Sailfish Istiophorus Platypterus Research Articles

Patrolling the border: Billfish exploit the hypoxic boundary created by the world's largest oxygen minimum zone.

Pelagic predators must contend with low prey densities that are irregularly distributed and dynamic in space and time. Based on satellite imagery and telemetry data, many pelagic predators will concentrate horizontal movements on ephemeral surface fronts-gradients between water masses-because of enhanced local productivity and increased forage fish densities. Vertical fronts (e.g. thermoclines, oxyclines) can be spatially and temporally persistent, and aggregate lower trophic level and diel vertically migrating organisms due to sharp changes in temperature, water density or available oxygen. Thus, vertical fronts represent a stable and potentially energy rich habitat feature for diving pelagic predators but remain little explored in their capacity to enhance foraging opportunities. Here, we use a novel suite of high-resolution biologging data, including in situ derived oxygen saturation and video, to document how two top predators in the pelagic ecosystem exploit the vertical fronts created by the oxygen minimum zone of the eastern tropical Pacific. Prey search behaviour was dependent on dive shape, and significantly increased near the thermocline and hypoxic boundary for blue marlin Makaira nigricans and sailfish Istiophorus platypterus, respectively. Further, we identify a behaviour not yet reported for pelagic predators, whereby the predator repeatedly dives below the thermocline and hypoxic boundary (and by extension, below the prey). We hypothesize this behaviour is used to ambush prey concentrated at the boundaries from below. We describe how habitat fronts created by low oxygen environments can influence pelagic ecosystems, which will become increasingly important to understand in the context of global change and expanding oxygen minimum zones. We anticipate that our findings are shared among many pelagic predators where strong vertical fronts occur, and additional high-resolution tagging is warranted to confirm this.

Hunting behavior of a solitary sailfish Istiophorus platypterus and estimated energy gain after prey capture

Foraging behavior and interaction with prey is an integral component of the ecological niche of predators but is inherently difficult to observe for highly mobile animals in the marine environment. Billfishes have been described as energy speculators, expending a large amount of energy foraging, expecting to offset high costs with periodic high energetic gain. Surface-based group feeding of sailfish, Istiophorus platypterus, is commonly observed, yet sailfish are believed to be largely solitary roaming predators with high metabolic requirements, suggesting that individual foraging also represents a major component of predator–prey interactions. Here, we use biologging data and video to examine daily activity levels and foraging behavior, estimate metabolic costs, and document a solitary predation event for a 40 kg sailfish. We estimate a median active metabolic rate of 218.9 ± 70.5 mgO2 kg−1 h−1 which increased to 518.8 ± 586.3 mgO2 kg−1 h−1 during prey pursuit. Assuming a successful predation, we estimate a daily net energy gain of 2.4 MJ (5.1 MJ acquired, 2.7 MJ expended), supporting the energy speculator model. While group hunting may be a common activity used by sailfish to acquire energy, our calculations indicate that opportunistic individual foraging events offer a net energy return that contributes to the fitness of these highly mobile predators.

Trends and variability in local abundances of sailfish Istiophorus platypterus in Pacific waters of Costa Rica: Controls and effects on recreational fisheries

Fishing tourism represents a vital industry in Costa Rica, generating over US$520 million and attracting 150,000 tourists every year. The main objective of this study is to examine trends and variability in local abundances of sailfish Istiophorus platypterus, the main sportfish in Pacific waters of Costa Rica, and quantify the influence of environmental and anthropogenic factors. We compiled and analyzed sailfish information collected from sportfishing operations. Sailfish abundances were examined in relation to environmental conditions and commercial fishing. Timeseries analyses showed significant declining trends in local abundances of sailfish in the southern and central Pacific of Costa Rica over the last decade. Bycatch records from the commercial purse seine fleet operating in Costa Rican waters also show a declining trend in sailfish numbers. On the other hand, commercial landings from the national longline fleet show a significant increase of 108%, on average, over the past decade. Different numerical models indicated that fishing pressure from the national fleet and also sea surface temperature with different time lags affect local abundances of sailfish. While other countries in Central and North America protect sailfish and other species of tourist interest, Costa Rica still allows the landing and sales of billfishes as seafood. The results presented in this study highlight the need to allow for the recovery of local abundances of sailfish and promote the development of the coastal communities that depend on marine tourism as their main source of income.

Lacunae rostralis: A new structure on the rostrum of sailfish Istiophorus platypterus.

