I have few field horror stories this week-probably because I was only out for one day. After sampling, we like to give fish a few days to calm down before tracking so that we aren’t documenting any movements that are from handling stress. My office to-do list has also been growing since May with deadlines now becoming more eminent and I think some no longer believe my “I’m in the field” excuse for not answering emails. So, I spent the majority of the week clearing my desk and staring at the data we’ve gotten so far.
We did go out once this week to track all fish locations. And, it was arguably the most interesting week for movement. As we started tracking one stream, we quickly noticed that a pool that normally contains five fish was down to one. It was irritating at first because we assumed they were lost to predation or post-handling stress mortality. But, as we walked upstream we started hearing the receiver “chirping” at odd locations indicating the location of a fish. They’re finally moving!
In total, several fish from one stream moved over half a mile with one fish approaching the one mile mark. A mile! That fish just moved >8000x it’s body length in a week.
What trigged the movements? It’s hard to tell because right now I don’t have a lot of movement data. But, a leading suspect is an increase in stream flow. A few days before we tracked there were several storms that dropped about four inches of rain. By the time we got out, stream flows had already gone back down to their near-drought conditions, but I think for a few days in there they increased just enough to trigger take off.
I’m always curious why fish decide to start moving after, in this case, two months of hunkering down. But, I’m probably more interested in why they decide to stop moving. Sometimes they stop in really bad habitat, and so maybe they just get tired or there is a resource (like food) there that I don’t immediately see. But, in this case, a more interesting first impression is that some fish seemingly made the decision to pass through some really great pools, swim up small falls, traverse through very shallow runs and find the exact same pool some other migrants chose to stop in. Did they know that habitat was there? Were they following each other? And, why is that pool better than all the others?
If fish could talk my job would be so much easier.