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the Current Status of the Lake Simcoe ColDwater FishERY

Introduction

The Lake Simcoe Fisheries Assessment Unit (LSFAU) has undertaken a variety of netting and angler surveys to monitor Lake Simcoe’s coldwater fish species. The LSFAU provides a broad spectrum of aquatic science and technical expertise to support the management of fish populations at the local, regional, and provincial scale.

We design and implement long-term aquatic monitoring programs, conduct scientific research, monitor the effectiveness of management actions, as well as perform data analysis and interpretation.

The results of these surveys was published by the Ministry of Natural Resources and Forestry (MNRF) called "A Review of the Status of Coldwater Fish". This article will summarize some of the findings including data on Lake Trout, Lake Whitefish and Cisco to provide some insight into the status of the Lake Simcoe Coldwater fish community.

The Current Status and Importance of Dissolved Oxygen

The concentration of Dissolved Oxygen is a key component to the survival of all coldwater fish species and fisheries habitat in Lake Simcoe. The overall goal for Lake Simcoe is to achieve a target for dissolved oxygen of 7mg/l in the lake. This target provides an essential amount of oxygen for coldwater fish survival.

The current water quality testing on Lake Simcoe shows an overall increase in the dissolved oxygen concentrations in its deeper depths. It has been increasing from an average of around 3 mg/L in the 1980's to 6 mg/L in 2016. This is great news for the fishery and a step in the right direction.

The main threat to lower Dissolved Oxygen is excessive Phosphorus in the lake. It leads to the overgrowth of aquatic plants and algae, and when they die, they require a lot of oxygen in order for decomposition to take place. This contributes to the depletion of dissolved oxygen in the deep waters of the lake and degradation of the critical habitat of coldwater species.

The main ways in which we can control phosphorus and in turn increase Dissolved Oxygen is by:

Limiting phosphorus discharges from municipal and industrial sewage treatment plants (through stringent regulations and state of the art technology);
making stormwater management facilities serving new development meet the highest design standards.

The Status of Lake Trout

In 2001, the offshore benthic index trawling (OSBIT) unit caught 2 juvenile Lake Trout. The first evidence of natural reproduction since the 1960's. Further netting programs show an increase in the wild lake trout populations between 2003 and 2008 before stabiliziing in 2009.

In response to the evidence of natural reproduction, the number of stocked lake trout has been reduced from 146,000 fish in 2002 to 44,000 in 2014.

The rationale for decreasing stocking numbers 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. The below table indicates the stocking numbers of lake trout to date by the MNR.

MNR Lake Trout stocking numbers by year.

MNR Whitefish stocking numbers by year.

Lake Whitefish

The number of lake whitefish stocked in Lake Simcoe has been relatively stable overall for most years with roughly 134,000 fish per year. Studies have seen a general downward trend in stocked lake whitefish between 2010 and 2017 with the catch per unit effort of wild lake whitefish increasing dramatically between 2005 and 2009. Stocked whitefish populations still make up a good portion of the overall whitefish numbers in Lake Simcoe but have been on a slow decline since 2008. The wild lake Whitefish population makes up less than half the overall population and has remained fairly steady/on a slight decline. The catch of wild lake whitefish is dominated by a small number of strong year classes; specifically ages 4, 8, 12, and 13.

Cisco

The Lake Simcoe cisco populations underwent a significant decline in the 1980s, resulting in the closure of the recreational fishery in 2001. Since 2003, cisco captured in the OSBIN program has increased significantly. In 2013, the fishery was re-evaluated and subsequently re-opened in 2014. Currently, cisco populations are closely monitored by MNRF through the OSBIN program. Strong year classes of cisco were reported in 2004, 2008, and 2012. The OSBIN data from 2016 also identifies 2012 as a strong year class. It is interesting to note the similarities between lake trout, lake whitefish, and cisco in terms of the strong year classes observed, suggesting a common driver of recent year class strength.

If we can continue to monitor and improve the current Dissolved Oxygen Levels and reach our target of 7mg/l in the deeper depths of Lake Simcoe, whilst continuing to monitor and manage our coldwater fisheries populations, the coldwater fishery in Lake Simcoe will continue to strive and provide a fantastic fishery for years to come.

The following information was taken from:

Finigan, P., L. Graham and T. Langley. 2018. The status of coldwater fishes of Lake Simcoe. Ontario Ministry of Natural Resources and Forestry, Science and Research Branch, Peterborough, ON. Science and Research Technical Report TR-23. 26 p.

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