Monday September 26, 2011
In a recent post (Summer Surveys) we wrote about conducting snorkel surveys to assess abundance and distribution of salmonid populations in rivers, but snorkel surveys are also useful for determining how different habitat types are used by fish seasonally and at each life-stage. While snorkeling in the lower Tuolumne River last week, this school of rainbow (steelhead) trout (Oncorhynchus mykiss) fry were spotted feeding in 2 feet of water. Preliminary results from focused habitat utilization surveys indicate that young-of-the-year O. mykiss (i.e. fish hatched this year that are smaller than 100 mm) are often found near the river bank, in flooded vegetation. But, as these fish grow, they quickly transition to utilizing higher velocity, mid-channel habitat. By establishing the habitat preference of protected species, biologists and water managers can work together to maximize the preferred habitat with the available water resources.