Wednesday, January 19, 2011

The Science Behind the Felt Sole Ban

There has been a lot of attention lately about the ban of felt soles.  Currently, New Zealand, Vermont and Alaska have banned felt soles and the legislatures in Oregon and Montana are considering a ban.  The main themes of opposition are that (1) there is no scientific proof that felt is worse than anything else and (2) it is just a ploy by gear manufacturers to get everyone to buy new boots.  Since I am a scientist and not a gear manufacture I'll examine the first point. 

Do anglers traffic invasive species from one watershed to another?  First off, how are invasive species being spread?  Multiple studies have correlated the spread of invasive species with angler movements.  Correlations are a risky business though.    Here is an example of a incorrect correlation: Every time I go fly fishing, I get a headache the next day.  Fly fishing gives me head aches.  What actually happens is I always get trashed at the bar with Steve after fly fishing because we suck and don't catch fish.  So the booze gives me a head ache, (or maybe sucking at fly fishing) but fly fishing in general does not cause a head ache.  So are anglers the booze or fly fishing?  Anglers may have entered the area infected with invasive species after a recent increase in fish stocking.  Did the anglers or the hatchery fish introduce the disease?  There is no study that directly shows that an angler introduced an invasive species.  Is it likely?  Yes.  A study by Kiza Kristine Gates, a masters student at Montana State University, showed that large amounts of sediment can be transported on waders and boots from one watershed to another.  Specifically, she measured an average of 16 grams of sediment that can be washed from boots and waders.  16 grams seems like a lot. Wet boots can have a lot of sediment on them by the time one gets them back to the car but how much of that is from the stream and carries invasive species?  I bet most of it is dry (and likely uncontaminated) soil from the bank or trail.  Extrapolating any spore or snail or whatever count from the 16 grams is a little dubious in my opinion.  In any case, do anglers transport soil with or without invasive species present from one watershed to another?  From Gates's work, I say yes it is likely but how much is up in the air. 

So we know transfer is likely but what about felt?  Is it worse or better than other materials?  For the transport of sediment there is no data.  My guess is felt transports a little more than rubber-soled boots because rubber washes off cleaner.  Still, no testing has been done on the different materials. 

Another factor is whether invasive species can be killed on the boots before transfer to another watershed.  Drying will kill most invasive species and rubber dries pretty quickly.  Felt can stay wet for weeks.  Sterilization is also not as effective on felt.  Felt mops up and holds on to everything in the soil due to the inherent structure of the material.  Spores or single celled didymo can sponge into the sole of a felt boot and sluff off once knocked around rocks or whatever in the next stream or drainage.  A study by Kilroy et al. in 2006 documented the survivability of didymo and scientifically examined felt compared to rubber.  After sterilization there were nearly 3,000 times more (11,000 to 3.9)  live didymo cells on felt-soled boots than on rubber-soled boots. 

The clear advantage of rubber boots is that they likely transport less sediment, and invasive species survival is greatly decreased either due to drying, easy cleaning or sterilization.

The unaddressed issue that seems to make a felt sole ban seem ineffective is that the same study by Kilroy et al.  showed that leather boot tops and neoprene actually had higher cell densities before washing than felt soles (table 3 below).  There were not as many live cells after washing but there were still live cells present.  Anglers can't become complacent about invasive species even if they switch to rubber soles.  If gear is not sterilized properly the difference between wearing felt or rubber soles becomes irrelevant.  It only takes one cell to transmit an invasive species like didymo. 

As others have stated the only way to stop invasive species is to ban fisherman and boaters.  Clearly, that is not an option.  Unfortunately, there will likely always be careless or uninformed individuals that will transmit invasive species.  I don't know what the answer is, but I think it is clear that we need a combination of increased angler awareness and more research to eradicate invasive species after they are established.   Banning felt soles may slow down the spread of invasive species but it is far form an effective solution.  For now, be informed about the streams you frequent and soak your wader bottoms or any part of your waders that touched the water and your boots (compeletely submerged, water gets inside too) in a dilute bleach solution (1% or a little more than a 1/3 of a pint glass in a 5 gallon bucket of water) for 5 minutes or if you don't want to bleach your $450 pair of patagucci waders use 1% dish detergent for a couple hours (or 2% for 10 minutes, see chart below).

These are the recommended cleaning procedures form a regional New Zealand counsel:
At least one minute of scrubbing in:
  • hot (60 degrees C) water, or
  • 2% solution of household bleach, or
  • 5% solution of salt or nappy cleaner, or
  • 5% solution of dishwashing detergent, or
  • 5% solution of antiseptic hand cleaner.
Not sure what nappy cleaner is but contact time is important.  You can go more dilute for longer if you are concerned about your gear.  

Leather boot tops and Neoprene wader bottoms actually collect more cells than felt.  Live cells still remain after extensive washing.  (Kilroy et al. 2005) 

Live cells are still found on leather and neoprene after 36 hours (Kilroy et al. 2005) 
Soaking waders and boots in a moderate amount of dish soap for an hour is all it takes to kill Didymo (Kilroy et al. 2005)