Field Notes: Barrens topminnow survey and collection

It may still be February, but the temperature has warmed and we're headed outside!  Yesterday, we joined staff from the Tennessee Aquarium for a day of field work to survey and collect Barrens topminnows (Fundulus julisia)- we call them BTMs for short.  We are some of the partners in an ongoing restoration effort for this imperiled Tennessee endemic species, a project that is unique in the amount of cooperation we have with private landowners, government agencies, and other nonprofits.

An adult male BTM.  Image courtesy of CFI

We met up with biologists from the US Fish & Wildlife Service and Conservation Fisheries, Inc. (CFI) at a site in rural Tennessee north of Manchester.  The site is a small spring and spring run that runs under a highway and through an adjacent cattle field--all on private land that we can access because of our cooperative partnership.  We split up into two groups and sampled different sections of the spring run.  For most of the length of the run the water was only a few feet across and rarely more than knee deep.  Using seines--long nets, each group made 12 hauls through different parts of the site.  All BTMs were set aside in a bucket and measured before being released after all sampling was finished.

The first group, who worked the upstream portion of the spring captured over 60 BTMs from juveniles through adult age classes.  That's a good indication because it shows there was breeding activity going at this site; a sign of a healthy population.  That same group also captured green sunfish (Lepomis cyanellus) and tadpoles in the seine hauls. 

Luckily, no western mosquitofish (Gambusia affinis) were captured this far upstream, hopefully indicating that this invasive species is not present in the spring.  Mosquitofish are a threat to BTMs because they can be aggressive towards the adults and actually prey on the juveniles.  Mosquitofish are one of the biggest continuing threats to BTMs across their entire range. 

The second sampling group was even more successful, surveying over 80 BTMs.  The second group did, however, capture mosquitofish.  Hopefully, the mosquitofish will not invade further upstream in the spring run.

Biologists surveying BTM populations in the field

We and CFI kept some of the adult BTMs from this site to use as broodstock in our ongoing captive propagation programs.


After sampling at the first site was completed, we piled into our vehicles and drove to another site a few miles north.  There, we accessed a small tributary to the same creek system that runs through a newer housing subdivision.  Pat Rakes, from CFI, recalled spotting a few BTMs during a quick visual survey of the site over a decade ago, and he wanted to see if they were still there.  Using a seine, we quickly collected a few BTMs and other small-stream fishes native to the area.  The creek appeared healthy, but the area immediately adjacent to the spring was being heavily impacted by development and will need close monitoring in the future.  A small number of fish were taken from this site, and we will use fin clips from them to analyze their DNA to see if they are a distinct population from the BTMs at the earlier site.