LAKE TROUT RESTORATION IN THE GREAT-LAKES - STOCK-SIZE CRITERIA FOR NATURAL REPRODUCTION

We examined the question of whether the lake trout restoration program in the Great Lakes has developed brood stocks of adequate size to sus tain natural reproduction. Stock size criteria were developed from are as of the Great Lakes where natural reproduction has been successful ( defined as detection of age-1 or older recruits by assessment fishing) . We contrasted them with stocks in areas with no natural reproduction . Based on the relative abundance of spawners measured in the fall and the presence or absence of natural reproduction in 24 areas of the Gr eat Lakes, we found three distinct sets of lake trout populations. In seven areas of successful natural reproduction, the catch-per-unit-eff ort (CPE) of spawners ranged from 17 to 135 fish/305 m of gillnet. Sto ck sizes in these areas were used as a gauge against which stocks in o ther areas were contrasted. We conclude that stock densities of 17-135 fish/305 m of gill net are adequate for natural reproduction, provide d that all other requirements are met. No natural reproduction has bee n detected in seven other areas, where CPEs of spawners ranged from on ly 3 to 5 fish/305 m. We conclude that spawning stocks of only 3-5 fis h/305 m of net are inadequate to develop measurable natural reproducti on. Natural reproduction has also not been detected in ten areas where CPEs of spawners ranged from 43 to 195 fish/305 m of net. We conclude that spawning stocks in these ten areas were adequate to sustain natu ral reproduction, but that some factor other than parental stock size prevented recruitment of wild lake trout.