Recent comparative studies of billfishes (Istiophoridae and Xiphiidae) have provided evidence of differences in the form and function of the rostra (bill) among species. Here, we report the discovery of a new structure, lacuna rostralis, on the rostra of sailfish Istiophorus platypterus, which is absent on the rostra of swordfish Xiphias gladius, striped marlin Kajikia audax and blue marlin Makaira nigricans. The lacunae rostralis are small cavities that contain teeth. They were found on the ventral rostrum surface of all I. platypterus specimens examined and dorsally in half of them. Ventrally, the lacunae rostralis were most prominent in the mid-section of the rostrum. Dorsally, they occurred closer to the tip. The density of lacunae rostralis increased towards the rostrum tip but, because they are smaller in size, the percentage of rostrum coverage decreased. The teeth located within the lacunae rostralis were found to be different in size, location and orientation from the previously identified micro-teeth of billfish. We propose two potential functions of the lacunae rostralis that both relate to the use of the bill in feeding: mechanoreception of prey before tapping it with the bill and more efficient prey handling via the creation of suction, or physical grip.

Biomimetics Design Optimization and Drag Reduction Analysis for Indonesia N219 Seaplanes Catamaran Float

Design optimization on the Indonesia N219 seaplane catamaran is necessary to provide better service to rural islands of Indonesia. This research aims at decreasing drag using a design based on biomimicry by imitating the hydrodynamic characteristics of sailfish (Istiophorus platypterus) for pontoon floats. The design is then validated using a numerical fluid test using ANSYS Fluent to see the reduction in drag due to the change from a conventional or Wipeline® 13000 design to a biomimetics adaptation design. Next, further optimization was carried out based on the adaptation design based on trim tests, clearance tests, and deadrise angle dimensions suitable for biomimicry designs at Froude number speeds of 0.4 to 0.7. The design results with the adaptation of biomimicry show that a change in the design with this optimization affects a drag reduction that reaches 30% of the total drag generated by the conventional design.

Global phylogeography of sailfish: deep evolutionary lineages with implications for fisheries management

Since the Miocene profound climatic changes have influenced the biology and ecology of species worldwide, such as their connectivity, genetic population structure, and biogeography. The goal herein is to evaluate the phylogeography of sailfish Istiophorus platypterus between the Atlantic, Indian, and Pacific oceans. Our results evidenced a high genetic diversity and three distinct populations among the ocean basins with limited gene flow among them. In addition, the species is characterized by two deep evolutionary lineages that diverged during the Miocene/Pliocene transition, one of them is circumtropical while the other is restricted to the Atlantic Ocean. These lineages evolved along the successive glacial-interglacial cycles from the Pleistocene and remained isolated from each other in glacial refugium until deglaciation. Assessments of sailfish suggest it may be subject to overfishing and the results herein imply the need to re-evaluate the current stock delimitations and management measures adopted by the Regional Fisheries Management Organizations, especially in the Atlantic and the Indo-Western Pacific oceans to effectively manage the species. In addition, this work highlights that both lineages should at least be treated as two distinct management units in the Atlantic Ocean until their taxonomic status is fully resolved, given their high genetic divergence.

Arsenic in the top predators sailfish (Istiophorus platypterus) and dolphinfish (Coryphaena hippurus) off the southeastern Gulf of California.

Distribution of arsenic (As) in tissues and gonads of the Indo-Pacific sailfish Istiophorus platypterus and the dolphinfish Coryphaena hippurus from the SE Gulf of California was evaluated. The bioaccumulation patterns of As were the same in the two species. In I. platypterus, As levels (mg kg-1, wet weight) were gonads (7.4 ± 1.1) > liver (3.1 ± 0.1) > kidney (2.7 ± 0.1) > muscle (1.6 ± 0.1); in C. hippurus, As (mg kg-1) levels were gonads (4.3 ± 0.6) > liver (3.2 ± 0.2) > kidney (2.3 ± 0.1) > muscle (1.2 ± 0.1). Differences in As distribution could be attributed to the biological functions of tissues. The hypothesis was confirmed that biomagnification was evidenced by the fact that As levels were lower in prey species than in predators. Intake of muscle from either fish did not represent a risk to humans if recommended portions a week are not exceeded, adults as much as 1802.4g and 2454.1g and children 257.5 and 350.6g, for sailfish and dolphinfish, respectively. In addition, the likelihood of developing cancer due to consumption of edible tissues from either of these top predators was in the acceptable range (6.4 × 10-5 to 27.3 × 10-6 for a population that consumes 50g of muscle in a week) but if a conservative combined slope factor is used the probabilities to develop bladder and lung cancer increments from 1.1 × 10-3 to 9.1 × 10-5.

