Spawning Site Water Chemistry and Lake Trout (Salvelinus namaycush) Sac Fry Survival during Spring Snowmelt

During the spring of 1982, lake trout (Salvelinus namaycush) sac fry were incubated at a spawning bed in a pH 5.7 lake with a history of lake trout recruitment failure. Four short episodes of substantial pH depression occurred at the spawning site. Observed sac fry mortalities (18%) occurred primarily during the longest depression (5 d at pH 4.5–5.0), which coincided with maximum surface runoff and peaks in concentrations (~50 μg/L) of inorganic (monomeric) Al. Although most mortalities were coincident with low pH and elevated inorganic Al concentrations, the high survival (82%) demonstrated that under natural conditions most sac fry could tolerate pH <5.0 and inorganic Al concentrations of 40–50 μg/L for at least 5 d. Substantially higher concentrations of inorganic Al (~80 μg/L) were observed in the interstitial waters of the spawning rubble than in ambient waters, which indicated that fry within a spawning substrate may be subjected to more toxic conditions than test fry in incubators above the substrate surface.