Lake whitefish

Description

Lake whitefish are similar in appearance to other whitefishes in the Coregoninae subfamily of the salmon family Salmonidae, such as the northern cisco (Coregonus artedi). As with all salmonids, they have an adipose fin. To the distinction from cisco, the lake whitefish has a snout which overhangs the short lower jaw, so that the mouth opens in a slightly inferior position. Thus the fish can feed on the bottom of lake beds or grab food particulates out of the water or from the surface of a water body. The cisco in turn has a short snout with a lower jaw that extends beyond the snout. Both the cisco and lake whitefish are discernible from the mooneye due to the small posterior dorsal adipose fin. In early life stages however, the cisco and lake whitefish are indistinguishable based on morphological characters alone with genetic analyses being necessary to reliably identify species. Another notable feature of the lake whitefish is the presence of two small flaps in each nostril. Their coloration is typically silver to white with an olive to pale-green or brown dorsal hues. The ventral fins are white and the tail has a dark posterior edge.

Lake whitefish from inland lakes can reach a weight upwards of 5 pounds (2,300 g); the largest Lake Whitefish caught on rod and reel weighted 15 pounds 6 oz, from Clear Lake Ontario Canada on May 21, 1983, by Chris T. D. Webster according to the Fresh Water Fishing Hall of Fame, in Hayward Wisconsin. On average, the lake whitefish weighs only 4 pounds. They can grow to 31 inches (79 cm) and commonly reach 20 inches (51 cm).

Life history

Habitat

Lake whitefish are cool water fish. They are found in a large number of inland lakes, and they have been known to enter brackish waters. The lake whitefish is distributed from Alaska and western Canada to the Atlantic coastal drainage of Maine and in New Brunswick north to Labrador.

Reproduction

Lake whitefish spawn from September through January in water two to four metres in depth during the night. In the autumn, mature lake whitefish enter the shallows to lay their eggs on shoals of rubble and gravel. There is no parental care of the young. In the following spring the young will hatch. In northwestern Canada, a large spawning migration enters the Athabasca Delta in late summer, moving upstream in the Athabasca River. The longest single movement of a tagged whitefish ever recorded was 388 km (241 mi), from Fort McMurray to the north shore of Lake Athabasca in Alberta, Canada.

Diet

Fish of larval and postlarval stages feed on plankton. Once the larvae reach 3–4 inches (76–102 mm) they switch to feeding on bottom-dwelling animals (snail, insect larvae, zebra mussels, and fingernail clams) which they will consume for the remainder of their lives. In late June and July, some inland lake populations of ciscoes and lake whitefish leave the deep, cool waters to feast on emerging mayflies and midges. The lake whitefish's natural predators include burbot, lake trout, and northern pike.

Fishing

Commercial fishing

Lake whitefish is one of the most important species for commercial inland fisheries in North America. The total annual catch in 1999 from Canada was 8 328 t and USA 5 353 t reported by the FAO.

Lake whitefish is the prime commercial species of the upper Great Lakes fishery, because this delicately flavored fresh fish has high local consumer acceptance. An average of 11 million pounds was harvested from the Great Lakes annually from 1981 to 1999. Although the harvest has declined from 9.5 to 8 million pounds in recent years, prices have not increased. Instead, the price for Great Lakes lake whitefish, which once reached as high as $1.04/lb., currently averages $.75/lb. and has dropped to as low as $.40/lb during periods of high production.

Sports fishing

Many amateur anglers also enjoy hooking this fish in the months of June, July and early August. A simple line and jig system is enough to catch the fish as they feast on mayflies and midges. In winter months, catching whitefish through the ice is very popular, particularly in northern Wisconsin, with many fishing guides specializing in this species. Successful icefishing techniques include using a jigging spoon, with at least one "slider hook" above and separated from the spoon with a barrel swivel, and all hooks tipped with wax worms. Commercial fishing has allowed for the spread of this fish into many different markets, restaurants, and grocery store shelves.

Conservation

A major threat to the lake whitefish is an invasive parasite species, the sea lamprey. It is one of a number of species (in addition to the lake trout and lake herring) aggressively attacked by sea lamprey. In Lake Michigan the sea lamprey began to decimate indigenous fish populations in the 1930s and 1940s. It may have entered the Great Lakes region through the Erie Canal which opened in 1825. and spread even further in 1919 with improvements to the Welland Canal from Lake Ontario to Lake Erie, Lake Michigan, Lake Huron, and Lake Superior.

Evolution

Since the end of the last glaciation (about 12,000 years ago), whitefish have re-colonized many North American lakes, from different directions, from refugia that represent genetically diverged stocks or races. After the invasions, the whitefish have also diversified into different populations locally, such that now in many lakes two main ecotypes are recognized within the species: a normal and a dwarf ecotype. These normal and dwarf ecotypes are mainly differentiated by the benthic and pelagic zone they occupy, respectively. Normal whitefish also grow much bigger and live much longer than the dwarf ecotype.

Many of these populations live in sympatry, yet are reproductively isolated. The fact that they are young species makes them prime candidate to study the evolutionary forces driving their ecological divergence and reproductive isolation.