Perhaps borne out of many blank sessions on a notoriously moody river, the list of complaints from most Lower Thames anglers is a long one. “Too many mitten crabs”, “Cormorants eat all the fish”, “Where’s all the fish gone?”. From the grassy banks of Windsor down to Wandsworth’s urban jungle, we all say the same.

To find out what could be done, the Thames Anglers’ Conservancy visited John Sutton, the Environment Agency’s Fisheries Team Leader for the South East Area and George Gerring, the Thames Catchment Officer.

We led with a subject close to Thames anglers’ hearts – Chinese mitten crabs. In a recent Thames study conducted by the Natural History Museum for DEFRA, 539 mittens were caught in 15 months from only 4 sites. They are also caught in high numbers both in the fyke nets of the commercial fishermen below Tower Bridge and by anglers upriver. We asked John, more in hope than expectation, how to control mitten crabs.

Half expecting to hear that further studies need to be done, we were delighted to hear that for the first time ever, the EA will be able to issue authorisations this year to trap mittens in the tidal Thames. Commercial operations have proved successful in Holland and the DEFRA study concludes that the Thames mitten is fit for human consumption. Details have to be finalised such as the best design to prevent other fish, such as eels, being caught in the trap. Also even on the tidal Thames, by legislation, otter guards need to be built in. Design details aside, this news will be warmly received by Thames anglers.

Cormorants were next on the agenda. The lock-keepers at Richmond report that squadrons of these fish-eating predators fly up the estuary daily, to hunt from the weir posts of Teddington, Molesey and many other vantage points upriver. They eat fish to survive and are following their instincts but numbers are so high now that anglers are looking at control options. We presumed shooting them as they pass over Westminster Bridge wasn’t an option, so what can be done?

John explained underwater cover is all important for the fish. Without natural refuge areas such as weedbeds and sunken trees, fish are vulnerable to predation by cormorants.

“Anglers say they see cormorants dive and come up without fish, so surely the fish are all gone. Studies have shown though that fish behaviour changes when cormorants are present, with the fish either moving or hiding.”

“On the Jubilee River, a Thames tributary, there is less refuge from predators and flood flows. This is due to the Jubilee being a flood channel, so the plant life is less able to take hold, and there is less in-stream habitat for fish. As a result, you see cormorants hunting the Jubilee rather than the nearby Thames which has higher plant growth and more in-stream cover, therefore, more hiding places for fish. When a by-pass chamber was run dry for maintenance works near Taplow Mill, we found roach of a good size up inside, seeking refuge from the cormorants. “

“Due to a cleaner river, plant growth is definitely on the increase. I remember working the Thames in the 70s and 80s, looking down from the boat at Chertsey and not being able to see any plant growth. Recently, you could see healthy plant growth there all the way down to the gravel in 10 feet of water.”

George made clear at this point that water abstraction is by far a greater cause of fish deaths than cormorants. We often hear how it slows the flow of the river but little of the impact on fish populations. When water gets abstracted at the intakes, fish eggs, fry and juvenile fish get sucked in as well, passing through the mesh of the screens. Abstraction is the silent killer on the Thames.

Electro-fishing results show markedly what a devastating effect these water intakes have. Electro-fishing temporarily stuns fish so that they float to the surface and can be inspected. Between Hurley and Teddington at 16 survey points, the lowest fish densities were found downstream of Walton intake and downstream of Surbiton intake. The greatest number of species in one spot (11) was found above Datchet intake yet the lowest number of species (4) was found below Datchet intake.

So how can this be fixed? The EA now instruct that mesh as small as 1-3 millimetres may be specified on Thames abstraction screens. This is small enough to protect elvers and glass eels. The one silver lining to the dark cloud of Thames eel decline is that it is now afforded protection. The EA Fisheries team can use new eel legislation to ensure water companies are not damaging eel stocks.

In addition, ‘behavioural screens’ are being investigated. Strobe lighting in front of intakes is a possibility. In Holland, strobe lighting has been shown to scare fish away but more study needs to be done on what species and ages are deterred. For it to be effective, strobes need to work on fry and juveniles. Most of the Thames Water intakes already have acoustic deterrents to help deter salmon smolts and other species from being sucked in. George had returned recently from a national assignment where he has been working on this very promising subject and will be pursuing options for the Thames.

Sticking with contentious issues, we asked John and George their feelings on zander and catfish populations in the Thames. Every season, several captures of each species are reported by anglers. A TAC member has captured in 2009 what is believed to be the Thames record zander at 13lb 12oz and pictures have been publicised in the angling press of a 64lb cat caught in 2010.

We found out catfish have not been caught in the annual nettings or electro-fishing surveys conducted by the EA, so it is extremely difficult to assess population figures for catfish. Of all species, they are possibly most resistant to electro-fishing and are hard to net, usually living in holes and snags. Angler captures would also indicate the population levels remain low. Despite being present in the Thames since the 1920s, they seem not to have disrupted populations of other species.

