HOUDE: ABUNDANCE AND POTENTIAL YIELD OF ROUND HERRING 



TABLE 4. — Abundance estimates of round herring eggs for each 

 cruise. Estimates were obtained using Equations (2) and (3), and 

 are not corrected for duration of the egg stage. 



' Positive area is defined as the area representing stations where either eggs 

 or larvae of round herring were collected. 



2 No stations on this cruise were located far enough offshore for round herring 

 egg or larvae to have been collected. 



during the spawning season, but because only 

 nearshore stations were sampled, the round her- 

 ring spawning area was not included in the cruise 

 area. Abundance estimates in Table 4 are based on 

 Equations (2) and (3). Cruise abundance estimates 

 for eggs were used to estimate adult biomass in 

 following sections. 



Adjusting Cruise Egg Abundance Estimates 



The cruise egg abundance estimates were ad- 

 justed for cruises GE 7127-TI 7131-8B 7132 and 

 GE 7208. On these two cruises only a part of the 

 round herring spawning area was sampled (Fig- 

 ures 3, 4). For cruise GE 7127-TI 7131-8B 7132 

 only 0.655 of the potential round herring spawn- 

 ing area was included, and for GE 7208 only 0.839 



of the area was included. Abundance estimates for 

 each of those cruises were adjusted by dividing the 

 cruise egg abundance estimates (Table 4) by their 

 respective area factors (0.655 or 0.839). Adjusted 

 cruise egg abundance estimates are: (GE 7127-TI 

 7131-8B 7132)— 38.56 x 10 10 ; (GE 7208)— 1.80 x 

 10 10 . The effect of adjusting egg abundance for 

 these cruises had a minor effect on biomass esti- 

 mation. Biomasses based on the adjusted and un- 

 adjusted egg abundance estimates were calculated 

 and are compared in subsequent sections. 



Annual Spawning and Biomass Estimates 



Method I 



The cruise abundance estimates (Table 4) were 

 adjusted for duration of the egg stage by dividing 

 each estimate by 2.0 days, the estimated time from 

 spawning until hatching, to give estimates of daily 

 spawning during each cruise (Table 5). Daily 

 spawning estimates for each cruise were then ex- 

 panded by Sette and Ahlstrom's (1948) method to a 

 representative number of days (D t defined in 

 Equation (4)) in the spawning season of 15 Octo- 

 ber to 31 May (Table 5). Variance estimates on 

 cruise and annual egg abundance were then ob- 

 tained (Equations (4) and (6)). Finally, the esti- 

 mated adult biomass was calculated (Equation 

 (7)) (Table 5). 



Estimates of biomass were obtained for 1971-72 

 and 1972-73 when sampling was carried out over 

 the entire spawning seasons. Estimated biomass 

 was 717,815 metric tons in 1971-72 but only 

 131,136 metric tons in 1972-73 (Table 5). The var- 

 iance estimates are relatively low, but because 

 only three cruises were made within the round 

 herring spawning season and no estimates of day 

 to day variation in spawning are available, there 

 is a large source of unaccounted variation. The 



TABLE 5. — Annual spawning and biomass estimates for round herring from the eastern Gulf of Mexico during the 

 1971-72 and 1972-73 spawning seasons. Estimates are based on the Sette and Ahlstrom's (1948) technique. 



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