Recorded data will be used to help understand the effect of stream temperatures on the spawning success and survival of salmon juveniles.
The River Wye has a historic reputation as England and
Wales leading salmon river, with a particular emphasis on
the size and fecundity of its spring salmon run. The Wye
Salmon Association is dedicated to improving the salmon
population by bringing together all individuals, associations and
representative bodies sharing their skills and knowledge in a
In the Wye catchment, average densities for both fry
(hatchling) and parr (young salmon) have fallen in recent
years. Parasites, disease and health causes have been
ruled out, although other reasons, including a shortfall in numbers
of spawning fish and damage arising from very high flows, have not
Scientific studies indicate salmonid breeding success
and juvenile survival are sensitive to high ambient
temperatures, with 66% mortality at 12°C compared to 14%
at 8°C. It has also been observed that salmon embryos incubated at
higher temperatures have a lower body weight. Increasing
water temperatures also adversely affect other environmental
conditions having potential to cause harm: toxicity of
many pollutants is greater at higher temperatures; solubility of
oxygen in water falls as temperatures rise and the ability of most
species to withstand depleted levels of oxygen is reduced at
elevated temperatures. The susceptibility of salmonids to pathogens
and parasites may also be influenced by temperature.
In September 2017, the Association began a Project to
continuously monitor selected streams over a period of four years
to gain a better understanding of the effect of in-stream
temperatures on spawning success and survival. Tinytag Aquatic 2 data
loggers are deployed on the river bed and in
the air at 25 sites identified by Natural Resource Wales (NRW) as
significant for salmon spawning.
The data loggers will record a water temperature reading
once an hour during the sampling period. The Association
will correlate this with air temperatures, fry and parr numbers and
other environmental and biological data and place the results
online in an open access database. The aim is that these results
will assist NRW and the Environment Agency in developing a
comprehensive management plan for salmon.
2 loggers are specifically designed to be anchored securely
underwater over long periods. They are compact, accurate and
reliable, and have been widely used for varied research into the
effects of temperature on aquatic species.
The image shows one of the Association's mounting devices
used to fix the data loggers in rivers.