Sharks and Seals

Biologist Steve Backshall’s recent illustrated hardback Deep Blue is a clear and lay-friendly introduction to the remarkable undersea world, a world holding more than 33,000 species of fish. In addition to his scientific background from Canterbury Christ Church, the author is a keen diver, with decades of experience to enthuse readers: encounters include seals, octopus, whales, anacondas, great white sharks, and the weighty saltwater crocodile. The book’s thirteen chapters allow easy access – and most are likely to prove both interesting and accessible to readers.

As with other subjects, there is jargon to assist communication, for instance the first three zones encountered as the sea’s depths are explored begin with the sunlight (or epipelagic) zone to 200 metres, followed by the twilight (or mesopelagic) zone, and then, deeper still, to 4000 metres, the equally appropriately named midnight zone – also known as the bathypelagic zone.

Life slows down at greater depths: an octopus can sit on her eggs for over four years in the darkness. Seals, sharks, and other creatures are classified into family trees and scientific names, though a keen moviegoer or lay enthusiast of nature documentaries could likely identify a great white by its terrifying bulk and uncanny menacing aura. Less well known is the voracious salmon shark, the great white’s fast-moving, cold-water equivalent which frequents Prince William Sound in Alaska.

Ecological relationships are acknowledged. In California’s Monterey Bay twenty years ago, the return of sea otters meant they hunted through forests of kelp for crabs, sea urchins and abalone – so reducing the dark forests to modest size.

During this period, around South Africa’s Dyer Island and parts of Namibia, the disappearance of great whites was traced to a pair of orcas: whenever the orcas appeared shark tourism suffered financial losses, inclusive of cage-diving trips best approached with caution. Backshall advises people of nervous disposition to avoid any underwater contact with such predators: they can detect higher heart rates. Nervous folk will rank as the most likely victims among swimmers with stronger mind sets. Expert advice given to the author states that as a twelve-foot-long predator approaches you must ‘own the water’. Hang on, what if the shark is also feeling more than a tad macho?

Neil Richardson Kirkheaton