We have been tracking tagged brook trout for about three weeks and officially surpassed the 500 detections milestone. This means that we’ve already documented every fish’s location about five times. We’ve seen some movement, but you’ll have to check back to learn more about that.
This week was a great reminder that the best qualifications for field work are patience and adaptability. We had a hard time finding some fish, lost a few to some sort of predation, and potentially even a few gone to angler harvest. Stream flows also decreased quite a bit allowing us to access deeper pools and see the stream bottom more clearly. Unfortunately, this also allowed us to find more tags that were dropped.
Dropped tags are problematic for several reasons. The most obvious is that a dropped tag is no longer collecting data and becomes a $300 research souvenir. But, dropped tags can also make for messy data analysis. At the end of the study there will be tags that don’t move very far and I’ll have to decide whether it’s a fish that didn’t move or a tag that was dropped and sitting on the stream bottom. So, as disappointing as it is to find dropped tags, it would be worse to have not found the tags and incorrectly assumed it was still a fish.
The other positive is that we recovered these tags fairly early in the field season, and so there is still plenty of time to collect data. So, we shuffled the schedule, worked long past quitting time, and got the tags swimming again in fish.
This also gives me a chance to discuss the tagging process. As I’ve mentioned, it is a surgery and we borrow many of the techniques from medical school training websites and videos. But, it all starts with a procedure dear to all fish biologists….electrofishing. Putting electricity into water isn’t typically recommended, but decades ago fish biologists found out that, with proper training and protective gear, it is an effective way to temporarily stun fish allowing them to be sampled non-lethally and returned to the stream without harm.
While one crew is electrofishing, another crew readies the processing station. When a fish is caught, it is taken directly to processing where it first gets anesthetized and then weighed and measured.
From there, we take tissue samples for genetic analysis. Different tissues give different pieces of information (I’ll explain that in a later post) and we take a clip from the tail fin, four filaments from the gills, and a blood sample.
At this point, the tagging process begins. The fish is turned upside down in a surgical board, a tube with flowing water is inserted in the mouth to allow the fish to “breath,” and the stomach is sterilized with iodine. A ½ inch incision is made in the abdomen, and a curved needle is placed in the incision and poked through the side of the fish. The tag antenna is threaded into the needle and then the needle, with the tag antenna, is pulled through the side of the fish. The body of the tag is then placed into the abdominal cavity.
From here, the incision is closed with two non-absorbable sutures. We use non-absorbable so that there is no question that the incision heals before the sutures fall out.
After the surgery is complete, fish are allowed to recover for several hours in net pins placed in pools in the stream. They are then returned to approximately the same location in the stream that the came from and, with any luck, they become roving data points for four months.
Looking ahead, summer stream flows are approaching, and so it will be interesting to see how fish respond. I’m hoping for fewer drops and a return to uneventful tracking. But, it’s all up to the fish now.