Mark Carwardine / Harbour porpoise (Phocoena phocoena) surfacing Bay of Fundy, New Brunswick, Canada

Richard Robinson / Shortfin mako shark (Isurus oxyrinchus) head on just below surface, another in background, off the West Coast of Auckland, New Zealand, February

Richard Robinson / Shortfin mako shark (Isurus oxyrinchus) profile portrait, just below surface, off the West Coast of Auckland, New Zealand, February

Nick Hawkins / Harbour porpoise, (Phocoena phocoena) Bay of Fundy, New Brunswick, Canada, September

Nick Hawkins / Harbour porpoise, (Phocoena phocoena) porpoising, Bay of Fundy, New Brunswick, Canada, August.

Chris & Monique Fallows / Mako shark (Isurus oxyrinchus) with sunrays, Cape Point, South Africa, March.

Chris & Monique Fallows / Mako shark (Isurus oxyrinchus) near surface, Cape Point, South Africa, March 2015

Roland Seitre / Finless Porpoises (Neophocaena phocaenoides) swimming in unison. Captive. Endemic to South East Asia and the Yangtse River.

Florian Graner / Harbour porpoise {Phocoena phocoena} Sognefjord, Norway. Composite

Todd Pusser / Dall's porpoise at surface {Phocoenoides dalli}, Central Bering Sea, Alaska

Flip Nicklin / Vaquita (Phocoena sinus) by-catch casualty, Baja California, Mexico

Florian Graner / Harbour porpoise {Phocoena phocoena} off Isle of Man, Irish Sea, UK. Digital composite