White Marlin Research Articles

Identifying pelagic fish eggs in the southeast Yucatan Peninsula using DNA barcodes.

In the waters surrounding Banco Chinchorro in the Mexican Caribbean are spawning and nursery areas for many types of fish. In this natural environment, as opposed to under controlled laboratory conditions, it is almost impossible to link an individual egg to the adult that laid it. This makes identifying the species of the eggs difficult. However, DNA barcodes have made this easier. In the present study, 300 eggs were processed for molecular analysis, from which 139 sequences were obtained. We identified 42 taxa (33 species with their binomial names), 35 genera, and 24 families. The identified eggs included those from Ariomma melanum, which is the first recording of this species in the Mexican Caribbean. Eggs from economically important fish species were also identified, including frigate tuna (Auxis thazard), crevalle jack (Caranx hippos), common dolphinfish (Coryphaena hippurus), sailfish (Istiophorus platypterus), white marlin (Kajikia albida), skipjack tuna (Katsuwonus pelamis), blackfin tuna (Thunnus atlanticus), and swordfish (Xiphias gladius). We have also described new morphological characteristics and captured photographs for 21 species, as well as obtained new information about spawning locality and time for 16 species. This valuable information will provide the basis to develop more effective conservation measures for sustainable fisheries and protection of the Mesoamerican Barrier Reef System.

Physiological stress and post-release mortality of white marlin (Kajikia albida) caught in the United States recreational fishery.

White marlin, a highly migratory pelagic marine fish, support important commercial and recreational fisheries throughout their range in the tropical and subtropical Atlantic Ocean. More than 10 000 individuals can be caught annually in the United States recreational fishery, of which the vast majority are captured on circle hooks and released alive. The probability of post-release mortality of white marlin released from circle hooks has been documented to be <0.02, but the associated physiological stress resulting from capture and handling techniques has not been characterized despite its importance for understanding the health of released fish. We examined the physiological response of 68 white marlin caught on circle hooks in the recreational fishery and followed the fate of 22 of these fish with pop-up satellite archival tags programmed to release after 30 days. Measures of plasma sodium, chloride, glucose and lactate concentrations taken from fish that were briefly and consistently (mean = 120 s, standard deviation = 40 s) removed from the water increased with angling time, but post-release mortality was inversely related to angling time. The probability of post-release mortality was predicted by elevated plasma potassium concentrations and was more than 10 times greater than has been previously reported for white marlin caught on circle hooks that were not removed from the water. This disparity in estimates of post-release mortality suggests that removal of fish from the water for physiological sampling greatly heightens stress, disrupts homeostasis and thus increases the probability of post-release mortality. Our results demonstrate that elevated concentrations of plasma potassium predict mortality in white marlin and that the probability of post-release mortality is highly dependent on post-capture handling procedures.

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.

Postrelease mortality in istiophorid billfish

Meta-analysis (inverse-variance, random-effects model) involving 46 studies was used to estimate the effect size of postrelease mortality (Fr) in six istiophorid billfish species (black marlin (Istiompax indica), blue marlin (Makaira nigricans), longbill spearfish (Tetrapturus pfluegeri), sailfish (Istiophorus platypterus), striped marlin (Kajikia audax), and white marlin (Kajikia albida)) following release from recreational, longline, and harpoon fishing gears. The studies involved 400 reporting pop-up satellite archival tags and 64 reporting acoustic (ultrasonic) tags. Despite fish being captured, tagged, and released under widely disparate conditions, locations, and gear types, Frwas homogeneous among species. Variability in Frwas principally due to random sampling error within studies with no evident patterns. Fifteen studies (33% of tags) indicated no mortality, and the overall summary effect size for Frwas 13.5% (95% CI: 10.3%–17.6%). Since the random-effects model decomposed to a fixed-effect model when the between-studies variance T2= 0.00, results were confirmed using exact nonparametric inferential tests and sensitivity analyses. Our results support earlier findings in the Atlantic and substantiate the majority of istiophorid billfish survive when released from recreational and longline fishing gear, clearly implying catch-and-release as a viable management option that permits fishing activity while protecting parental biomass and the fishery.