Biología reproductiva del pez vela Istiophorus platypterus en la Bahía de Acapulco, Méxic

Biología reproductiva del pez vela Istiophorus platypterus en la Bahía de Acapulco, Méxic

Biología reproductiva del pez vela Istiophorus platypterus en la Bahía de Acapulco, Méxic

Background. The sailfish Istiophorus platypterus is a viviparous billfish species, it is caught by trolling in the sports fishery in Mexico. However, to date, there has been no reproductive biology studies of sailfish in Acapulco Bay, although the reproductive aspects of any species represent essential information for the design of management plans. Goals. Estimate the spawning frequency and batch fecundity to quantify reproductive characteristics of sailfish in waters off Acapulco, Bay. Methods. During the period 2008–2019, a total of 581 fish were sampled. Macroscopy analysis and quantitative histology was used to describe reproductive characteristics of the sailfish gonads. Results. 55.8% of the organisms analyzed were males, the remaining 44.2% were females, the sex ratio (1.26 M: 1 H) was different from the expected theoretical ratio (X2 = 7.53). The ovaries of 155 females were classified into five ovarian development phases based on histological analysis of the most advanced group of oocytes. Sailfish are multiple spawners with asynchronous oocyte development. Batch fecundity for 14 females with the presence of hydrated oocytes but without postovulatory follicles ranged 0.330 to 2.092 × 106 eggs with an average of 1.07 × 106 eggs. Gonadosomatic indices (GSI) indicated that sailfish have a reproductive period with peaks in August and October (mean monthly GSI= 4.3% and 5.4%). Conclusions. Population sailfish in Acapulco Bay is composed of males and females in similar proportions, with a gonadal development by groups that can be described in five development phases, a reproductive maximum during the warm months of the year and a relatively high fecundity.

Nuevos registros de peces para el área marina del Parque Nacional Sistema Arrecifal Veracruzano, suroeste del Golfo de México

Presentamos cinco nuevos registros de peces para el área marina del Parque Nacional Sistema Arrecifal Veracruzano, con evidencia fotográfica y se proveen los datos morfométricos y merísticos básicos: el miraestrellas Gillellus greyae (70.3 mm, Longitud total), el góbido Oxyurichthys stigmalophius (36 mm, Longitud total), el cochito manchado Canthidermis maculata (342.4 mm, Longitud total) y el pez vela Istiophorus platypterus (?1,800 mm, Longitud total) se distribuyen ampliamente en el Caribe; además del primer registro en el Golfo de México del lenguado manchado Bothus maculiferus (250 mm, Longitud total).

Incorporating depth into habitat use descriptions for sailfish Istiophorus platypterus and habitat overlap with other billfishes in the western North Atlantic

The sailfish Istiophorus platypterus is a circumglobal billfish species. It is commonly targeted in recreational fisheries and caught as by-catch in commercial fisheries, and therefore fisheries management would benefit from an enhanced understanding of basic patterns of the species’ daily and seasonal movements. Between 2002 and 2007, 87 billfish were tagged with pop-off satellite archival tags in the Atlantic waters off the coast of South Carolina, USA, including sailfish (n = 54), blue marlin Makaira nigricans (n = 15), and white marlin Kajikia albida (n = 18). Only fish meeting specific tag program criteria and length of tag attachment were selected for further analysis (sailfish, n = 19; blue marlin, n = 4; white marlin, n = 3). Differential horizontal and vertical movement patterns were observed within sailfish by season. Two- and three-dimensional (3D) analyses showed differential spatial niche use by sailfish. Among the istiophorid species, 3D analysis showed less overlap when occupying similar horizontal areas. The results from this study, in conjunction with similar studies from other areas, provide a better understanding of habitat usage that can be applied to address uncertainties in ecology or management, such as characterization of stock structure, identifying potential spawning habitat or intra-specific competition, providing correction factors for indices of abundance, and characterizing vulnerability to fishing gear.

