Britain’s seas are home to an amazing array of wildlife, from whales and basking sharks to fish as small as the tompot blenny and as curious as the sunfish — usually found in much warmer waters but spotted off the Cornish coast last week.

But do we value and care for our sea as much as we should? I think the most shocking statistic I came across while making Seawatch for the BBC was that there has been a 94% increase in beach litter in the past decade.

The rubbish that winds up on our beaches may have been dumped at sea or carried thousands of miles on ocean currents, but a substantial percentage is simply left by people after their day at the seaside. Plastic bottles, crisp packets, Styrofoam trays, empty drinks cans all abandoned, left for the tide to carry away.

Except that it doesn’t: that refuse stays on the beach or ends up on another one, strewn among the seaweed and driftwood, making the tide line resemble a squalid ring of grime around a bath. It’s not just a question of aesthetics. The sea and its shoreline provide a home and sustenance for thousands of animals and birds. Rubbish on the beach can lead to injury, entanglement and often a slow, needless death. Bits of plastic and Styrofoam can easily be confused for food and many of our seabirds make that mistake. And plastic bags, floating in the water, can be mistaken for jellyfish, the principal diet of the leatherback turtle.

The fact that leatherback turtles are found in British waters is perhaps something of a surprise, but these vast animals migrate to our shores from their egg-laying grounds in the Caribbean. They come for our jellyfish, which start to appear in great numbers after the first plankton blooms in the spring.

Sadly, though, jellyfish and plastic bags look remarkably similar in the water and a hungry leatherback won’t be too discerning. Now you may well be thinking that an animal as big as a leatherback turtle isn’t going to be overly bothered by the odd plastic bag ending up in its gut. But almost all the leatherbacks washed up on Britain’s beaches are found to have died of starvation.

Jellyfish, as you can probably imagine, aren’t the most nutritious of beasts and so a several hundred kilo leatherback is going to need to eat a lot of them to sustain itself. It doesn’t want any to escape or slip out the wrong way, so once the jellyfish is in the mouth of the turtle, it has to ensure that it has a one-way journey straight into its gut. The same goes for a plastic bag. The difference is that a jellyfish will slip through, but a plastic bag is likely to stick, blocking the passage for anything else and slowing starving the animal to death.

It seems all the more bizarre that we are so careless with our marine environment when we eat the fish that live in it. Hundreds of thousands of tons are pulled out of our sea every year. Our fishing industry may have got smaller, but those still fishing are using ever more sophisticated and destructive methods to meet their quotas — satellite navigation, fish finders, bottom trawlers, drift nets. Fishing methods like these are indiscriminate and the “by-catch” huge.

Species such as cod are in danger of being wiped out, as they were in Newfoundland, once the richest cod fishing grounds in the world.

The only way to preserve our fish stocks and the future of our fishing industry will be through constructive collaboration between fishermen, scientists, conservationists and government. Tough decisions will have to be made, fishing banned or restricted in certain areas and at certain times of year. And we, as consumers, can help bring about change. If we buy fish only from sustainable sources and avoid species that are under threat we’ll help ensure the future both of our fish stocks and the fishing industry.

You may be pleased to know, as you contemplate having a dip, that sea temperatures are rising. It’s all thanks to our old friend global warming. They haven’t risen much, the North Sea has warmed by about 0.5C in the past 40 years, but that’s enough to cause chaos. It is not uncommon for fishermen in Aberdeen to catch red mullet and squid, species more familiar to the Mediterranean.

That doesn’t seem particularly bad news, but for our traditional native species that happen to like their water half a degree or so colder it’s not good at all. The only thing to do is head north and as they do, the food chain starts to kink. Our cold water plankton, which feeds the rich, oily sand eels so vital to the success of breeding seabirds, is being forced north and is being replaced by warm water plankton that doesn’t behave in the same way at all.

This means our sand eels are either immature or ill nourished by the time our seabirds need them to feed their chicks with the result that many seabird colonies, particularly on Shetland, are finding it increasingly difficult to breed successfully.

But given a bit of help wildlife can and does bounce back. We almost hunted our seal population to extinction but since it has been protected we now have the largest grey seal population anywhere in the world. If we are careful about our use of energy, think about how we dispose of our litter, become a little more discerning about the fish we eat, we can help preserve arguably the greatest nature reserve we have.

Seawatch is on BBC1 on Wednesday at 8pm