Effects of 17/0 circle hooks and bait on fish catches in a Southern Atlantic swordfish longline fishery

Abstract This paper reports the results of using different hook style and bait type combinations on the catches of targeted, bycatch and discarded fishes in the Portuguese commercial longline fishery targeting swordfish (Xiphias gladius) in the South Atlantic Ocean. In total, 310 longline experimental sets (446 400 hooks) were deployed between October 2008 and February 2012. Three different hook styles were tested; the traditional J‐hook (9/0) 10o offset was compared with two 17/0 circle hooks (a non‐offset and a 10o offset), and squid (Illex spp.) bait was compared with mackerel (Scomber spp.). Catch per unit effort (CPUE) was calculated for each fish species per fishing set and compared between the different hook style and bait type combinations. Results indicated that the effects of hook style and bait on the CPUEs were species‐specific. For example, swordfish (target species, Xiphias gladius) CPUEs were higher with J‐hooks baited with squid, while for the blue shark (most important bycatch species, Prionace glauca) the highest CPUEs were obtained with circle hooks baited with mackerel. For tuna (Thunnus spp.) and marlin (blue, Makaira nigricans and white, Kajikia albida) only the bait effect was significant, with higher catches with squid. For the discarded species, the proportions of alive vs dead specimens at the time of fishing gear retrieval were also species‐specific. The total retained catch value per unit of effort (VPUE) did not changed between the different hook and bait combinations, but these VPUEs are highly dependent on market fluctuations. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Broad geographic distribution of roundscale spearfish (Tetrapturus georgii) (Teleostei, Istiophoridae) in the Atlantic revealed by DNA analysis: Implications for white marlin and roundscale spearfish management

The recent validation of the roundscale spearfish (Tetrapturus georgii) within the western North Atlantic has introduced new complexities in the management of the overfished white marlin (Kajikia albida) in this region due to historical and contemporary misidentification between the two morphologically similar species. Compounding the management challenge for white marlin, which is currently assessed as a single Atlantic-wide stock, is an unclear picture of the extent of the roundscale spearfish's overall Atlantic distribution. By using genetic tools (mitochondrial DNA ND4L-ND4 locus sequences) for species identification, we confirm that the roundscale spearfish has a much broader distribution than previously known, including the central North Atlantic and much of the western South Atlantic to at least 28°52′S. This much wider Atlantic distribution of the roundscale spearfish sympatric with its morphologically similar congeners, the white marlin and longbill spearfish (Tetrapturus pfluegeri), raises further management complexities: it increases the geographic scale for species misidentification in catch records that form the basis for stock assessments and uncertainty in currently accepted white marlin biological parameters. Additional vigilance in obtaining accurate species identification by improved fishery onboard observer training and incorporation of genetic tools is recommended for informing management of white marlin, longbill spearfish and roundscale spearfish throughout the Atlantic.

Assessment of trophic dynamics of cephalopods and large pelagic fishes in the central North Atlantic Ocean using stable isotope analysis

Pelagic ecosystems in the central North Atlantic Ocean support numerous commercially-exploited tuna, shark, and billfish species, which rely largely on cephalopod as well as fish and crustacean prey. Carbon and nitrogen stable isotope analyses were performed on tuna and billfish predators as well as cephalopod prey species sampled during two research longline cruises (2001–02) to study their trophic structure. Nitrogen stable isotope (δ15N) analyses revealed similarity in trophic position (TP) among sampled fish predator species, with large swordfish occupying the highest TP. Species with wider vertical distributions (swordfish and bigeye tuna) had higher δ15N values than species more constrained to the epipelagic zone (yellowfin tuna and dolphinfish). Analysis of tissue nitrogen isotope values showed an ontogenetic increase for swordfish and white marlin but no effects for other sampled fish species. For cephalopods as a group, δ15N increased with size. Smaller cephalopods sampled in this study had δ15N values that were about one TP below co-occurring tunas and billfishes, confirming their importance as a prey resource. Larger cephalopods had similar δ15N values to tunas and billfishes, indicating that these large cephalopods occupy a comparable TP to their fish predators. Both carbon and nitrogen stable isotope values of large pelagic fishes showed spatial gradients relative to conspecifics analyzed in coastal regions, which can be used to trace large scale movements.

