella coeruleoalba), Delphinidae (Wildlife Art Company).

Sergey Gorshkov / Salmon (Salmonidae) migrating to spawn in Lake Kuril, Kamchatka, Far East Russia, August

Juan Carlos Munoz / Great white shark (Carcharodon carcharias) with dorsal fin showing above water. False Bay, South Africa, July 2010

Jeff Rotman / Great White shark (Carcharodon carcharias) surfacing with head and dorsal fin visible, Dyer Island, South Africa, Atlantic Ocean.

Jeff Rotman / Detail of dorsal fin of Bluespine Unicornfish (Naso Unicornis) Red Sea, Egypt

Pete Oxford / Whale Shark (Rhincodon typus) swimming with other tropical fish, note satellite tag to right of dorsal fin, Wolf Island, Galapagos Islands, Ecuador

Flip Nicklin / Orca (Orcinus orca) adult and breaching calf, southeast Alaska

Doug Perrine / Dorsal fin of Great white shark at surface {Carcharodon carcharias} Gansbaai, South Africa

Todd Pusser / Large dorsal fin of male transient killer whale {Orcinus orca} Monterey Bay, California, USA.

Konrad Wothe / Orca (Orcinus orca) female surfacing and spouting beside conifer-covered coastline, Inside Passage, Alaska

Flip Nicklin / Sperm Whale (Physeter macrocephalus) surfacing, New Zealand

Flip Nicklin / Orca (Orcinus orca) resident pod A-5 at rest, Johnstone Strait, British Columbia, Canada

TOM WALMSLEY / Killer whale (Orcas) two adult males at surface {Orcinus orca} Tysfjord, Norway. winter

TOM WALMSLEY / Killer whale (Orca) surfacing showing dorsal fin, eyepatch and blowhole {Orcinus orca} Iceland

Jeff Rotman / Fisherman holding dorsal fin cut from Scalloped Hammerhead shark {Sphyrna lewini} caught on longline, Cocos Island, Costa Rica, Pacific Ocean

Staffan Widstrand / Minke whale (Balaenoptera acutorostrata) surfacing near coastal ice, Svalbard, Norway, July

Staffan Widstrand / Fin whale (Balaenoptera physalus) at surface, Svalbard, Norway, July

Staffan Widstrand / Fin whale (Balaenoptera physalus) at surface, Svalbard, Norway, July

Mark Carwardine / Fin whale (Balaenoptera physalus) close-up showing stalked barnacles on dorsal fin, Sea of Cortez (Gulf of California), Baja California, Mexico, Endangered

Mark Carwardine / Fin whale (Balaenoptera physalus) dorsal fin at surface, Sea of Cortez (Gulf of California), Baja California, Mexico, Endangered species

Mark Carwardine / Shortfin pilot whale (Globicephala macrorhynchus) surfacing, Baja California, Sea of Cortez (Gulf of California), Mexico

Mark Carwardine / Two Humpback whales (Megaptera novaeangliae) diving together, Baja California, Sea of Cortez (Gulf of California), Mexico, Threatened or endangered species (Vulnerable)

Mark Carwardine / Pacific white-sided dolphin / Lag (Lagenorhynchus obliquidens) swimming fast, showing dorsal fin, Johnstone Strait, Vancouver Island, British Columbia, western Canada

Mark Carwardine / Humpback whale surfacing {Megaptera novaeangliae} South Sheltand Is, Antarctica.

Mark Carwardine / Three Humpback whales at surface {Megaptera novaeangliae} Sea of Cortez, Mexico

Mark Carwardine / Humpback whale surfacing {Megaptera novaeangliae} New England, USA

Mark Carwardine / Humpback whale diving {Megaptera novaeangliae} South Sheltand Is, Antarctica.

Mark Carwardine / Basking shark, dorsal fin at surface {Cetorhinus maximus} Isle of Man, UK.

Mark Carwardine / Dorsal fin of Great white shark at surface {Carcharodon carcharias} South Africa

Konrad Wothe / Fin whale (Balaenoptera physalus) at surface, Antarctica. February.

Alex Mustard / Whale shark (Rhincodon typus) spotted dorsal fin breaks the surface, Isla Mujeres, Quintana Roo, Yucatan Peninsular, Mexico. Caribbean Sea.

Alex Mustard / Whale shark (Rhincodon typus) spotted dorsal fin breaks the surface, Isla Mujeres, Quintana Roo, Yucatan Peninsular, Mexico. Caribbean Sea.

