Tony Wu / Humpback whale (Megaptera novaeangliae australis) male calf playing at ocean surface after coming up to breathe. Vava'u Islands, Tonga.

Gary Bell/ Oceanwide / Oriental Flying Gurnard (Dactyloptena orientalis) with pectoral fins extended in defense posture, Anilao, Philippines

Tony Wu / Humpback whale (Megaptera novaeangliae) lying on its side while executing a series of pectoral fin slaps on ocean surface. Vava'u, Tonga, South Pacific.

David Fleetham / Humpback whale (Megaptera novaeangliae), mother and calf swimming just below surface in front of the West Maui Mountains. South of Lahaina, West Maui, Hawaii.

Tony Wu / Humpback whale (Megaptera novaeangliae) calf 'Tahafa' male with injured pectoral fin and scarred body, with mother. Vava'u, Tonga, Pacific Ocean. COP26 Countdown Photo Competition 2021 Finalist.

Espen Bergersen / Humpback whale (Megaptera novaeangliae) with fin above water, Andfjorden close to Andoya, Nordland, Northern Norway. January.

Chris & Monique Fallows / Orca male (Orcinus orca) raising pectoral flipper out of the water, Prince William Sound, Alaska, USA.

Jeff Rotman / Pectoral fin of a Steepheaded parrotfish (Chlororus gibbus) in the Red Sea, Egypt.

Norbert Wu / Flying Fish (Exocoetidae) uses large pectoral fins to glide through the air, Saba Island, Dutch Antilles

Gabriel Rojo / Southern right whale pectoral fin {Balaena glacialis australis} Patagonia, Argentina

Alex Mustard / Pink anemonefish (Amphiprion perideraion) fans its clutch of eggs with its pectoral fin (these eggs are aged 3-4 days), beneath its Magnificent sea anemone (Heteractis magnifica). Dauin, Dumaguete, Ne...

David Hall / Blackfoot firefish (Parapterois heterurus), blue stripes on pectoral fin when threatened, on gravel. Pantar, Alor Archipelago, Indonesia.

David Hall / Blackfoot firefish (Parapterois heterura), blue striped pectoral fins displayed as a response to threat. Pantar Island, Alor Archipelago, Indonesia.

Felis Images / Fisherman removing Shark (Elasmobranchii) pectoral fins. Negombo Fish Market, Sri Lanka. 2017. Photo Vydhehi Kadur/Felis Images

Gary Bell/ Oceanwide / Oriental Flying Gurnard (Dactyloptena orientalis) with pectoral fins extended in defense posture, Anilao, Philippines

Tony Wu / Humpback whale calf (Megaptera novaeangliae) male calf peeking out from underneath his pectoral fin as he swims upside-down beneath the ocean surface. His mother was resting about 20 meters below. Vav...

Espen Bergersen / Aerial shot of Humpback whales (Megaptera novaeangliae) socialising, splashing with pectoral fins, Troms, Norway, January.

David Pattyn / Humpback whale (Megaptera novaeangliae) raising both pectoral fins to slap, Puerto Lopez , Santa Elena Peninsula, Manabi Province, Ecuador, July

Shane Gross / Nurse shark (Ginglymostoma cirratum) male biting onto the pectoral fin of a female whilst mating, Eleuthera, Bahamas.

Shane Gross / Nurse shark (Ginglymostoma cirratum) male biting onto the pectoral fin of a female whilst mating, Eleuthera, Bahamas.

Shane Gross / Nurse shark (Ginglymostoma cirratum) two males bite onto the pectoral fins of a larger female while trying to mate with her, Eleuthera, Bahamas

Shane Gross / Nurse shark (Ginglymostoma cirratum) male biting onto the pectoral fin of a female whilst mating, Eleuthera, Bahamas.

Shane Gross / Nurse shark (Ginglymostoma cirratum) male biting onto the pectoral fin of a female whilst mating, Eleuthera, Bahamas.

David Fleetham / Reef manta ray (Manta alfredi) with black colour variation cruising over coral drop off. Fiji.

David Fleetham / Humpback whale (Megaptera novaeangliae) pectoral fin with Whale barnacles (Coronula diadema) upon it. Whale at surface, Hawaii.

