Simms et al.: Distribution, growth, and mortality of larval Istiophorus platypterus in the northern Gulf of Mexico 
483 
Table 4 
Exponential growth models arranged by survey 
and oceanographic feature for sailfish (Istiopho- 
rus platypterus) larvae collected from the northern 
Gulf of Mexico in 2005 and 2006. Number of larvae 
collected within each feature is given ( n ). Cyclones 
excluded from analysis because of low sample sizes 
within this type of feature. * indicates significant 
growth difference among features. 
Survey 
Feature 
n 
Growth model 
July 2005 
Anticyclone 
135 
1.289e 0128(a s e) 
Front 
45 
1.458e° 122(agc) 
Open ocean 
108 
1.331e 0124(age) 
June 2006 
Anticyclone 
21 
1 7i3e° 
Front 
108 
1.415e° 120<a ^ e) 
Open ocean 
118 
1.526e 0112(a ^> 
August 
Anticyclone 
131 
1.682e 0105(a ^ e, * 
2006 
Front 
166 
1.480e° u4(a « e) 
Open ocean 
149 
1.442e° 117(a ^ e) * 
Sailfish length and age distributions 
No significant difference in mean standard lengths 
of sailfish was observed between 2005 (5.1 mm, 
standard deviation [SD]=2.1) and 2006 (4.9 mm, 
SD=2.0) (ANOVA, F (1 2352) = 3.3, P-0.07) (Fig. 2). 
Sailfish were most abundant in the 3-6 mm size 
range, with 70.4% and 65.9% of the catch in this 
size range in 2005 and 2006, respectively. Intra- 
annual differences in mean lengths of sailfish were 
observed in 2005 (ANOVA, F (2 1034) =62.6, PcO.Ol) 
and 2006 (ANOVA, F (1 1315) =75.8, PcO.Ol); small- 
est mean lengths were observed in May 2005 (4.1 
mm, SD-1.6) and June 2006 (4.5 mm, SD-1.6), 
and larger larvae were collected in July 2005 (5.4 
mm, SD-2.2) and August 2006 (5.4 mm, SD-2.3). 
Mean ages were statistically similar between 
2005 (10.1 days, SD-3.1 days) and 2006 (10.5 
days, SD-3.2) (ANOVA, F (1 1234) =2.7, P-0.10) 
(Fig. 2). Sailfish larvae were most abundant in 
the 7-11 day range, with 60.7% and 53.9% of 
the catch in this age range in 2005 and 2006, 
respectively. Significant intra-annual variation 
in sailfish mean ages was observed in 2005 
(ANOVA, P (2 521) =51.6, PcO.Ol) and 2006 (ANOVA, 
F(\ 7ioi = 47.9, P<0.01), when youngest mean age was ob- 
served in May 2005 (8.0 days, SD-2.3) and June 2006 
(9.4 days, SD-3.1), and older larvae were observed in 
July 2005 (11.0 days, SD-3.3) and August 2006 (11.0 
days, SD-3.1). 
Spatial and temporal patterns of growth 
Spatial variation in growth was analyzed across oceano- 
graphic features (anticyclone, front, and open ocean) for 
three of the five surveys, and significant differences in 
100 -i 
□ 
Anticyclone 
■ 
Open ocean 
0 
Front 
□ 
Cyclone 
May 2005 July 2005 September June 2006 August 
surveys 
2005 
2006 
100 
w 2 
03 to 
CO CD 
2 ^ 
o a 
<D 
75 
50 
25 
& 2 
B 
i 
M 
May 2005 July 2005 September June 2006 August All 
2005 2006 
surveys 
2005 
2006 
Figure t 
(A) Percentage of sample collections of sailfish (Istiophorus 
platypterus) conducted within each oceanographic feature 
during ichthyoplankton surveys the northern Gulf of Mexico 
in 2005 and 2006. (B) Percentage of sailfish larvae collected 
within each oceanographic feature. (C) Mean density of sail- 
fish larvae within each feature. Error bars represent one 
standard deviation (SD). 
growth were observed during August 2006 collections 
(Table 4). Cyclones were excluded from our analysis 
because of low sample sizes within this type of feature. 
During the August 2006 survey, daily instantaneous 
growth rates (g) of larvae collected within anticyclones 
(g= 0.105) was significantly slower than growth of larvae 
collected in the open ocean (g=0.117) (ANCOVA, slopes, 
F( 2 44 o> = 3-4’ P-0.03) (Table 4). In contrast, growth did 
not differ significantly among the three features in July 
2005 (anticyclones g=0.128, fronts g=0.122, and open 
ocean g= 0.124) and June 2006 (anticyclones g-0.101, 
fronts g-0.120, and open ocean g-0.112) (ANCOVA, 