John said how zander are caught in low numbers in the electro-fishing surveys but relayed the welcome news for anglers that they have all been in very fit condition. Again, as they are being caught by anglers and surveys in such low numbers, it is not thought they pose a threat to native species in the Thames and this is despite being present in the river for several decades.

John did clarify that “zander and catfish seem to have a very limited range in the Thames, with all specimens having been caught within a few stretches of river. The catfish range in particular is within a few short miles and over the years it seems the range for both species has not increased appreciably. The EA are most definitely not looking to expand the range of zander and have refused applications to stock them in any stillwaters that are located within the floodplain or have a connection to a river.”

It may be a case of “let them be” in the Thames. If a decision was made to remove all cats and zander from the Thames, how would you do it anyway? Especially as nettings and electro-fishing produce very few captures. It may be that zander and catfish remain a very special one-off capture and a great surprise for most Thames anglers.

Of course, the usual scenario is less exciting. While we sit behind inactive alarms session after session, many of us Thames anglers wonder if there is something ‘wrong’ with the river; whether there is unreported pollution. We asked if the Thames water quality is monitored and were pleased to learn that there are over 60 monitoring points on the Thames. AWQMS (Automated Water Quality Monitoring Stations) take samples every 15 minutes and check for chlorophyll, blue green algae, ammonium, ammonia, PH, turbidity (clarity), nitrates, phosphates, dissolved oxygen levels and temperature. This realtime data is transmitted to the EA and alerts sent to staff mobiles.

In addition to live sampling, post-pollution reactive monitoring is performed. Fish and invertebrate life above and below suspected points of pollution are surveyed to assess the impact.

Speaking about the recent fish kills on the Thames tributary, the River Wey, you could tell pollution annoys the EA Fisheries as much as it does us anglers. “As well as putting appeals out to fishing clubs, the local and angling press, Fisheries officers and their colleagues were out in the town centre on a Saturday asking the public if they knew anything about the spill, or had seen anything”.

Before visiting, the TAC canvassed members for questions to ask the EA. One of the common questions was “Are there less fish in the river, as everyone seems to be catching less?”.

We have seen the electro-fishing and hydroacoustic results going back to 2002 and can confirm that although mean fish population figures are down, figures are skewed partly due to exceptional figures for 2005 and 2006. The river was flourishing in 2005 and 2006 but then the big floods of 2007 hit, meaning population figures took a marked dip in 2008. Populations started building again in 2009. Currently, bream and bleak figures at the 16 survey sites are down sharply, whereas dace and gudgeon are thriving in number, as are perch and carp by weight. This ties in with anglers’ observations.

John’s theory on why older TAC members are complaining they’re catching less than decades ago rings true, especially now we have seen confirmation of the healthy fish numbers. “The river may have fished better for some species before but its clearer now – clear water changes fish behaviour as we all know. Also the profusion of aquatic plant growth at some locations due to the clearer water means there is more natural food, both the plants themselves and the life being harboured within, so maybe there is less need for angling bait.”

Perhaps us anglers need to change our approach and adapt. There’s no doubt that there are some excellent catches being reported by some anglers.

Whilst on the subject of fish stocks, the TAC asked whether the Thames would be stocked. We have attended restockings on tributaries but we pointed out to the EA that most angling is done on the Thames itself, not some of the brooks and small rivers that flow into it. Why not put the fish into the main river? George’s explanation made sense to us – “ we will only stock where that particular fish’s life stage can be supported – the tributaries are a better, more sheltered environment than the main river for juvenile fish. There are less predators and the water is flowing and oxygen-rich. Some eventually come down into the main river, either naturally or in floods. They need to acclimatise in the tributaries first though. If stocked in the main river as juveniles, we’d just be feeding the pike.”

“There’s also no point in stocking a stretch just because its popular with anglers. Fish move between areas anyway and will naturally migrate in search of suitable spawning substrate. Some barbel have been shown to move 30km on the River Severn in order to spawn. Plus bathymetric studies show the gravel beds shift each year, so although fish are on a gravel bed one year and it’s fishing well, it doesn’t mean the gravel bed or the fish will be there next year.”

Well, we covered some hot subjects in Thames angling – mitten crabs, cormorants, abstraction, zander, catfish, current fish populations, water quality, pollution, how the river is fishing and restocking.

We came away from the EA’s Frimley office reassured and encouraged. Reassured by seeing the hard data from fish population levels but more than anything, encouraged by the attitude and knowledge of the EA’s Thames Fisheries team. Combined with the work Thames fishing clubs could help them with, it seems the framework is in place to keep the river healthy. George’s work on deterring fish from abstraction intakes is crucial and we follow that with much interest. It would result in thousands more fish in the river. Of course, we also look forward to hearing about nets full of mitten crabs later this year!

Steve Holmes, Thames Anglers’ Conservancy