AGE DETERMINATION- FROM SCALES OF LAKE TROUT 

 Table 2. — Recoveries of •■ iiicirhed" liike trout from Lake Miehuion. hi/ i/eor of eiipliire 



' Includes 2 fish from pxtromo northern part of area 7. Sec figure .') for biiuiiilaries of the statistical areas. 

 2 See table t for number of marked lake trout released. 



Marked lake trout captured by fishcnncn in 

 Micliijian waters of Lake Michigan weio de- 

 livered to local conservation officers who recorded 

 data given l>y the fishermen. Initially, the 

 officers removed the fin scar from each fish (in 

 some cases, also a scale sample) and sent them to 

 the Institute for Fisheries Research of the Michi- 

 gan Department of Conservation in Ann .\rl)or 

 for payment of the reward. Later, however, most 

 of the fish weic shi])ped iced, either in the round 

 or (hcssed," to the Institute where the scale sam- 

 ples were taken, measurements recorded, and the 

 deformed or missing fin described in some detail. 

 Sex was not recorded. 



Vp to July 22, 1952, 1,603 fish had been sent 

 to the Institute for Fisheries Research. Of this 

 number, 96 could not be identified with any one 

 of the three plantings or lacked essential records: 

 ?'. e., record of the missing fin was lacking, the fin 

 or combination of fins rcporteil missing or ab- 

 normal had not been used in the experiment, or 

 fins were reported by the State observer as normal 

 in every resptH't, length measurement was not re- 

 coi-ded, or scale sample was not taken. 



For the 1 ,.507 fish that, on the basis of fin records 

 alone, could have been marked lake trout, the 

 annual recoveries were as given in table 2. Al- 

 though this group includes individuals with 

 "natinally (h'formed" fins (malformations not 

 resulting from earlier clipping), tlie data of table 

 2 give a rougii estimate of th(> percentage return 

 from the several [jhnitings. Because it is (loui)tful 

 that the recoveries from area 8 were fish with l)()na 

 fi(h" markings, the percentage of returns arc shown 

 for aieas 1-6 only. Recoveries from the 1945 

 planting exceech'd those from the 1946 planting 

 almost 4:1, aiul c.Nreeded recovei-ics from tile 1944 



" tvills and \ iseera n'lnoveil. 



planting 11:1. but the I'ccoveries of marked lake 

 trout from all plantings were in exceedingly small 

 percentages of the numbers of fish released. 

 About 0.67 percent of the marked lake trout re- 

 leased in 1945 but only O.Oti percent of the 1944 

 planting and O.IS percent of those planted in 1946 

 were recovered. The low |)ercentages of return 

 and abrupt termination of ca|)tiires probably were 

 due to the rapid reduction of the population by 

 the sea lamprey. Xo explanation can be ottered 

 for the higlu'i- percentage of return irom the 1945 

 than from the 1944 and 1946 plantings. 



A large majority of the recoveries of marked 

 lake trout in northern Lake Michigan (areas 1-6) 

 were made in the fourth year after planting. 

 The fish had evidently reached a sufficiently large 

 size at that age to be most easily caught in the 

 nets employed in the fishery at the time. 



The localities and relative numbers of recov- 

 eries are shown in sectional maps of Lake Michigan 

 (figs. 1 and 2). Bouiithiries of tliese sections are 

 superimposed on a map of tiic entire lake (fig. 3) 

 to indicate their position with reference to the 

 houiuhiries of the statistical areas or districts 1-8 

 regularly employed in analyses of commercial 

 fishery statistics for the State of Michigan waters 

 of Lake Michigan (Van Oosten, Hile. and .lobes 

 1946; Hile, Eschmeyer, and Lunger 1951). 



The largest catclies of niaiked lake trout were 

 made out of Manistitiue, Mich., in area 2, and in 

 the vicinity of the islands of areti 3, with the great 

 est concentrati'in about lieaver Ishiiid and tiie 

 shoals to the east of tiiis island. A few s[)ecinieiis 

 were caught in each of areas 1, 5, and ti; 2 trout, 

 taken just across tlie line in tiie northern i)art of 

 area 7 by fisliernieii from I'entwater, are included 

 witii tliose caught in area 6. .\o recoveries were 

 made between Little Saliie Point in the nortltern 



