Here a question that's always puzzled me, whats the survival rate of trout either brown or rainbow, over the winter period.I suppose this applies to stocked reservoirs. I've heard of figures as low as few percent.
Assuming that the reservoir/loch is healthy and containing enough feeding, what do you think the mortality rate would be
I think survival is pretty high. As all stocked trout have to be triploid now they will feed all year round.
I would say 'normal' :)
Sick/unhealthy fish will die. If there are too many fish for the feeding then the ones with the less fat will die. The fattest healthiest fish will survive as their metabolism will slow as the temperature of the water lowers and they will have more reserves to fall back on.
So anything from 90% to 99% survival rate...maybe :)
Most mortality may well be from cormorants and goosanders !
Hmm, i know of a fishery that stocks with over 10,000 fish EVERY year because they say that most of them die over the winter, and and their kill rate is not that high that accounts for the loss of fish.
10,000 fish every year might be a drop in the ocean if we are talking about a Rutland sized water. Some more context is required - what fishery is this? Stocked rainbow trout have a lifespan of approx. 5 years. Their sheer mass at stocking will factor in how well they survive a winter as they'll require more energy in the colder months than our typical small loch trout. And not to mention all the other factors mentioned above such as threats from predators and even a prolonged winter.
On our local river the behaviour of stocked trout (triploids) is very different from the wild fish in winter. The stockies feed in winter and can even be see taking midge on the surface in January. It is especially noticeable at the start of the season when the water is very cold. The wild fish seldom show before April while the overwintered stock fish (and smolts) take freely on the opening day. Many of these fish show damage from cormorant and sawbill attacks. As Bobfly said above these predators are most likely the greatest threat.
They do have a bit of a cormorant problem to be fair, I think it was 13,000 last year stocked - Cobbinshaw