Introduction
Gates Creek, a significant tributary of the Seton-Anderson Watershed is a key habitat for a variety of Salmon and Trout species including Sockeye Salmon, Pink Salmon , Rainbow and Steelhead Trout. Most notable of the fish population is the Sockeye Salmon.
The main objective of the Gates Creek Salmon Project is to provide accurate estimates of egg to fry survival rates from both Gates Creek and the spawning channel. The interim report summarizes the results of adult sampling of Sockeye Salmon in Gates Creek in the fall of 2012, data which will later be combined with Spring 2013 data to calculate egg to survival rates.
Background
In 1986 the International Pacific Salmon Fisheries Commission created the Gates Creek spawning channel with the goal of increasing Sockeye escapement. In 2008 significant restorative work to the spawning channel at Gates Creek was undertaken to assist in increasing egg to fry survival rates of the Sockeye.
Although migration and adult escapement data has been recorded since the 1980’s, a significant lack of contemporary estimates of fecundity and egg deposition (information which is required to estimate egg to fry survival) exists, with last estimates obtained in 1988.
Methods and Material / Study Area
The sampling period for the study was established from August 26th to September 23rd 2012. Data was collected under the following methods:
- Mechanical counters (up to three mechanical counters are used in both the spawning channel and Gates creek)
- Visual survey (involving the removal and enumeration of carcasses, performed on an annual basis)
- Classification of female percent spawn (estimates based on Department of Fisheries and Oceans Canada criteria applied to female carcasses)
- Fecundity sampling (using intact egg skeins from 45 un-spawned females over the length of the sampling period)
- Egg retention (85 spawned females sampled over the sampling period)
- Percent spawn and total egg deposition (calculations using estimate of spawned females, total females, the pre-spawn mortality rates, and estimated mean fecundity)
- Comparison to 2011 Fecundity and Retention data (analyzed using a single factor one way ANOVA and either Welch’s or Student’s t test)
Results
The data collected demonstrated a small margin of difference between the visual estimates (17, 079) and the mechanical counter estimates (17, 598) of escapement.
Estimated mean egg retention in 2012 was 3.7 times 2011’s mean egg retention.
Estimated egg deposition for 2012 was 47.3% lower than estimated egg deposition in 2011 in the spawning channel and 81.0% lower than the estimated egg deposition in 2011 for Gates Creek.
There was no change observed in the mean fecundity from 2011 to 2012.
Discussion
This difference between the visual and mechanically counted estimates was attributed to fish being miscounted due to swim patterns, the presence of debris moving through the counters and the inability of the counters to differentiate between species.
Total egg deposition had reduced in the spawning channel and Gates Creek when comparing data from 2012 to 2011 although no change was observed in the mean fecundity per female.
The reduction in egg deposition in Gates Creek and the spawning channel was a result of both increased Pre-Spawn Mortality (PSM) and a lower percentages of effective spawning and reduced escapement from 2011 to 2012.
Due to improved staff training and communication, and more consistent application of research methodology, it is advised that greater confidence can be attributed to the estimated PSM values identified in 2012 than 2011.
Percent spawn was higher in Gates Creek than the spawning channel in both 2011 and 2012 and as Sockeye are assumed to have experienced the same migration conditions and exposure to pathogens in both location, PSM is expected to be a similar value in both areas.
The correlation between increased spawner density to higher rates of PSM is not fully understood, therefore it is difficult to explain why the small increases in spawner density in the channel had the effect of doubling the PSM between 2011 and 2012.
Suggested Action
Improvements in data collection methods and in comparative analysis were identified as the key recommendations in the report. The addition of video validation to the mechanical counters and development of technical skills for channel staff would provide greater consistency in both the scientific methods and the data collected, thus providing more effective and accurate estimates.
Conclusion
Although reductions in egg deposition and egg retention were identified, ongoing observation and data collection from Gates Creek and the spawning channel are necessary to better assess egg to fry survival.
- Source Lingard, S.L., J.J. Ladell and D.J.F. McCubbing. 2014. Gates Creek Adult Sockeye Escapement, Fall 2013. Report prepared for Lillooet Tribal Council and Fisheries and Oceans Canada. 34 p. Available at : https://a100.gov.bc.ca/pub/acat/documents/r43742/Gates_2_2013_juv_salm_1411406145422_1405145208.pdf [Accessed 03/2021].