FISHERY BULLETIN: VOL. 75. NO. 1 



TABLE 12. — Estimated numbers and percentages of survivors of round herring larvae at hatching, 5.5 mm SL and 15.5 mm SL in 

 1971-72 and 1972-73. Estimates are made for three possible growth rates (see Table 11). Duration of the nonfully vulnerable larval 

 stages was set at 6.0 days for 2.1-5.0 mm larvae in 1971-72 and 2.5 days for 2.1-4.0 mm larvae in 1972-73. The number of spawned 

 eggs in each year was based on estimates by Method I (Table 5). Predicted numbers at hatching, 5.5 mm and 15.5 mm are calculated 

 from exponential functions based on Table 11 data. 



'Hatching assumed to occur at 2.0 days. 



more than 99.4% at 15.5 mm in 1971-72 and by 

 more than 98.3% in 1972-73. The 15.5-mm stage 

 would be attained at about 31 days if the instan- 

 taneous growth coefficient was 0.0498 (equal 

 0.5-mm mean daily growth increment). At that 

 growth rate, approximately 4 larvae/1,000 eggs 

 spawned in 1971-72 and 12 larvae/1,000 eggs 

 spawned in 1972-73 would have survived to 15.5 

 mm and 1 mo of age. 



SUMMARY 



1) Surveys of eggs and larvae were used to inves- 

 tigate spawning, to determine adult stock size, 

 and to study aspects of the early life history of 

 round herring in the eastern Gulf of Mexico during 

 1971-74. 



2) Spawning takes place from mid-October 

 to the end of May between the 30- and 200-m 

 depth contours. About 60% of the total spawning 

 occurred at depths greater than 50 m. Most spawn- 

 ing apparently occurred during January and 

 February. 



3) Eggs occurred when surface temperatures 

 ranged from 18.4° to 26.9°C, and surface salinities 

 from 34.5 to 36.5%o. Larvae =s5.0 mm SL were 

 collected when surface temperatures were from 

 20.5° to 26.9°C, and surface salinities from 34.1 to 

 36.8%o. Of the eggs 82.5% and of the ^5.0-mm 

 larvae 87.5% were collected when surface temper- 

 atures were from 21° to 26°C. More than 50% of the 

 eggs and =£5.0-mm larvae were collected where 

 surface salinity exceeded 36.0%o. 



4) There is a major spawning area between lat. 

 27°00' and 28°00'N and long. 083°30' and 

 084°30'W. The center of the area is located about 

 150 km west by southwest of Tampa Bay in depths 

 of 50-200 m. 



5) The fecundity of eight round herring females 

 130-165 mm SL ranged from 7,446 to 19,699. 



Mean relative fecundity was 296.5 ova/g (S~ = 

 33.7). Gonads of round herring collected from Au- 

 gust to November were ripening or near ripe. 

 Those collected in June were spent. The sex ratio 

 of 71 round herring adults did not differ sig- 

 nificantly from 1:1. 



6) The time from spawning to hatching, based on 

 observations of development stages in planktonic 

 eggs, was about 2.0 days at 22°C. 



7) Adult biomass was determined by three 

 methods from data on estimated annual spawn- 

 ing. The Sette and Ahlstrom's (1948) and 

 Simpson's (1959) techniques gave estimates that 

 ranged from 130,000 to 715,000 metric tons in 

 1971-72 and 1972-73. The geometric mean of eight 

 individual estimates by Saville's (1956) method 

 was 181,200 metric tons, the arithmetic mean 

 being 415,175 metric tons. But, the best estimates 

 by Saville's method were from two individual 

 cruises in midwinter. These were 673,481 metric 

 tons in 1971-72 and 136,330 metric tons in 1972- 

 73. Those estimates were nearly the same as esti- 

 mates obtained by the other two methods. Spawn- 

 ing biomass apparently was higher in 1971-72 

 than in 1972-73. 



8) The estimated concentration of biomass be- 

 tween the 30- and 200-m depth contours, based on 

 the stock size estimates, was from 67.6 to 120.0 

 kg/hectare in 1971-72 and from 5.9 to 28.3 kg/hec- 

 tare in 1972-73. 



9) The annual potential yield of round herring to 

 a fishery, if instantaneous natural mortality 

 coefficients lie in the range 0.5-1.0, ranged from 

 32,750 to 420,700 metric tons. The most probable 

 mean annual potential yield estimates are in the 

 range 50,000 to 250,000 metric tons. This is equiv- 

 alent to 6.5-32.5 kg/hectare in the 30- to 200-m 

 depth zone. 



10) Total abundance of larvae was estimated in 

 1971-72 and 1972-73. The 4.1- to 5.0-mm length 



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