FISHERY BULLETIN: VOL. 85, NO. 3 



larvae were never very abundant except at the 

 inshore San Bias station on the December 1980 

 cruise (Table 1), when a single dense patch of 

 larvae was encountered on two successive MOC- 

 NESS casts (Govoni et al. 1985). Densities were 

 as high as 993 larvae x 100 m"'^, an abundance 

 not observed for other species and not approached 

 by spot densities in any other sample. On the 



Table 2. — Mean standard length (mm, SE in parentheses) of gulf 

 menhaden caught on three cruises at inshore (18 m isobath) and 

 combined offshore (91 and 183 m isobaths) stations off Southwest 

 Pass, LA. F values are results of a two-way ANOVA comparing 

 lengths among cruises and between stations. 



Feb. 1980 15.2(0.3) 8.9(0.2) 21.8" 81.8" 62.6" 



Dec. 1980 13.5 (0.3) 8.7 (0.3) 



Feb. 1981 12.3 (0.2) 12.3 (0.2) 

 "P< 0.001. 



Inshore 

 2/80 



>- 

 o 



z 



UJ 



ID 



o 



LU 



cc 



LL 



LU 

 O 

 < 



z 



UJ 



o 



cr 



lU 



a. 



Offshore 

 2/80 



Inshore 

 12/80 



Offshore 

 12/80 



Inshore 

 2/81 



n= 383 Offshore 

 2/81 



LENGTH (mm) 



Figure 2. — Length-frequency distributions of gulf menhaden 

 larvae collected from inshore (18 m isobath) and offshore (91 

 and 183 m isobaths combined) stations off Southwest Pass, Lou- 

 isiana, on three cruises (February 1980, December 1980, and 

 February 1981). n = number of larvae measured. 



February 1981 cruise, no spot larvae were col- 

 lected at this station. The occurrence of this ag- 

 gregation, then, appeared to be a reflection of 

 patchiness rather than geography. 



An inshore-offshore comparison (Southwest 

 Pass stations) of menhaden lengths revealed that 

 on two of three cruises (February 1980 and De- 

 cember 1980) larvae were larger at the inshore 

 station (Table 2). This was not the case on the 

 third cruise, however, when mean lengths were 

 similar. Results of a two-way ANOVA (Table 2) 

 indicated significant differences in mean length 

 for both main effects of station and cruise and for 

 their interaction (P < 0.001). Thus, the pattern to 

 the data is more complex than can be summarized 

 by main effects alone. Length-frequency distribu- 

 tions indicated a bimodal pattern at the inshore 

 station with most larvae in the larger size mode 

 (Fig. 2). Larger larvae were not as common at the 

 offshore stations except on the final cruise, when 

 a bimodal pattern occurred offshore as well as 

 inshore. 



At the inshore stations, total larvae were gen- 

 erally distributed evenly among the three sam- 

 pling depths at all times of day (Fig. 3), although 



Table 3. — Mean density (larvae x lOO m^S) at each dis- 

 crete depth during each time period. MOCNESS casts in 

 which no larvae of the target species were caught at any of 

 the discrete depths were not included in calculation of 

 means. 



Time 



Station/species 



0600 



1200 



1800 2400 



Inshore 

 Total larvae 

 1 m 

 6 m 

 12 m 

 Gulf menhaden 

 1 m 

 6 m 

 12 m 

 Spot 

 1 m 

 6 m 

 12 m 

 Atlantic croaker 

 1 m 

 6 m 

 12 m 

 Offshore 

 Total larvae 

 1 m 

 30 m 

 70 m 

 Gulf menhaden 

 1 m 

 30 m 

 70 m 



68.23 120.97 341.10 76.36 

 56.01 25.76 144.20 86.82 

 42.44 25.24 69.20 173.78 



31.72 



4.54 



13.16 



1.36 

 0.76 

 0.82 



2.05 



4.08 



12.65 



103.90 

 35.41 

 23.38 



23.70 

 7.47 

 0.22 



37.35 48.83 

 0.14 101.06 

 0.60 29.93 



1.99 

 1.04 

 0.39 



1.07 

 4.05 

 1.32 



57.37 



21.30 



8.35 



35.60 

 0.00 

 0.39 



154.35 

 2.02 

 1.79 



2.47 

 3.61 

 4.57 



57.64 

 63.37 

 14.93 



14.36 

 7.77 

 0.42 



12.44 

 22.74 

 22.37 



8.13 



5.12 



34.63 



1.62 

 1.66 

 6.43 



49.65 

 42.37 

 14.29 



14.19 

 3.76 

 0.29 



604 



