Hi Again Graham,
This 10 year decline you speak about, does it really makes sense or stand up to scrutiny? If it were down to a simple reason of these type of pellets you speak of, why hasn't every other species of fish been affected in the same way barbel appear to have been on some rivers? Like I said, which no one answered by the way, what about fish eating birds? Have these declined along with so called declining populations or have had their breeding cycles altered because they have been eating fish supposedly infected with MT's? The Trent has a very high number of fish eating birds and Kingfishers are on the increase nationally according to the RSPB.
So what is behind the declines of wild fish stocks on some rivers? Water quality as we know is falling behind the standards as laid down by the EU Water Directive. Is this alone responsible? I seriously doubt it. Agricultural practices, are they solely responsible for ongoing destruction of spawning habitats? The Salmon and Trout Association think it has a lot to do with it and I agree. But is this alone causing the problem on some of our rivers?
The river Trent is fortunate in that most of the land directly adjacent to the river on both banks is predominantly pasture and even along the Trent Valley as a whole 28% of the land is pasture. And given that the spawning habitat along the Trent is excellent has agricultural practices got a lot to do with the river Trent's on going success?
Your other theory of Boom and Bust periods for rivers doesn't make sense either Graham. If it were a case of that then we merely accept this as some type of reason where we all have to simply wait it out until particular rivers come good again?
What about water treatment plants? An extract from the roach research, which Tyler is best known for,
" We set up an extensive survey to investigate this hypothesis. Rainbow trout and carp (Cyprinus carpio) were placed in cages in or close to the effluent discharges at 28 WWTW throughout England and Wales, and we measured blood VTG concentrations after a two-to three-week exposure period (Purdom et al. 1994). The results were astonishing. Almost all of the effluents studied were estrogenic and induced up to a millionfold increase in the amount of circulating VTG in males. Some concentrations of VTG measured in males were in excess of 50 milligrams per milliliter, representing more than half the blood protein content. These concentrations were higher than those found in fully mature females with thousands of large, yolky eggs in their ovaries. The phenomenon of estrogenic effluents has subsequently been established more widely across Europe—for example, in Germany (Hecker et al. 2002), Sweden (Larsson et al. 1999), Denmark (Bjerregaard et al. 2006), Portugal (Diniz et al. 2005), Switzerland (Vermeirssen et al. 2005), and the Netherlands (Vethaak et al. 2005)—and in the United States (Folmar et al. 1996), Japan (Higa****ani et al. 2003), and China (Ma et al. 2005).
Further studies using caged fish (rainbow trout, carp, and roach) and measuring VTG induction have demonstrated that WWTW effluent discharges in the United Kingdom vary widely in their estrogenic potency, depending on the influents received by the WWTW, the level and type of treatment that takes place in the WWTW (Kirk et al. 2002), and the level of influent and effluent dilution (Williams et al. 2003). Seasons also have been shown to affect the estrogenic potency of effluent, probably in connection with changes in the level of microbial activity (Harries et al. 1999). Studies on rivers receiving treated WWTW effluent have shown that the estrogenic activity can persist in the receiving rivers for many kilometers downstream of the point source of discharges and with considerable dilution of the effluent (Harries et al. 1995, 1997, Rodgers-Gray et al. 2000, 2001, Liney et al. 2005). Effluent concentrations as low as only 10% have been shown to induce a vitellogenic response in juvenile roach exposed for four months, and this effect concentration may be even lower for longer-term exposures (Rodgers-Gray et al. 2000). These findings have important implications for wild roach populations that spend much or all of their lives in effluent-contaminated rivers, where the river flow is often composed of 10% WWTW effluent (figure 2). In some rivers in the United Kingdom, during the summer months and periods of low water flow, half of the flow of the river can be composed of WWTW effluent, and in the most extreme cases, the complete flow of the river can be made up of treated WWTW effluent (Jobling et al. 1998). This situation in the United Kingdom is somewhat unusual compared with mainland Europe and the United States, where dilution rates in rivers are generally far higher. Indeed, this very likely explains why levels of VTG induction in wild male fish in the allied carp family in mainland European and US rivers are generally lower than those levels in wild roach in English rivers."
From my understanding of just some of the problems our rivers face, apart from cases of severe pollution which is caused by sheer negligence, you should be looking closely at agricultural practices adjacent to the rivers you suspect are in decline generally whilst looking at the water quality especially the levels of certain chemicals entering our rivers from water treatment outfalls.
Lastly, there is the case for looking at predation along some rivers. We already know for instance that the Upper Great Ouse and The Wensum have suffered the loss of huge barbel via otter predation. How many other Southern rivers are similarly affected?
This whole subject is huge and if way too big for the BS to take on because they don't have the number of members, the expertise or the money. Neither has the Angling Trust or the EA Fisheries who are strapped hard for cash already. We already have the organisations in place to take this job on and its the Rivers Trusts many of which are already on the case for rivers and their wild fish populations.
Regards,
Lee.
