Ocean Of Life: How Our Seas Are Changing, By Callum Roberts

It says a great deal about our attitude to the oceans that the film director James Cameron, a private individual, could scoop world headlines recently by being the first person for over 50 years to visit the deepest abyss, the Mariana Trench. Countless billions have been spent on space exploration but the deep sea is still the province of the occasional amateur foray. Given the importance of the oceans for our food supply and climate regulation, and their staggering beauty, it is hard to understand this neglect. Of course the deep sea is a challenging environment: but more so than space?

In the past, awe at the ocean's size, power and remoteness led to an "out of sight, out of mind" mentality. We used to think that the sea was too large and autonomous to be seriously damaged by us. Even the poets, who might have had a little more imagination, fell for this. This book has an epigraph by Byron ("Man marks the earth with ruin – his control/ stops with the shore") which is rebutted by the succeeding 390 pages. As late as the 1970s, Philip Larkin could write, in a poem predicting ecological doom on land: "Chuck filth in the sea, if you must:/ The tides will be clean beyond". It is Callum Roberts's mission to show just how wrong this is.

Professor of marine conservation at York University, Roberts has excellent early chapters that give a concise evolutionary history of the oceans and the complex patterns of their currents. The chapters in which he details humankind's various assaults on the sea by way of over-fishing, global warming, pollution of every kind, including aural, and habitat degradation, are a bit relentless. Confronted by this barrage of negative data, the reader could be forgiven at times for wanting to stick to dry land.

But persistence is rewarded. For me, the most revealing passages concern plastics. There are great punctuation marks in the oceans – gyres – in which detritus collects and whirls around. Before our trash formed the contents, the best example was the Sargasso Sea in which great masses of seaweed congregate. Now our plastic rubbish piles up in what has become known as the Great Pacific Garbage Patch. Most plastics don't biodegrade but they do break up into smaller and smaller particles. Many creatures, from birds down to microscopic plankton, consume these as if they were food. Roberts has a photograph of a dead flamingo whose stomach contents consisted entirely of bits of plastic.

The least known form of marine pollution is sound, but Roberts is able to conjure up a soundscape of the sea before we joined in with our disorientating ships' noise and sonar. Sound travels five times more quickly in the sea and the communications systems of the whales and dolphins are beautifully adapted to this.

The great whales travel thousands of miles between feeding and breeding grounds. They command the sea: blue whales can bellow at over 190 decibels and can hear each other over hundreds of miles. Or at least they could before we got in the way.

The careless damage we wreak on marine ecosystems through aggressive over-fishing, pollution and habitat destruction is on a massive scale, but the most anxious part of our ocean-watching now concerns global warming. A recent UK government report details how Mediterranean species of fish are now appearing in the North Sea, while traditional northern species such cod migrate pole-wards and deeper into colder waters.

Most creatures live in an environment very finely tuned to temperature and will move when the temperature changes. Even a one degree rise in average temperature could reduce mussel production in Scotland and Northern Ireland by 50 per cent. Temperature is not the only factor: Roberts is an expert on the world's coral reefs and they are at risk from ocean acidification, caused by excess dissolved carbon dioxide from burning fossil fuels.

Dealing with global warming is going to take a long time; how we fish the oceans is more immediately in our power, or ought to be. The perennial story of fisheries is the war between the industry and marine scientists. Roberts is roused to great passion on this: "Over the years I have come across spectacular levels of denial among fishing industry representatives". The industry's mantra is "there are always more fish in the sea" even when the evidence of collapsed fish stocks and smaller catches of dwarfed fish is staring them in the face. This is a problem for psychologists rather than marine biologists.

Roberts describes aggressive fishing techniques that destroy entire ecosystems, raking up the seabed as if it were of no consequence. Perhaps "before and after" is the only way to illustrate the folly of this. In 1938, the peak year, bottom trawlers caught more than five times as many fish as are caught today. To put that in context, the human population was then around 2.2 billion; today it is more than seven billion. The actual global fish population is, of course, not known but, given the vastly more efficient means we now have of finding and catching fish, that five-fold decline tells its own story.

Anecdotal, but heartbreakingly vivid, are three photographs of recreational catches from Key West, Florida, dated 1950s, 1970s and 2007. The goliath groupers in the first photograph are as tall as the man posing against them and much fatter; the 1970s catch is abundant but the fish are much smaller; in 2007, the haul wouldn't raise an eyebrow on your local fishmonger's slab.

But, as Roberts says, "the grins on the anglers' faces are just as broad today as they were in the 1950s". This is what he calls the "shifting baseline syndrome", taking for granted "things that two generations ago would have seemed inconceivable". Those not wedded to a belief that we can blindly take forever from nature should read Roberts's book, wake up and smell the troubling odour that wafts from the sea.

Roberts has good advice for those who are concerned enough to do something about the state of fisheries and the oceans, with appendices on the main conservation bodies and recommendations for the consumer. There has been conflicting advice on what seafood can be eaten with a good conscience: Roberts recommends the UK Marine Conservation Society's fishonline.org. And if you've ever wondered why prawns and clams loom so large in supermarkets and restaurants these days, it's because in many waters, such as the Firth of Clyde, they are all that is left.

Peter Forbes's book 'Dazzled and Deceived: mimicry and camouflage' is published by Yale