Excerpts from IDFG Fisheries Biologist, Jennifer Vincent’s Quarterly Report –
The lower than expected trout in the gill nets this year suggests trout may have experienced a higher than normal mortality rate over the last few years. Potential factor(s) limiting trout production in the lake may be temperature and oxygen. However, limited information exists on water quality in the lake.
As many of you may know the IDFG has partnered with the Henrys Fork Foundation, the Henrys Lake Foundation and the Idaho Department of Environmental Quality to implement a new sampling program to monitor water quality in Henrys Lake. Our first sampling date was August 7th and we have been out each week since.
What data are we collecting? We take water samples, zooplankton samples and collect water quality measurements at six different sampling locations. During the winter our water quality sampling equipment will remain deployed under the ice at one of our sampling locations allowing us to collect continuous water quality information throughout the winter. Water samples will be analyzed for total Nitrogen and total Phosphorus concentrations. We also collect data on dissolved oxygen (DO), temperature, conductivity (a measure of how much “stuff” is in the water column), and algal production (tied to the cyanobacteria blooms we’ve observed in recent years) as well as measuring water clarity. We collect zooplankton on a bi-weekly basis.
Our goal here is to gather information on the availability of zooplankton, which is used as a food source for Trout. This is important as we edge closer to the end of September, when we stock all our fish. Along with our partners, we will be evaluating our water quality monitoring program this winter to ensure we are collecting the appropriate data to monitor water quality and its impact on trout. More information regarding this project along with other current activities of the IDFG regarding Henrys Lake can be found at this PDF.