David Fleetham / Humpback whale (Megaptera novaeangliae) breaching with tourists looking on. Maui, Hawaii. December 2012.

David Fleetham / Humpback whale (Megaptera novaeangliae) breaching with town of Lahaina in background. West Maui, Hawaii. February 2010.

Karine Aigner / Scientist Nathan Cooper blowing feathers out of the way while measuring the size of the pectoral muscle of a Kirkland's Warbler (Setophaga kirtlandii) during research. Cat Island, Bahamas. April 2...

Karine Aigner / Scientist Nathan Cooper measuring the size of the pectoral muscle of a Kirkland's Warbler (Setophaga kirtlandii) during research. Cat Island, Bahamas. April 2017.

David Fleetham / The pectoral fin of a Humpback Whale (Megaptera novaeangliae) off the coast of Lanai, Hawaii.

David Fleetham / Close-up of the pectoral fin of a Black Durgon / Pinktail Triggerfish (Melichthys vidua). Hawaii.

David Fleetham / Oriental flying gunard (Dactylopterus orientalis) with enormous pectoral fins. Hawaii.

David Fleetham / Oriental flying gunard (Dactylopterus orientalis) with enormous pectoral fins. Hawaii.

David Fleetham / Breaching humpback whale calf (Megaptera novaeangliae) off the Big Island, Hawaii.

Andy Trowbridge / Sharp-tailed sandpiper (Calidris acuminata) in winter plumage standing short vegetation. Lake Ellesmere, New Zealand. November.

Andy Trowbridge / Sharp-tailed sandpiper (Calidris acuminata) in winter plumage, standing in short vegetation. Lake Ellesmere, New Zealand. November.

Doug Perrine / Humpback whale (Megaptera novaeangliae) adult female with acorn barnacles are attached to her lower jaw. Image showing throat pleats, and pectoral fin, near Lahaina, in the A'u A'u Channel, off West M...

Jussi Murtosaari / Pectoral sandpiper (Calidris melanotos), Finland, September

Alex Mustard / Pair of Mandarinfish (Synchiropus splendidus) spawning. The larger male (behind) is lifting the female into the spawning rise on his pectoral fin, the smaller female (foreground) is releasing eggs, cl...

Alex Mustard / Mandarinfish (Synchiropus splendidus) pair spawning. The larger male (behind) is lifting the female into the spawning rise on his pectoral fin, the smaller female (foreground) is releasing eggs, clear...

Melvin Grey / Pectoral sandpiper (Calidris melanotos) juvenile vagrant during migration. Llanrhystud, Ceredigion, West Wales, UK. September.

Inaki Relanzon / Fishermen on beach carrying large shark with pectoral fins removed, Bali, Indonesia, August 2014.

Inaki Relanzon / Dead shark on beach with tail and pectoral fins removed, Bali, Indonesia, August 2014.

Sue Daly / Tub gurnard (Trigla lucerna) swimming and resting on the seabed, showing use of finger like pectoral fins, Sark, British Channel Islands, UK, August.

Alex Mustard / Longfin waspfish (Apistus carinatus) with its distinctive pectoral fins extended, on the sand at night. Anilao, Batangas, Luzon, Philippines. Verde Island Passages, Tropical West Pacific Ocean.

Alex Mustard / False clown anemonefish (Amphiprion oceallaris) male tending his eggs, cleaning them with his mouth and aerating them by beating his pectoral fins. Dauin, Dumaguete, Negros, Philippines. Bohol Sea, T...

Rick Price / Humpback whale (Megaptera novaeangliae) waving pectoral fin at water surface, St. Andrews Bay, South Georgia, Antarctica. January.

Rick Price / Humpback whale (Megaptera novaeangliae) waving pectoral fin at water surface with people in a boat in the distance, Antarctic Peninsula, Antarctic Sound, Antarctica. January.

Rick Price / Humpback whale (Megaptera novaeangliae) waving pectoral fin at water surface with people in a boat in the distance, Antarctic Peninsula, Antarctic Sound, Antarctica. January.

