HOUDE: ABUNDANCE AND POTENTIAL YIELD OF ROUND HERRING 



TABLE 7. — Annual spawning and biomass estimates for round herring from the eastern Gulf of Mexico during 

 1970-71 through 1973-74 spawning seasons. Estimates are based on the method of partitioning the spawning 

 season into component parts of the normal curve ( Saville 1956). The spawning season is assumed to be 229 days in 

 length, ranging from 15 October to 31 May. 



were not made near the middle of the spawning 

 season. 



Mean biomass estimates for the 1971-72 and 

 1972-73 seasons were 841,373 and 164,474 metric 

 tons, respectively (Table 7). These estimates do 

 not differ much from those obtained by Methods I 

 and II (Tables 5, 6). Also, it is interesting to note 

 that the midwinter estimates in the 1971-72 

 (673,481 metric tons) and 1972-73 ( 136,330 metric 

 tons) seasons, each based on a single cruise, gave 

 estimates of round herring biomass nearly identi- 

 cal to those obtained by Methods I and II. A single 

 cruise in January or February, with a subsequent 

 biomass estimate by Method III, seems to be as 

 good for obtaining estimates of round herring 

 biomass as three cruises spaced over the entire 

 spawning season. Multiple cruises within the 

 November through February peak spawning 

 period would, of course, be the best approach to 

 gain precision in estimating biomass of this 

 species from spawning surveys. 



The annual spawning estimates, based on 

 Method III from the eight cruises (Table 7), are 

 log-normally distributed and an estimate of the 

 mean biomass present from 1970 to 1974, with 

 confidence limits at the 0.95-probability level, was 

 calculated based on the eight log 10 egg abundance 

 estimates. Geometric mean annual spawning es- 

 timate for 1970-74 was 2,685.11 x 10 10 and the 

 confidence limits are: P( 792.08 x 10 10 ^ P a =s 

 9,103.32 x 10 10 ) = 0.95. Expressed in terms of 

 biomass, the geometric mean was 181,120 metric 

 tons with confidence limits, P(53,429 *£ B «= 

 614,052) = 0.95. If the arithmetic mean of the 

 eight biomass estimates is considered a valid es- 

 timate of mean biomass, its value is 415,175 met- 



ric tons. A reasonable conclusion is that round 

 herring biomass in the eastern Gulf is less than 1 

 million metric tons but probably greater than 

 100,000 metric tons. 



Concentration of Biomass 



The largest positive areas (i.e., areas where 

 either round herring eggs or larvae were collected) 

 occurred in cruises 8B 7201-GE 7202 and IS 7303 

 when more than 78 x 10 9 m 2 were in that category. 

 This is nearly equivalent to the 76.5 x 10 9 m 2 in 

 the survey area between 30- and 200-m depths 

 that was determined by planimeter. The biomass 

 of adult round herring is primarily located in the 

 30- to 200-m depth zone. If the confidence limits on 

 biomass, based on Method I, are considered then 

 biomass per unit area of sea surface must have 

 been between 67.6 and 120.0 kg/hectare in 1971- 

 72 and between 5.9 and 28.3 kg/hectare in 

 1972-73. 



Potential Yield to a Fishery 



Using Equation (9), the potential yield to a 

 fishery, C max , can be estimated, based on the range 

 of biomass estimates that is available. Although 

 the natural mortality coefficient, M, is not known, 

 it probably lies between 0.50 and 1.00 for round 

 herring in the eastern Gulf of Mexico. The esti- 

 mated values of C max if Af equals 0.50, 0.75, or 1.00 

 are given in Table 8. 



Potential yield estimates range from 32,749 to 

 420,687 metric tons (Table 8). The best estimates 

 almost certainly lie midway between the ex- 

 tremes, so that 50,000-250,000 metric tons are in 



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