Reproductive biology and space–time modelling of spawning for sailfish Istiophorus platypterus in the western Atlantic Ocean

ABSTRACTThis study presents data and estimates reproductive parameters of the sailfish Istiophorus platypterus (Shaw, 1792) in the western Atlantic, useful for future stock assessments of the species in the Atlantic Ocean. During the period 2006–2011, a total of 1132 fish were sampled by scientific observers on board Venezuelan and Brazilian longline vessels and from artisanal fisheries based out of Cumaná, Puerto La Cruz and Playa Verde, Venezuela and Cabo Frio, Rio de Janeiro, Brazil. The ovaries of 543 females were classified into five ovarian development phases based on microscopic analysis of the most advanced group of oocytes. Generalized additive models were applied to the gonadal index and sex ratio data in order to assess spatio-temporal trends of the reproductive activity and identify the spawning areas. Space–time effect was a significant factor contributing to changes in sex ratio and reproductive activity. Spawning activity was observed in two distinct areas. On the south-east Brazilian coast spawning peaked during December–February, while in the south-eastern Caribbean Sea spawning occurred between March and September, with its peak in March and April. Using a Bayesian approach, size at 50% maturity was estimated to be 146.12 cm (credibility interval of 95%, 138.45–152.09 cm). Batch fecundity ranged from 436,800 to 2,492,500 hydrated oocytes per female. This study confirms multiple aggregation spawning for this species in the western Atlantic Ocean.

Trace metals in target tissues and stomach contents of the top predator sailfish Istiophorus platypterus from the Eastern Pacific: concentrations and contrasting behavior of biomagnification

Cadmium, lead, copper, and zinc were analyzed in the dorsal muscle, liver, gonad, and stomach contents of 67 sailfish, Istiophorus platypterus, from the Eastern Pacific. Muscle exhibited the following pattern (μg/g wet weight): Zn (15.05±1.24)>Cu (0.461±0.026)>Cd (0.434±0.099)>Pb (0.025±0.001); liver Zn (119.1±7.6)>Cd (95.1±11.0)>Cu (39.7±2.6)>Pb (0.047±0.004); and gonad Zn (96.8±7.8)>Cd (2.16±0.38)>Cu (2.08±0.14)>Pb (0.033±0.003). Significant (p<0.05) correlations were observed between elements, length, and weight. I. platypterus feed mainly on fishes and cephalopods with variable concentrations (μg/g wet weight) of Cd (0.081-11.41), Pb (0.002-0.057), Cu (0.204-4.35), and Zn (3.23-86.6). Of the four analyzed elements, only Pb was biomagnified (BMF=1.85). According to the regulatory limits, muscle exhibited Cd concentrations higher than the Official Mexican Standard, WHO, FDA (28% of samples), and the European Union (40%) regulations.

Size structure, sex ratio and weight-length relationships of the sailfish Istiophorus platypterus from Mazatlan, sinaloa, Mexico.

We describe the size frequency distribution, sex ratio and weight-length relationship of the IndoPacific sailfish Istiophorus platypterus off the coast of Mazatlan, Sinaloa, Gulf of California. Data were collected from the sports fishery during several sampling periods from 2002 to 2009. A total of 354 Sailfish were sampled, including 185 females, 161 males and 8 of unknown sex. Total weight (TW) varied from 14 to 41 kg, and sizesranged between 128 and 195 cm postorbital length (PL), with significant differences between the sexes (P &lt; 0.05). The sex ratio throughout the period analyzed was 0.87: 1 (M:H). The total length (TL) and postorbital length (LPO) of organisms were related through the linear fit model for both sexes TL = 57.204 + 1.15 x LPO (r2 = 0.65). There were no significant differences in the weight-length relationship between the sexes (ANCOVA, P&gt;0.05).The general equation relating weight and length for both sexes was TW = 0.0009 x PL2.009. The value of the slope b was significantly different from 3, indicating negative allometric growth (t, P &lt; 0.05). Indo-Pacific sailfish exploitation is currently limited to the sports-recreational fishery; however, there are initiatives to promote the commercial exploitation of this resource. Therefore, results derived from this study are of importance, since they providebasic information on the biology of this species, and can serve as a baseline for the management of this resource.