Claudio Contreras / Pectoral Sandpiper (Calidris melanotos), Socorro Island, Revillagigedo Archipelago Biosphere Reserve / Archipielago de Revillagigedo UNESCO Natural World Heritage Site (Socorro Islands), Pacific Ocean...

Franco Banfi / Nurse shark (Ginglymostoma cirratum) using its pectoral fins to walk on the seabed, South Bimini, Bahamas. The Bahamas National Shark Sanctuary, West Atlantic Ocean.

Franco Banfi / Nurse shark (Ginglymostoma cirratum) using pectoral fins to walk along the seabed, with Bar jacks (Caranx rubus) nearby, South Bimini, Bahamas. The Bahamas National Shark Sanctuary, West Atlantic Ocea...

Franco Banfi / Close up of Nurse shark (Ginglymostoma cirratum) using pectoral fins to walk along the seabed, South Bimini, Bahamas. The Bahamas National Shark Sanctuary, West Atlantic Ocean.

Espen Bergersen / Humpback whales (Megaptera novaeangliae) lunge feeding on herring (Clupea harengus) being watched by tourists in Zodiac boat very close, Kvaloya, Troms, Norway, November

Espen Bergersen / Humpback whale (Megaptera novaeangliae) photograped from above, showing pectoral fin length, Kvaloya, Troms, Norway January

Espen Bergersen / Humpback whales (Megaptera novaeangliae) photograped from a bridge, showing pectoral fin length, Kvaloya, Troms, Norway January

Alex Mustard / Dwarf lionfish (Dendrochyrus brachypterus) opens its wings' (in fact enlarged pectoral fins) Seraya, Tulamben area, Bali, Indonesia, Java Sea.

Tony Wu / Whitespotted bamboo shark (Chiloscyllium plagiosum) male biting the pectoral fin of a female shark during courtship, Kannoura, Shikoku, Kochi-ken, Japan

Melvin Grey / Pectoral sandpiper (Calidris melanotos) juvenile feeding around edge of shallow flood, Llanrhystud, Ceredigion, West Wales, UK, September.

Melvin Grey / Pectoral sandpiper (Calidris melanotos) juvenile, migrant, Llanrhystud, Ceredigion, West Wales

Roger Powell / Sharp-tailed sandpiper (Calidris acuminata) in winter plumage, feeding along the tideline, Point Wilson, Port Phillip Bay, Victoria, Australia.

Roger Powell / Sharp-tailed sandpiper (Calidris acuminata) in winter plumage, feeding along the tideline, Point Wilson, Port Phillip Bay, Victoria, Australia.

Tony Wu / People examining pectoral fins of a Fin whale (Balaenoptera physalus) the bone structure reflects the animal's link to terrestrial mammals, Tokyo, Japan, November 2013

Tony Wu / Southern right whale (Eubalaena australis) lifting a pectoral fin out of the water near shore, photographed with the permission of the Department of Environmental Affairs, South Africa, August

Tony Wu / Humpback whale (Megaptera novaeangliae) male extending his pectoral fins into the air, social behaviour, Vava'u, Tonga, South Pacific

Tony Wu / Humpback whale (Megaptera novaeangliae) male on its side, getting ready to slap its pectoral fin on the ocean surface, Vava'u, Tonga, South Pacific

Tony Wu / Humpback whale (Megaptera novaeangliae) pectoral fin raised in late afternoon sunlight near coast, Vava'u, Tonga, South Pacific

Tony Wu / Humpback whale (Megaptera novaeangliae) female extending her pectoral flukes into the air to slap the water for attention from males, Vava'u, Tonga, South Pacific

Tony Wu / Humpback whale (Megaptera novangliaea) calf breaching with a scar clearly visible on its pectoral fin that most likely resulted from the bite of a Cookie cutter shark (Isistius brasiliensis) Vava'u, T...

Tony Wu / Humpback whale (Megaptera novaeangliae) juvenile playing by raising and slapping its pectoral fin, with snow-capped mountains visible in the background, Chatham Strait, Alaska, USA July

Tony Wu / Humpback whale (Megaptera novangliaea) breaching, Vava'u, Tonga, South Pacific

Tony Wu / Humpback whale (Megaptera novaeangliae) mother and calf accompanied by male with a white pectoral fin. Photographed in Vavau, Kingdom of Tonga.

