Felt soles and Dirty Feet exonerated of Didymo bloom, say it ain’t so …

feltsoleThere’s new evidence published today that’ll have the fishing community in a tizzy, given their common belief that unclean anglers and felt soles are the root cause of the intercontinental spread of Didymo.

The article, “The Didymo story: the role of low dissolved phosphorus in the formation of Didymosphenia geminata blooms,” cites research done in both Canada and New Zealand (by their respective governments) that suggests anglers have little to do with Didymo blooms.


Specifically, it mentions the linkage between our feet and the spread of Didymo bloom has proven less of an issue since the original indictment, “On the Boots of Fisherman” was published in 2009.

“The analysis of these data entitled, ‘On the Boots of Fishermen: a History of Didymo Blooms on Vancouver Island, BC’ was published in Fisheries (Bothwell et al. 2009), with the statement:

….all of the evidence suggesting that recreational fishermen
have played a role in the movement of Didymo regionally
and globally is circumstantial.

Nevertheless, the publication was widely accepted as an
important step in initiating management actions aimed at
controlling the spread of aquatic invasive species. Yet,
the explanation for the spatial and temporal occurrence of
blooms of D. geminata as the result of human vectors was
based on coincidental timing.” (my italics –KB)

Unfortunately us fishermen don’t get a free pass to trod crap through the watershed, as the article plainly suggests that we might have introduced the lifeform to the continent, but introduction of the diatom doesn’t provide the environment for it to bloom.

“However, while the presence of cells is obviously prerequisite, introduction alone is not the cause of bloom formation.”

Instead, the research suggests four factors are attributable to the natural occurrence and reoccurrence of Didymo, and are man-influenced issues consistent with exploitation of the planet and unrelated to shoe hygiene per se ..

“… we propose four mechanisms operating at
global or regional scales that could potentially result in a
decline of Phosphorus, i.e., oligotrophication, entering fluvial systems.
We outline the following as hypotheses of the potential
ultimate causes of D. geminata blooms: (1) atmospheric
deposition of reactive nitrogen resulting from the burning
of fossil fuels and urbanization; (2) climate-induced
shifts in the timing of snowmelt and growing season that
decreases P(hosphorus) inputs to rivers; (3) N(itrogen)-enrichment of landscapes
during agricultural and silvicultural activities that result in
greater retention of terrestrial P(hosphorus); and (4) a decline in marine derived nutrients, particularly P(hosphorus), resulting from widespread depletion in spawning salmon. Although these processes do not apply to all regions, they are not mutually exclusive and could act synergistically. These processes are in need of further investigation for their role in driving blooms of D. geminata.

Rather than demand the revocation of your state’s felt sole ban, and the subsequent restoration of your favorite footwear, note the final sentence of the above quote, “further investigation is needed.”

I caught hell the last time I mentioned the issue, and am likely going to do so again, but it just proves my initial beef that crowd-sourced science via fly rod, pitchfork, and public outcry, is typically a bit less exacting than that practiced by the fellows in white lab coats.

3 thoughts on “Felt soles and Dirty Feet exonerated of Didymo bloom, say it ain’t so …”

  1. Interesting to note that the same authors are involved in both publications so in some ways good they corrected themselves even if they were a bit weasel-worded about it.

    Having now read the “On The Boots of Fishermen” paper it is clear that it was that old coupling again – correlation leading to the impression of causation.

    Nice post as ever.

  2. I have gotten to know Dr. Bothwell and attended the International Didymo Conference last spring in Providence where he presented these recently published findings. I also attended another presentation he made recently at the University of Idaho. While felt soled boots have been “exonerated” for spreading Didymo, ALL of the authors of this new paper agree that these findings should in no way lead anglers away from the practices of clean angling. The list of AIS threats is significant and growing. Glad we’re not spreading Didymo, but this new research should not lead us to abandon the effort to reduce the spread and introduction of other aquatic invasive species.

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