32 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



for trout with more than 5 fin rays at least half 

 normal length offers a slight inconsistency, since, 

 on the basis of the assumptions made, this per- 

 centage should have been the largest. 



Table 11. — Relation of extent of the regeneration of pectoral 

 fins, expressed in terms of number of regenerated rays and 

 length {fraction of normal) to percentage disagreement 

 between ages as determined from scales and as indicated 

 by deformed fins 



Length of fin 



Less than half 

 normal. 



Half normal or 

 longer. 



All lengths 



Item 



Xiiiiibcr tif fish 



|-j\uiiihiT i)f <lisaKreements. 

 FfU'i'iitat^c «lis;mrot'mt'nt--- 



Xumher of fish 



Number of disagreements- 

 Percentage disagreement-. 

 { Number of fish 

 Number of disagreements. 

 Percentage disagreement... 



Totals I 



981 

 39 



4.0 



312 

 21 



6.7 



1,293 



60 



4.6 



I Information not available on both the number of rays regenerated and 

 the length of regeneration for 55 specimens. 



Despite tlie one inconsistency, the data of 

 table 1 1 provide evidence that the collections from 

 northern Lake Michigan did contain enough un- 

 marked fish to affect appreciably the percentage 

 of disagreements between supposed ages and ages 

 as read. 



Relation of disagreements to year and locality of 

 capture 



Evidence from the capture of marked fish has 

 been presented by Smith and Van Oosten (1940), 

 and Eschmeyer and otliers (19.53), that lake trout 

 tend to remain local in habit but that their move- 

 ments lead to a gradual scattering from a point 

 of release. If this concept of the behavior of the 

 young fish is accepted as established, and if it is 

 assumed that marked lake trout entered the 

 fishery gradually over a period of years and then 

 disappeared from tlie fishery gradually, and as- 

 sumed further that fishermen of northern Lake 

 Michigan in their search for marked fish, found 

 and turned in most or all of tlie wild-stock lake 

 trout with natural abnormalities of the fins in- 

 volved in tlie marking experiments, it is possible 

 to set up, a priori, an expected relation for dis- 

 agreements between supposed ages and ages read 

 from the scales. It should be expected first that 

 the percentage disagreement would be high when 

 the marked fish of a particular planting were just 

 entering the fishery, for they would be taken only 

 in small numbers and thus would make up a small 



percentage of the combined total of marked and 

 unmarked fish with abnormal fins. The per- 

 centage disagreement should decrease as marked 

 fish become more abundant and hence dominate 

 strongly this same combined total, but should 

 increase again as the marked fish disappear from 

 the grounds. It should be anticipated further 

 that within a single year the percentage disagree- 

 ment would be least among lake trout taken in 

 areas in which marked fish are plentiful and great- 

 est wliere marked fish are scarce. These expecta- 

 tions are fulfilled rather well by the records of the 

 1945 year class, tlie planting from which the 

 greatest number of "marked" fish was recovered 

 (table 12). 



Table 12. — Annual distribution of the "marked" lake trout 

 of the 1945 year class, and the relation of the locality of 

 capture to the percentage disagreements between supposed 

 age and the age read from the scales 



' Some lake trout were omitted from this table because the description of 

 the locality of capture was indefinite. 



2 All disagreements were on lake trout captured along the north and east 

 shores of Lake Michigan, areas 2, 3, 5, and 6. There were no disagreements 

 on those captured in areas 1 and 4. 



The sequence of changes through the years fol- 

 lowed the expected pattern. The percentage dis- 

 agreement (between supposed age and age read 

 from scales) was relatively high (13.9 percent) in 

 1947 when only 36 recoveries were made. As the 

 number of recoveries rose to a maximum of 528 

 in 1949, the percentage disagreement dechned to 



