FISHERY BULLETIN: VOL. 75, NO. 3 



Cruise Egg Abundance 



The estimated abundance of thread herring 

 eggs in the area represented by each cruise is 

 given in Table 2. For cruises in which eggs oc- 

 curred, abundances ranged from 0.86 to 91.66 x 

 10 10 eggs. The Table 2 estimates, which represent 

 abundance of eggs present on a day during a 

 cruise, were corrected for egg stage duration and 

 then expanded to represent the number of days 

 encompassed by the cruise period (Sette and 

 Ahlstrom 1948; Houde 1977a). 



TABLE 2. — Abundance estimates of thread herring eggs for each 

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

 (Houde 1977a) and are not corrected for duration of the egg 

 stage. 



Cruise 



Area represented 



by the cruise 



(m 2 x 10 9 ) 



Positive area 1 

 (m 2 x 10 9 ) 



Cruise egg 



abundance 



(eggs x 10'°) 



GE7101 

 8C7113 and 



TI7114 

 G7117 

 8C7120 and 



TI7121 

 GE7127, 8B7132 



andTI7131 

 8B7201 and 



GE7202 

 GE7208 

 GE7210 

 IS7205 

 IS7209 

 IS7303 

 IS7308 

 IS7311 

 IS7313 

 IS7320 

 CL7405 

 CL7412 



25.79 



120.48 

 101.10 



189.43 



72.99 



148.85 



124.88 



48.43 



104.59 



149.80 



149.80 



151.42 



156.50 



153.18 



153.89 



52.00 



91.33 



0.00 



55.81 

 48.73 



26.26 



0.00 



0.00 



65.98 



38.93 



11.16 



0.00 



0.00 



54.09 



53.21 



21.75 



0.00 



6.70 



47.89 



0.00 



34.25 

 0.86 



1.37 



0.00 



0.00 



11.93 



1.02 



0.00 



0.00 



0.00 



91.66 



44.26 



0.00 



0.00 



0.00 



12.77 



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

 or larvae of thread herring were collected. 



Adjusting Cruise Egg 

 Abundance Estimates 



Because the entire potential spawning area was 

 not sampled on cruises GE7117, 8C7120-TI7121, 

 GE7208, and GE7210 (Figures 3, 4), an area ad- 

 justment factor was applied to correct the egg 

 abundance estimates in Table 2. The area adjust- 

 ment factor was equal to the fraction of the poten- 

 tial spawning area that was sampled on a given 

 cruise. For cruise GE7117 it was 0.404; for 

 8C7120-TI7121, 0.746; for GE7208, 0.746; and for 

 GE7210, 0.753. The abundance estimate for each 

 of those cruises (Table 2) was corrected by dividing 

 it by its area adjustment factor. Corrected abun- 

 dance estimates are: GE7117— 2.12 x 10 10 ; 

 8C7120-TI7121— 1.83 x 10 10 ; GE7208— 15.98 x 



10 10 GE7210— 1.36 x 10 10 . 



Annual Spawning and Biomass Estimates 

 Method I 



Estimates of total annual spawning by thread 

 herring in the eastern Gulf ranged from 140.528 x 



10 11 eggs in 1972 to 1,105.932 x 10 11 eggs in 1973 

 (Table 3). Estimated adult biomasses were 

 110,024 metric tons in 1971, 47,316 metric tons in 

 1972, and 372,367 metric tons in 1973 (Table 3). 

 The 1972 estimate is unreliable because a cruise 

 that was scheduled during the peak of the spawn- 

 ing season was terminated before completion, due 

 to a hurricane. The actual biomass in 1972 prob- 

 ably is much higher than the estimate. Consider- 



TABLE 3. — Annual spawning and biomass estimates for thread herring from the eastern Gulf of Mexico during 

 1971, 1972, and 1973 spawning seasons. Estimates are based on the Sette and Ahlstrom (1948) technique. The 

 1972 estimate is unreliable because a hurricane curtailed survey cruise GE7210 during the peak of the spawning 

 season. Details of the estimating procedure are given in Houde (1977a). 



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