In recent years, seals have become almost commonplace on the Thames all the way through Richmond and Twickenham. Even dolphins and smaller whales have reached Teddington Lock.

Just this week, scientists from the Zoological Society of London (ZSL) reported that several species of shark can now be found in the Thames estuary – including the aggressive Tope, venomous Spurdog and Starry Smoothhound.

Here Richmond's 'Man of the river', Keith Arthur, presenter of Tight Lines on Sky Sports and an expert on all things fishing, offers his insight on whether river users in the area are going to need a bigger boat!

Keith Arthur

It might come as news to many Londoners that 'sharks' inhabit their home river but don't worry because while the species may be distant relatives of 'Jaws', the relationship is as tenuous as that between your pet cat and a lion.

The report from the ZSL this week suggested it had found three species from the shark family – the Spurdog, Tope and Starry Smoothhound. But I would argue this understates the real situation.

We also see the lesser spotted dogfish, while an angling charter boat recently found a bull huss, or greater spotted dogfish.

Of these five, the Tope is the closest to a 'real' shark, with a decent set of dentistry that can take lumps out of their prey…mostly other fish, both dead and alive, and squid.

They can also grow to over 6ft and 100lb in weight but are now heavily protected as an endangered species.

While we might be worried about a shark taking a bite out of us, in fact, both the huss and spurdog – at least – might have more reason to be afraid of us. For, in the past, they have been regulars in fish and chip shops under the names rock eel and rock salmon.

Smoothhound, known as 'gummy sharks' in South Africa probably due to their lack of teeth, are present in what seems to be ever-increasing numbers.

Although they don't have teeth as such, their eating equipment contains hard, crushing pads, giving away their proclivity for shellfish, especially small crabs and hermit crab.

Another species doing very well, thank you, in the lower estuary are rays, especially thornback ray but blonde ray have turned up recently and stingray are fairly prolific in some areas of the Essex coast.

What has caused the increase in these fish that go under the 'cartilaginous' banner?

There can be no definite answer but my theory is that cod numbers have fallen through the floor. Cod have very big mouths and appetites to match and possibly feasted on immature dogfish and rays. What can't be in doubt is that their decline has created a lot more food available for everything else.

The Thames is an important nursery area for those species but not only them. Two of the most desirable British eating fish have large breeding populations; the very expensive Dover sole and sea bass.

Interestingly, the affordable small bass on sale in fishmongers are farmed, mostly in the Mediterranean: wild, usually line-caught bass are most certainly not cheap!

The list of species identified in the estuary, measured from Teddington to what's known as the Yantlet Line, an imaginary line between the Thames Stone by Yantlet Creek on Kent's Isle of Grain and the Crow Stone at Southend on Sea, runs to a staggering 115.

Part of the tidal Thames was declared 'biologically dead' in 1957 although I don't believe that to be the case. I think it was more of a lack of looking and assumption.

In fact, in the early 1960s the Thames Angling Preservation Society organised the 'Thames Experiment' with anglers fishing from Battersea Park at the upstream end right down to Gravesend with the result that freshwater fish were caught in the heart of London. Dace, bleak, roach and perch were the most common catches and considering the difficulty of fishing down there, and the tackle available at the time, that's quite remarkable.

In 1986 producers of London Weekend's Six O'clock Show asked me if we could catch fish outside their studios in Upper Ground, near London's Waterloo Station, live for the show to celebrate the opening of the coarse fishing season on June 16th. Five pals and I managed 26 fish of five different species in the show's thirty minutes!

Whilst we have had several visits from sea mammals upstream to Richmond, including dolphins and two separate whales recently, they aren't new by any means.

I recall a pilot whale washing up at Kew when I was a schoolboy. It ended up very close to the school rowing club but I wasn't allowed to take my fishing rod and pose beside it. It's very unlikely that any cetacean makes it back to its natural habitat.

Seals too have 'invaded' the freshwater sections, to my certain knowledge since the 1970s but the increase in semi-residency recently seems to have had a massive impact on fish stocks as bream, barbel and carp have been noticeable by their absence over the past 18 months.

One thing is for certain though: there are no sharks capable of making it this far upstream…although if our seas get much warmer, the semi-tropical and aggressive bull shark regularly makes its way 100 miles or more into freshwater.

They grow to in excess of 10ft and over 700lb and if that happens we certainly will need a bigger boat!