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Seldom seen native sucker occurs in Kenai lakes

Posted: December 13, 2012 - 6:04pm
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Photo by Doug Palmer, USFWS Mature semi-dwarf Longnose suckers from Wolf Lake (below) are 50 percent shorter and 80 percent lighter than normal-sized Longnose suckers from Kelly Lake (above).
Photo by Doug Palmer, USFWS Mature semi-dwarf Longnose suckers from Wolf Lake (below) are 50 percent shorter and 80 percent lighter than normal-sized Longnose suckers from Kelly Lake (above).

Years ago, during a visit to Kelly Lake in late May, I noticed swirls and upwellings in front of the boat launching ramp. From a willow bush at the water’s edge, I was able to see at least 50 actively spawning Longnose suckers. I was familiar with this fish since I’d worked with them previously in Yellowstone National Park where they were stream spawners. This was my first observation of lake spawning by this species.

There are 23 recognized species of suckers in North America. Our species, the Longnose sucker (Catostomus catostomus), occurs in freshwater from the Atlantic to the Pacific coasts, and as far north as the Arctic coast in Alaska and northwestern Canada. This is the only sucker that has made it across the Bering land bridge and occurs in northeastern Siberia.

On the Kenai Peninsula, Longnose suckers are known to occur in at least 60 lakes associated with several watersheds: Beaver Creek, Bishop Creek, Chickaloon River, Moose River, Swanson River, and the Finger Lakes. Suckers have not been reported from lakes tributary to the Kenai River upstream from the Moose River or from any lake or stream south of the Kenai River. The absence of suckers from these areas suggests that Longnose suckers did not reach the lower Kenai River until long after trout and salmon colonized these same waters after glaciers receded 10,000 or so years ago.

Longnose suckers are a cold water species with a preferred temperature of 53 degrees F. This is a large sucker, growing to almost 22 inches and 5.6 pounds on the peninsula. Males mature a year earlier than females. Females live longer, up to 28 years in Kelly Lake, and grow larger.

Spawning occurs at 55-60 degrees, most successfully on gravel-bottomed streams tributary to lakes. Their eggs are scattered in shallow water over gravel and rocks up to 8 inches wide. Incubation is rapid, with eggs hatching in about 8 days at 59 degrees. The fry stay in the gravel for 1-2 weeks after hatching, before drifting downstream (if hatched in inlet streams), primarily at night. Sucker fry feed on zooplankton but expand their diet to freshwater shrimp and aquatic insects as they mature.

An unusually small Longnose sucker occurs in a cluster of four land-locked lakes in the Finger Lakes, as well as the open-basin Wolf Lake, on the Kenai National Wildlife Refuge. In 2003, Refuge staff, several volunteers and I conducted a preliminary study in which we compared the semi-dwarf form with normal-sized suckers from Kelly and Sucker Lakes.

Mature semi-dwarf suckers were about 50 percent shorter in length and 80 percent lighter in weight than normal suckers. By looking at fork lengths in relation to age as determined by counting annuli (growth rings) on opercular bones, we found that semi-dwarf suckers have slower growth rates and reduced longevity. There was good evidence to suggest that semi-dwarf suckers spawn later and perhaps for a longer period than normal suckers.

This kind of size and life history dimorphism typically occurs as a result of geographic isolation. All evidence indicates that the Finger Lakes were land-locked before the 1964 Good Friday Earthquake, as they are now. In contrast, Wolf Lake is now part of an open system that drains into the Swanson River. The presence of semi-dwarf suckers in Wolf Lake and upstream in the Finger Lakes suggests that a connection has existed in the past. Water levels in the West Finger Lake would have to be substantially higher for overflow towards Wolf Lake to occur now.

The Conservation Genetics Lab in the Anchorage office of the U.S. Fish and Wildlife Service has explored the genetic relationships among these different populations. Looking at 165 alleles from 10 loci, semi-dwarf suckers from the East and West Finger Lakes were, in fact, more closely related than they were to fish from Wolf Lake. Surprisingly, normal suckers from Kelly and Sucker Lakes were as genetically different from each other as they were from the semi-dwarf form found in the Finger and Wolf Lakes.

There are still many questions surrounding these two apparent forms of Longnose suckers on the Kenai Peninsula. Did the Finger Lakes semi-dwarf sucker evolve from the normal-sized form since the end of the Wisconsin glaciation and become smaller because of some unusual set of physical, biological or limnological conditions unique to this cluster of lakes? Or perhaps the semi-dwarf sucker was the first one to colonize the Kenai Peninsula after the last (Wisconsin) glaciation and has persisted as a small form because of isolation? If they reached the Kenai Peninsula as a small form, where did they come from? Are there semi-dwarf sucker populations elsewhere in the Cook Inlet Region that could have served as the source? 

As a retired fisheries biologist, I never get tired of wondering about the ecology of our fisheries here on the Kenai. My hope is that some young biologist will come along and figure this all out.

 

Jack Dean is a former fisheries biologist with the U.S. Fish and Wildlife Service. He has studied fish on the Kenai Peninsula for 28 years. You can find more information about the Refuge at http://kenai.fws.gov or http://www.facebook.com/kenainationalwildliferefuge.

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