The Slot Limit – A management tool: Part One

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I first arrived in Roblin Manitoba during the spring of 1990. I had just finished a five year tour conducting fish research on the Lower Nelson River. Previous to that, I spent another five years doing the similar work all across the Province.

This ‘new’ Fisheries job was more involved in the day to day management of fish and where they live. I hadn’t seriously angled for 10 years, due to my dedication to work, music and a passion for wilderness adventures. I’d heard of Lake of the Prairies (LOTP) and how ‘you could catch pickerel all day for years but now not so good and now this slot limit’. However, I had no familiarity with slot limits other than the realization it was another tool used to manage recreational fish populations.

Three things needed to happen. Firstly, I had to research the function/use of slot limits as a management tool for recreational walleye fisheries. Secondly, I needed to gain as much knowledge as possible regarding the fishery of LOTP and start a long term fish stock monitoring program. Thirdly, I needed to relay this information as I came to collect, analyze and fully understand it, to as many people as possible.

In the early 1980’s, LOTP was the place to go for quick limits and lots of big walleye. This 30+ kilometer impounded section of the Assiniboine River had matured into the perfect storm for walleye production. Especially since the Northern pike boom crashed due to loss of spawning habitat with fluctuating water levels, walleye were the number one predator years after the initial establishment through a fry stocking program. However, fisheries managers at the time realised the massive annual harvest by anglers could not be sustainable with current regulations.

The first regulation change (1985) was a reduced creel limit from 6 to 4 walleye in possession. However the introduction of the slot limit in 1989 (all walleye between 45 cm (18”) and 70 cm (28”) must be released) turned out to be the management initiative to sustain this robust fishery.

Through our annual monitoring program and sporadic creel census surveys detailing population dynamics of walleye (and other species), I was able to accurately follow the ‘comeback’ of the walleye fishery in LOTP. It did not happen overnight. It took until 1995 until the remnants of the walleye fishery had ideal conditions for spawning and egg incubation during the spring of that year (we had found the prime spawning areas in the upper reaches of the Assiniboine River using radio telemetry technology). I eventually found that over the years every time this section of the river experienced a certain minimum level of sustained flow during the months of April and May, a strong year class of walleye was produced. In 1995, the one year class that was remaining in the LOTP walleye fishery (it represented about 75% of the walleye fishery at the time) was 100% protected by the slot limit. In other words, most of the walleye fishery that remained in the lake were in their prime spawning years. They had ‘escaped’ harvest by entering the lower end of the slot limit (45 cm) and were allowed to spawn in the upper reaches of the river in great habitat with decent hydrologic conditions for a successful hatch.

The progeny of this event (the 1995 year class) started to show in the anglers’ creel by 1997 as two year olds. I was always forthright with the local municipalities and towns regarding the state of the LOTP fishery. My message was patience. Now that the 2 year old walleye were ‘on the bite’ locals wanted a minimum size limit to protect them as well. There was also huge pressure to start stocking the lake again. We politely rejected both requests but at the same time educating folks on how the walleye fishery could sustain itself given the reduced creel, implementation of the slot limit and without the need to stock additional walleye. Patience.

By the year 2000 LOTP was cruising along quite nicely and all was good in the world. By the time my tenure ended in the Roblin area in 2005, LOTP had continued to produce decent years classes of walleye every other year. I cannot speak for the next 10 years however I know the lake is still hanging in there even after some massive flooding and reservoir drawn down events, and of course increasing angler harvest pressure.

Slot limits were first introduced in Manitoba in 1989 on LOTP (must release all walleye between 45 cm and 70 cm). In this case the species was walleye and for this article I will discuss the slot limit with reference to walleye only.

The basic purpose/function of a slot limit is to improve/sustain angling opportunities on a particular body of water. The range of the slot is based on protecting sexually mature fish during their most productive years. This protection would also require that the population of fish involved would have the appropriate amount of spawning habitat required to sustain the population through natural reproduction, given the ideal environmental parameters (water depth/flow, temperature, etc.). This premise allows for an ‘untouchable’ spawning stock to grow in numbers and when environmental parameters are favourable, produce bumper year crops of young fish. This ‘bumper crop’ are in turn eventually available in the anglers’ creel. The fish which avoid harvest by anglers (and a litany of additional natural mortality encounters) escape into the slot (greater than 45 cm). In a perfect world there are enough small fish for the frying pan as well as larger fish for that trophy or near trophy experience.

Ideally, the lower end of the slot should encompass close to 100% protection of sexually mature females. Female walleye are generally 100% sexually mature by five years of age. The slot limit prescription also allows for fish to be harvested once they ‘exit’ the top end of the slot (greater than 70 cm). Generally anglers do not keep this larger size of walleye, however the slot limit model theoretically allows for more fish to reach ‘trophy’ size, given the waterbody has suitable forage to support fish of this size.

There are many factors which can impact this type of management strategy. Forage base shifts, overall lake species compostion shifts, partial winterkill, post release mortalities, invasive species introductions, large lake or river level fluctuations, rapid temperature changes during spawning and massive harvest rates, to name a few. But, with the adequate slot size range, reduced creel and periodic prime environmental spawning conditions, most waterbodies can usually overcome most negative impacts, eventually.

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About Author

Ken Kansas

Ken has recently retired from a 30+ year career in fisheries research and management conducted all across Manitoba. From the Theliwaza and Lower Nelson Rivers, to Manitoba’s Parkland and Whiteshell areas, Ken has worked tirelessly in efforts to improve fish populations and recreational angling opportunities through science and common sense based realities. A rabid fisher himself, with a penchant for tossing flies at rather large salmonids, Ken hopes to share his knowledge with all Hooked Magazine readers through the unique combination of biologist and angler.

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