HOUDE: ABUNDANCE AND POTENTIAL YIELD OF THREAD HERRING 



3 20 



^100 



s 

 3 9° 



z 80 



u 



a 70 - 



a. 

 60 - 



50  



40 - 

 30 



TEMPERATURE 



Opisthonema oglinum 

 eggs 



SALINITY 



O oglinum 

 eggs 



VH 1 1 t--f — I 1 1 1 1 1 t 1 1^ — • — • — I — ' — I — ' — I — I — !■ 



C oglinum 

 larvae - 5 mm 



ie i- 



19 ( 



r 



C? oglinum 

 larvae 4 5mm 



• .«\ 



210' 

 TEMPERATURE CLASS CO 



2701- 2801- 2901- 30 01- 3101- 32 01- 3301- 34 01- 35 01- 36.01- 

 2750 2B50 2950 30 50 3150 32 50 3350 34 50 35 50 36 50 

 SALINITY CLASS (V..) 



FIGURE 7.— Percent cumulative fre- 

 quency distribution of 1971-74 stations 

 where thread herring eggs occurred in 

 relation to surface temperatures (A) 

 and to surface salinities (C), and *£5.0- 

 mm SL larvae occurred in relation to 

 surface temperatures (B) and surface 

 salinities (D). 



stations with eggs and 68% with =£5.0-mm larvae 

 occurred where salinity ranged from 35.0 to 

 36.5%o. Spawning rarely occurred at surface 

 salinities <33%o. 



Egg and Larval Abundance in 

 Relation to Zooplankton 



There was no clear relationship between abun- 

 dance of thread herring eggs or larvae and zoo- 

 plankton volume at stations for 12 cruises in 

 1972-74. Houde and Chitty (1976) determined 

 that mean zooplankton volume from the 333-^tm 

 mesh bongo net was 153.4 cm 3 /l,000 m 3 in that 

 period. Egg abundances showed no relationship to 

 zooplankton volumes; larvae did appear to be most 

 abundant at stations where zooplankton volumes 

 exceeded 153.4 cm 3 / 1,000 m 3 . But, zero catches or 

 low catches of larvae also were common where 

 zooplankton volumes were high. The lack of sig- 

 nificant correlation between larval abundance 

 and zooplankton volume was not surprising be- 

 cause the 333-ju.m mesh does not sample zoo- 

 plankton of the size eaten by small thread herring 

 larvae. 



Relative Fecundity 



The mean relative fecundity of thread herring 

 females is 594.0 ova/g (S* = 29.4 ova/g), calculated 

 from Martinez's ( 1972) weight and fecundity data 

 that he obtained from nine females of 53.8 to 109.4 

 g. There was no apparent relationship between 



relative fecundity and either length or weight of 

 the nine thread herring used in this analysis. The 

 mean relative fecundity value was used in all sub- 

 sequent biomass estimate calculations. Because 

 mean relative fecundity with its 0.95 confidence 

 limits is x — 594 ± 68, the maximum biomass 

 estimating error attributable to the relative 

 fecundity estimate is about ±11%. 



Time Until Hatching 



Thread herring eggs apparently hatch in <24 h 

 at temperatures of 25° to 30°C, where most spawn- 

 ing takes place in the eastern Gulf. The evidence is 

 indirect because no living thread herring eggs 

 were available for incubation experiments. Eggs 

 did not occur in more than one stage of develop- 

 ment from any single sample during these sur- 

 veys. Newly fertilized eggs were collected only at 

 night, mostly from 2200 to 0200; and full-term 

 embryos were found only during the afternoon 

 from 1400 to 1800. I assigned a mean estimated 

 hatching time for eggs as 0.84 days (20 h) from the 

 evidence that was available. Thread herring eggs 

 were rarely caught at stations sampled between 

 the hours of 1600 and 2100, presumably because 

 they had already hatched. Thus, abundance of 

 thread herring eggs spawned during each cruise 

 was underestimated. Annual spawning estimates, 

 as well as variances, were corrected for egg stage 

 duration (equations 4, 5; Houde 1977a) and cor- 

 rected estimates were subsequently used to calcu- 

 late biomasses. 



501 



