New GWCT study investigates the link between human-induced Environmental Change and Salmonid populations.
Human induced environmental change has thrust a significant amount of survival stresses onto many wild fish populations with many commercial fish now on the precipice of habitat collapse. Despite this, there have not been many formal studies into the matter. Now, at the conclusion of their fifteen-year study, the Game & Wildlife Conservation Trust(GWCT)* has assessed the impacts of human-induced environmental changes and found it to be the basis of several significant stressors on freshwater Salmonid populations.
In the study, the GWCT focused their research on Thymallus Thymallus, more commonly known as Graylings, who are in the Salmonid family of fish. It used a variety of models and datasets to map the innate stressors that Graylings experience independent of human-induced environmental changes. The study took place over a fifteen-year period, from 2003-2004 to 2018-2019, and witnessed a marked decline in the overall population of Grayling Salmonids.
The study demonstrates that the stressors placed upon Salmonids often synergize together in order to precipitate serious population decline. This is because one stressor may affect a Salmonid in a particular life stage, but have little to no effect in another. That is, the variety of habitats in rivers needed by Salmonids in their various life stages means that it is very rare for there to be one particular human-led environmental stressor that has a blanket effect on the species throughout its life cycles.
For example, a Salmonid in one of its growth phases may experience the overall population decline as an opportunity to speed up its growth cycle as a result of lessened same-species competition. Conversely, some stressors’ impacts upon their respective population do not open up any gap for that kind of same-species competition and thus have a more consequent impact on overall Salmonid populations.
The human-induced environmental change stressors took a series of forms; Macrophyte cover tended to have the most marked impact upon juveniles and subadults, hot and low-flow summers impacted adults and low flow winters impacted hatch rates. The former, in its impact upon juveniles and sub-adults, has a less significant impact on overall population numbers than the latter two which, when synergizing together, can seriously impact the river’s Salmonid population.
That is to say, environmental change’s impacts upon adult survival and hatch rates means a heavy decrease in Salmonid populations. Moreover, these conditions had proven to be more and more regularly occurring in the river the study took place in. Given the river studied is in the southern band of Graylings habitable range, it suggests a considerable risk for significant habitat loss in the coming years.
If you would like to read the study in full, follow this link to the study.
*This study was conducted by, the Salmon and Trout Research Centre at the Game & Wildlife Conservation Trust, along with the Department of Life and Environmental Sciences in the Faculty of Science and Technology from Bournemouth University, the Natural Resources Wales/Cyfoeth Naturiol Cymru, the Piscatorial Society, and Wessex Water
As an Alliance of five organisations, we will build on the existing work of our partners and maximise our impact by taking a coordinated approach and vital action in order to halt and reverse the decline of wild Atlantic salmon.
The goal of the Missing Salmon Alliance is to build an evidence-base to influence national and international decision-makers to regulate activities that adversely impact wild Atlantic salmon.
The Missing Salmon Alliance
The MSA is comprised of the following members:
Game & Wildlife Conservation Trust, Atlantic Salmon Trust, the Angling Trust with Fish Legal, The Rivers Trust and Fisheries Management Scotland.
https://www.missingsalmonalliance.org