Recruitment Dynamics of Lake Trout in Western Lake Superior during 1988–1995

Abstract

Stocks of lake trout Salvelinus namaycush in Lake Superior are recovering from historical collapse. Stocking, control of sea lampreys Petromyzon marinus, and harvest restrictions have aided lake trout recovery, but the contribution of stocked lake trout to contemporary recruitment has not been quantified in western Lake Superior. Using variants of the Ricker stock-recruit model, we evaluated the production of age-7 lake trout (recruits) by examining age-8 and older wild and stocked parental lake trout (spawners). We found that density of wild lake trout spawners and recruits increased during 1980-2003, whereas the density of stocked spawners decreased in all management areas. Two competing models best described recruit density of the 1988-2003 year-classes: (1) wild and stocked parents each contributed to recruitment but stocked parents contributed negatively and (2) only wild parents contributed to recruitment. Recruitment rates declined significantly with increasing spawner density in four of five management areas, which suggests that recruitment is density dependent in much of western Lake Superior. We conclude that stocked lake trout did not contribute significantly to lake trout rehabilitation in western Lake Superior during 1980-1995.

Can pelagic forage fish and spawning cisco (Coregonus artedi) biomass in the western arm of Lake Superior be assessed with a single summer survey?

“…Results from night acoustic surveys in 1997 indicated that daytime bottom-trawl biomass estimates were likely conservative (Mason et al, 2005), as hypothesized by Negus (1995), and thus the likely cause of the D-S discrepancy. Corradin (2004) found growth of wild lake trout in the Apostle Islands region of Lake Superior (Fig. 1) decreased significantly from 1980 to 2003, but varied without trend in the rest of the western arm, suggesting that lake trout in some parts of this region may be experiencing food limitation when compared with the past.…”

“…Bronte et al (2003) and Wilberg et al (2003) provided evidence that lake trout numbers in Lake Superior gradually increased from 1970 to 1999 with present population levels exceeding historical levels in some regions. Corradin (2004) documented evidence of density dependent recruitment of wild lean lake trout in the western arm of Lake Superior, evidence that most stocks in this region have been rehabilitated. The deepwater morphotype of lake trout, siscowet, has also recovered and is much higher in abundance than lean lake trout .…”

Modeling the sustainability of lake trout fisheries in eastern Wisconsin waters of Lake Superior

“…Abundance of wild lake trout from unknown parentage generally increased during 1970-1992(Hansen, 1990Hansen et al, 1994b), but abundance of stocked lake trout decreased despite relatively consistent stocking rates (Hansen et al, 1994a,b). An early stock-recruitment analysis indicated that stocked lake trout contributed to recruitment more than wild lake trout (Hansen et al, 1995), but subsequent analyses indicated that wild and stocked lake trout contributed equally to recruitment in Michigan waters (Richards et al, 2004) and wild lake trout drove recruitment in Wisconsin and Minnesota waters (Corradin et al, 2008). Survival of the 1963-1986 year-classes of stocked lake trout was limited by large-mesh gill-net fishing in Michigan and Wisconsin waters and by wild lake trout predation in Minnesota waters .…”

“…We developed an age-structured, density-dependent model to simulate long-term effects of various commercial and recreational harvest allocations. The model focused on the wild lean lake trout morphotype because this morphotype is the most highly sought by commercial and recreational fisheries, and because stocking was discontinued in our study area in 1996 and wild lake trout drive recruitment (Corradin et al, 2008).…”

Lake trout (Salvelinus namaycush) suppression for bull trout (Salvelinus confluentus) recovery in Flathead Lake, Montana, North America

“…Lake trout stock-recruitment is over-compensatory (Hansen et al, 1997a;Richards et al, 2004;Corradin et al, 2008), so the number of age-0 lake trout N i?1, j=0 that recruited to the population in each year i ? 1 was predicted from the number of adult lake trout N i,j=8?…”