The Lincolnshire Bird Club

I visited the reservoir in calm sunny conditions this morning; a rare visit for me. Very rough estimates of most species, none of which seem particularly high:
Coot 90
Gadwall 75
Wigeon 70
Mallard 30
Tufted Duck 100
Goldeneye 45

Also
Shelduck 17
Pochard 1 male
Shoveler 2 males
Oystercatcher 3
Redshank 2
Avocet 1 flying about, being pursued by common gulls and settled on the water

Perhaps most notable was the complete absence of fish-eating birds - no cormorants, grebes or sawbills. Is that normal in mid morning at this time of year?

There was a Forum exchange 4 years ago about GCGrebes being found dead at Covenham, see viewtopic.php?f=22&t=17729. Does anyone know if any results from analysis of the corpses is readily available, or where one might go to get it? And while I'm asking, does anyone know anything of the history and composition of fish populations in the reservoir. ... and what species are the mussels scattered around the banks?

According to the LBR, the GCGrebe peak for March, 2013, was only one. In March, 2012, it was nil.

Looking on the bright side aren't they just dispersing to prospective breeding habitats?

Re the mortalites of yesteryear, were these local to Covenham or were there records of similar instances from further afield?

Also, were any other species similarly affected?

Good point, Jim. I have checked more data and indeed grebe etc numbers do fall off by mid March - though not usually to zero (but I am probably just unobservant).

On the mussels, I've now looked at the specimen I brought home, and as I thought it appears to be the introduced zebra mussel Dreissena polymorpha. There is scientific literature about these in Covenham Res. For more on this species see http://www.nonnativespecies.org/factshe ... iesId=1250.

I have still to locate any detailed information on fish at Covenham, though the reservoir is know to hold (at least sometimes) large numbers of small fish/fry. I have come across literature suggesting the reservoir is ecologically unstable. It does, like many such artificial ponds, get blue green algal blooms.

Interesting that angling is not listed as a permissible leisure activity at Covenham - by contrast with some of Anglian Water's other reservoirs such as Rutland Water (where the trout fishing is said to be world-class).

Could this be because fish populations at C'ham fluctuate according to the levels of chemical treatment?

Is it chemical treatment that is partly attributable to the reservoir being described as "ecologically unstable"?

Water companies tend to be a bit cagey about their dosing activities - though Severn Trent have this week had to come clean (partially) about the chlorine added to water at Castle Donington (which, I understand, is also a non-angling reservoir).

According to past LBRs, Covenham does attract significant counts of GC Grebes in some months, so, as you point out, Andrew, there must be substantial quantities of small fish during parts of the year.

It's unfortunate that the trail seems to have gone cold on the grebe mortalities of 2012
Did DEFRA carry out the post mortems? If so, were their findings released?

Or (forgive the conspiracy theory!) was there a hush-up to spare Anglian Water any embarrassment and the possibility of action?

In the past, water companies (including Anglian at Covenham ) used ferric sulphate dosing to help combat algal bloom and encourage sediment settlement. But this chemical has been implicated in causing damage to the gills of fish and the capacity of the females to release eggs, so perhaps it is no longer deemed acceptable.

Returning to the dead grebes, if absence of fish was to blame, why did they not simply fly to fish-rich waters elsewhere well before starvation set in?

Or was their wellbeing fatally compromised by chemical treatment or some other factor such as disaese?

Possibly someone from outside LBC might be able to shed light on what happened. Were grebes also succumbing , in 2012, in other parts of the U.K?

It's shame that there is a continuing restriction on non-members posting because it would be interesting to hear from any experts on grebe mortality.

Some interesting questions in need of answers.
Would a Freedom of Information request from AW, EA etc. be feasible, especially on the question of chemical additives to the Reservior. Results may give a direction for your other questions.

I have been intermittently exploring Covenham Res data and have now bumped into other mentions of grebe mortality. One event goes back to the early days of the reservoir, when in 1974 there were up to 56 great crested grebes in October "most of which had died by the end of the month".

When I have some time spare, I will contact AW and see if they have any record of these events and their explanations. I won't use FoI though, as there is nothing to suggest that a simple direct approach won't result in a helpful response! There is published scientific material dealing with reservoir management that includes information on Covenham Reservoir, e.g. Brierley & Harper, 1999, Ecological principles for management techniques in deeper reservoirs, Hydrobiologia 395/396: 335–353. These record chemical treatments. I haven't yet come across anything that touches on bird mortality but clearly control of phosphates and consequent algal blooms is a real problem in lowland reservoirs (and perhaps especially in one like Covenham that is no more than a giant concrete basin).