Cheryl-Samantha Owen / Spinner dolphin (Stenella longirostris) surfacing, Aldabra Atoll, Seychelles, Indian Ocean

Cheryl-Samantha Owen / Blacktip reef shark (Carcharhinus melanopterus) profile of dorsal fin, Aldabra Atoll, Seychelles, Indian Ocean

Alex Mustard / 2020VISION / Dorsal fin of a Basking shark (Cetorhinus maximus) at the surface, Cairns of Coll, Inner Hebrides, Scotland. UK, June.

Brent Stephenson / Dusky dolphin (Lagenorhynchus obscurus) surfacing to take a breath, off Kaikoura, Canterbury, New Zealand.

Brent Stephenson / Hector's dolphin (Cephalorhynchus hectori) breaking the surface as it breathes showing the distinctive patterning and rounded dorsal fin. Akaroa Harbour, Canterbury, New Zealand.

Roland Seitre / Bottle-nosed Dolphin (Tursiops truncatus) dorsal fin at sea surface. Senegal, West Africa.

Roland Seitre / Indian Ocean Bottlenose Dolphin (Tursiops aduncus) with head and dorsal fin above water. Monkey Mia, Western Australia.

Roland Seitre / Australian humpback dolphin (Sousa sahulensis) back with scratch marks and dorsal fin. Scratches are thought to be from interaction or competition with other dolphin. Tin Can Bay, Queensland, Austral...

Roland Seitre / Bottle-nosed Dolphin (Tursiops truncatus) dorsal fin at sea surface. Senegal, West Africa.

Brent Stephenson / Harbour porpoise (Phocoena phocoena) surfacing showing its sharp dorsal fin. Endicott Arm, Alaska, United States, July.

Brent Stephenson / Bryde's whale (Balaenoptera edeni) breaks the surface of the sea showing its back and dorsal fin, Hauraki Gulf, Auckland, New Zealand, November.

Brent Stephenson / Bryde's whale (Balaenoptera edeni) breaks the surface of the sea showing its back and dorsal fin, Hauraki Gulf, Auckland, New Zealand, November.

Brent Stephenson / Bryde's whale (Balaenoptera edeni) breaks the surface of the sea showing its back and dorsal fin, Hauraki Gulf, Auckland, New Zealand, November.

Flip Nicklin / Humpback Whale (Megaptera novaeangliae) mother and calf at the ocean surface, Maui, Hawaii - notice must accompany publication; photo obtained under NMFS permit 13846

Alex Mustard / Sailfin blenny (Emblemaria pandionis) male displaying his large dorsal fin, East End, Grand Cayman, Cayman Islands, British West Indies, Caribbean Sea.

Hiroya Minakuchi / Orca (Orcinus orca) male with curved dorsal fin, Shiretoko, Hokkaido, Japan

Pedro Narra / Dorsal fin of Bottlenose dolphin (Tursiops truncatus) silhouetted at sunset, Sado Estuary, Portugal, November

John MacPherson / 2020VISION / Bottlenose dolphin (Tursiops truncatus) racing through the water, dorsal fin showing, Moray Firth, Inverness-shire, Scotland, UK, September 2011

Hiroya Minakuchi / Orca (Orcinus orca) with flaccid dorsal fin, Prince William Sound, Alaska

Juergen Freund / Steinitz' shrimp goby (Amblyeleotris steinitzi) with parasitic nudibranch (Gymnodoris nigricolor) feeding on its dorsal fin, the goby lives in symbiosis with the shrimp who digs a burrow which the gob...

Juergen Freund / Steinitz' shrimp goby (Amblyeleotris steinitzi) with parasitic nudibranch (Gymnodoris nigricolor) feeding on its dorsal fin, the goby lives in symbiosis with a shrimp who digs a burrow which the goby...

Hiroya Minakuchi / Orca (Orcinus orca) males surfacing, Johnstone Strait, British Columbia, Canada

Pete Oxford / Orca (Orcinus orca) female dorsal fins, East Falkland Island, Falkland Islands

Pete Oxford / Orca (Orcinus orca) female dorsal fins, East Falkland Island, Falkland Islands

Pete Oxford / Orca (Orcinus orca) female followed by gulls picking up scraps of meat from Southern Elephant Seal (Mirounga leonina) kill, East Falkland Island, Falkland Islands

Pete Oxford / Orca (Orcinus orca) female dorsal fins, East Falkland Island, Falkland Islands

Suzi Eszterhas / Short-finned Pilot Whale (Globicephala macrorhynchus) surfacing, Sea of Cortez, Baja California, Mexico

Luciano Candisani / Humpback Whale (Megaptera novaeangliae) surfacing, southern Bahia, Brazil

Hiroya Minakuchi / Orca (Orcinus orca) male surfacing, Prince William Sound, Alaska

Hiroya Minakuchi / Orca (Orcinus orca) female surfacing, Prince William Sound, Alaska

Sergey Gorshkov / Sockeye Salmon (Oncorhynchus nerka) doral fins of group swimming upstream, Kamchatka, Russia

Doug Perrine / Dorsal fin of Bryde's whale (Balaenoptera brydei / edeni) with copepod parasite near tip, off Cabo San Lucas, Baja California, Mexico (Eastern Pacific Ocean)

Doug Perrine / Salmon shark (Lamna ditropis) finning at surface (swimming in circles with dorsal fin exposed) in the rain, Port Fidalgo, Prince William Sound, Alaska, USA

Jeff Rotman / Close up of dorsal fin of California hornshark (Heterodontus francisci) of with horn spine, Channel Islands, California (USA) Pacific Ocean.

