In celebration of World Fish Migration Day, a day focused on restoring fish migration routes, and in recognition of the Buffalo River Fish Ladder as an integral piece for trout migration in the upper Henry’s Fork, I’m writing this blog to share information on what we are seeing so far this sampling season.
Quick statistics and historical context
This infographic gives a quick summary of the kinds of fish (species, size, and maturity) that have been utilizing the fish ladder in the last twelve weeks. In the first six weeks of sampling (February 18 – March 31), when winter still had a foothold in Island Park, over half of the upstream migrating rainbow trout were juveniles. In the last six weeks of sampling (April 1 – May 15), winter has washed downstream, spring has emerged, and we have caught more spawning-aged and in-between rainbows in the trap than in the previous six week sampling period. As a result, the cumulative maturity class distribution has evened out (40% juvenile, 32% in-between, 27% spawning-aged).
Of the fish moving upstream so far this sampling season, most have been rainbow trout (82%). We have seen more brook trout moving upstream since April 1 (21%) than we did in the first six week period (12%), but it is not cause for concern as this April 1 – May 15 brook trout percentage is comparable to that of the last decade.
The 2016 spring migration season has seen above average upstream movement of rainbow trout in all age classes (juveniles, spawners, and those in-between). In fact, 2016 is on track to becoming one of the most successful migration springs on record! Although these numbers may be skewed due to differing capture efficiencies and record accuracies of research crews over the last decade, more rigorous data analysis and continued monitoring will determine how magnitude of migration is influenced by environmental factors like flow and temperature. I am currently working on a decadal report per our Federal Energy Regulatory Commission (FERC) licensing requirements and will finalize this analysis in July after we wrap up sampling for this spring.
Of course, I couldn’t write a blog without sharing a few pictures of the fish we get to interact with almost daily. As a reminder, a “recaptured” fish is a fish that was fitted with a P.I.T tag upon initial capture while migrating upstream in previous sampling seasons (September 2013 – July 2015). Upon recapture, we scan the fish with a P.I.T tag reader to obtain its unique tag code and then cross reference that code with those in our system to track its migration history.
Fish 3DD.003BD64356: This male was initially captured migrating upstream March 30, 2015 and was detected by our tag antenna migrating back to the Henry’s Fork three weeks later on April 20. When we recaptured this trout on April 4, 2016, it had grown almost an inch and a half in the last year – coming in at 18.6 inches.
Fish 3DD.003B9F9FE2: We encountered this female on May 6, 2016 and measured her at 17.8 inches. Strangely, her tag code is not in our database and does not match the general pattern of others in our database (it starts with 003B9, while our others are 003BC or BD). Upon initial capture, a handful of fish were released before their tag code could be recorded, so it is possible that this trout is a fish HFF previously tagged. However, this is unlikely given that the tag code is also not in the antenna detection database – a database that records tagged fish migrating out of the Buffalo River to the Henry’s Fork. Perhaps this fish was tagged by another agency or organization for another project elsewhere in the river.
Regardless, both these beauties have migrated upstream to spawn trout that will one day contribute to the fishable Henry’s Fork population!