Friday, April 26, 2013

Suckers Spawning on Virginia Tech Campus in Stormwater Inlet, by Don Orth



On Wednesday, April 24th, I hiked over to the VT Veterinary Medicine stormwater pond to check for spawning activity.   In April 2010 I got an email from Mike Rosenzweig, Director of Blacksburg Nature Center and Biology Instructor, who asked me about the identity of large fish in the pond inlet.    When I went to investigate I discovered these were white suckers and they were spawning in the inlet.    I have been watching the inlet since late March but have seen no evidence, presumably because of our cool spring this year.  Last Wednesday I observed at least 2 dozen large adult males congregating near the pond inlet.   Two had already swam up the bedrock shelf that separates the pond and the culvert under the walking path.   So sucker spawning season has begun and one can easily observe this phenomenon on campus.   
Male white sucker with breeding coloration pattern.  Photo by Ryan McManamay.



In 2010, Ryan McManamay, Tyler Young, and I took advantage of the opportunity to ask several questions:  Was this suboptimal spawning microhabitat or is it similar to habitats where white sucker normally spawn?  Did the spawning result in successful fertilization and development of embryos?   Are the reproductive needs of this population being met in small remnants of a natural channel in an otherwise human created system?     Over a two-week period we counted spawning suckers, collected and measured males and females, described spawning habitats, and collected drifting larval white suckers.  These observations are summarized in “Spawning of White Sucker (Catostomus commersoni) in a Stormwater Pond Inlet,” published in the American Midland Naturalist.  
  
We learned that the water source for this stormwater pond originates in a heavily modified subwatershed that is 41% impervious surfaces; the remainder is the VT baseball and softball fields, sports practice fields, track and football stadium, all of which are designed to rapidly shed rainwater.    The upper areas of the watershed include Stadium Woods and many grated inlets that intercept runoff and route the flow to a cluster of culverts that merge in to a concrete-lined tunnel feeding the inlet.  The day-lighted portion of the inlet is only 45 meters before entering the pond.   Stadium Woods, a controversial site for expansion of athletics practice fields, is a forest on the border of campus, and features 46 white oaks that are over 250 years old.   From a hydrological standpoint, this forest is the source of the cool, perennial flow that enters the pond inlet, yet the original spring and stream channel is buried, replaced by culverts.  All that remains of the natural channel is the 45 meters stretch.

Stormwater pond inlet stream used by spawning white suckers.  Photo by Ryan McManamay.


White suckers are known for their migratory runs in spring.  They spawn in swift flowing, shallow waters over gravel or cobbles, where they deposit adhesive eggs.   On a single day we estimated there were between 200 and 300 white suckers spawning in this small inlet.  We believe this to be the peak day of spawning as numbers dwindled appreciably thereafter.   These fish were demonstrating all the classic sucker spawning behaviors in the inlet stream as well as in the concrete tunnel, which has a thick deposit of fine gravel.    The stream temperature at this time (12.4 C) was 7.6 C cooler than the pond’s littoral zone.    Further, we documented fertilized eggs in the drift 8 days later and larval stages 12 days later.   Although I have unwittingly driven by this small pond inlet numerous times, I have never sampled it for fish.  But at least once per year it becomes an essential habitat for completing the life cycle.    It is shallower than other streams where white suckers spawn, but the velocities and bottom sediments were within the preferred range established by other investigators. 

Underwater photo of white suckers in inlet stream. Photo by Ryan McManamay.


The good news is that this highly modified watershed and pond system has a remnant 45-meter natural channel that sustains the reproductive needs of the pond population.  For local fish enthusiasts, now is the time to sit near the bank and observe the spawning behavior.   It will be over soon.     Observe and report.   I think you will agree that "Fish are awesome!"

2 comments:

  1. Very cool looking fish! Thanks for posting pics :]
    -Jack @ inlet protection

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