Juergen Freund / Richard Fitzpatrick inserting depth and time recording device to base of dorsal fin of Grey reef shark {Carcharhinus amblyrhynchos} part of the Coral Reef census, Lizard Island, Queensland, Australia,...

Hiroya Minakuchi / Orca (Orcinus orca) transient pod surfacing, one with a damaged dorsal fin, southeast Alaska

Hiroya Minakuchi / Orca (Orcinus orca) transient surfacing, Monterey Bay, California

Hiroya Minakuchi / Orca (Orcinus orca) male and females, part of the resident pod, Prince William Sound, Alaska

Hiroya Minakuchi / Orca (Orcinus orca) male and females, part of the resident pod, Prince William Sound, Alaska

Hiroya Minakuchi / Orca (Orcinus orca) females, part of the resident pod, Prince William Sound, Alaska

Wild Wonders of Europe / Campbell / Bottlenosed dolphin (Tursiops truncatus) by yacht, dorsal fin showing above surface, Moray Firth, Nr Inverness, Scotland, April 2009

Wild Wonders of Europe / Campbell / Bottlenosed dolphin (Tursiops truncatus) porpoising, dorsal fin showing, Moray Firth, Nr Inverness, Scotland, April 2009

Jeff Rotman / Whitetip reef shark (Triaenodon obesus) close-up of dorsal fin, Cocos Island, Costa Rica

Tim Laman / Giant mudskipper (Periophthalmodon sp.) on the mangrove mudflat in the Matang mangroves with its dorsal fin up. Taiping vicinity, Perak, Malaysia. May 2006

Tim Laman / Giant mudskipper (Periophthalmodon sp.) on mangrove mudflat in the Matang mangroves. Dorsal fin raised in display. Taiping vicinity, Perak, Malaysia. mAY 2006

Stephen Belcher / Great White Shark (Carcharodon carcharias) swimming at the surface, Seal Island, False Bay, South Africa

Stephen Belcher / Great White Shark (Carcharodon carcharias) swimming at the surface, Seal Island, False Bay, South Africa

Fred Bavendam / Whale Shark (Rhincodon typus) fin with propeller caused scars, Ningaloo Reef, Australia

Suzi Eszterhas / Humpback Whale (Megaptera novaeangliae) pair surfacing, Sea of Cortez, Baja California, Mexico

Suzi Eszterhas / Fin Whale (Balaenoptera physalus) surfacing, Baja California, Mexico

Suzi Eszterhas / Bryde's Whale (Balaenoptera edeni), Baja California, Mexico

Juergen Freund / Back and dorsal fin of Humpback whale (Megaptera novaeangliae) with sailing boat in background, off coast of Tonga

Michael Pitts / Killer whale / Orca {Orcinus orca} dorsal fin of female in tide pool, Sealion island, Falkland Islands

Pete Oxford / Scalloped Hammerhead Shark (Sphyrna lewini) being released after researchers attached a satellite tag to its dorsal fin, Wolf Island, Galapagos Islands, Ecuador

Pete Oxford / Scalloped Hammerhead Shark (Sphyrna lewini) released after it had a satellite tag attached to its dorsal fin by researchers, Wolf Island, Galapagos Islands, Ecuador

Pete Oxford / Scalloped Hammerhead Shark (Sphyrna lewini) tag placed on dorsal fin, Wolf Island, Galapagos Islands, Ecuador

Pete Oxford / Scalloped Hammerhead Shark (Sphyrna lewini) tag on dorsal fin, Wolf Island, Galapagos Islands, Ecuador

Pete Oxford / Scalloped Hammerhead Shark (Sphyrna lewini) tag placed on dorsal fin, Wolf Island, Galapagos Islands, Ecuador

Pete Oxford / Whale Shark (Rhincodon typus) dorsal fin, Wolf Island, Galapagos Islands, Ecuador

Doug Perrine / Dorsal fin of Porbeagle shark (Lamna nasus) with spaghetti tag inserted from University of New Brunswick / Canadian Shark Conservation Society research program, New Brunswick, Bay of Fundy, Canada 20...