LIFE HISTORY OF LAKE HERRING OF LAKE HURON 



281 



Two methods suggest themselves by which we may try to determine the con- 

 stancy in the number of scales throughout life. We may compare either the scale- 

 number averages of the several age groups (fish of the same age) taken in one and the 

 same haul, or the averages of the age groups taken in different years but belonging to 

 the same year class (fish hatched at the same time). In the fii'st case we compare 

 fish of different ages, hatched in different years, but taken at the same time; in the 

 second case we compare fish of different ages, hatched at the same time, and taken 

 in successive years.^ In the first case we must assume that the number of scales 

 remains constant with the year classes, in the latter we must determine that all the 

 collections consist of homogeneous material. By both methods we assume either 

 that scale number does not vary with sex or size in an age group, or, if so, that both 

 sexes and all sizes are represented in correct proportions. 



Table 3. — Average number of scales in the lateral line of males and females for different size groups of 



Bay City lake herring of various ages ' 



Size groups, millimeters 



Oct. 29, 1921, age group IV 



Average scale number 



Male 



Female 



Male 



and 



female 



Average size 



Male 



Female 



Nov. 1, 1922, age group IV 



Average scale number 



Male 



Female 



Male 



and 



female 



Average size 



Male 



Female 



211-220. 

 221-230. 

 231-240. 

 241-250. 

 251+... 



77.00 (1) 75.7.5 (4) 



79. 36 (39) 81. 04 (26) 



81.08 (25)81.94 (16) 



82.60 (5) 82.40 (10) 



Grand average - 



80.17 (70) 



■6.00 (5) 



80 03 (65) 



81.41 (41) 



82.47 (15) 



216 (1) 



226 (39) 



234 (25) 



260 (5) 



218 (4) 



227 (26) 



235 (16) 



266 (10) 



76.35 (20)77.60 (15) 



77.94 (5;)) 1 79. 09 (22) 



79.22 (32)79.78 (9) 



78.00 (5) 80.80 (5) 



76.89 (36) 



''8.28 (75) 



79.31 (42) 



■9.40 (10) 



227 (20) 

 236 (53) 

 244 (32) 

 257 (5) 



227 (IS) 



236 (22) 



244 (9) 



262 (5) 



81.16 (56) 



232 (70) 



236 (56) 



78.03 (110)78.94 (51) 



238 (110) 



237 (51) 



Size groups, 

 millimeters 



211-220. 

 221-230. 



231-240. 



241-250- 

 251+... 



Grand av- 

 erage 



Nov. 12, 1923, age group IV 



Average scale number Average size 



Male 



80.41 (27) 



81.43 (49) 



Female 



79.74 (19) 



81.96 (23) 



81.75 (16):83.00 (11) 



81.18 (92)^81.38 (53) 



Male 



and 



female 



80.13 (46) 



81.60 (72) 

 82.26 (27) 



Male 



238 (27) 



246 (49) 

 254 (16) 



245 (92) 



Female 



236 (19) 



245 (23) 

 263 (11) 



244 (53) 



Size groups, 

 millimeters 



Under 226... 

 Over 226 



Grand av- 

 erage 



Under 251. 

 Over 251.. 



Grand av- 

 erage. -- 



Average scale number of 

 all 1921 herring, age 

 group III 



Average scale number of 

 all 1923 herring, age group V 



Male 



77.83 (18) 

 82.08 (12) 



79.53 (17) 

 79.73 (15) 



79.63 (30) 



Female 



79.63 (32) 



Male 



and 



female 



Male 



78.66 (35) 

 80.78 (27) 



81.36 (25) 

 82.80 (25) 



82.08 (50) 



Female 



80.30 (10) 

 81.27(11) 



80.81 (21) 



Male 



and 



female 



81.06 (35) 

 82.33 (36) 



1 Numbers in parentheses indicate the number of specimens employed. 



In connection with the last-mentioned assumptions Table 3 is significant. In 

 this table is given the average number of scales in the lateral line of males and females 



6 It is not feasible to arrange the fish according to size groups instead of age groups on the assumption that the small fish are 

 also the young fish. This we know is not strictly true. Further, the fact that the smaller fish of an age group have fewer lateral- 

 line scales than the larger fish of that age group (see p. 2S3) introduces an error in tlie size-group method, which tends to reduce the 

 average scale number of the small fish below that of fish of equal size but of younger age. 



