244 
Fishery Bulletin 11 6(3-4) 
Table 2 
Mean values, with standard errors (SEs), for sample displacement volume (mL), total 
number of larvae caught (raw counts), standardized larval abundances, volume filtered 
(m 3 ), and total number of eggs (raw counts) of samples collected with bongo nets that 
had different mesh sizes, 0.202 mm (rc=81) and 0.333 mm (n=81), during Southeast Area 
Monitoring and Assessment Program surveys in the northern Gulf of Mexico during 
2005-2007. The standardized larval abundances were calculated as the number of larvae 
per 1000 m 3 of filtered sea water and as the number of larvae caught in a sample by the 
volume of water filtered during the tow, multiplied by the maximum depth of the tow in 
meters and the factor 10 (abundance under 10 m 2 of sea surface). P-values and adjusted 
a levels are listed for paired Wilcoxon signed-rank tests. Asterisks denote significant 
differences between samples from the nets with the 2 mesh sizes. 
Mean 
0.202 mm 
(SE) 
0.333 mm 
P-value 
Adj. a 
Displacement volume 
32 (2.7) 
19(1.3) 
<0.0001 
0.0083* 
Total number of larvae 
465(102.1) 
299(73.5) 
<0.0001 
0.01* 
Abundance per 1000 m 3 
4665(1340.7) 
2660(797.3) 
<0.0001 
0.0125* 
Abundance under 10 m 2 
2455(557.3) 
1537(342) 
<0.0001 
0.0167* 
Volume filtered 
171 (9.3) 
170 (9.5) 
0.1888 
0.025 
Total number of eggs 
778 (591.6) 
596 (390.4) 
0.9498 
— 
Table 3 
Summary of total number of larvae caught and standardized total and mean larval abundances in samples collected with 
nets of 2 different mesh sizes in the northern Gulf of Mexico during 2005-2007. Values are given for unidentified larvae 
and larvae of 6 taxa of interest: Percoidei, Engraulidae, Clupeidae, Scombridae, Sciaenidae, and Lutjanidae. Asterisks rep¬ 
resent significant statistical differences in mean larval abundances (paired t-tests) and length-frequency distributions (K-S 
test) between paired samples from the nets with 2 different mesh sizes, 0.202 mm and 0.333 mm. Larval abundance was 
calculated as the number of larvae caught in a sample per the volume of water filtered during the tow multiplied by the 
maximum depth of the tow in meters and the factor 10 (number under 10 m 2 of sea surface). 
Total larvae Total abundance Mean abundance (SE) 
Taxa 
Body shape 
0.202 
mm 
0.333 
mm 
0.202 
mm 
0.333 
mm 
0.202 
mm 
0.333 
mm 
P-value 
K-S 
test 
Unidentified 
Undetermined 
3808 
430 
22,141 
2335 
273(125) 
29 (9) 
0.02* 
* 
Percoidei 
Perciform 
1227 
180 
4614 
699 
58 (28) 
9(3) 
0.03* 
* 
Engraulidae 
Clupeiform 
1261 
1306 
5246 
5642 
65(22) 
69 (26) 
0.31 
* 
Clupeidae 
Clupeiform 
8283 
7102 
36,207 
31,290 
447(373) 
386 (330) 
0.09 
* 
Scombridae 
Perciform 
432 
256 
2447 
1404 
30 (10) 
17 (4) 
0.06 
* 
Sciaenidae 
Perciform 
4674 
1901 
32,874 
10,582 
406 (297) 
131(66) 
0.18 
* 
Lutjanidae 
Perciform 
307 
292 
1525 
1448 
19 (4) 
19(4) 
0.33 
* 
a total of 111,283 eggs and 61,950 fish larvae repre¬ 
senting 252 taxa. Samples collected from nets with 
the finer mesh (0.202 mm) contained more larvae than 
samples from nets with the larger mesh (0.333 mm)— 
37,696 versus 24,254 larvae—an increase of 55.4%. 
For all tows combined by mesh size, samples from nets 
with a 0.202-mm mesh had significantly higher mean 
displacement volumes (68.4% difference), number of 
larvae (55.5%), larvae per 1000 m 3 (75.4%), and larvae 
under 10 m 2 (59.7%) than samples from nets with a 
0.333-mm mesh (Table 2). Mean number of eggs did not 
vary significantly between mesh sizes (0.6% difference). 
Volume of water filtered, by mesh size, ranged from 27 
to 382 m 3 for the samples from nets with a 0.202-mm 
mesh and from 40 to 380 m 3 for the samples from nets 
with a 0.333-mm mesh. Mean volume filtered did not 
vary significantly between the mesh sizes (30.5% dif¬ 
ference; Table 2). Additionally, regressions of volume 
filtered by tow depth revealed similar filtering efficien¬ 
cies for both mesh sizes over the range of sampling 
depths, tow durations, and the broad spatial extent of 
our study (y=1.1003x+55.036, coefficient of determina- 
