According to marine biologist Callum Roberts, the oceans have changed more in the last 30 years than in all of human history before. Most of the Earth's seas have lost more than 75 percent of their megafauna - large animals like whales, dolphins, sharks, rays and turtles - and the populations of many fish species humans like to eat have plummeted. Roberts says the loss of large marine animals is mainly down to widespread fishing and hunting, while the decline in smaller fish populations is due to a combination of environmental damage and overfishing.

In his new book, 'The Ocean of Life', Roberts looks at the big picture relationship between people and the sea. He points out that most marine research and science is confined to one area, so that pollution is studied separately from fishing, which is considered apart from shipping or climate change. He suggests that "a view of the whole is far more alarming than the sum of its parts".

We spoke to Canadian professor Peter Sale, author of 'Our Dying Planet: An Ecologist's View of the Crisis We Face', and he believes the situation is at least as serious as Roberts suggests: "The pace of change is more rapid than in at least the last several million years. I do not think we yet have a full grasp of the extent of the damage we are causing to ocean ecology, but the fact that we can talk about something as profound as the total disappearance of coral reefs from the planet by 2050 suggests the changes are serious".

Roberts and Sale are not the only ones calling for a big picture approach to marine damage. In the Canadian context, a February report from The Royal Society of Canada Expert Panel, chaired by Professor Jeffrey A. Hutchings, found that "Canada faces significant challenges in its efforts to conserve and sustain marine biodiversity in light of climate change, fisheries and aquaculture", and pointed out that "human-induced climate change represents the greatest challenge primarily because its effects on marine biodiverstiy will not be readily reversed". The panel recommends a unified strategy to protect and improve the health of Canadian oceans.

Another recent study, this one from the UK, called 'Valuing The Ocean' estimates that failure to tackle climate change today "will damage the world's oceans to the tune of GBP270 billion (CAD$433 billion) a year by mid-century".

That figure is based on the economic losses expected to result if damage to the world's oceans continues unchecked, and the study's authors say the worst hit areas would be "poorer places such as Africa, where artisan fishermen could lose their catches, and Asia's low-lying and heavily populated Mekong Delta". The study's authors call for integrated management of the seas on both a local and a global level in order to tackle the problem.

Roberts says he is often asked what people can do to help at an individual level. His advice is to start by avoiding "eating fish that are overexploited in the wild or taken using methods that harm other wildlife". He recommends avoiding prawns, scallops, plaice, cod, and hake, and focusing on smaller fish who are "low in the food web", like anchovies, herring, and sardines, and vegetarian fish like tilapia and carp.

Professor Sale also weighed in on how individuals can mitigate the damage to our oceans, saying "every one of us can shift away from use of fossil fuels, from purchase of unsustainably caught fish, and from support of other activities that degrade the environment."

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