Biological Projects

Life History of Togiak River Dolly Varden:

Dolly Varden (Salvelinus malma) populations on Togiak National Wildlife Refuge support important subsistence and sport fisheries. Due to the importance of these resources, and concerns about population status, a long term study to document the habitat areas and population characteristics of Dolly Varden in the Togiak River drainage was initiated in 1998.

Dolly Varden were captured using seine nets, hoop traps, hook and line, and minnow traps. In 1998, 1,240 Dolly Varden were captured; 2,501 were captured in 1999. Fish over 11.7 inches (300 mm) in length were marked. In 1998, 942 Dolly Varden were marked (97 with radio tags); 1,409 were marked in 1999.

Togiak Refuge staff estimate that Togiak River Dolly Varden reach maturity at age 2-8, most doing so by age 4. This estimate is based on length frequency distributions, otolith microchemistry and known maturity index of sacrificed fish. Otoliths are bony structures in the heads of Dolly Varden that accumulate elements differently in freshwater than in saltwater. Analysis of otoliths allows biologists to determine the periods of time Dolly Varden spend in each habitat. In Dolly Varden from the Togiak River, 54 out of 55 fish subjected to otoliths microchemical analysis were anadromous, having spent time in marine or estuarine waters. These Dolly Varden made their first seaward migration at age 0 - 3. None of the 13 Arctic char included in this analysis showed signs of marine or estuarine residence. The photo at left shows an otolith cross-section; the black line shows the transect of the electron microprobe used to analyze the otolith.

Beginning fall of 1998, 97 fish were radio tagged and tracked in an effort that continued until October 1999. Eighty of these fish were prespawners and provided spawning site locations by inference of their movements into and out of tributary streams. Spawning occurred in all but one tributary stream, and in the upper half of the main Togiak River. Spawning is estimated to occur between mid-September and mid-October. Fifty-one separate spawning areas where identified.

All fish overwintered in the main Togiak River and Togiak Lake between November 1998 and April 1999. Overwintering fish consisted of a mix of all spawning groups. Fifty-seven fish (59 percent) survived until spring and exited the Togiak River to saltwater between May 5 and June 21, 1999. Thirty-one radiotagged fish returned to the Togiak River between July 7 and August 23, 1999, after having spent an average of 40.5 days at sea. One fish was never documented to leave the Togiak River. Two fish were harvested at sea in other areas of Bristol and Kuskokwim Bays.

Dolly Varden tagged in the Togiak River have continued to show up in other river systems in southwest Alaska. So far fish have been caught in the Egegik, Yukon, Kanektok, and Arolik rivers.

Returning fish exhibited apparent homing instinct to spawning streams and consecutive year spawning. Of 26 fish thought to spawn in 1998, 23 (88.5 percent) spawned in the same area in 1999.

In 2000 and 2001 tissue samples were collected from individual spawning groups of Dolly Varden from three tributaries to the Togiak River and subjected to genetic analysis. Mature, prespawning fish were captured using nets, and a small (1 cm²) piece of tissue was cut from one of the lower fins. Using DNA analytical techniques, geneticists in the U.S. Fish and Wildlife Conservation Genetics Laboratory were able to distinguish Togiak tributary populations from each other and from populations sampled in other Alaska waters. Continuation of this work to identify other spawning groups in southwest Alaska will eventually allow biologists to estimate population contributions to subsistence catches and large overwintering mixtures.

For more information on the Life History of Togiak River Dolly Varden, contact the Togiak National Wildlife Refuge.

Last updated: July 24, 2008