Read on Twitter
But the devil is in the detail @AliDriverUK. If one reads the next line 'However, the degree of repeated movements and the overall proportion of fish moving varied between beaver-dammed and control sites’
A thread https://twitter.com/AliDriverUK/status/1327251305421819908?s=20
A thread https://twitter.com/AliDriverUK/status/1327251305421819908?s=20
Therein lies a concern based upon what we know from a greater range of studies on the impacts of low-head weirs & dams https://link.springer.com/content/pdf/10.1007/s11160-007-9076-4.pdf
Yes, I know there are differences between man-made and beaver-made structures but we can still draw appropriate inferences for fish passage re delays, increased energy expenditure, increased predation risk etc https://link.springer.com/article/10.1007/s10750-017-3364-3
So if we focus on ‘structures’ being passable to some degree, theoretical projections of passability across multiple structures are revealing: https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/406520/Cumulative_effects_of_hydropower_schemes_on_fish_migration_report.pdf
The Malison 2020 study of juveniles does not clearly state that there were fewer fish upstream of beaver ponds but one can infer that from the inability to analyse some parameters. eg insufficient 0+ salmon.
Does this hold for adults?
Does this hold for adults?
‘..trout have been recorded passing two beaver dams during higher flows’ (ROBT) – yes, some fish did BUT more did not (55% limited observations), despite repeated attempts https://www.exeter.ac.uk/media/universityofexeter/research/microsites/creww/riverottertrial/ROBT__Science_and_Evidence_Report_2020_(ALL).pdf
Personal and general observation from reviewing the scientific & grey literature – fish passage studies at man-made weirs / culverts / fishways assert <100% passability = bad, whereas only some fish making it past beaver dams = fine, no problem...
Yet we know that introducing selective pressures (only some fish making it past structures) can lead to, for example, genetic isolation and loss of genetic diversity: https://onlinelibrary.wiley.com/doi/full/10.1002/ece3.5191
This is particularly pertinent for UK rivers where eg salmon / sea trout populations are already imperilled. Hence, the concerns raised by fisheries scientists and organisations re another potential stressor
So, there is a difference between a thriving and a surviving population, and just because we observe salmonids in beaver streams, we should not assume that they are ‘thriving’ unless we have evidence to support that claim
Unfortunately, no population level impact was assessed in this 2020 Malison beaver study, nor emigration, adult movement etc, but as @stuartpengs pointed out, the authors hedge their bets: https://twitter.com/stuartpengs/status/1327264062842040320?s=20
Looking at responses to @alidriveruk's tweet, it is not ‘just sour old duffers that stick with that one’ @gow_derek – there are other equally valid and robust papers demonstrating negative impacts of beavers on salmonids eg https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0123107
Indeed, Malison elsewhere has demonstrated that the introduction of beavers could have negative consequences for salmon production: https://pubmed.ncbi.nlm.nih.gov/27635357/
‘Sour old duffer’ divisive statements aren’t healthy or helpful in any area of #conservation. I am concerned for the plight of fishes just as some are about their particular furry ‘critter of choice’, and I have taken the time to critically review the science evidence-base
Don’t get me wrong. As an ecologist & river restoration practitioner, I would love beaver to be integrated back in our river systems but I don’t subscribe to ‘the answer is beaver, now what was the question?’ seemingly prevalent today
As @blackyhimself neatly summed up, and I paraphrase: beavers are a force amplifier – where it’s good, they’ll do good, but where it’s bad they might just exacerbate some intolerable problems
https://www.wildtrout.org/assets/reports/Mike-Blackmore-62-67-TP-RH.pdf
https://www.wildtrout.org/assets/reports/Mike-Blackmore-62-67-TP-RH.pdf
If we can make rivers functional again, as eg @wildtrouttrust @theriverstrust etc have always pushed for - ample, diverse & connected riparian zones - also now promoted by @beavertrust, then they’ll be fit for beavers AND salmonids
OK, yes, beaver & salmonids co-existed here ~600y ago but there are no data on relative abundance from then.
Let’s give them the chance to co-exist again in this very different, highly pressured landscape. But let’s not overlook or ignore valid concerns of fishy folk on the way
Let’s give them the chance to co-exist again in this very different, highly pressured landscape. But let’s not overlook or ignore valid concerns of fishy folk on the way
All too often, to quote @GlassJet - ‘life is cheap when you’re a fish' https://www.glassjet.co.uk/2020/05/life-is-cheap-when-youre-fish.html
I promise this is the end....
I promise this is the end....
