By Dr. David Wartinbee, for the Redoubt Reporter
Photo courtesy of Dr. David Wartinbee. Sculpin are found in many of our streams and lakes. They are bottom dwellers and can be an important predator, as well as important food items for a number of larger fish.
Many a halibut fisherman has pulled up a multicolored fish called an Irish lord. These fish have a big flat head, an equally rounded belly, a short tail and looks that only a mother could love. If you have ever seen one, you know exactly what I’m talking about.
When we leave the ocean habitat and look in our streams and lakes, the basic creatures are found there, too, but in much smaller form. Both the marine and freshwater versions are called sculpins, although they may be categorized into several different genera.
Those found in Alaska’s fresh waters are in the genus Cottus. These fish do not have scales and they are also missing a swim bladder to adjust their body buoyancy. So they are pretty much stuck on the bottom wherever they live. Perhaps the most obvious trait of all the sculpins is their enormous pectoral fins. These lateral fins are a primary means of propulsion and movement around the bottom. The combination of large pectoral fins and a weakly powered caudal tail causes them to swim in a jerky, stop-and-start fashion.
The sculpins found in most Alaska streams and lake bottoms are Cottus cognatus, or the slimy sculpin. They only reach 3 to 5 inches in length during their three- to six-year lifespan. Slimy sculpins are found all across North America, but there is some confusion, and probably some hybridizing, between other closely related species.
No matter what name we give them, these tiny fish play a big role in our streams and rivers because they are very abundant. They are active predators in the stream and, in turn, they provide food for a number of our favorite sport fish, like rainbow and lake trout.
Since they aren’t proficient swimmers, sculpins wedge themselves in between a couple rocks and wait for the current to bring them food. They also use their large pectoral fins to create downforce to prevent them from being washed away by the moving water. When a possible food item drifts by, they simply open their large mouth and dinner is served.
Research done on an almost indistinguishable close relative (Cottus bairdi) on the East Coast indicates that their food preferences include anything they can get into their mouth. Stomach analyses found a variety of aquatic insects, aquatic worms and various fish. Many of those fish were smaller relatives. In the world of sculpins, cannibalism is alive and well.
Within streams, the youngest members of the population remain in the shallowest sections to avoid their hungry, older relatives. As they grow larger and are less likely to become someone’s dinner, they move into deeper-water sections. As they continue to grow, they eventually move into even deeper parts of the stream. The deepest water is where the most food items are drifting by and there is less predation from above the water.
Sculpins usually breed in spring with the male selecting a rock-covered area. He uses his tail to excavate a small area and to clear away any silt. During mating season, the males acquire a darker, almost black pigment. A female who is appropriately impressed with the redd will attach a few eggs to the underside of the rock and be on her way. It is likely that several females will contribute to the clutch of eggs. The males protect the eggs from possible predators and fan away silt until the eggs hatch. Once the eggs hatch, the young scatter around and seek out safer, shallow stream areas.
Many stream fishermen are aware that an egg-sucking leech fly pattern works well in the spring and early summer. The reason is it mimics the jerky swimming patterns of darkened, breeding sculpins. Other colors, like green leech patterns, are mimicking the coloration of sculpins during other color phases. So sculpins turn out to be a favorite food item for Dolly Vardens, rainbow and steelhead trout.
Sculpins are found in a large number of Alaska lakes, as well. There, sculpins are ambush predators on a variety of amphipods, insects and worms. Researchers on some of our high-latitude lakes have found that sculpins are a very important food item for lake trout populations. During winter months, sculpins can be their major food source.
The next time you catch an Irish lord, remember that there are miniature versions found in local streams and lakes. While much smaller than their marine relatives, they play a very big role in the local food web.
David Wartinbee, Ph.D, J.D., is a biology professor at Kenai Peninsula College’s Kenai River Campus. He is writing a series of columns on the ecology of the Kenai River and Cook Inlet watershed.
The Mouth of The Kenai 