FISHERY BULLETIN: VOL. 75, NO. 1 



a 7112 



Etrikeus teres eggs 



a 7112 



Etrueus teres LARVAE 



May 1971 



FIGURE 6. — Distribution and abundance of round herring eggs and larvae on cruise CL 7412, May 

 1974. Catches are standardized to numbers under 10 m 2 of sea surface. 



our survey and the relative abundance of adults in 

 water >50 m deep may be higher than the esti- 

 mated 58.4%. Because the intensity of spawning 

 was the same in depths, =£50 and >50 m, adults 

 apparently are not more abundant per unit of sea 

 surface in deeper water but their greater abun- 

 dance reflects the larger area of habitat suitable 

 for round herring where shelf waters are >50 m 

 deep. 



Temperature and Salinity Relationships 



Round herring eggs were collected when surface 

 temperatures ranged from 18.4° to 26.9°C. They 

 occurred at surface salinities of 34. 50-36. 50°/oo. 

 Because no vertically stratified tows of the Bongo 

 sampler were made, the percentage of eggs or lar- 

 vae that occurred in surface waters is unknown. 

 Surface temperatures from November to May 

 were 0°-3°C higher than those at 50 m when verti- 

 cal sections along transects at three latitudes were 

 examined for each cruise in which round herring 

 eggs or larvae were collected. Surface salinities 

 differed by less than 0.5°/oo from those at 50-m 

 depth, except on cruise IS 7320 when surface 

 salinities ranged from 0.6 to 1.0%o less than those 

 at 50 m. It is reasonable to believe that surface 

 temperatures and salinities are representative of 

 conditions where pelagic eggs were incubated and 

 where larvae were found. Salinity may not be an 

 important factor affecting spawning since the 

 range of surface salinities at which eggs were col- 

 lected nearly encompasses the entire range of 



salinities found in offshore waters of the eastern 

 Gulf. Larvae =£5.0 mm SL are from to about 6 

 days old. They occurred where surface tempera- 

 tures ranged from 20.5° to 26.9°C and surface 

 salinities from 34.10 to 36.80%o. 



The percentage cumulative frequency distri- 

 butions (Figure 7) of stations where eggs or 

 =s5.0-mm larvae occurred in relation to tempera- 

 ture and salinity were examined. For eggs, 82.5% 

 of the occurrences were between 21° and 26°C sur- 

 face temperature, while 87.2% of the =s5.0-mm 

 larvae occurrences were in that temperature 

 range. Only 10.5% of the egg occurrences were at 

 stations where surface temperatures exceeded 

 26°C and only 6.4% of the =£5.0-mm larvae occur- 

 rences were at such stations. The distribution of 

 egg occurrences in relation to temperature was 

 similar in the 1971-72 and 1972-73 spawning sea- 

 sons. In 1971-72, 78.3% of the eggs occurred at 

 stations where surface temperatures were less 

 than 25°C; in 1972-73, 79.0% of the occurrences 

 were at temperatures below 25°C. Comparable 

 data were not available for the 1973-74 spawning 

 season. 



More than 50% of round herring eggs and 

 =s5.0-mm larvae were collected at stations where 

 surface salinity exceeded 36.00%o (Figure 7). For 

 eggs, considering all years' data, 79.7% of the oc- 

 currences were at surface salinities from 35.50 to 

 36.50%o; for «5.0-mm larvae, 80.0% of the occur- 

 rences were in that salinity range. In 1971-72, 

 88.0% of the egg occurrences were at stations with 

 surface salinities from 35.50 to 36.50%o; in 1972- 



74 