Genetic diversity and population structure of Indo-Pacific sailfish Istiophorus platypterus in the eastern Pacific

Population genetics provides information for the management and conservation of species, because it supports the delimitation of population units. A mitochondrial DNA marker was used to determine the genetic structure of the sailfish Istiophorus platypterus at four locations in Mexico (Mazatlan, Colima, Acapulco, Oaxaca) and one location in Ecuador. We analyzed 250 nucleotide sequences of the mitochondrial control region, where 134 haplotypes were identified. Genetic diversity was relatively low in relation to other regions in the world, and other billfish species. Analysis of molecular variance indicated that genetic differences were significantly different from zero (P = 0.029), although the Φ ST value (0.0061) was very low. Pairwise comparisons of Φ ST indicated that the difference was attributable mainly to individuals of Ecuador, which were statistically different from those at other sampling sites. However, the genetic structure in this species could not be inferred using Bayesian analysis. Furthermore, a test of isolation by distance showed significant correlation between genetic distance and geographic distance. Phylogeographic analysis revealed a distribution of haplotypes with a star-type pattern, and mismatch distribution showed a unimodal pattern for the five sampled areas, indicative of recent demographic expansion. We estimated that the beginning of the sudden expansion happened between 80,000 and 215,000 years ago. Our results did not support a clear pattern of genetic differentiation. Capture of this species occurs in several countries, and the overall management of the resource could depend on local efforts. Further sampling is need, and additional analysis using molecular markers with high resolution (microsatellites, SNPs) must be implemented in order to gain a more robust understanding of sailfish population structure in the eastern Pacific.

Vertical and horizontal habitat use by white marlin Kajikia albida (Poey, 1860) in the western North Atlantic Ocean

Abstract Pop-up satellite archival tags were deployed on 40 white marlin Kajika albida (synonym: Tetrapturus albidus) off the coasts of Maryland and North Carolina (United States), and the island nation of Aruba in the Caribbean. Useful data were available for analysing vertical and horizontal habitat use from 28 individuals. Time at liberty ranged from 10 to 181 d (mean 115, SD 53.3). Seasonal southerly fall migration routes were documented for fish released off the northeastern United States, while those released off Aruba remained in the Caribbean basin. Horizontal movements ranged from 228 to 8084 km (19–100 km d−1) based on light-level geolocation estimates using a sea surface temperature and bathymetry-corrected Kalman filter. Analyses included an evaluation of vertical movements using ΔT, the time spent at temperature relative to the uniform temperature surface layer. Movements included exploration of depths as great as 387 m and ambient temperatures as low as 7.8°C. However, the greatest proportion of time was spent in the upper 20 m of the water column for both day (50.8%) and night (81.6%), and time spent in water colder than 7°C below the uniform temperature surface layer was negligible. Overall, this group showed less variability in vertical movement, and less tolerance to colder temperatures compared with similar studies for blue marlin Makaira nigricans and sailfish Istiophorus platypterus. Values for ΔT are presented in tabular format to allow direct input into habitat standardization models used to estimate vertical distribution and population abundance. The large spatial dispersion and disparate tracks illustrated in the present study serve to underscore the complexity of white marlin behaviour and habitat use, and further emphasize the many challenges facing the management and conservation of this overexploited species.

Stomach content and stable isotope analysis of sailfish (Istiophorus platypterus) diet in eastern Taiwan waters

Stomach content analysis (SCA) and stable isotope analysis (SIA), coupled with isotopic-mixing model analysis, were used to estimate diet composition of sailfish Istiophorus platypterus in eastern Taiwan waters. SCA provided information on diet, but the high occurrence of empty stomachs (48.5%) limited this analysis. According to the index of relative importance (%IRI), the most important prey items were Priacanthus macracanthus (38.7%), followed by Auxis spp. (35.9%), and Trichiurus lepturus (8.5%). However, the most important prey groups for adult sailfish (>181cm, LJFL) as estimated by the stable isotope-mixing model were T. lepturus (32.6%), Katsuwonus pelamis (15.8%), and P. macracanthus (11.3%), and for maturing sailfish were K. pelamis (12.9%), P. macracanthus (10.4%), and T. lepturus (32.6%), respectively. Juvenile sailfish feed primarily on smaller prey items with lower δ15N values, while adult sailfish preferred larger prey items with higher δ15N values. Our findings suggested that an integrated SCA and SIA is considerably more powerful than using SCA alone in determining diet composition of sailfish over long time scales. In summary, a high diversity in the diet composition of sailfish was found and included an array of coastal, benthic, pelagic, and mesopelagic species. Sailfish are most likely opportunistic feeders consuming the most abundant prey items in eastern Taiwan waters.

