Table 3.— Continued. 



Gulf of Maine 



Nova Scotia 



'Sample size too small to fit regression. 



were significant results in tests of adjusted means, decreasing 

 from 1975 to 1977. 



Differences in length-weight regressions for /. illecebrosus 

 were not as consistent as for L. pealei. Overall, the adjusted 

 mean was significantly greater for female than for male /. //- 

 lecebrocus (Table 5a.). The slope of the male regression was 

 significantly greater than the female's during the summer, in- 

 dicating statistical differences in the two regression lines, for 

 that season, while in autumn the adjusted mean of females was 

 greater than for males. There was no significant difference be- 

 tween regressions of either sex during the spring. Significant dif- 

 ferences in the slope of male and female regressions from the 

 Georges Bank and Nova Scotian areas indicate statistical dif- 

 ferences between sex in both these areas. The Mid-Atlantic area 

 is the only area that did not exhibit statistical significance in ad- 

 justed means between sexes. In all other areas females were 

 significantly larger than males. When compared by year, slopes 

 of male and female /. illecebrosus vvere only significantly dif- 

 ferent in 1977, but in both 1975 and 1976, adjusted means for 

 females were statistically greater than for males. 



Differences in length-weight regressions due to seasons (Table 

 5b) were only significant for /. illecebrosus between the summer 

 and autumn, with the slope of the summer regression greater 

 than in autumn. 



Tests of slopes were significant for all area comparisons 

 (Table 5c) except between the Mid-Atlantic and the Gulf of 

 Maine and between southern New England and the Gulf of 

 Maine, implying statistical differences between length-weight 

 regressions from all other areas. However, the adjusted mean 

 from the Gulf of Maine was also significantly greater than those 

 from either the Mid-Atlantic or the southern New England 

 areas, in pairwise comparisons. 



Tests of slopes revealed significant differences between 1975 

 and 1977 and between 1976 and 1977 samples (Table 5d), in- 

 dicating thai separate equations were appropriate for these 

 areas. The 1975 adjusted mean was significantly greater than 

 that of 1976. 



Comparisons of total calculated versus total empirical weights 

 were made for each species, for all data, and for various com- 

 binations of data (Table 6). Weights were calculated on an in- 

 dividual basis from sampled lengths, summed within length (cm) 

 interval and then summed over all lengtlis. Percent differences 

 were calculated between these values and those obtained by 

 summing the individual empirical weights for the data set. 

 Predicted weights were consistently less than empirical weights 

 due to bias in linearization by log transformations. These dif- 

 ferences were very small, ranging from 0.08% to 6.60% for L. 

 pealei and from 0.17% to i.dlVo for /. illecebrosus. This in- 

 dicates that the dorsal mantle length-total weight relationship 



produces relatively precise approximations of total empirical 

 weight, and that the functions used for each species are fairly ac- 

 curate representations of this relationship. 



DISCUSSION 



Results of these analyses indicate that the weight of L. pealei 

 of a given size differs significantly, depending on the sex of the 

 individual. The consistency of this difference in tests within 

 areas, seasons, and years is evidence that it is not merely a pro- 

 duct of the statistical procedures employed. Major factors, in- 

 fluencing differences between sexes, are the relative weight of 

 gonads, with mature ovaries heavier than fully developed testes; 

 differences in rates of maturation, with females developing over 

 a longer time interval than males; and differential feeding during 

 different stages of maturation and at different sizes (Vinogradov 

 and Noskov 1979). This study also suggests significant seasonal 

 differences in the length-weight relationship of L. pealei. A 

 possible explanation of this is that in spring larger individuals 

 are more mature and, therefore, heavier than later in the year, 

 while in summer the many individuals which are not yet mature 

 begin to feed, so by autumn individuals throughout the size 

 range are heavier as a result of summer feeding. Area and an- 

 nual differences, also shown significant for L. pealei, may 

 possibly be explained by various physical and biological factors 

 such as temperature, nutrients, and availability of food. 



Differences in length-weight relationships for various group- 

 ings of /. illecebrosus were less consistent than for L. pealei. 

 Overall, tests between sexes were not significant, except in sum- 

 mer samples (possibly due to maturation of males, or differen- 

 tial feeding). Seasonal and annual differences were not signifi- 

 cant for /. illecebrosus, but area differences proved to be impor- 

 tant. As with L. pealei these differences are most likely due to 

 physical and biological factors such as temperatures, nutrients, 

 and food availability. 



CONCLUSIONS 



This study indicates that differences in the length-weight rela- 

 tionships of Loligo pealei (by sex, year, season, and area) and of 

 Illex illecebrosus among areas (but not between sexes, seasons, 

 and years) do exist. However, comparisons within categories, of 

 sums of total empirical weight versus sums of total weight 

 predicted by equations obtained for all data within a given set, 

 indicate that the new results of using a single equation for each 

 species is approximately as precise as using separate equations 

 for each area, season, year, or sex. This implies that for pur- 

 poses of predicting total numbers taken in a fishery, from length 



13 



