JUVENILE ATLANITC SALMON POPULATION ASSESSMENT
Each spring from 2013 to 2017, the HRAA installed and operated a smolt wheel upstream of the French Village Bridge. A smolt wheel, or rotary screw trap, is a device that turns with the current and is oriented upstream so that it will capture and hold fish swimming downstream. While installed, the wheel was checked daily. The number and size of any smolts captured was recorded, a scale sample was taken and the caudal fin of each smolt was clipped. Smolts were then released upstream of the wheel and the number of recaptured smolts (with clipped fins) were used calculate the efficiency of the wheel and the total abundance of smolts in the Hammond River system. Since the first implementation of the smolt wheel, in 2013, the HRAA has learned about the timing of smolt migration. Reliable estimates of the number of smolts in the watershed (above French Village) were obtained in:
- 2014, there were an estimated 4,850 smolts (95% C.I.: 2,872 - 9,761)
- 2015, there were an estimated 2,861 smolts (95% C.I.: 1,597 – 5,134)
In 2013, 2016, and 2017 the HRAA was unable to obtain a smolt population estimate. Overall, the timing and duration of the smolt migration is suggested to be extremely dependent on the weather conditions of each year. Here is a summary of our findings and lessons learned from each of the years the smolt wheel did not produce a statistically sound population estimate of the migration.
In 2013, it was identified that smolt migration can begin as soon as water temperatures reach at 4°C (Ross Jones, DFO). The timing of the Hammond River smolt migration had not been known previously to this year, when we captured the tail end of the smolt run from May 2-May 10. In 2013, the HRAA staff also spent a great deal of effort learning how to install, operate, and decommission the wheel. This knowledge led to the successful and timely deployment of the wheel in 2014-2015.
In 2016, the smolt wheel was successfully deployed after the final freshet on the Hammond River, when temperatures reached 4°C. However, two early freshets (February and March), which may have enabled conditions for the smolt run earlier than the final thaw, had also occurred. No smolt were caught in 2016, and these results suggest that the smolt run may have occurred earlier than the Hammond River’s final freshet. Another possible explanation is that the smolt wheel was not effective at capturing smolts due to low flow conditions in the river.
In 2017, even though the smolt wheel was deployed much earlier than previous years and captured the beginning of the smolt run, high water flow resulted in the run being largely missed when the smolt wheel was removed (May 4th, 2017) to protect the infrastructure from a storm. No smolt were captured after the wheel was reinstalled and this data suggests that the smolt run may occur over a much shorter time period during fast water flows.
Overall, the success of the smolt mark-recapture efforts have been hindered greatly by weather conditions, which make it unsafe for staff and the infrastructure itself to operate the smolt wheel during the actual smolt run. These data suggest that the timing and duration of the smolt migration may vary greatly from year to year, depending on weather conditions.
This project has been completed each year, with the support of the Atlantic Salmon Conservation Foundation and the New Brunswick Wildlife Trust Fund. The smolt wheel was donated by the Atlantic Salmon Federation. The HRAA deeply appreciates the support of all of their project funders.