Figure 1. PIT tags are about the size of a grain of rice
Members of the Dworshak Fisheries Resource Office (FRO) and Dworshak Hatchery production staff have been working the last few weeks to mark the 2011 broodyear of steelhead with passive integrated transponder (PIT) tags as an integral part of our steelhead monitoring and evaluation program.PIT tags are small tags, about the size of a grain of rice (Figure 1), that are injected into the body cavity of juvenile salmon and steelhead.They are passive in that most of the time they are inert when being carried by the fish.But when fish swim near a PIT detector site, signals being emitted will energize the tag and it then bounces back an electronic code unique to that fish.Currently most of the dams between the Snake River and the ocean have the ability to detect PIT tagged smolts as they migrate to the ocean.Those data are used to estimate travel times and survival of the ocean bound smolts.For those fish that return as adults one to three years later, the PIT tags will also be picked up at five locations as they migrate upstream, including Bonneville Dam near Portland, OR, Lower Granite Dam a few miles downstream from Lewiston, ID, and in our trap as they are collected for broodstock.Those detections collected over three years are used to estimate the total number of steelhead that return from each broodyear released from Dworshak to determine if we are meeting our mitigation goal for Clearwater River steelhead production.
Figure 2. FRO PIT tag trailer.
This year’s effort, coordinated by Carrie Bretz, involved tagging 30,500 steelhead over three weeks.Tagging is conducted using the FRO tagging trailer (Figure 2).Fish are pumped from a pond into the trailer where they are anesthetized and the PIT tag is injected using a hypodermic needle (Figure 3 & 4). The tagged fish are then returned to the pond through a pipe.There is a bit of work to get it all set up but once up and running the process works very well.Fish to be tagged are representative of all production, including early through late takes, fish reared in each of the three systems, and for those that will be released on- and offsite.This required tagging fish from 12 different ponds and to move the trailer several times over the three weeks.The next step is to see if any of the tagged fish show up in the pond mortalities and to look for any tags that might be shed (using a magnet pushed along the bottom of the ponds) and then wait for fish to be released in few months so we can start collecting data.
Figure 3&4. PIT tags are injected into fish using a hypodermic needle.