Cottus bairdii
mottled sculpin

Mottled sculpin are widespread in North America, with a broadly disjunct range. Eastern populations occur throughout the Great Lakes region, north to Hudson Bay and throughout much of eastern Canada and south to northern Alabama and Mississippi. There is a disjunct population in Missouri and a large western population in the northern Rocky Mountain states, from British Columbia and Alberta south to southern Nevada and northern New Mexico. (Becker, 1983; Froese, 2008)

Mottled sculpin are found in gravel bottoms and sandy riffles of small headwaters, streams, and small rivers or in rocky shoreline areas of lakes, including the Great Lakes. The type of bottom may be less important than the presence of cover, which can be gravel, stones, or submerged vegetation. They can be found at up to 16 meters depth. Mottled sculpin seem to prefer depths of 0.1 to 0.5 meters and cold, clear water. (Becker, 1983; Froese, 2008)

Mottled sculpin are small, stout fish with relatively flattened bodies. They have round snouts and are cryptically colored, with brown to black mottling on their backs, sides, and fins and whitish bellies. They have 2 dorsal fins, the first with 6 to 9 soft spines and the second with 17 to 19 rays. There is a small black spot on the first part of the first dorsal fin, which helps to distinguish them from round gobies, and a larger spot on the back of the first dorsal fin. They do not have obvious scales, although they have a line of small prickle-like scales below their lateral line, which is incomplete and ends just under the second dorsal fin. Males are slightly larger than females and during the breeding season males have a dark band on the first dorsal fin and a broad, orange band on the edge of the fin. (Becker, 1983)

Mottled sculpin egg development depends on water temperature, at temperatures of 11 to 13 degrees Celsius eggs hatched in 17 days. Mottled sculpin larvae are about 5.9 mm in length when they hatch and leave the nest when they reach about 6.7 mm long and have used up their yolk sac, at about 14 days after hatching. (Becker, 1983)

Average recorded lifespan in mottled sculpin is 2 years. (Froese, 2008)

Mottled sculpin are found in areas with fast water movement, their flattened body shape helps them to take refuge from fast currents among the rocks and debris along the bottom. They take refuge during the day under rocks or vegetation. In the still areas along lake shores they may stir up the sand and let it cover them to hide. They swim in small, darting motions which make it seem as if they are hopping from one spot to the next. Outside of the breeding season mottled sculpin are not aggressive and can often be seen near or next to each other. They may occur at densities of up to 5 per square meter. Mottled sculpin are more active at night, feeding in open areas. (Becker, 1983)

Mottled sculpin are found in areas with fast water movement, their flattened body shape helps them to take refuge from fast currents among the rocks and debris along the bottom. They take refuge during the day under rocks or vegetation. In the still areas along lake shores they may stir up the sand and let it cover them to hide. They swim in small, darting motions which make it seem as if they are hopping from one spot to the next. Outside of the breeding season mottled sculpin are not aggressive and can often be seen near or next to each other. Mottled sculpin are more active at night, feeding in more open areas.

Home Range

In a dense population of sculpin in Montana, home range sizes were estimated at less than 50 meters and the longest movements were 180 meters. (Becker, 1983)

Based on courtship behaviors, visual and tactile cues are likely to be used by mottled sculpin in communication. They may also have good chemoreception, as in most fish. Mottled sculpin have a lateral line system that helps them to perceive water movements and pressure changes. (Becker, 1983)

Mottled sculpin eat mainly aquatic insect larvae, such as mayfly nymphs, caddisfly larvae, stonefly larvae and midges, but also eat small crustaceans, such as amphipods, copepods, and ostracods, they also eat leeches, smaller fish, fish eggs, and some aquatic plant material and algae. (Becker, 1983; Froese, 2008)

Mottled sculpin have been reported as prey by brook trout, brown trout, northern pike, common mergansers, and water snakes. They are also likely prey of wading birds, such as herons.

Mottled sculpin are very important intermediate predators in native aquatic ecosystems. They prey on small aquatic animals, mostly invertebrates, and form an important prey base for larger fish, such as brook trout and northern pike. They may also help trout populations through their predation on stoneflies, which each trout eggs and young. Mottled sculpin are hosts for the glochidia of several native clam species, including cylindrical papershells and slippershell mussels. Mottled sculpin may compete directly with round gobies, an invasive species in the Great Lakes. (Becker, 1983)

Mottled sculpin are very important intermediate predators in native aquatic ecosystems. They prey on small aquatic animals, mostly invertebrates, and form an important prey base for larger fish, such as brook trout and northern pike. They may also help trout populations through their predation on stoneflies, which each trout eggs and young. Mottled sculpin are hosts for the larvae of some native clam species, including cylindrical papershells and slippershell mussels. Mottled sculpin may compete directly with round gobies, an invasive species in the Great Lakes.

There are no negative effects of mottled sculpin on humans. Some have regarded them as serious predators of trout eggs, but research suggests that their predation on trout eggs is usually on drifting eggs that won't develop anyway. Healthy mottled sculpin populations are used as an indicator of healthy trout populations because they are important prey of trout. (Becker, 1983)

Healthy populations of mottled sculpin are used as an indicator of healthy trout populations, which are very important gamefish. Mottled sculpin have been demonstrated to have a positive effect on trout populations through preying on stoneflies, which prey on trout young and eggs, and because they are important prey for large trout. (Becker, 1983)

Mottled sculpin populations are not considered threatened currently. This is a widespread species with large populations. However, introduced round gobies may dramatically effect mottled sculpin populations through predation and competition. (Becker, 1983)

Mottled sculpin are also known as common sculpin, northern muddler, muddler, blobs, gudgeons, muffle-jaws, bullheads, springfish, lake sculpin, spoonheads, and miller's thumbs. Their generic name, Cottus, is from an old European name for sculpin. (Becker, 1983)