SILVER AND THE ART OF LAKE SURVEYS

0

 

P1000630

Rumour has it there were several UFO sightings on numerous lakes after sunset in the cottage country in the Whiteshell and Nopiming Provincial Parks over the last few years. Well, you might want to call that ‘UFO’ an ‘ Unidentified Floating Object’ and be happy to know that it is actually a new fisheries sampling tool hard at work assessing fisheries populations on your local waters. We call that tool Silver!

OLYMPUS DIGITAL CAMERA

In the spring of 2010, Manitoba Conservation and Water Stewardship – Eastern Region Fisheries Branch, initiated a series of new field programs targeting most of the road accessible recreational fishing lakes in both the Whiteshell and Nopiming Provincial Parks as well as other area lakes. The main objective was to assess fisheries populations in a non-lethal fashion and also to evaluate our walleye fry stocking program in an effort to maximize efficiency on a lake by lake basis.

One of the main tools utilized in these lake evaluations is indeed ‘Silver’, a twenty foot long electrofishing boat procured with monies from the Fisheries Enhancement Fund (FEF). Some of you folks might have seen Silver at the 2009 and 2013 Mid Canada Boat Shows with its’ raised bow deck, all aluminium body and 200hp jet drive. Silver is an impressive beast.

Fisheries personnel have used gill nets as a fish stock assessment tool for decades, and continue to this day. This technique is indeed an effective method to collect fish population data and has greatly assisted fisheries staff to make the best management decisions necessary to ensure the sustainability of our fisheries resources. Long term assessment programs utilizing gill nets occur on our large multi-use fisheries across the province where the sheer size of these lakes is not negatively impacted by the removal of fish during this process. A few examples of this would be programs on Lakes Winnipeg and Manitoba, Lake of the Prairies, and Lac du Bonnet.

OLYMPUS DIGITAL CAMERA

However on our smaller, developed (cottages and/or campgrounds) and sometimes intensely angled target lakes, removal of hundreds of fish at any time could have a negative impact on overall stocks, depending on the species and a host of other biological and ecological factors. That is why we developed a set of non-lethal sampling protocols, specifically for these lakes. These protocols involve utilizing the technology of electrofishing and subsequently, Silver.

Electrofishing is a widely used technique across North America. Electricity is pulsed through the water to essentially ‘stun’ fish. Silver uses an on-board generator to create electrical currents (direct current-DC) to pass through positive (anodes-hanging in front of the boat) and negative (cathode) electrodes. This current precedes the boat and creates an maximum active ‘field’ of about four meters by four meters and 3 meters deep, emanating from the extended anodes. Pulsing direct current provokes taxis, which is an invol­untary muscular response that causes fish to swim towards the anodes. Once fish reach an anode, they stop swim­ming and go into narcosis (stunned), usually floating belly up. Fish are quickly scooped by the bow deck netters and placed in a large aerated live well on board Silver, where they revive quickly. Mortality rates for this method are generally less than 2% when the gear is used properly.

OLYMPUS DIGITAL CAMERA

Silver is essentially a shallow water tool, most effective in about three meters or less of water. We subsequently design our survey methods to fish a certain percentage of shoreline or littoral areas with Silver by pre-mapping 100 meter transects by GPS. The number of transects reflect the size or area of a lake. For example a relatively small waterbody like Barren Lake in the South Whiteshell we used a total of seven, one hundred meter transects and a larger lake like Crowduck had twenty eight, one hundred meter transects.

Each transect is fished approximately one to five meters from shore and continuously ‘shocked’ for the full length at a speed of around 2-4 km/hour. Stunned fish are dip netted and placed into the live well on the move until the transect is finished. While moving to the next transect, the dip net crew samples the fish caught. All sport fish (Walleye, Smallmouth Bass, Northern Pike, Black Crappie, Lake Whitefish, Lake Trout, etc) are counted, measured and have a dorsal spine or fin ray removed for ageing. All other species are counted and measured. All fish are then released.

Fisheries branch typically conducts these surveys during May, June, September and October. The latter two months work best for assessing recruitment success for spring spawning fish. We prefer this timing for a number of reasons, one being the cooler waters temperatures during these time frames result in less stress on fish. Another is that there is generally less cottagers out at these times and kids are in school. We also prefer to stay away from electrofishing directly in front of cottages.

Fisheries Branch has conducted these non-lethal assessments on over 25 lakes in the Eastern Region with still many more lakes to be assessed. All this data should be available on our forthcoming Fisheries website sometime in the near future as well fisheries survey data from other regions of the province. The style of non-lethal sampling protocols we have developed for these lakes allows us to return to lakes years later to compare previous survey data, assess regulation impacts on certain species (Area A walleye slot limit for example) and perhaps see how a lake has responded to walleye fry stocking, which is another major component of our work with Silver.

Fisheries Branch stocks up to twelve million walleye fry annually in various lakes in the Eastern Region of Manitoba. Our ultimate goal is to use those valuable walleye fry in the most efficient and effective manner possible. One way of doing this is to be able to identify naturally recruited walleye from stocked walleye in the field. With the relatively new OTC (oxytetracycline) marking technology and the help of Silver, we are now able to make this happen.

Annually our Whiteshell Fish Culture staff set up walleye spawn taking operations on Falcon Creek. Fertilized walleye eggs are then taken to the hatchery facility near Westhawk Lake and placed in aerated jars to incubate and subsequently hatch. Two days after hatch they are immersed in an OTC solution which basically sets a mark on one of the first boney structures to develop, the otolith. Otoliths are hard, calcium carbonate structures located directly behind the brain of fish. Otoliths help with orientation, balance, and sound detection, similar to the inner ear of mammals.

The newly hatched and marked fry are then stocked in various lakes throughout the region. We use Silver in the fall to capture a subsample of walleye once they have had a summers worth of growth (young of the year). These fish are sacrificed in order to remove the otolith. The sample size is large enough to make valid assumptions on mark frequency and small enough not to negatively impact existing stocks. The otolith is sent to the lab, prepared and analyzed for the absence or presence of a mark. We then use this data to adjust our stocking activities.

For example, White Lake in Whiteshell Provincial Park was normally stocked annually with hundreds of thousands of walleye fry. Our surveys showed two important facts. One was a very robust and strong walleye population and the other was a 3% or less mark rate on walleye fingerlings captured in the fall. This tells us that stocking on an annual basis is not an efficient way to manage this walleye population In other words, a waste of walleye fry. Non-lethal assessments also showed us that the Area A slot limit was definitely a good fit for White Lake showing excellent natural recruitment and a strong mature spawning stock. Habitat data told us that sufficient spawning habitat was available for these mature fish. And that my angling friends, is a good thing.

OLYMPUS DIGITAL CAMERA

Eastern Region Fisheries Branch has worked with many partners on a multitude of projects since obtaining Silver. Some of these awesome partners include Fish Futures, Lac du Bonnet Wildlife Association, Walleye Anglers Association of Manitoba (WAAM), Whiteshell Cottage Owners Association, Swan Valley Sport Fishing Enhancement (SVSFE), Central Region and Western Region Fisheries Branch to name a few. But ultimately, the purchase, utilization and maintenance of Silver would not be possible if it were not for each and every angler in Manitoba, and for that we thank you. HI HO SILVER!

Share.

About Author

Leave A Reply