478 
Abstract — Ichthyoplankton surveys 
were conducted in shelf and slope 
waters of the northern Gulf of Mexico 
during the months of May— September 
in 2005 and 2006 to investigate the 
potential role of this region as spawn- 
ing and nursery habitat of sailfish 
( Istiophorus platypterus). During the 
two-year study, 2426 sailfish larvae 
were collected, ranging in size from 
2.0 to 24.3 mm standard length. Mean 
density for all neuston net collections 
(n= 288) combined was 1.5 sailfish per 
1000 m 2 , and maximum density was 
observed within frontal features cre- 
ated by hydrodynamic convergence 
(2.3 sailfish per 1000 m 2 ). Sagittal 
otoliths were extracted from 1330 
larvae, and otolith microstructure 
analysis indicated that the sailfish 
ranged in age from 4 to 24 days after 
hatching (mean=10.5 d, standard de- 
viation [SD] = 3.2 d). Instantaneous 
growth coefficients ( g ) among survey 
periods (n = 5) ranged from 0.113 to 
0.127, and growth peaked during 
July 2005 collections when density 
within frontal features was high- 
est. Daily instantaneous mortality 
rates ( Z ) ranged from 0.228 to 0.381, 
and Z was indexed to instantaneous 
weight-specific growth (G) to assess 
stage-specific production potential 
of larval cohorts. Ratios of G to Z 
were greater than 1.0 for all but one 
cohort examined, indicating that 
cohorts were gaining biomass during 
the majority of months investigated. 
Stage-specific production potential, 
in combination with catch rates and 
densities of larvae, indicates that 
the Gulf of Mexico likely represents 
important spawning and nursery 
habitat for sailfish. 
Manuscript submitted 4 March 2010. 
Manuscript accepted 28 July 2010. 
Fish. Bull. 108:478-490 (2010). 
The views and opinions expressed 
or implied in this article are those 
of the author (or authors) and do not 
necessarily reflect the position 
of the National Marine Fisheries 
Service, NOAA. 
Distribution, growth, and mortality 
of sailfish (Istiophorus platypterus ) larvae 
in the northern Gulf of Mexico 
Jeffrey R. Simms 1 (contact author) 
Jay R. Rooker 1 
Scott A. Holt 2 
G. Joan Holt 2 
Jessica Bangma 3 
Email address for contact author: jsimms@entrix.com 
1 Department of Marine Biology 
Texas A&M University at Galveston 
P.O. Box 1675 
Galveston, Texas 77553 
2 University of Texas Marine Science Institute 
University of Texas at Austin 
750 Channel View Dr. 
Port Aransas, Texas 78383 
3 Department of Zoology 
University of British Columbia 
6270 University Boulevard 
Vancouver, BC, Canada V6T 1Z4. 
Declining populations of Atlantic 
sailfish (Istiophorus platypterus) 
(ICCAT, 2001) emphasize the need 
for a better understanding of their 
biology, especially processes affect- 
ing growth and mortality during 
early life because these mechanisms 
often regulate recruitment (Fuiman, 
2002). To date, studies on sailfish 
biology during the early life interval 
are limited; however, recent research 
conducted in the Straits of Florida 
indicates that sailfish grow rapidly 
and experience high mortality during 
early life (Luthy et al., 2005; Rich- 
ardson et al., 2009a). Although our 
understanding of the early life ecol- 
ogy of sailfish has improved in recent 
years, work to date has been limited 
in geographic scope and basic life his- 
tory data on sailfish are limited or 
not available for other regions of the 
Atlantic that may represent essential 
spawning and nursery habitat of sail- 
fish. In particular, bycatch data from 
pelagic longline fisheries in the Gulf 
of Mexico indicate that catch rates 
for sailfish are twofold higher in the 
Gulf than in other areas of the North 
Atlantic during the presumed spawn- 
ing season (May-September; de Sylva 
and Breder, 1997; NMFS 1 ). Because 
spawning stock biomass appears high 
in this region, a better understand- 
ing of the role of the Gulf of Mexico 
as spawning and early life habitat of 
Atlantic sailfish is essential. 
The Gulf of Mexico supports one 
of the most productive fisheries in 
the world (Chesney et al., 2000), and 
oceanographic features within the 
Gulf are influenced by inflow from 
the Mississippi River and large-scale 
oceanographic features, such as the 
Loop Current and associated warm 
and cold core eddies (Govoni and 
Grimes, 1992; Sturges and Leben, 
2000). Physicochemical conditions 
and primary production vary mark- 
edly within and across these features 
(Grimes and Finucane, 1991; Biggs, 
1992), and have been shown to af- 
fect the distribution and growth of 
pelagic larvae in the Gulf (Govoni et 
al., 1989; de Vries et al., 1990; Lang 
et al., 1994). Namely, higher densities 
1 NMFS (National Marine Fisheries Ser- 
vice. 2008. NMFS Pelagic Longline 
Logbook data, (http://www.sefsc.noaa. 
gov/flslandingsdata.jsp, accessed Decem- 
ber 2008). 