Hooking Survival of Fishes Captured by the United States Atlantic Pelagic Longline Fishery: Impact of the 2004 Circle Hook Rule

We examine the impact on pelagic fish hooking survival rates (defined as the proportion of fish alive upon gear retrieval) of the rapid switch from J-hooks to circle hooks that was required of the us pelagic longline fishery operating in the atlantic ocean and gulf of mexico after august 2004. Our focus was on 12 fish taxa that are commonly caught as bycatch or retained for the market, and for which individual disposition (live or dead) information was available from 1992 to 2010. To test the hypothesis of no change in survival before vs after the circle hook rule went into effect, we utilized a repeated measures logistic regression approach which accounted for variation in several operational, environmental, and biological covariates, including bait, fishery target, fishing zone, soak duration, water temperature, maximum fishing depth, and fish size (length). For white marlin and albacore, results were mixed, with both increases and decreases in hooking survival varying by fishing zone. For blue shark and lancetfish, no significant differences in hooking survival were detected between the pre- and post-circle hook rule time periods. However, for the remaining eight taxa (swordfish, yellowfin tuna, dolphinfish, bigeye tuna, escolar, silky shark, blue marlin, and sailfish), significant increases in survival were evident. Our results are generally consistent with previous experimental and fishery observer longline studies which suggested circle hook use has the potential to increase hooking survival. Results imply that the 2004 circle hook rule has provided increased opportunities for: (1) live release for several bycatch species; and (2) improved quality (and perhaps prices) of targeted and incidentally-caught taxa that are retained for the market.

Distribution and habitat associations of billfish and swordfish larvae across mesoscale features in the Gulf of Mexico.

Ichthyoplankton surveys were conducted in surface waters of the northern Gulf of Mexico (NGoM) over a three-year period (2006–2008) to determine the relative value of this region as early life habitat of sailfish (Istiophorus platypterus), blue marlin (Makaira nigricans), white marlin (Kajikia albida), and swordfish (Xiphias gladius). Sailfish were the dominant billfish collected in summer surveys, and larvae were present at 37.5% of the stations sampled. Blue marlin and white marlin larvae were present at 25.0% and 4.6% of the stations sampled, respectively, while swordfish occurred at 17.2% of the stations. Areas of peak production were detected and maximum density estimates for sailfish (22.09 larvae 1000 m−2) were significantly higher than the three other species: blue marlin (9.62 larvae 1000 m−2), white marlin (5.44 larvae 1000 m−2), and swordfish (4.67 larvae 1000 m−2). The distribution and abundance of billfish and swordfish larvae varied spatially and temporally, and several environmental variables (sea surface temperature, salinity, sea surface height, distance to the Loop Current, current velocity, water depth, and Sargassum biomass) were deemed to be influential variables in generalized additive models (GAMs). Mesoscale features in the NGoM affected the distribution and abundance of billfish and swordfish larvae, with densities typically higher in frontal zones or areas proximal to the Loop Current. Habitat suitability of all four species was strongly linked to physicochemical attributes of the water masses they inhabited, and observed abundance was higher in slope waters with lower sea surface temperature and higher salinity. Our results highlight the value of the NGoM as early life habitat of billfishes and swordfish, and represent valuable baseline data for evaluating anthropogenic effects (i.e., Deepwater Horizon oil spill) on the Atlantic billfish and swordfish populations.

