Crooked Lake is in Ecological Lake Class 1, which consists of 34 lakes in northeast Minnesota that are large, very deep, have irregular shoreline shapes, and have soft (unmineralized) and clear water. Crooked Lake is larger than most of the lakes in this lake class.
Crooked Lake was thermally stratified on 7/9/2007 with surface temperatures about 72 F and bottom temperatures of 46 F in Friday and Sunday bays, and 41 F in Thursday Bay. Adequate oxygen for cold-water fish species (more than 5 ppm) was present to near the bottom in all three basins.
Fish populations in 2007 were sampled with 15 standard gillnets and 3 smelt gillnets (100' x 6' x 0.375" bar mesh and 100' x 6' x 0.5" bar mesh). Two previous investigations, in 1983 and 1995, used 16 and 15 standard gillnets, respectively. Small mesh smelt gillnets were also used in the 1995 investigation. The smelt nets were set in or below the thermocline. No fish of any species were caught in the smelt nets in 1995 or 2007.
The inshore depths of the standard gillnets in 2007 ranged from 8 ft to 25 ft (average of 19 ft), while the offshore depths ranged from 10 ft to 55 ft (average of 33 ft). The thermocline in Crooked Lake in 2007 ranged from 20 ft to 50 ft.
The total fish catch (all species combined) in 2007 of 24 fish/gillnet (31 lb/gillnet) was in the third quartile for this lake class and was very similar to previous total fish catches in Crooked Lake. Fish populations in 2007, as in previous investigations, were dominated by walleye and northern pike. Fewer ciscos were caught in 2007 than in previous investigations, but more black crappie and walleye were caught. Smallmouth bass are likely more abundant in Crooked Lake than indicated by the gillnet catch. Bass are "net-shy" and tend to avoid standard sampling nets.
Walleye numbers in 2007 (6.7/gillnet) were in the third quartile for this lake class and were higher than the walleye catches of 3.4/gillnet in 1983 and 4.4/gillnet in 1995. Walleye sizes in 2007 averaged 13.2" (1.1 lb), which was at the first quartile for this lake class and was smaller than the average size of 14.6" in previous investigations on this lake. The largest walleye caught in 2007 was 29.5". Most of the walleye (61 percent) were age three, from the 2004 year-class. Growth of walleye from the strong 2004 year-class was slower than normal by area standards, but growth of walleye from other year-classes appeared to be normal.
Northern pike numbers in 2007 (4.9/gillnet) were in the fourth quartile for this lake class and were higher than previous pike catches of 2.6/gillnet in 1983 and 4.4/gillnet in 1995. Pike sizes in 2007 averaged 23.3" (3.1 lb), which was in the second quartile for this lake class and was similar to pike sizes in previous investigations on this lake. The largest pike caught in 2007 was 38.5". Many of the pike (37 percent) were age four, from the 2003 year-class. Pike growth appeared to be erratic and no conclusion could be made about growth rates.
Cisco numbers in 2007 (3.1/gillnet) were in the second quartile for this lake class and were lower than the average cisco catch of 9.4/gillnet in previous investigations on this lake. Cisco sizes in 2007 averaged 7.5"; the largest cisco was 12.4".
Black crappie numbers in 2007 (1.7/gillnet) were higher than the average crappie catch of 0.1/gillnet in previous investigations on this lake. Crappie sizes in 2007 averaged 9.7"; the largest crappie was 12.7".
Smallmouth bass numbers in 2007 (1.3/gillnet) were in the third quartile for this lake class and were higher than the average smallmouth catch of 0.3/gillnet in previous investigations on this lake. Smallmouth sizes in 2007 averaged 14.8"; the largest smallmouth was 19.2". Most of the smallmouth (86 percent) were age five, from the 2002 year-class. Smallmouth growth was faster than normal by area standards.
Sauger numbers in 2007 (0.1/gillnet) were lower than the average sauger catch of 1.3/gillnet in previous investigations on this lake. Sauger are uncommon in the area, being confined to sparse populations in Crooked Lake, Iron Lake, Lac La Croix, and lakes downstream to Lake of the Woods, where they are fairly abundant.
Many of the smallmouth bass examined in 2007 had bass tapeworm larvae in their viscera, and some of the northern pike were infected with neascus. Neascus (black spot) and bass tapeworm are common parasites that are native to the area. They cannot infect humans, are often removed by filleting fish, and are killed at temperatures used to cook fish.
- Spiny Waterflea
Recreational activities such as recreational boating, angling, waterfowl hunting, and diving may spread aquatic invasive species. Some aquatic invasive species can attach to boats, while others can become tangled on propellers, anchor lines, or boat trailers. Many species can survive in bilge water, ballast tanks, and motors or may hide in dirt or sand that clings to nets, buckets, anchors, and waders. Fortunately, completing simple steps can prevent the transport of aquatic invasive species.