COWAN AND SHAW: LARVAL SCIAENIDS COLLECTED OPT WEST LOUISIANA 



sand seatrout larvae v^'ere somewhat surface 

 oriented. 



Atlantic croaker, 

 Micropogon ias undiilatus 



The second most abundant sciaenid taken was 

 Atlantic croaker (A'^ = 567). Larval Atlantic 

 croaker density was greatest in February at 3.2/ 

 100 m'^, but density was relatively constant from 

 December through March (Table 1). Mean densi- 

 ties for December, January, March, and April 

 were 2.0, 2.2, 2.2, and 0.2/100 m^, respectively. 

 Atlantic croaker was the only sciaenid collected 

 in all months of the study. Their overall distribu- 

 tion (all sizes combined) was generally uniform 

 over most of the shelf (Fig. 3) except in March and 

 April when they were more often found inshore. 

 Recently spawned larvae (<3.0 mm TL) were also 

 collected over much of the shelf at station depths 

 ranging from 15 to 115 m or from about 20 to 200 

 km from shore. However, most small larvae were 

 collected near midshelf about 65-125 km from 

 shore. In December and January the majority of 

 the larvae were small. By April, no recently 

 spawned individuals were collected (Fig. 2B). For 

 the study overall, larvae were found in salinities 

 and temperatures ranging from 22 to 36 ppt and 

 from 10 to 20.5°C (Table 2). 



Spawning by Atlantic croaker in Gulf of Mexico 

 waters is reported to occur from September to 

 March, with a distinct peak in October (Hoese 

 1965; Sabins and Truesdale 1974; White and 

 Chittenden 1977; Benson 1982) and to occur pri- 

 marily offshore over a wide area (Pearson 1929; 

 Hildebrand and Cable 1930; Wallace 1940; Haven 

 1957; Bearden 1964; Hoese 1965; Nelson 1967). 

 Atlantic croaker larvae, however, have been 

 taken on the outer continental shelf off Texas 

 from September to May (Finucane et al. 1979). 



As with sand seatrout, a four-way ANOVA was 

 used to determine patterns in larva density and 

 distribution (Table 3). Larval Atlantic croaker 

 density by month was a highly significant main 

 effect (P <0.01). Densities at the end of their 

 spawning period were low, increased only slightly 

 in February, and then dropped off by April (Table 

 1). The interaction between month and day-night 

 was not significant. The highly significant inter- 

 action between month and depth group was not 

 surprising. Larvae were in more offshore waters 

 early in the study while later becoming more 

 abundant inshore (Fig. 3). However, as a main 

 effect, depth gi'oup was not significant. Larval 



Atlantic croaker mean densities for depth groups 

 1 through 4 were 3.9, 0.8, 0.4, and 0.7/100 m^, 

 respectively. Day-night, as a main effect, was 

 highly significant (P < 0.01). Larval Atlantic 

 croaker density was over 5 times higher at night 

 (all tow types combined) than during the day (3.7 

 vs. 0.7/100 m'^). However, the interaction between 

 day-night and horizontal tow type was not signif- 

 icant. The fourth main effect tested, horizontal 

 tow type, was not significant. Average catch rates 

 at the surface and near-bottom were similar (1.0 

 and 1.8/100 m'\ respectively). 



Spot, Leiostomiis xcmthurus 



The third most abundant sciaenid collected was 

 spot (A^ = 264). Density of spot larvae was highest 

 in December at 7.8 larvae/100 m'^ (Table 1). How- 

 ever, the high December value must be viewed 

 with a consideration of the abbreviated cruise 

 track for that month and the resultant reduction 

 in spatial coverage. Mean densities for January to 

 March were 1.3, 0.9, and 0.1/100 m"^, respectively. 

 No spot larvae were collected in April. In general, 

 larva density was low and their distribution was 

 uniform over the shelf out to the 40 m isobath, 

 about 130 km offshore (Fig. 4). Spot were col- 

 lected in temperatures and salinities ranging 

 from 10° to 18°C and from 26 to 36 ppt (Table 2), 

 and at stations with depths ranging from 5 to 65 

 m. 



Larvae >7 mm TL in our mid-December (Fig. 

 2C) collections and small larvae (<3.0 mm TL) in 

 all but the last cruise indicate that spawning 

 probably began by at least November and contin- 

 ued through March. Spawning occurred from 

 near midshelf (about 65 km) out to 175 km from 

 the coast. Data presented here partly concur with 

 previously published information on spot spawn- 

 ing periodicity. In the northern Gulf, spawning 

 reportedly occurs from late December to March, 

 peaking in January, and takes place well offshore 

 in moderately deep water (Pearson 1929; Kilby 

 1955; Townsend 1956; Dawson 1958; Springer 

 and Woodburn 1960; Pacheco 1962; Nelson 1967; 

 Joseph 1972; Music 1974; Sabins and Truesdale 

 1974). 



A four-way ANOVA indicated that month, as a 

 main effect for spot larvae, was highly significant 

 (P < 0.01 ), which probably reflects the decreasing 

 catch rates seen from January to March (Table 3). 

 The interaction between month and depth group 

 was also highly significant (P < 0.01) as was 

 depth group as a main effect. Larval spot 



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