Redescription and New Host Record of Capsala laevis (Monogenoidea: Capsalidae: Capsalinae) from Gill of Roundscale Spearfish, Tetrapturus georgii (Perciformes: Istiophoridae) in the Northwestern Atlantic Ocean

Specimens of a capsalid collected from the gill arches of 2 roundscale spearfish, Tetrapturus georgii Lowe, 1840, (Perciformes: Istiophoridae), captured in the northwestern Atlantic Ocean were identified as Capsala laevis (Verrill, 1875) Johnston, 1929 by having the combination of papillae on the ventral surface of haptor, dorsomarginal body sclerites in a single column extending the entire body length, haptoral accessory sclerites, conical papillae distributing over the ventral body surface, and an anterior attachment organ with a fimbriated posterior margin. The new specimens plus the holotype were used to conduct a taxonomic redescription of C. laevis using light and scanning electron microscopy. We documented that the holotype (USNPC No. 7179) and the new specimens of C. laevis from roundscale spearfish each had papillae on the ventral surface of the anterior attachment organs and sensory papillae on the dorsal body surface. Although data are insufficient at this time to justify proposal of a new species, the new specimens differed from the holotype and published accounts of C. laevis by having a sinistral dorsomarginal patch comprising 27-35 sclerites whereas the holotype has a dorsomarginal patch comprising 60 sclerites. Capsala laevis morphologically most closely resembles Capsala ovalis (Goto, 1894) Price, 1938 , but can be most easily differentiated from it by having dorsomarginal body sclerites. This represents the first record of any parasite from the recently taxonomically resurrected roundscale spearfish, long considered by some as a junior subjective synonym of white marlin, Tetrapturus albidus Poey, 1860 and, concomitantly, a new host record for Capsalidae Baird, 1853. An updated list of host records for C. laevis is provided. A perusal of that literature reveals that the identity of the type host for C. laevis is indeterminate beyond Istiophoridae species and that subsequent reports of the type host as ' T. albidus ' are presumptuous (originally reported in 1875 by Verrill as "bill-fish" only). Our results indicated that 2 records of C. laevis from the swordfish, Xiphias gladius Linnaeus, 1758, (Perciformes: Xiphiidae) are dubious, i.e., study of the museum voucher USNPC No. 8154 indicates that Linton's 1940 record from the northwestern Atlantic Ocean likely represents a new species of Capsala Bosc, 1811 and that the Kayiş et al. 2010 record from the Aegean Sea likely depicts a species of Capsaloides Price, 1938.

An Exploratory Analysis to Identify Reproductive Strategies of Billfishes

This contribution is aimed to the identification of reproductive patterns of billfishes, which is in turn a key issue supporting management and conservation policies. Information reported in the literature on features of reproductive processes of billfishes was examined with a Principal Components Analysis (PCA) to identify groups of species with similar reproductive strategies. PCA was applied based in a correlation matrix and the significances (p<0.05) of the factors and loadings of the variables were used as criteria for the identification of reproductive patterns. In general, four groups were found. The first group consists of Tetrapturus albidus and T. audax, which are characterised by rapid growth, an early age at first maturity with respect to maximum age (T/Tmax) and high values of reproductive variables (e.g., Spawning Duration (Sd), Spawning Frequency (Sf), Annual Fecundity (AF) and Relative Fecundity (RF). A second group consists of T. belone, T. georgii and T. pfluegeri, which present rapid growth, high Tm/Tmax ratios and Batch Fecundity (BF) values and low Sd values. Another group consists of the genera Makaira and Xiphias, which present low Lm/Lmax ratios and high values for AF, RF, Sf and BF. The last group consists of species of the genus Istiophorus, which present the lowest AF values and the highest RF and BF values. In billfishes, the reproductive pattern is strongly influenced by the growth process and the age at which a species reaches sexual maturity relative to its maximum age. The observed differences in reproductive variables result from adaptive mechanisms that allow species greater reproductive success in the epipelagic environment.

