Tuesday, June 26, 2007

Big Hole River grayling: cooked for another year

Today's grayling survival index is -102.5, based on a flow at Wisdom (see http://waterdata.usgs.gov/mt/nwis/uv?06024450) of 19 cfs (cubic feet per second). This is not even what biologists consider a "survival flow" that allows fish to escape being stranded in pools. Any gain from spawning and recruitment will likely be lost to a dewatered river. [see below for explanation of the grayling survival index calculation]

Flows have went low very early this year with what appears to be little or no general effort to conserve water. Expect grayling populations to nose down even lower. The Big Hole Watershed Committee has implemented its so-called "Drought Management Plan," but does not seem to be able to demonstrate any water savings and increased flows.

Hard questions that the Big Hole Watershed Committee and other responsible parties need to ask:

1. How efficient is water use in the upper Big Hole Basin? E.g. is it really necessary to saturate meadows day-after-day?

2. Has the overuse of water harmed agricultural productivity? E.g. has overuse shifted grass hay production to less nutritious sedges? And has overuse lowered soil productivity through leaching or binding of nutrients?

3. How large a role has the shift in agricultural methods from hay production to season-long pasture grazing played in the chronic and increasingly severe dewatering of the upper river?

4. Does the myth of return flows play a role in the overuse of water?

5. Should a private group be dictating water management and recreational (i.e. fishing) policy?

6. Are water rights an absolute private property right?

Don't expect answers to these questions. The Big Hole Watershed Committee appears to have a very narrow comfort zone. No matter how scientific or data-based a question might be, it is a "non-question" whenever it challenges myth or well-established practice. E.g. it is a myth that the more water you use, the more hay is produced. Never mind good agronomical evidence that too much water actually decreases grass production (and harms soil, and shift grasses over to sedges).


EXPLANATION OF THE GRAYLING SURVIVAL INDEX:Less than 0 means a loss of grayling; 0 means minimum sustainable level; 100 means maximum survival.For this blog, the flow of the Big Hole River at Wisdom, Montana, provides an index of how well the Big Hole Watershed Committee is doing in its efforts toward water conservation and grayling restoration. Today, the Watershed Committee is doing a lousy job.According to fisheries biologists, the upper wetted perimeter at Wisdom is 160 cfs (cubic feet per second). The lower wetted perimeter is 60 cfs. The minimum "survival flow" is 20 cfs. This "survival flow" is not scientifically based, but it is the flow level that fisheries biologists "feel" allows grayling the ability to escape warm water and to seek cold water refugia (tributary streams).Criteria for grayling survival index ratings:*At 160 cfs, grayling recruitment and survival is rated at 100. At this level, the streambed is fully wetted or bank-full. This level allows grayling the maximum use of stream "pasture" for foraging, hiding, spawning, etc. This level maximizes grayling recovery.*At 60 cfs, grayling recruitment and survival is rated at 0. At this level, the streambed is minimally wetted. This level allows grayling to maintain their population. This level does not aid in the recovery or increase of the grayling population. At best, this level might maintain the current population level. Below this level, the streambed rapidly becomes dry and thus barren of aquatic life.*At 20 cfs, grayling recruitment and survival will be rated at -100. At this level, some grayling will be able to move to cold water refugia (tributaries), but many will perish due to lack of cover, exposure to predators (such as pelicans), and high water temperatures. For stream flows above 60 cfs, the grayling survival index = y = mx + b = x - 60. For stream flows below 60 cfs, the grayling survival index = y = mx + b = 2.5x - 150. Thus, today's grayling survival index = 2.5(19) - 150) = -102.5.

1 comment:

Anonymous said...

At last, I found your article once again. You have few [url=http://tipswift.com]useful tips[/url] for my school project. Now, I won't forget to bookmark it. :)