Fish Stocking in Lake Simcoe
Stocking Lake Trout in Lake Simcoe
The stocking programs in Lake Simcoe have generally transformed over time from a focus on stocking of non-native species and supplemental stocking, to a program consisting of stocking native species for rehabilitation purposes (McMurtry et al. 1997).The Yellow Perch in Lake Simcoe are a completely, wild, natural, self sustaining population.
Recent Evidence of Natural Recruitment
Eutrophication and habitat loss since 1950 has resulted in a complete loss of naturally recruited lake trout in Lake Simcoe. Since 2001, indicators of natural recruitment have been observed in Lake Simcoe Fisheries Assessment Unit (LSFAU) monitoring programs. This increased natural reproduction and survival of wild lake trout coincides with improvements in water quality.Two young (<1 year old), wild lake trout were caught in 2001 during a bottom trawling program conducted to index the abundance of juvenile coldwater fish species in their summer habitat. In surveys conducted in 1991 and 1992 no wild lake trout were caught (Willox 2001). Since 2002, a small number of young (1-5 year old) wild lake trout have been caught annually in the trawling program, and multiple age classes of wild, naturally produced lake trout have been documented in other assessment programs. These observations indicate that naturally reproduced fish are surviving to adulthood (La Rose and Willox 2006). Figure 3 shows the results of three LSFAU programs that all illustrate three distinct periods of wild lake trout. The first period being prior to the mid 90’s where there were a decreasing number of older, larger wild lake trout present which are the remains of the remnant population, the second period between the mid 90’s to approximately 2002 where there were virtually no wild lake trout present in the lake and then a subsequent increase in the number of young wild lake trout. In addition to this assessment information, anglers continue to catch wild lake trout in good numbers.
Figure 1: Wild lake trout catch results from three LSFAU programs, Fall Index Trap Netting (FITN), Offshore Benthic Index Netting (OSBIN), and the Winter Creel (WCR).
According to La Rose and Willox (2006) these observations do not signal the recovery of wild lake trout in Lake Simcoe, they do indicate however, that “a change has occurred in the status” of lake trout. This combined with other cold water species reproducing naturally, indicates that the system has the potential to recover.
Potential Impacts of Stocking
In any system, there is a biological limit to the number of fish that can be produced or supported based on available habitat and forage. Stocking beyond this
natural limit will not significantly increase contributions to angler catches and may potentially destabilize the fish community (OMNR 2002; Powell and Carl 2004). Naturally reproduced lake trout in Lake Simcoe could theoretically be replaced or prevented from establishing if (based on Evans and Willox 1991):
- Numerically they were outnumbered because artificial (stocked) recruitment exceeded natural recruitment- At high rates of exploitation, naturally reproduced wild fish are equally susceptible to being harvested- Large numbers of adult stocked fish will continue to cannibalize on young wild juveniles- Large numbers of juvenile stocked fish will continue to compete with young wild juvenilesDespite good intentions, in some cases, the stocking strategies employed to rehabilitate fisheries have been found to inhibit rehabilitation (Marsden et al. 1993; MacLean et al. 1981). It is unknown if similar consequences are occurring in the Lake Simcoe lake trout stocking program given recent evidence of natural reproduction (Willox 2001) and recruitment (La Rose and Willox 2006) of lake trout. The complexity of the Lake Simcoe system and possible consequences of management actions must therefore be considered when evaluating stocking levels and strategies (McMurtry et al. 1997).ProposalBased on the assessment of considered options, the recommended approach is to set a new stocking target of 50,000 yearling lake trout to be stocked annually starting in 2010 for a period of 5 years. A new target will be established again in 2013 prior to fall egg collections, based on the assessment of the impacts of this change to the fish community and recreational fishery.
The rationale for this recommendation is based on the assumption that the implementation of this annual stocking reduction will increase the natural recruitment of lake trout. It should also reduce the number of stocked lake trout which in turn will decrease the amount of competition and predation on wild lake trout from hatchery fish. This will also serve to reduce the predation pressure on the prey base.
This information was taken from:
Borwick, J. Philpot, A. and K. Wilson. 2009. Review of Lake Simcoe’s Coldwater Fish Stocking Program. Ontario Ministry of Natural Resources. Midhurst/Aurora districts, Pp. 23.