DNA barcoding of billfishes

DNA barcoding is a method promising fast and accurate identification of animal species based on the sequencing of the mitochondrial c oxidase subunit (COI) gene. In this study, we explore the prospects for DNA barcoding in one particular fish group, the billfishes (suborder Xiphioidei—swordfish, marlins, spearfishes, and sailfish). We sequenced the mitochondrial COI gene from 296 individuals from the 10 currently recognized species of billfishes, and combined these data with a further 57 sequences from previously published projects. We also sequenced the rhodopsin gene from a subset of 72 individuals to allow comparison of mitochondrial results against a nuclear marker. Five of the 10 species are readily distinguishable by COI barcodes. Of the rest, the striped marlin (Kajikia audax) and white marlin (K. albida) show highly similar sequences and are not unambiguously distinguishable by barcodes alone, likewise are the three spearfishes Tetrapturus angustirostris, T. belone, and T. pfluegeri. We discuss the taxonomic status of these species groups in light of our and other data, molecular and morphological.

Using head measurements to distinguish white marlin &lt;I&gt;Kajikia albida&lt;/I&gt; from roundscale spearfish &lt;I&gt;Tetrapturus georgii&lt;/I&gt; in the western North Atlantic

Using head measurements to distinguish white marlin &lt;I&gt;Kajikia albida&lt;/I&gt; from roundscale spearfish &lt;I&gt;Tetrapturus georgii&lt;/I&gt; in the western North Atlantic

Sailfish Habitat Utilization and Vertical Movements in the Southern Gulf of Mexico and Florida Straits

AbstractPop‐up satellite archival tags (PSATs) were deployed on 19 sailfish Istiophorus platypterus captured in the southern Gulf of Mexico and Florida Straits between 2005 and 2007 on commercial pelagic longline gear (n = 18) and recreational rod‐and‐reel gear (n = 1). The data from three tags indicated mortality events and were excluded from subsequent analyses. All PSATs were programmed to collect pressure (depth), temperature, and light‐level data for 10 d at approximately 90‐s intervals. These transmitted point data subsequently allowed the reconstruction of vertical movement patterns. The remaining 16 PSAT data sets indicate that sailfish are primarily associated with the upper surface waters within the top 20 m (75.7% of total time during the day versus 46.7% at night) but undertake numerous short‐duration vertical movements below the local mixed layer to depths of 50–150 m, presumably to feed. Analyses of 2,279 individual vertical movements among all 16 tagged sailfish indicated two distinct types (short‐duration “V” and longer‐duration “U” movements) similar to those reported for white marlin Kajikia albida. Sailfish also exhibited movement type differences between diel periods (having higher proportions of V movements in daytime), suggesting directed foraging at depth. Although short‐duration movement to depths by these tagged fish contribute a small percentage of the total time at depth, these depths overlap with the monitored shallow‐set pelagic longline gear depths actively targeting swordfish by the vessel in the local fishery. These results suggest that time‐at‐depth histograms alone may be insufficient to capture feeding motivations at depth and, therefore, true interaction potentials between individual sailfish and pelagic longline gear.Received August 14, 2010; accepted April 24, 2011

Regional variation in the otolith chemistry of blue marlin ( Makaira nigricans) and white marlin ( Tetrapturus albidus) from the western North Atlantic Ocean

