AGE DETERMIXATIOX FROM SCALES OF LAKE TROUT 



a hisjli desirco of ronfidcncc*. Tlic findings on tlu'sc 

 fish are detailed more appropiiately in later s(><- 

 tions l)ut a summary of tlie basis for the rejection 

 of the samj)les from area S is given at tliis |)()int. 



GEOGRAPHICAL DISTRIBUTION OF RECOVERIES 



In areas l-(>, tiie earliest reeoveries were made 

 near the loeality of planting. As the fish grew 

 oldei- and larger the captiiies were more widely 

 disti-ibuted. They scattered to some extent in 

 all directions, hut the principal movement was in 

 a northwest I'lly direction toward Maiustiqiie and 

 thence westerly and southwesterly until some fish 

 were recaptured along tlie Wisconsin shore. 

 Captures of lake trout with deformed fins were 

 fewer and the distribution was discontinuous 

 southward from the localities in which the plant- 

 ings were made. No recoveries at all were made 

 between the extreme northern part of area 7 and 

 the neighborhood of .South Haven.'" If it is as- 

 sumetl that lake trout reported off South Haven 

 were actually marked fish, it is difficult to under- 

 stand why none were caught in the heavily fished 

 60-mile-long area en route to the more southerly 

 waters. On the other hand, if the lake trout 

 reported from area 8 are considered to be wild- 

 stock lake trout with abnormal fins, the trouble- 

 some question arises as to why no trout of the 

 same category were reported from that 60-mile 

 stretch." The discontinuity of distribution of the 

 recoveries does not provide convincing evidence, 

 but does, nevertheless, give cause to regard with 

 suspicion the genuineness of the mark (deformed 

 fin) on the fish caught at South Haven. 



FINS ON RECOVERED LAKE TROUT 



Records of degree of regeneration of the pectoral 

 fins '- in terms of regenerated rays (table 3) 

 and lengths of the abnormal fins (table 4) on 

 recovered lake trout were similar in that they 

 suggested no basis for the separation of marked 



"> \'an Oosti'ii (19511) dcsciibcd the distribution of rccovprios of these sanu' 

 fish tlirougli 1949. Subsequent captures did not chanKe the general situation 

 greatly, except that the progressive scattering of the growing fish continued. 



" The answer possibly may lie in the enterprise of a single fi.sherman. 

 Of the 102 recaptures from southern Lake Michigan, 94 were turned in by 

 the same operator. Conceivably fishermen in the waters to the north 

 observed similar al)normalities hut did not believe them to be thi' result of 

 fin-clipping. 



" The collection of fish with dorsal and adipose fins dijjped is too small to 

 give reliable results, but 43 (75.4 percent I of a total o( 57 specimens were jurtgi'd 

 to have true marks. .lust one lake trout with this mark was caught in area 

 8. The mark (dorsal and adipose fins removed) proved somewhat confusing 

 becau.se of the presence of fish w itll oni' fin deformi'd anil the other normal. 



37832G O — 50 2 



lake trout of areas 1-6 from naturally propa- 

 gated individuals of this region, but did indicate 

 rather conclusively that the samples from areas 

 1-6 and area 8 could not have been drawn from 

 the same population. Despite certain disagree- 

 ments as to detail between data on the right and 

 left pectoral fins of trout frotn areas 1-6 (dis- 

 crepancies which could have been the result of the 

 small number of fisii recaptured with a deformed 

 left pectoral fin), the general situation can be de- 

 scribed satisfactorily from the combined records 

 of the two fins. The extent of regneration of 

 fins on lake trout from areas 1-6 was relatively 

 small. In a total of 1,348 individuals, 57.5 per- 

 cent had no regeneration of the fin rays, and 77.5 

 percent had fewer than 5 rays regenerated. With 

 respect to length of regeneration, 58.2 percent 

 of the fins were without regeneration, and 75.2 

 percent were not more than K normal length. 

 In area 8, to the contrary, regeneration of most 

 fins was advanced. Of 74 fish, for which there 

 were records of the number of rays in the de- 

 formed fin, but 1.4 percent had no rays regenerated, 

 and only 4.1 percent had fewer tlian 5 rays re- 

 generated as compared with 77.5 percent in areas 

 1-6. Of 89 fish, for which the length of the fins 

 was recorded, just 1.1 percent of the fins were 

 without regeneration, and only 13.5 percent were 

 not more than ji normal length as compared 

 with 75.2 percent in areas 1-6. The very small 

 percentage (1.1) of fins showing no regeneration 

 in area 8 is strikingly difl'erent from that (58.2) 

 of fins on fish from areas 1-6. 



The data of tables 3 and 4 have a usefulness in 

 addition to that of demonstrating that samples 

 from areas 1-6 and area 8 were drawn from stocks 

 that were dissimilar with respect to the character- 

 istics of abnormal fins. If the thesis is accepted 

 that most or all of the lake trout from area 8 were 

 unmarked, it can be anticipated that most of the 

 unmarked lake trout in the samples from areas 

 1-6 also will be among the fish whose fins exhibit 

 more advanced regeneration. 



DISCREPANCIES BETWEEN AGES READ FROM 

 SCALES AND INDICATED BY ABNORMAL FINS 



Agreement between ages indicated by fins and 

 read from scales was high (substantially above 90 

 percent) in fish from areas 1-6, but in area 8 

 only 39.2 percent of the scale readings agreed with 

 the ages indicat(>d bv abnormal fins. p]ven 



