**The title, authors, and abstract for this completion report are provided below.  For a copy of the completion report, please contact the GLFC via e-mail or via telephone at 734-662-3209**



The reproductive cycle of Lake Superior siscowet lake trout

Frederick W. Goetz2, Shawn P. Sitar3, Charles R. Bronte4, Penny Swanson5


2 Great Lakes WATER Institute

U. Wisconsin-Milwaukee

600 E. Greenfield Av.

Milwaukee, WI, 53204


3Marquette Fisheries Research Station

Michigan Department of Natural Resources

484 Cherry Creek Rd.

Marquette, MI, 49855


4U.S. Fish and Wildlife Service

Green Bay Fish and Wildlife Conservation Office

2661 Scott Tower Drive

New Franken, WI 54229


5Northwest Fisheries Science Center

National Marine Fisheries Service

2725 Montlake Blvd. East

Seattle, WA 98112


May 2010



Lean and siscowet lake trout (Salvelinus namaycush) morphotypes in Lake Superior are thought to be genetically separate but the reproductive isolating mechanism is unknown. In this project we tested the hypothesis that lean and siscowet lake trout are reproductively isolated by differences in the seasonal timing of reproduction. The testicular and ovarian cycle of these morphotypes were determined monthly from May to October in siscowet and lean populations east of the Keweenaw Peninsula, and in May, August and October in lean and siscowet populations west of the Keweenaw Peninsula. At each sampling time, total length, weight, sea lamprey wounding, sex, visceral fat index, gonad maturation (gross examination and digital photography) and total gonad weight were recorded from each fish. Gonadal samples were collected from each fish for histological analysis, and a blood sample was analyzed for estradiol 17β (E2:females) and 11-ketotestosterone (11KT:males) and pituitaries for gonadotropin beta subunit transcript levels. In addition, during September and October of 2008, ovaries from 17 leans and 25 siscowets were collected to assess fecundity. The gonadosomatic indexes (GSIs; gonad wt/body wt X 100) for maturing females and males of lean and siscowet lake trout east of the Keweenaw and for siscowet west of the Keweenaw all increased from July to October. Thus, there appears to be little difference in the timing of gonadal maturation between lean and siscowet lake trout, suggesting that morphotypes in these populations are not genetically isolated by reproductive timing. GSIs and histological analyses of the gonads indicate that a significant proportion of lean and siscowet lake trout in these populations do not reproduce each year. While the amount of spawning omission appears to be about 20% of the population for each morphotype, exact figures will require additional sampling over broader ranges of sizes since this study was restricted in terms of the size of fish sampled. The percent of spawning omission is likely to be much higher, particularly for female siscowets. Fecundity was significantly higher in lean versus siscowet lake trout even though siscowets were approximately twice as old. Lean fecundity was slightly lower than that measured historically, and is likely related to density-dependent declines in growth due to higher total lake trout populations and lower prey biomass. E2 and 11KT levels generally mirrored the changes in GSIs for both siscowets and leans; however, while E2 levels increased gradually and continuously from June to October, 11KT levels increased more abruptly in September even though there was a large increase in the testicular GSIs in August. This suggests that testosterone production lags behind the development of the testis. The beta chain of the lake trout luteinizing hormone (LH) and follicle stimulating hormone (FSH) were cloned and quantitative polymerase chain reaction assays were developed for both. When analyzed on a whole pituitary level, FSH beta subunit transcript levels were low in May and June, increased in August and September and then declined in October. This increase coincided with the largest increases in GSI. Transcripts for the LH beta subunit were not observed in pituitaries until October and only in some individuals. Overall, the results show that siscowet reproduction is synchronous in a population and at least for the populations we analyzed, maturation of the gonads occurs from July to October and is similar to the timing of lean lake trout reproduction.