Billfish CPUE standardization in the Hawaii longline fishery: Model selection and multimodel inference

This paper presents catch per unit effort (CPUE) standardizations and model selection procedures for four billfish species (Family Istiophoridae) caught primarily as bycatch in the Hawaii-based pelagic longline fishery during 1995–2011: Blue marlin Makaira nigricans; Striped marlin Kajikia audax; Shortbill spearfish Tetrapturus angustirostris; and Sailfish Istiophorus platypterus. The first three species were analyzed on a fishery-wide basis. For sailfish, the fishery data came exclusively from tuna-targeted longline sets in the deep-set sector of the Hawaii-based fishery. We used fishery observer data from the NOAA Fisheries Pacific Islands Regional Observer Program to fit the CPUE standardization models. In this context, our objective was to investigate the quality of model fit for five types of generalized linear models (GLMs: Poisson; negative binomial; zero-inflated Poisson; zero-inflated negative binomial; delta-Gamma). Each of these models represented a different hypothesis about the capture process for a bycatch species for which the catch data primarily consisted of zero catch observations. The five GLMs were fitted by forward entry variable selection, and the best fitting GLM for each species was selected on the basis of Akaike Information Criterion values and calculated Akaike weights. The best-fitting model selected for each species was a zero-inflated negative binomial GLM (ZINB). The ZINB model was comprised of a negative binomial counts model for expected zero catch sets and a positive catch per set distribution along with a binomial inflation model to account for excess zeros. For each species, the important explanatory variables for standardizing CPUE were fishing year, fishing (i.e., calendar) quarter, and fishing region. The best-fitting models indicated that standardized CPUE for striped and blue marlins decreased significantly during the study period. Because the ZINB model was selected as the best fitting model for all species, we suggest that longline CPUE for incidentally caught billfishes is best represented as a process characterized by zero inflation and overdispersion in the positive catches and expected zero catches. We therefore recommend that ZINB models be considered as an a priori model for CPUE standardizations of billfishes and other bycatch species in longline fisheries.

Trophic size‐structure of sailfish Istiophorus platypterus in eastern Taiwan estimated by stable isotope analysis

To examine trophic dynamics over different size classes, an isotopic study of sailfish Istiophorus platypterus life-history stages was carried out. Samples were collected from eastern Taiwan and the South China Sea during April 2009 and February 2012. A total of 263 samples (111-245 cm, lower jaw fork length, LLJFL ) were examined for changes in trophic structure in relation to LLJFL by using stable isotope analysis of carbon (δ(13) C) and nitrogen (δ(15) N). The δ(15) N values for I. platypterus ranged from 7·51 to 14·19‰ (mean ± s.d. = 12·06 ± 1·16‰) and the δ(13) C values ranged from -22·04 to -15·48‰ (mean ± s.d. = -17·62 ± 1·10‰). The δ(15) N values were positively dependent on LLJFL (r(2) = 0·377), whereas δ(13) C were negatively dependent on LLJFL (r(2) = 0·063). There were significantly different seasonal changes in nitrogen and carbon isotopic concentration, but no significant differences in concentrations between eastern Taiwan and the South China Sea were reported. The trophic level (TL ) of each LLJFL class was correlated, starting from 2·84 TL for size class I (LLJFL < 140 cm) and reaching 5·03 TL for size class VI (LLJFL > 221 cm). The mean ± s.d. TL was 4·43 ± 0·19 for all samples. The results reveal that I. platypterus occupies a wide range of trophic levels and different size classes occupy different trophic positions in the pelagic ecosystem.

Sex ratio and reproductive condition of four istiophorid billfishes in tropical regions of the eastern North Pacific Ocean: with special reference to striped marlin Kajikia audax (Philippi, 1887)

Summary Sexual differences in the distribution pattern, sex ratio and the gonad condition of four istiophorid billfishes were investigated in three different tropical areas of the eastern North Pacific Ocean from September to November 2004. Sex ratios of striped marlin Kajikia audax were equal (female : male = 11 : 11) in the open-ocean area (16–18°N, 118–134°W), biased to males (32 : 62) in the near-continental area (13–16°N, 103–107°W), and biased to females (19 : 6) in the near-equatorial area (5°N, 104–120°W). Sex ratios of sailfish Istiophorus platypterus in the near-continental area and shortbill spearfish Tetrapturus angustirostris in the open-ocean area were not biased from 1 : 1 (43 : 36, 11 : 13), and that of blue marlin Makaira nigricans in the near-equatorial area was biased to females (14 : 1). Reproductively active females were found for striped marlin, sailfish and shortbill spearfish. Striped marlin showed a specific spawning area (the near-continental area), and sexual dimorphism in its temporal distribution pattern, which was presumably related to reproduction. On the other hand, the limited distribution with evidence from spawning of sailfish and shortbill spearfish imply that these species complete their life history within limited areas.