Part 3 – One Stream At A Time

The third part of the story of the restoration of the turquoise darter in Sixmile Creek was initiated after the darters had become established and were abundant. There was very little previously published about the life history of the turquoise darter in the decades since its initial description as a species. Reasons for this are related to the fact that it is a small non-game species with no sport or economic value and that it is limited to the Savanah River drainage of South Carolina and Georgia. Darters of course have ecological value. They are indicators of stream health. They are sensitive to change in water quality. That is why they are typically the first species to disappear from a polluted creek, stream or river.

The third graduate student was Steph Irwin. 

His thesis would determine the timing of the turquoise darter’s spawning, the fecundity (number of eggs produced) of females, and the abundance of the darters on Sixmile Creek’s riffles measured in number of fish per unit area. This would require sampling the darters periodically over the course of a year and utilizing “depletion” sampling to ascertain abundance. 

Depletion studies sounds ‘bad” but in fact all it involves is thorough sampling of a section closed with upstream and downstream block nets and briefly holding the fish captured on each pass in tanks representing the first, second, third and perhaps fourth pass. 

The fish are enumerated. The theory is that as you capture most of the fish with each successive pass the catch per unit effort (CPUE) goes down with each pass. If this happens a depletion abundance estimate can be made by extrapolation to zero CPUE. 

Example from actual data that shows how a depletion study does not need to sample all the fish in a closed section, but can predict how many fish are there based upon a negative slope and projection of K to zero CPUE

The fish are returned unharmed to the stream less than an hour after capture. In order to sample the entire stream with each pass students in my wildlife fisheries classes provided the “manpower” needed to cover the stream left to right. 

In order to determine timing of spawning and fecundity a periodic small sample of darters had to be captured and sacrificed in order to measure the size of their gonads and egg counts. 

All work was performed with approved Clemson University Institutional Animal Care and Use Protocols. 

Darter density on Sixmile Creek’s riffles was 0.37 per meter squared. This is equal to 3691 per hectare and compares to Jay Delong’s estimate of 2799/ha for Twelve Mile Creek. This compares to reports for other darter species in other states where values ranged from  0.17 to 0.42 darters per square meter.

GSI is the gonadosomatic index of darters from January to June.

GSI peaked in mid to late April (above). The percentage of ova that were mature also peaked in late April to mid May (below). Clearly, the darters spawn in late April and early May.

Jay Delong’s M.S. thesis research provided data to predict the habitat needed by turquoise darters. Kevin Kubach’s M.S. thesis used Jay’s data to develop and implement a model for restoration of darters to Sixmile Creek in the Clemson Forest. Steph Irwin’s M.S. thesis evaluated the status of the darters following restoration efforts and described the reproductive cycle of the darter. Fellow faculty and working professionals who had graduated from Clemson Wildlife helped out on darter restoration sampling. More than 200 Clemson Wildlife and Environmental Science undergraduates assisted in field sampling Sixmile Creek and its darters over a period of more than ten years. Jay Delong (deceased) would be pleased that his work was used. Kevin and Steph are working professionals. I am retired. The darters are abundant.