Stable carbon ( δ 13C) and oxygen ( δ 18O) isotopes in the whole otoliths of blue marlin ( Makaira nigricans) and white marlin ( Tetrapturus albidus) were quantified, and regional variation in otolith composition was used to examine the population structure of both species in the western North Atlantic Ocean from collections taken over three decades (1981–2007). Otolith δ 13C and δ 18O of blue marlin and white marlin varied significantly among the regions investigated (Gulf of Mexico, Straits of Florida, Caribbean Sea, and U.S. Atlantic). Overall cross-validated classification success was 62% for blue marlin and 46% for white marlin (collected in three of four regions), with highest classification success for blue marlin in the Gulf of Mexico (85%) and for white marlin along the U.S. Atlantic (58%). Variability in otolith δ 18O of blue marlin and white marlin was higher in regions where individuals displayed a greater degree of movement based on previous tagging studies in the same regions. Reduced variability in otolith δ 18O of blue marlin in the Gulf of Mexico combined with high classification success of individuals from this region suggests that movement out of this basin may be more limited than in other regions investigated. Conversely, higher variability in otolith δ 18O and lower classification success for white marlin signifies that mixing among regions may be more common for this species. These results suggest that the concept of migratory contingents may have some application to istiophorids in the western North Atlantic Ocean (i.e. blue marlin), but continue to support the concept of single Atlantic wide stocks for both species.

Larval assemblages of large and medium-sized pelagic species in the Straits of Florida

Critical gaps in our understanding of the distributions, interactions, life histories and preferred habitats of large and medium-size pelagic fishes severely constrain the implementation of ecosystem-based, spatially structured fisheries management approaches. In particular, spawning distributions and the environmental characteristics associated with the early life stages are poorly documented. In this study, we consider the diversity, assemblages, and associated habitat of the larvae of large and medium-sized pelagic species collected during 2 years of monthly surveys across the Straits of Florida. In total, 36 taxa and 14,295 individuals were collected, with the highest diversity occurring during the summer and in the western, frontal region of the Florida Current. Only a few species (e.g. Thunnus obesus, T. alalunga, Tetrapturus pfluegeri) considered for this study were absent. Small scombrids (e.g. T. atlanticus, Katsuwonus pelamis, Auxis spp.) and gempylids dominated the catch and were orders of magnitude more abundant than many of the rare species (e.g. Thunnus thynnus, Kajikia albida). Both constrained (CCA) and unconstrained (NMDS) multivariate analyses revealed a number of species groupings including: (1) a summer Florida edge assemblage (e.g. Auxis spp., Euthynnus alleterattus, Istiophorus platypterus); (2) a summer offshore assemblage (e.g. Makaira nigricans, T. atlanticus, Ruvettus pretiosus, Lampris guttatus); (3) an ubiquitous assemblage (e.g. K. pelamis, Coryphaena hippurus, Xiphias gladius); and (4) a spring/winter assemblage that was widely dispersed in space (e.g. trachipterids). The primary environmental factors associated with these assemblages were sea-surface temperature (highest in summer-early fall), day length (highest in early summer), thermocline depth (shallowest on the Florida side) and fluorescence (highest on the Florida side). Overall, the results of this study provide insights into how a remarkable diversity of pelagic species spatially and temporally partition spawning within a region that is characterized by dynamic oceanography and strong habitat gradients.

Effects of species misidentification on population assessment of overfished white marlin Tetrapturus albidus and roundscale spearfish T. georgii

The white marlin Tetrapturus albidus (Istiophoridae) is considered to be among the most overexploited species under international management jurisdiction in the Atlantic Ocean, resulting in diverse stakeholder concerns. Efforts have been made to add it to the US Endangered Species List. Its population status has become uncertain with the realization that: (1) longstanding misidentifica- tions of white marlin have occurred with the recently recognized, morphologically similar and sym- patric roundscale spearfish T. georgii; and (2) the 2 species have unknowingly been assessed and managed as a species group. We show that roundscale spearfish currently constitute a substantial proportion (~27%) of the overall 'white marlin' catch in the western North Atlantic, with high spatial variation within this region. Consequently, the accuracy of current biological knowledge on white marlin, some of which has formed the input for past population status modeling, is compromised by 'contamination' due to misidentification. Population assessment simulations in the western North Atlantic incorporating the proportion of roundscale spearfish (27%) were run; these indicated that historical changes in the ratio of the 2 species, as well as differences in the population growth rates between T. albidus and T. georgii, affect simulation results. Our findings suggest misidentifications between the species may have affected the accuracy of past T. albidus population assessments in the western North Atlantic, which therefore need re-visiting to permit improved management and recov- ery of this species. New collection of life history data for T. albidus and T. georgii is also recom- mended to corroborate the results of historical studies.

