FISHERY BULLETIN: VOL. 75, NO. 3 



CL 7105 



opisthoneha ogl1nuh larvae 



February - March 1974 



24' 



CL 7112 



0p1sthonema oglinum eggs 



May 1974 



82° 80" 



CL 7412 



opisthoneha oglinum larvae 



Hay 1974 



26° - 



26" 



24' 



86° 



82° 



80° 



84° 



82° 



FIGURE 6. — Distribution and abundance of thread herring eggs and larvae. Catches are standardized to numbers 

 under 10 m 2 of sea surface. A. Cruise CL7405, February-March 1974. No eggs were collected on this cruise. B, C. 

 Cruise CL7412, May 1974. 



2° to 3°C, with a maximum difference of 5°C ob- 

 served. At the 50-m depth, temperatures differed 

 from the surface by as much as 9°C, but usually by 

 3° to 5°C. Because most spawning takes place at 

 depths less than 30 m, it is unlikely that spawning 

 and surface temperatures differed by more than 

 2°C. Salinity did not differ by more than l%o from 

 surface to the 50-m depth, except in 1973, when 

 surface salinities over wide areas during summer 

 were depressed (Anonymous 1975) 4 due to Missis- 



"Anonymous. 1975. Compilation and summation of historical 

 and existing physical oceanographic data from the eastern Gulf 

 of Mexico. State Univ. Syst. Fla., Inst. Oceanogr., St. Petersburg, 

 Fla. Final Rep. to U.S. Bur. Land Manage., Contract No. 

 08550-CT4-16, 97 p., 10 app. 



sippi River runoff some months earlier. In 1973 

 salinity differences as great as 4%o between sur- 

 face and 50 m were observed in areas where some 

 thread herring spawning occurred. Small larvae 

 (s=5.0 mm standard length [SL]), <5 days old, were 

 collected where surface temperatures were 18.5° 

 to 30.9°C and salinities were 27.3 to 36.9%o. The 

 ranges were greater for larvae than for eggs. 



Based on combined 1971-74 data, most thread 

 herring eggs and $5.0-mm larvae were collected 

 at surface temperatures from 25.1° to 30.0°C (Fig- 

 ure 7). All stations with eggs and more than 98% of 

 the stations with s=5.0-mm larvae had surface 

 temperatures above 22°C. More than 74% of the 



500 



