Buffalo River Spawning Migration Off to a Good Start

As of this posting, we have been trapping fish moving up the Buffalo River Fish Ladder for the past six weeks. As promised, I have put together some information to share what we have seen so far this sampling season and how that compares to what we have seen in the past.

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 ladder in the last few weeks of winter. Most of the fish that have been migrating upstream are juvenile Rainbow Trout likely seeking preferable habitat in the Buffalo River, given continued low flows in Box Canyon. 

Of the fish moving upstream so far this sampling season, the percentage of Rainbow Trout (88%) is the largest we have seen in the last ten years (excluding 2009 and 2014 due to incompleteness of data), while the percentage of Brook Trout (12%) is among the smallest. More rigorous data analysis and continued monitoring will determine if this apparent increase in the fraction of Rainbow Trout is statistically significant.

In regards to size, the largest Rainbow we have trapped in the ladder so far this season is among the largest we have ever handled at the Buffalo during spawning season – measuring in at 22.7 inches. The largest Rainbow ever trapped in the ladder during spawning season was 23.8 inches and was captured on March 13, 2013. On the opposite end of the spectrum, the smallest Rainbow we have caught so far this season – measuring in at 3.6 inches – is comparable to that of past seasons by this date. The smallest Rainbow recorded migrating upstream between mid-February and the end of March was 0.85 inches on March 25, 2006 – an incredible feat given that the ladder was built to pass fish that are at least 4 inches in length!

Movement Trends

When we did not see spawning-sized Rainbows, defined as trout greater than 12 inches, in the middle of March for two weeks, I became interested in looking into movement trends to see if there was cause for concern. Thankfully, there is not. In fact, by March 15, more spawners had migrated upstream than ever recorded, and we are well above average for the number of spawners migrating upstream by this time of year. There are many factors that could have influenced the lull in spawner movement, including low temperatures, but in looking at past trends, spawning-sized Rainbows move en masse between April and June so we expect more spawners in the coming months.

Juvenile trout, defined as trout less than 6 inches in length, move upstream in consistent numbers throughout the mid-February to June sampling period. However, the number of juveniles that have moved upstream so far this year is the maximum ever recorded. With an above average number of “in-between” Rainbows, trout that are between 6 and 12 inches in length, migrating upstream so far this season, 2016 is shaping up to be a healthy migration year. I look forward to sharing more information as the season progresses.

Recapture Histories

Most of these stories have been shared via Facebook or The Monthly Hatch, but I thought I would share our recapture histories in one place in this blog as well. 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 (Sep 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.003BD64311 (not pictured): This female was initially trapped on February 23, 2015 and was recaptured migrating upstream almost exactly a year later on February 22, 2016. In the year since its initial capture, it has grown almost an inch – from 15.4 inches to 16.3 inches.

​Fish 3DD.003BC9ADA (pictured to the left): Recaptured on February 22, 2016 and measuring in at 22.7 inches, this female is the largest Rainbow Trout we have captured migrating upstream in the Buffalo River Fish ladder since we began trapping on February 18th. She was initially tagged with the 2014 spawning cohort on March 19, 2014 and has grown an impressive 4.2 inches since!

Fish 3DD.003BD64366 (center picture): Recaptured on March 9, 2016, this trout is the only male we have recaptured so far this sampling season. Initially tagged on March 30, 2015, this fish has grown an inch in the last year – from 15.2 inches to 16.2 inches.

Fish 3DD.003BC59AD5 (pictured to the right): Another female from the 2014 spawning cohort, this fish was initially tagged on April 7, 2014 and was recaptured on March 25, 2016. Measuring in at 20.2 inches, she has only grown an inch in two years – an amount our other recaptures have grown in half the time.

All of these fish are spawning in the Buffalo for at least the second time in their lives!