KISHERY BULLETIN; VOL. 86, NO. 1 



pled at 10-, 17-, 24-, and 31-d posthatch were ex- 

 amined. 



In January 1984 additional larvae were reared 

 to compliment results of the earlier experiment. 

 Smaller tanks with 60 larvae in 10 L of filtered 

 water were used. Experimental conditions were 

 the same as for the first experiment. The otoliths 

 of larvae sampled at 7-, 14-, and 20-d posthatch 

 were examined. 



Larval Collections 



Larval gulf menhaden were collected in the 

 northern Gulf of Mexico during six cruises of the 

 RV Oregon II. Sampling stations (Fig. 1) along 

 transects LA (off Louisiana) and FL (off Florida) 

 were occupied during 11-19 December 1979, 5- 

 15 February 1980, and 2-12 December 1980 and 

 along transects LA, FL, and TX (off Texas) during 

 9-24 February 1981, 2-13 December 1981, and 

 4-16 February 1982. Transect LA is near the 

 Mississippi River outflow off Southwest Pass, LA; 

 transect FL is southwest of Cape San Bias, FL; 

 and transect TX is located off Galveston Bay, TX. 

 Sampling stations were in water depths of 18, 91, 

 and 183 m except off Texas where only the 18 and 

 91 m depths were sampled. 



A multiple opening-closing net and environ- 

 mental sensing system (MOCNESS) as described 

 by Wiebe et al. ( 1976) were the primary sampling 

 gear used to capture larvae. Additional samples 

 were taken in oblique tows with a 60 cm bongo 



frame also fitted with 505 fjim mesh nets. Samples 

 were collected day and night and were preserved 

 in 95Vf ethanol (final concentration ^757^ ) within 

 5 minutes of collection. The ethanol was changed 

 in all samples at least once after initial preserva- 

 tion to prevent dissolution of otoliths in fish from 

 any samples that may have been inadequately 

 preserved. Data from larvae collected at all sta- 

 tions within a transect were combined for that 

 transect. 



Estimating Age and Growth 



All gulf menhaden larvae were measured to the 

 nearest 0.1 mm standard length (SL). The largest 

 otolith pair (sagittae) was teased from the sur- 

 rounding tissue, cleaned in distilled water, and 

 then placed on a glass microslide under a thin 

 layer of Flo-Texx-^ mounting medium. 



Otoliths were viewed with a compound micro- 

 scope fitted with a television camera. Growth in- 

 crements were counted from otolith images on a 

 video monitor at magnifications of at least 400 x. 

 An increment appeared as a light, wide incremen- 

 tal band and a dark, narrow, discontinuous band 

 (Tanaka et al. 1981). Increments were generally 

 clearly discernable and easily counted (Fig. 2). 

 Estimated age was the number of increments 

 counted plus an empirically derived value for the 



2Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



96 00' 94° 00' 92° 00' 90° 00' 88° 00' 86° 00' 84° 00' 



30° 00' 



28° 00' 



26° 00' 



Figure l. — Location of sampling sites from which larval gulf menhaden were collected during crui-ses of the RV Oregon II in 



December 1979-81 and February 1980-82. 



78 