Age estimation of billfishes (Kajikiaspp.) using fin spine cross-sections: the need for an international code of practice

Fin spine ageing is the most common technique used to estimate age and growth parameters of large pelagic billfishes from the families Istiophoridae and Xiphiidae. The most suitable methods for processing and interpreting these calcified structures for age estimation have not been clearly defined. Methodological differences between unvalidated ageing studies are of particular concern for highly migratory species because multiple researchers in different regions of the world may conduct age estimates on the same species or stock. This review provides a critical overview of the methods used in previous fin spine ageing studies on billfishes and provides recommendations towards the development of a standardized protocol for estimating the age of striped marlin, Kajikia audax and white marlin, Kajikia albida . Three on-going fin spine ageing studies from Australia, Hawaii, and Florida are used to illustrate some of the considerations and difficulties encountered when developing an ageing protocol for highly migratory fish species. Particular areas of concern that may influence age and growth estimates included differences in fin spine selection, sectioning methods, criteria for identifying and measuring annuli, distinguishing false annuli, validation procedures, identification of the first annulus, and methods used to replace annuli lost due to vascularization of the fin spine core.

Postrelease Survival of Sailfish Caught by Commercial Pelagic Longline Gear in the Southern Gulf of Mexico

AbstractThe biomass levels of several target species of the Atlantic pelagic longline fishery, including various tunas of the genus Thunnus and swordfish Xiphias gladius, are estimated to be close to those required to support the maximum sustainable yield. In contrast, several species captured incidentally are severely depleted. Live release of incidental catch is one means of reducing the fishing mortality of these species without sacrificing the target catch, but the efficacy of such a measure is predicated on the assumption that postrelease survival is relatively high. Prior work has evaluated postrelease survival from pelagic longline gear for the larger istiophorid billfishes, such as blue marlin Makaira nigricans and white marlin Kajikia albida, but survival rates are unknown for sailfish Istiophorus platypterus. To estimate the postrelease survival of sailfish caught on pelagic longline gear in the southern Gulf of Mexico, short‐duration pop‐up satellite archival tags (PSATs) were deployed on captured sailfish for 10‐d periods. Of the 29 sailfish captured, 20 (68.9%) were alive at the time of longline haulback, and the first 17 encountered alive were tagged. All tags transmitted at the preprogrammed times, and data from 15 of the 17 PSATs (88.2%) were consistent with the survival of the tagged sailfish for the 10‐d tag deployment. Our results clearly demonstrate that sailfish can survive the trauma from interaction with pelagic longline gear and that management measures promoting the release of live individuals from this fishery can significantly reduce sailfish mortality without reducing the catches of target species.

Sex ratios, spawning seasonality, sexual maturity, and fecundity of white marlin ( Tetrapturus albidus) from the western central Atlantic

Some aspects of the reproductive biology of white marlin from the western central Atlantic were analyzed. A total of 2488 fish were sampled by scientific observers on board Venezuelan pelagic longline vessels and from port sampling during the period of January 2002 to December 2006. Reproductive activity was assessed using histology, maximum whole oocyte size; maturity related size frequency distribution of whole oocytes, and a gonadosomatic index. Sex ratio, defined as the proportion of females to males, increased steadily in size beyond 160 cm LJFL and reached 100% at sizes >200 cm. White marlin females with relatively high gonad index values associated with advanced stages of maturity spawned from April to June in the areas NE of Dominican Republic, and N-NE of the Puerto Rico Trench. Estimated sexual maturity ( L 50) for females was 160.46 cm, and the smallest mature female was 151 cm. Batch fecundity for female fish between 152 and 172 cm LJFL was 190,400–596,200 hydrated oocytes per female. The average interval between spawns was 1.5 days.