Weirs oxygenate the water, weir pools (the area next to the weir) provide a habitat for fish species such as Barbel and Chub. Weir pools provide a rest area for Salmon prior to leaping over the weir in the journey upstream. Weirs are good for rivers, especially during extended periods of hot weather when oxygen levels are low.

Thank you so much for your kind words and for supporting our project.

The smaller ones look like a mix of Roach, Dace, Small chub and young Bream, usually there will be some Bleak in there too. I saw a Perch 0:19 Lamprey. 0:40 Bleak 1:25 Roach 2:33 Brown trout. 2:52 Salmon following the Roach . 2:59 Adult Bream. 5:43 Tench at 9:20

Hi Greg, allis shad are the larger, rarer species compared to the smaller twaite shad. However many shad are now hybridised so without genetics we cannot tell by sight whether a fish is an allis or twaite. Sturgeon are very impressive fish. Although sturgeon aren't part of our project, there are other UK organisations working to spread awareness of these fish and improve the chances of their return.

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With apologies for the delay in reply, due to staff leave over the summer, your comment has only just been picked up. We are a small team and unfortunately unable to continuously monitor all social channels. However, we did want to respond. To your second point which seems to be about the fish passes not being necessary. Unlocking the Severn is focused on twaite shad - this endangered species has not been able to spawn successfully upstream of the weirs since they were installed. The shad spawn around May when the river is typically at lower levels. However even in the unlikely event of high flows at that time of year (as we experienced on the Severn last year), our acoustic tagging efforts have shown that during periods of high flow the shad leave the river system and only attempt to return when levels have reduced again. This seems to be an adaptive behavioural response as eggs spawned by shad in flood condition would simply be washed away without the chance to hatch successfully. The weirs have also been a barrier that has impacted all fish on the river - as all fish (whether classified as ‘migratory’ or not) naturally move around on the river either to either spawn, for feeding opportunities or for shelter/avoid predation. The weirs have to a large extent prevented this for most species of fish for over 170 years. The ‘migratory species’ for example salmon, sea lamprey, rivers lamprey, shads, eels, sturgeon have either been delayed or blocked in their spawning migration. In the case of Salmon, this is to the detriment of overall condition/fitness, and in the case of sturgeon and allis shad they have become locally extinct. Salmon do have an amazing ability to negotiate in-river obstacles and certainly salmon have been able to progress upriver to spawn when condition have allowed by either swimming over the weirs in flood conditions or by using the rudimentary baulk passes that were on the weirs. However, delays caused by the weirs (most severe in an exceptionally dry year like we have just seen in 2022) would have reduced the ability of salmon to spawn successful through lack of condition, failing to reach the optimal spawning areas or through mortality. The new fish passes allow salmon to move and distribute themselves naturally through the river this will certainly improve their spawning success. The viewing window has seen a constant stream of other species of fish from pike, to cyprinids in their thousands, migrating to complete their spawning in the spring. These fish would not previously have been able to do this, and these spawning migrations will only benefit the river ecology, as fish reach suitable spawning habitat and their juveniles re-colonise the river through downstream drift. That will in turn lead to better recruitment and distribution of these species for the benefit of the ecology of the river and recreational anglers. The fish passes also allow non-native species to migrate, this includes zander, to date we have only seen a handful of this species use the pass. It should be remembered that Zander were introduced by anglers to the Severn and can now really be considered naturalised and experts consider there is no real hope of ever removing this species. There were also already present upstream of Diglis, although in limited number, probably entering the river through the connected canal network or illegal movements. Zander have been able to persist on the Severn because they have occupied a niche that was previous underused. Their gape (mouth size) is relatively small compared to the native pike and can only really prey on fish up to around 10cm, concentrating their feeding on small silver fish. The population of zander are controlled by the availability of prey fish so their population performs in a cyclic manner to these smaller silver fish and also through natural predation by either larger zander or pike and probably even otters. There is no hope of this non-native species being removed now, so like carp and barbel before them they will remain a component of the Severn’s mixed stock. The fish passes will facilitate to a limited degree their movement, but consideration has been given to zander's pretty exacting habitat requirements: they need deep, relatively slow-moving habitats that are only found in the navigation reach of the Severn and associated canals, so zander as a species are unlikely to move much further upstream than Stourport. There has been some eDNA research by Natural England on the Severn to record this baseline of distribution and in years to come future monitoring (assuming funding is secured) should be able to show if this has changed.

@@SevernUnlocked What a fantastic answer. Interestingly I have heard of Zander being caught way further up the Severn than Stourport. I have seen pictures too. Prior to the unlocking. I am waiting to see a giant Wels catfish rocking up through the fish pass myself. It is the apex predator in that river. They have been caught as far up as Iron bridge.

Found this now, thank you kzbin.info/aero/PL5tw6FzDfCrkS77ENWiN8OUDEoFtFuHG6

Thank you John. That's a brilliant suggestion. When we get a mo, we'll add the fish names in the description. That'll be a good test of our ID skills too!

Thank you Clare

We certainly will. We've got lots of footage to look through from this year's spring migration, so there'll be more on the way!

@@SevernUnlocked More please

Yes - whilst we are in spring migration monitoring - the light panel stays on and we capture fish movements 24/7.

Unfortunately every time it rains the local water authorities deem it necessary to dump unprocessed effluent into our rivers. Thames water where I live are one of the main culprits but I've heard they are all getting away with it now