Tony Wu / Humpback whale (Megaptera novaeangliae) calf 'Tahafa' male with injured pectoral fin and scarred body, with mother. Vava'u, Tonga, Pacific Ocean.

Tony Wu / Humpback whale (Megaptera novaeangliae) calf 'Tahafa' male with injured pectoral fin and scarred body, with mother. Vava'u, Tonga, Pacific Ocean.

Tony Wu / Humpback whale (Megaptera novaeangliae) entangled in longline fishing gear immobilizing both pectoral fins, and infested with Whale lice (Cyamus boopis) Vava'u, Tonga, Pacific Ocean.

Tony Wu / Humpback whale (Megaptera novaeangliae) pectoral fin of female, with barnacles and parasites, Vava'u, Tonga, Pacific Ocean.

Tony Wu / Humpback whales (Megaptera novaengliae) male close up of his belly, with pectoral fin raised, taken during a heat run. Vava'u, Kingdom of Tonga. Pacific Ocean.

Tony Wu / Humpback whale (Megaptera novaeangliae) playing, skimming the ocean surface with the tips of his pectoral fins. Vava'u, Kingdom of Tonga. Pacific Ocean.

Tony Wu / Humpback whale female calf (Megaptera novaeangliae) posing with her pectoral fins held together, with her mother resting in the background. Vava'u, Kingdom of Tonga. Pacific Ocean.

Tony Wu / Sperm whale (Physeter macrocephalus) close up developing fin in preserved male calf fetus measuring 60cm to 70cm. Origina unknown presumably removed from mother during necropsy.

Suzi Eszterhas / Humpback whale (Megaptera novaeangliae) waving pectoral fin in air, Prince William Sound, Alaska, July.

Jordi Chias / Blue shark (Prionace glauca) seen from above with pilot fish, Azores Islands, Portugal, Atlantic Ocean

Alex Mustard / Red Sea anemonefish (Amphiprion bicinctus) fans oxygen rich water over its clutch of eggs with its pectoral fin. The eggs are close to hatching and laid next to the red skirt of a magnificent sea anem...

Espen Bergersen / Humpback whale (Megaptera novaeangliae) at surface with pectoral fin raised and whale safari tourists on boat in background, at sunset. Andfjorden close to Senja, Troms, Northern Norway. January.

Espen Bergersen / Humpback whale (Megaptera novaeangliae) at surface raising pectoral fin. Kvaloya, Troms, Northern Norway. November.

Alan Murphy / Pectoral Sandpiper (Calidris melanotos), Alaska

Alan Murphy / Pectoral Sandpiper (Calidris melanotos), Alaska

Alan Murphy / Pectoral Sandpiper (Calidris melanotos) calling, Alaska

Alan Murphy / Pectoral Sandpiper (Calidris melanotos), Alaska

Pascal Kobeh / Roundhead parrotfish (Scarus viridifucatus) close up of fin, coast of Dhofar and Hallaniyat islands, Oman. Arabian Sea.

Pascal Kobeh / Detail of the pectoral fin of Roundhead parrotfish (Scarus viridifucatus) coast of Dhofar and Hallaniyat islands,Oman. Arabian Sea.

Pascal Kobeh / Masked porcupinefish (Diodon liturosus) detail of pectoral fin, coast of Dhofar and Hallaniyat islands, Oman. Arabian Sea.

Gabriel Rojo / Southern right whale (Eubalaena australis) surfacing behaviour Valdes Peninsula, Chubut, Patagonia, Argentina.

Gabriel Rojo / Southern right whale (Eubalaena australis) surfacing behaviour Valdes Peninsula, Chubut, Patagonia, Argentina.

Gabriel Rojo / Pectoral fin of white Southern right whale (Eubalaena australis) calf at surface. Valdes Peninsula, Chubut, Patagonia, Argentina.

Angelo Gandolfi / Southern right whales (Eubalaena australis), one breaching (right) the other turned belly-up and showing pectoral fins. Santa Catarina, Brazil, September.