Our Liviiii^ Hi'.soitiriw — Aquatic F.cosxstems 



245 



Long-term nioiiiioring of lake imut popula- 

 tions relied on ealcli records of commercial 

 fisheries before the populations collapsed. Later 

 monitoring of lake trout populations relied on 

 assessment fisheries to measure the increase in 

 abundance of stt)cked fish and, subsequently, of 

 naturally produced fish. At present, natural 

 reproduction by lake trout has been widespread 

 only in Lake Superior. In contrast, lake trout 

 reproduced in only limited areas of Lakes 

 Huron, Michigan, and Ontario, and only in 

 Lake Huron have progeny survived to adult- 

 hood. We describe the historical collapse and 

 subsequent restoration of lake trout populations 

 in U.S. waters of Lake Superior. We also 

 describe the limited natural repri)duction that 

 has occuiTcd in the other Great Lakes. 



We compiled data describing abundance 

 trends of lake trout in Lake Superior during 

 1929-93, expressed as the number of fish caught 

 in a specified length of gill net. Data sources 

 were for Michigan during 1929-49 (Hile et al. 

 1951), Michigan and Wisconsin during 1950-70 

 (Pycha and King 1975), and Michigan and 

 Wisconsin during 1970-93 (Hansen et al. 1995). 



Fishing was by commercial fishers during 

 1929-58 and by commercial-fisher contractors 

 or state agencies during 1959-93. Lake trout 

 populations in Lake Superior during 1929-43 

 sustained stable yields in commercial fisheries, 

 providing a benchmark for judging restoration 

 status. Therefore, lake trout abundance, 

 expressed as a percentage of the 1929-43 aver- 

 age, directly compares lake trout abundance 

 during the various phases of population collapse 

 and recovery. Hatchery lake trout were all 

 marked by removal of one or more fins before 

 stocking. Thus, we show the abundance of 

 stocked lake trout (one or more fins missing) 

 separately from that of wild-origin lake trout 

 (no fins missing). Comparable data are not 

 available for Canadian waters of Lake Superior. 



Status and Trends 



Lake Superior 



Abundance of wild lake trout in Michigan 

 declined from stable levels in the 1930's to 

 nearly zero in the late 1960"s (Figure; Hansen et 

 al. 1995). In the 1970"s and 1980's, abundance 

 of wild lake trout increased steadily, but in the 

 late I980"s and eariy 1990"s decreased slowly 

 because of increased commercial fishing and 

 sea lamprey predation. The abundance of 

 stocked fish increased in the late I960"s well 

 beyond the 1929-43 average and remained there 

 during most of the 1970"s. 



Abundance of stocked lake trout declined 

 rapidly in the late 1970's and 1980"s and has 

 remained less than 10% of the 1929-43 average 



250 



200 - 



— Total 



Michigan 



— Stocked 



- Wild 



" 150 



29 33 37 41 45 49 53 57 61 65 69 73 77 81 85 89 93 

 Year 



29 33 37 41 45 49 53 57 61 65 69 73 77 

 Year 



85 89 93 



since 1988. Stocked lake trout reproduced in the 

 late 1960"s and produced an increased abun- 

 dance of wild fish in the 1970's and 1980's. 



The key to this successful natural reproduc- 

 tion was the presence of abundant inshore 

 spawning grounds that inexperienced stocked 

 lake trout easily located. Also, the decline in 

 abundance of wild lake trout in the late 1970's 

 and 1980"s was evidently due to the earlier 

 decline in stocked lake trout. The decline was 

 less severe, however, because of reproduction 

 by wild fish, the progeny of the first stocked 

 spawners. 



By 1993. 80%-90% of the lake trout in 

 Michigan were wild, but abundance of wild lake 

 trout was only 61% of the 1929-43 average. 

 Fishery management agencies defened lake 

 trout restoration in eastern Michigan (Whitefish 

 Bay) so that court-affirmed Native American 

 fisheries could maximize their harvest in that 

 area. 



In Wisconsin, abundance of wild lake trout 

 declined irregularly through 1968 and increased 

 after that (Figure; Hansen et al. 1995). The 

 abundance of wild lake trout in Wisconsin, even 

 at its lowest point, remained higher than in 

 Michigan in the late I960"s. Increased abun- 

 dance in the I970"s was mostly of stocked lake 

 trout, as in Michigan, and peak abundance also 

 greatly exceeded the 1929-43 average. The 

 abundance of stocked lake trout declined earlier 

 than in Michigan, though not as much, and 

 remained at 19% of the 1929-43 average. 



Abundance of wild fish in Wisconsin 

 increased irregularly from the 1970's through 

 the early 1990's, but remained lower in 1993 

 than in Michigan and was only 53% of the 



Figure. Abundance of stocked 

 and wild lake trout {Siilveliniix 

 iiamayciish) in Michigan and 

 Wiscon.sin waters of Lake 

 Superior in 1929-93. expressed as 

 a percentage of the 1929-43 mean 

 (from Hansen et al. 1995). 



