FISHERY BULLETIN: VOL. 75, NO. 1 



TABLE 3. — Fecundity estimates and related data from eight female round herring collected in 



the Gulf of Mexico, November 1974. 



'Gonad index is the ratio of ovary weight to weight of the female, expressed as a percentage. 



spawned in a spawning season, the estimate of 

 relative fecundity is too high and biomass esti- 

 mates are low. Because no modes of yolked oocytes 

 remained in ovaries of spent females from the 

 June collection, I believe that yolked oocytes were 

 spawned and that biomass estimates were not 

 biased by this possible source of error. 



Ito ( 1968) estimated mean fecundity of Japanese 

 round herring to be 9,212 ova. His estimates were 

 based only on the most advanced mode of yolked 

 oocytes, although two modes usually were present. 

 Ito's estimates are lower than the estimated 

 fecundities of Gulf of Mexico round herring. Also, 

 the diameters of near-ripe ova that he reported 

 averaged 1.4 mm which is greater than that for 

 spawned eggs in the Gulf of Mexico which average 

 only 1.29 mm in diameter (Houde and Fore 1973). 

 Diameters of ovarian ova reported by Ito (1968) 

 are not in accord with those reported for pelagic 

 eggs of Japanese round herring by Uchida et al. 

 (1958), who gave the diameter as 1.25 mm. The 

 length at first maturity, which Ito observed to be 

 approximately 170 mm SL in Japanese specimens, 

 exceeded that of my specimens by about 70 mm. 



Time Until Hatching 



Duration of the egg stage from spawning until 

 hatching was estimated indirectly from the oc- 

 currence of three distinct embryonic stages during 

 cruise IS 7303, at stations where surface tempera- 

 tures were 21°-22°C. Spawning by round herring 

 takes place at night, and early embryonic stages 

 were collected only between midnight and 0400 

 e.s.t. Two other distinct embryonic stages were 

 collected during those hours, one of which was a 

 full-term embryo that was about to hatch. I as- 

 sumed 2200 e.s.t. to be the peak spawning time. 

 The time from spawning to hatching is approxi- 

 mately 2.1 days at 21°-22°C. Watson and Leis 

 (1974) reported that Hawaiian round herring eggs 



incubated approximately 2 days when surface 

 temperatures were in the range 23°-25°C. 



The value of 2.0 days was used for hatching time 

 in subsequent abundance estimation procedures 

 (Equations (4), (5), and (8)). It probably over- 

 estimates duration for cruises during fall and 

 spring, but it is a good estimate for the winter 

 season when most spawning occurs. Over- 

 estimating duration would result in an under- 

 estimate of daily spawning and an underestimate 

 of adult biomass. Because there were no data on 

 duration of the egg stage for fall and spring 

 cruises, I chose to accept a possible small bias of 

 underestimating round herring biomass. O'Toole 

 and King (1974) incubated South African round 

 herring eggs at 11°-20.5°C. The eggs had been 

 collected in plankton tows when surface tempera- 

 ture was 16.5°C. They estimated that round her- 

 ring eggs hatched in 135 h at 11°C and 36 h at 

 20.5°C. They assumed that the blastodermal cap 

 stage eggs, with which they began experiments, 

 were only 4-6 h old. Gulf of Mexico round herring 

 probably do not spawn at the low temperatures 

 that O'Toole and King observed in South African 

 waters. Temperatures as low as 16.5°C during the 

 spawning season in the Gulf of Mexico occurred 

 only at depths of 150 m and greater, on the outer 

 edge of the continental shelf. Also, the rate of 

 development of Gulf of Mexico eggs at tempera- 

 tures above 20°C apparently is slower than that of 

 South African eggs. 



Cruise Egg Abundances 



The estimated abundances of round herring 

 eggs present in areas represented by each cruise 

 are given in Table 4. Egg abundances, including 

 all developmental stages, ranged from 0.24 to 

 209.31 x 10 10 for cruises during the spawning 

 season. No round herring eggs (or larvae) were 

 collected on cruise CL 7405. That cruise was made 



76 



