482 
Fishery Bulletin 108(4) 
Table 2 
Mean environmental conditions (± standard deviation [SD]) for ichthyoplankton surveys in the northern Gulf of Mexico in 
2005 and 2006. Environmental parameters were recorded at the surface for each sampling station. Dissolved oxygen is 
not reported for the August 2006 survey because of a probe malfunction (NA). 
Year 
Survey 
Date 
Temperature (°C) 
Salinity (ppt) 
Dissolved oxygen (mg/L) 
2005 
May 
17-22 
26.4(0.9) 
35.5 (0.7) 
7.1 (0.7) 
July 
23-28 
30.4(0.7) 
35.2(1.3) 
6.8 (1.2) 
September 
16-19 
29.8(0.6) 
36.5 (0.6) 
6.3 (0.4) 
All surveys 
28.8(2.0) 
35.6 (1.1) 
6.8 (1.0) 
2006 
June 
15-20 
28.7 (0.5) 
35.8 (0.4) 
6.6 (0.1) 
August 
31 July- 5 Aug 
30.1 (0.3) 
36.2(0.4) 
NA 
All surveys 
29.4(0.8) 
36.0 (0.5) 
NA 
Table 3 
Total catch, frequency of occurrence, and density (± standard deviation [SD] ) of sailfish ( Istiophorus platypterus ) larvae collected 
from the northern Gulf of Mexico in 2005 and 2006 arranged by survey. Number of stations during each survey (n) shown. Per- 
cent frequency of occurrence was based on collection stations during each survey that yielded 1 or more larvae. 
Survey 
n 
Sailfish 
catch 
Frequency of 
occurrence 
Density 
(± SD) (no. /1000m 2 ) 
Maximum 
density 
Larvae/hour 
May 2005 
60 
212 
26.7 
0.6 (1.8) 
10.5 
10.6 
July 2005 
62 
755 
56.5 
2.1 (7.5) 
51.4 
36.5 
Sept 2005 
39 
134 
46.2 
0.6 (1.3) 
4.5 
10.3 
June 2006 
62 
691 
48.4 
2.0 (4.7) 
22.1 
33.4 
Aug 2006 
65 
634 
47.0 
1.7 (3.0) 
10.2 
25.4 
Total 
288 
2426 
45.0 
1.5 (4.5) 
24.4 
PcO.Ol) (Table 2). Spatial variation in salinity was 
detected among oceanographic features (ANOVA, P l3 
270) =16.8, PcO.Ol), and lowest salinity observed within 
open ocean and cyclonic features (35.5 ppt and 35.6 ppt, 
respectively) and higher salinity in anticyclonic and fron- 
tal features (36.1 ppt and 36.1 ppt, respectively) (Table 
1). Mean salinity was 35.6 ppt and 36.0 ppt in 2005 
and 2006, respectively, and significant variation was 
observed among the five surveys (ANOVA, P (4 270) =11.1, 
PcO.Ol) (Table 2). Dissolved oxygen (DO) varied sig- 
nificantly among oceanographic features (ANOVA, P (3 
270) =2.7, P=0.048) and surveys (ANOVA, P (4 270) =38.9, 
PcO.Ol) (Table 2). Lower DO levels were observed within 
anticyclones, fronts, and the open ocean (6.8 mg/L, 6.6 
mg/L, and 6.7 mg/L, respectively) compared to those 
within cyclonic features (7.2 mg/L) (Table 1). 
Spatial and temporal patterns of abundance 
A significant interaction effect between oceanographic 
feature and survey on the density of sailfish was detected 
(ANOVA, F (10 271) =2.1, P=0.02), and highest densities 
were observed within frontal features in three of five 
surveys and in the open ocean during the remaining 
surveys (Fig. 1). No individual effect of oceanographic 
feature or survey on density was observed (feature 
P=0.06, survey P=0.11), although density was lowest 
within cyclones during all surveys. When data from all 
surveys were combined, significant spatial variation 
in the density of sailfish among oceanographic features 
was observed (ANOVA, P (3 285) =3.3, P=0.02); density 
within cyclones was lower than that within other fea- 
tures (P<0.05). 
Frequency of occurrence and relative abundances 
were highest in June (48.4%), July (56.5%), and August 
(47.0%) surveys and lowest during the May 2005 survey 
(26.7%) (Table 3). The overall density of sailfish was 1.5 
larvae per 1000 m 2 ; lowest densities were observed in 
May and September 2005 surveys (0.6 larvae per 1000 
m 2 and 0.6 larvae per 1000 m 2 , respectively) and higher 
densities during July 2005 (2.1 larvae per 1000 m 2 ), 
June 2006 (2.0 larvae per 1000 m 2 ), and August 2006 
(1.7 larvae per 1000 m 2 ) (Table 3). Catches peaked in 
July 2005 and June 2006 when maximum densities of 
51.4 larvae per 1000 m 2 and 22.1 larvae per 1000 m 2 
were observed, respectively (Table 3). The overall catch 
per unit of effort (CPUE) for sailfish in the northern 
Gulf was 24.4 larvae per hour, and highest CPUEs 
were reported for July 2005 (36.5), June 2006 (33.4), 
and August 2006 (25.4) (Table 3). 
