QUAST: BODY WEIGHT, FAT, AND GONADS OF PACIFIC HERRING 



nearly ready to spawn in November but females 

 delayed readiness until perhaps 4 mo later (Fig. 6), 

 a delay that was confirmed by visual judgments of 

 maturity, see table below (sample size in paren- 

 theses): 



Percentage of herring judged ripe 

 Sept. Oct. Nov.- Jan. Mar. 



Males 

 Females 



4(23) 

 0(31) 



92(12) 

 11(18) 



95(19) 

 79(38) 



94(18) 

 90(20) 



These data differ in some important respects from 

 those of Hay and Outram (1981) for Pacific herring 

 in British Columbia. Their gonadosomatic index has 

 sharper peaks in maturity of gonads and different 

 timing of the peaks than the Pacific herring from 

 Auke Bay. For example, in their data, testes were 

 only developing (a low gonadosomatic index) in Oc- 

 tober (the fish spawned in late February and early 

 March), but testes were near maximum fullness 

 (high index values) in October in herring from Auke 

 Bay (Fig. 6). However, Hay and Outram used total 

 weight in their index. If total weight is used for the 

 index, the divisor will include a considerable weight 

 of fat about the viscera in the fall and negligible 

 weight in the spring, with the result that even if 

 gonad weights remain the same from November to 

 February, the decline in the amount of fat would 

 cause the index to increase. In my study of the 

 Pacific herring in Auke Bay, I divided gonad 

 weight by eviscerated body weight, which should 

 avoid an appreciable error in the gonadosomatic 

 index that would be caused by variation in visceral 

 fat. 



Within each sex, seasonal profiles for gonad in- 

 dices are nearly opposite the profiles for indices of 

 visceral fat (Fig. 6). The annual cycles in fat and 

 gonad indices (Fig. 6) in Pacific herring from Auke 

 Bay resemble those noted by Blaxter and Holliday 

 (1963) for spring spawning in Atlantic herring: "In 

 winter-spring herring the good feeding conditions 

 in late spring and early summer (after spawning) 

 build up the fat reserves. With development of the 

 gonads in late autumn feeding stops and spawning 

 in December-March means that the fish overwinter 

 and spawn with fat reserves considerably lower than 

 the autumn spawners." Visceral fat in male Auke 

 Bay herring is lowest in winter (perhaps as early 

 as November), but in females does not reach lowest 

 values until April. Correspondingly, the testes build 

 rapidly in late summer and fall and appear to be 

 heaviest by October or shortly after, but the ovaries 



are not at their heaviest until shortly before spawn- 

 ing, in April or May. Hydration is not responsible 

 for sexual differences in development of gonad 

 weight from January to March because, as the 

 following table indicates, hydration remains virtual- 

 ly constant from November to March in both sexes 

 (Table 4). 



Table 4. — Average hydration of gonads, as a 

 percentage of wet weight, by month in Pacific 

 herring from Auke Bay. AK. 



This seasonal, mirror imagery between develop- 

 ment of fat and gonads, with the images differing 

 for sexes, is evidence for a strong physiological 

 coupling between fat depots and gonads. Fat depots 

 enable Pacific herring to accommodate two critical 

 cycles in their life history that are badly out of phase: 

 The zooplankton cycle, with its brief, summer peak 

 that builds fat depots rapidly and is followed by low 

 levels of food abundance from October to March; and 

 the gonad cycle that slowly removes fat from the 

 depots with the slow building of testes from July 

 through October and the slower building of ovaries 

 from July through March. 



Are the seasonal cycles of gonad maturity in 

 Pacific herring from Auke Bay determined by gene- 

 tics or are the gonads responding principally to 

 cyclical changes in the immediate environment? lies 

 (1984) felt that Atlantic herring are remarkably in- 

 dependent of their environment. Genetic control of 

 gonad maturity seems likely except for spawning, 

 which appears to respond to local temperatures 

 (Outram 1965, see footnote 3). Gonads must build 

 well in advance of spawning, and spawning dates 

 vary from November in the southern limits of the 

 eastern Pacific range (Spratt 1981) to June in Auke 

 Bay. Female Auke Bay herring mature sexually and 

 use fat deposits later in the fall than do males and 

 thus anticipate a later spawning date. Male herring 

 in the eastern Pacific Ocean, in contrast, appear to 

 build testes early enough to spawn at any date be- 



715 



