Non-lethal Measurement of Fish Fat Content
Traditional measures of condition or health of a fish tend to be either related to length-weight data (e.g. Fulton’s condition factor) or lethal to sampled fishes (e.g. percent body fat). A new tool from the Scottish company Distell called the Fish Fatmeter has shown promise for measurement of fish percent body fat without the need to kill the fish. However, the fatmeter needs to be calibrated for each different species biologists want to use it for – I have partnered up with Drs. Robert Al-Chokhachy (USGS) & Christine Verhille (Montana State University) to create calibrations for a suite of coldwater species.
How Often Do We Need to Sample?
How Often Can We Sample?
There are always more streams than we can sample in a single year. I am working on a 20-year trout sampling dataset, collected by Chris Clancy, Leslie Nyce, Larry Javorski, and others, from Skalkaho Creek, Bitterroot Drainage, Montana. We are trying to determine what the maximum interval of sampling is (i.e. every other year, every 3rd year, etc.) that still adequately represents trout population trends.
On the other hand, sometimes we want to sample fish multiple times in a year to see how growth, condition, or diet changes over time. Very few studies have addressed how often fish can be captured and handled before there are negative effects on their growth. I am using data from my master’s work on Bear Creek to see if increased handling of trout led to decreased summer growth.