Originally Posted by chubbdarter
From SRD
2.3 million Walleye fry were stocked in Pine Coulee Reservoir in the spring of 2000, with another 1.8 million stocked in the spring of 2002. Stocking of cyprinids and suckers collected from Willow Creek was also done in 2000 to try to establish a forage base for Walleye. Since then we have sampled the reservoir to monitor the Walleye population as it develops. In 2003, 2004, 2007, and 2009 gill netting was conducted to sample for larger Walleye in open, deeper areas of the reservoir. In 2005 and 2006 test angling was conducted to further sample larger Walleye for mercury analysis. In 2003, 2004, 2007, 2008, and 2009 beach seine netting in shallow areas of the reservoir was conducted to sample for juvenile Walleye (young of the year).
Gill net results
In 2003 over 60 Walleye were caught with an average fork length of about 10-11 inches. These were from the 2000 stocking event.
In 2004 close to 100 Walleye were caught with an average fork length of about 11-12 inches.
In 2007 about 50 Walleye were caught with an average fork length of about 13 inches.
In 2009 almost 130 Walleye were caught with an average fork length just over 13 inches. Stomach contents were analysed and ages determined. Only a single Walleye was less than 12 inches fork length. Its fork length was about 9.5 inches and it was aged 2 years old. This fish is believed to have resulted from natural spawning (not a stocked fish). All the other Walleye were between 12 and 15 inches long and either age 6 or age 9. They came from either the 2000 or 2003 stocking events. Stomach content analysis showed that of all the Walleye caught in 2009, only one contained partially digested fish, while all others either had empty stomachs or only invertebrates in their stomachs, mostly amphipods (Gammarus).
Test angling results
In 2005 35 Walleye caught in the spring had an average fork length of 12 inches.
In 2006 31 Walleye caught in the spring had an average fork length of 13 inches.
Beach seining results
In 2003 no young of the year Walleye were captured.
In 2004 no young of the year Walleye were captured.
In 2007 5 young of the year Walleye were captured at a single site.
Walleye spawning was also confirmed in 2007 though the use of egg traps set over spawning habitat, mid-April though mid-May.
In 2008 5 young of the year Walleye were captured at two sites.
In 2009 7 young of the year Walleye were captured at four sites.
All young of the year Walleye were around 1.5 inches long.
Ten years after completion of the Pine Coulee Project, the overall conclusion from these results is that a dense population of Walleye from the 2000 and 2003 stocking events has developed, but the growth rate of these fish has gradually decreased to the point that they have almost stopped growing now. Although spawning is occurring, there appears to be very limited survival of naturally spawned young (only one fish caught in gill nets in 2009 was a two year old). Stomach content analyses demonstrate Walleye are not feeding on fish, but primarily on amphipods (invertebrates). This is likely limiting their growth. All fish but the one age 2 fish sampled in 2009 did appear to have mature gonads, suggesting they could spawn, but the limited prey base may mean not all Walleye have sufficient energy to actually spawn. Another possibility is that despite successful spawning, very few young of the year survive the first summer due to poor conditions for survival (cold weather, wind and wave action, poor rearing habitat) or larval predation by other forage species present in the reservoir. Beach seine netting in shallow areas of the reservoir has shown White Suckers and Longnose Suckers are abundant, but the Walleye are not feeding on them. Other species of forage fish such as Lake Chub, Spottail Shiners, Emerald Shiners, and Fathead Minnow are also present, but in lower numbers.
Walleye fisheries across Alberta are classified into one of four management categories. In southern Alberta, all waterbodies were classified into one of two categories: newly stocked or vulnerable. Reservoirs and lakes in the first category have a zero catch limit (catch and release) while those in the vulnerable category allow for limited harvest. According to Alberta's Walleye Management and Recovery Plan, changes to the management status category (e.g., from newly stocked to vulnerable) are based on five biological characteristics: age-class distribution, age-class stability, growth, age-at-maturity, and catch rate. Although catch rate meets the criteria for changing the status category of Pine Coulee Reservoir,growth rate, age-at-maturity, age-class distribution, and age-class stability do not. Walleye in Pine Coulee Reservoir have reached maturity rapidly, the age-class distribution is extremely narrow (essentially only fish from the 2000 and 2003 stocking events are represented), and age-class stability is very low (if these two age classes were lost to overharvest there would be no younger age classes to fill their place). In order to change Pine Coulee Reservoir from the newly stocked to vulnerable category we need to have biological evidence that juvenile Walleye are surviving, reaching sexual maturity, and spawning successfully.
We will continue to monitor the reservoir and evaluate the feasibility of various options for establishing a sustainable fishery. A risk assessment considering the impacts to the reservoir itself, as well as to Willow Creek, would be required before considering introducing another prey species for Walleye. In terms of allowing limited harvest, a decision will have to be reach on whether a self sustaining Walleye fish can be established before this is considered. One factor to note is that a consumption advisory is in place for Walleye from this reservoir. Although concentrations of total mercury in analysed walley from Pine Coulee Reservoir (0.52 to 0.79 micrograms/gram) were within reported ranges for Walleye from rivers and lakes elsewhere in Canada and the United States, they were also above the threshold (0.5 micrograms/gram) where Health Canada recommends limits for consumption for different consumer groups (women, children, adults).
If you have any further questions about fisheries management on Pine Coulee Reservoir, please feel free to contact me again.
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