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 Delta T, 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 degrees 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 degrees 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 Delta T 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.

For centuries, the mechanisms surrounding spatially complex animal migrations have intrigued scientists and the public. We present a new methodology using ocean heat content (OHC), a habitat metric that is normally a fundamental part of hurricane intensity forecasting, to estimate movements and migration of satellite-tagged marine fishes. Previous satellite-tagging research of fishes using archival depth, temperature and light data for geolocations have been too coarse to resolve detailed ocean habitat utilization. We combined tag data with OHC estimated from ocean circulation and transport models in an optimization framework that substantially improved geolocation accuracy over SST-based tracks. The OHC-based movement track provided the first quantitative evidence that many of the tagged highly migratory fishes displayed affinities for ocean fronts and eddies. The OHC method provides a new quantitative tool for studying dynamic use of ocean habitats, migration processes and responses to environmental changes by fishes, and further, improves ocean animal tracking and extends satellite-based animal tracking data for other potential physical, ecological, and fisheries applications.

This paper links 50 years of ongoing ocean scale deoxygenation trends in the tropical Atlantic Ocean to changes in vertical habitat use of large pelagic predators, and the Atlantic fisheries that exploited them. Climate induced warming in this large ocean area (Oxygen Minimum Zones, OMZs) has compressed the volumes of surface mixed layer habitat by about 1 m y-1 over the last 5 decades, concentrating predators, preferred prey, and influencing Atlantic-wide fishing effort patterns into progressively shallower surface zones. This phenomenon increases the catchability of these predators and may contribute to overly optimistic abundance estimates derived from surface fishing gears. Overall, deoxygenation is estimated to have caused a 15% reduction in suitable habitat for tropical pelagic tunas and billfishes in the tropical Atlantic during this time period. To demonstrate ocean scale changes in available habitat we use Hydrobase 3 database to compute decadal matrices of OMZ size (volume and surface area), as well as the reciprocal decline in surface mixed layer from 1955 through 2004. Further, we tracked fishing effort and catch inside and outside of the Atlantic OMZ for 9 major ICCAT assessment species to examine potential compression impacts. We found that during the last decade analyzed (1995-2004), longline fishing effort has coalesced on-top of the Atlantic OMZ, while hooks from outside the OMZ have decreased by about the same proportion. During the initial decade (1955-1964), 3 longline fleets deployed about 500,000 hooks, while by the last decade (1995-2004) longline effort had expanded to 94 fleets and almost 4.2 billion hooks. We determined that at least 7 out of 9 major ICCAT stock assessment species examined here are severely impacted by the OMZ expansion and resulting loss of available habitat. We also point out some significant ecosystem interactions between predators and preferred prey that appear to fuel predator assemblages.in progressively shallow OMZ areas, including some predators that are not sensitive to low ambient DO levels. As deoxygenation is expected to continue during the current cycle of climate change and global warming, and has been observed in other oceans as well, this suggests it may have broad-scale impacts on the sustainability of pelagic fisheries and their management. In order to maintain sustainable fisheries for tropical pelagic fishes, we feel its incumbent upon the assessment community to incorporate hypoxia-based habitat compression impacts for species of concern (identified here) into the assessment process. One potential approach might be accomplished during the Catch-Per-Unit-Effort standardization process, by scaling catchability coefficients (by species and gear) using the progressive decadal decline in available surface mixed layer habitat (in volume) presented here.

Background: Misidentifications between exploited species may lead to inaccuracies in population assessments, with potentially irreversible conservation ramifications if overexploitation of either species is occurring. A notable showcase is provided by the realization that the roundscale spearfish (Tetrapturus georgii), a recently validated species, has been historically misidentified as the morphologically very similar and severely overfished white marlin (Kajikia albida) ( IUCN listing: Vulnerable). In effect, no information exists on the population status and evolutionary history of the enigmatic roundscale spearfish, a large, highly vagile and broadly distributed pelagic species. We provide the first population genetic evaluation of the roundscale spearfish, utilizing nuclear microsatellite and mitochondrial DNA sequence markers. Furthermore, we re-evaluated existing white marlin mitochondrial genetic data and present our findings in a comparative context to the roundscale spearfish.Results: Microsatellite and mitochondrial ( control region) DNA markers provided mixed evidence for roundscale spearfish population differentiation between the western north and south Atlantic regions, depending on marker-statistical analysis combination used. Mitochondrial DNA analyses provided strong signals of historical population growth for both white marlin and roundscale spearfish, but higher genetic diversity and effective female population size (1.5-1.9X) for white marlin.Conclusions: The equivocal indications of roundscale spearfish population structure, combined with a smaller effective female population size compared to the white marlin, already a species of concern, suggests that a species-specific and precautionary management strategy recognizing two management units is prudent for this newly validated billfish.

Pop-up satellite archival tags (n = 31) were deployed on Yellowfin Tuna Thunnus albacares in the Gulf of Mexico for periods ranging from 14 to 95 d. Differences in diel vertical behavior were assessed by comparing time spent at temperature relative to the surface temperature ( T). Pooled samples revealed that 31% of darkness hours, 20% of twilight hours, and 12% of daylight hours were spent in the uniform-temperature surface layer (i.e., T = 0). Total time spent above 100 m was less during daylight (90.0%) than during darkness (99.8%), suggesting greater exploration of deeper depths during daylight hours. Maximum depth visited ranged from 208 to 984 m, and minimum temperature visited ranged from 5.4◦C to 11.8◦C. Only a small proportion of total time was spent at temperatures colder than 8◦C below the surface temperature. Horizontal excursions for the majority of individuals were less than 100 km from the point of release; however, three individuals moved distances of 411–1,124 km, suggesting that this species has the capability to move relatively long distances within the Gulf of Mexico. The T values are provided in tabular format and serve as direct input variables for use in habitat standardization models. Subject editor: Michelle Heupel, James Cook University, Queensland, Australia *Corresponding author john.hoolihan@noaa.gov Received January 7, 2014; accepted June 8, 2014 211 D ow nl oa de d by [ 71 .4 6. 64 .2 22 ] at 0 8: 36 0 2 N ov em be r 20 14

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 degrees 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. (C) 2012 Elsevier B.V. All rights reserved.

The vertical movement patterns of eight Swordfish Xiphias gladius from 109- to 249-cm lower jaw fork length in the western North Atlantic were studied utilizing pop-up archival transmitting tags. Deployments ranged from 120 to 151 d. Swordfish demonstrated significant differences in depth and temperature distributions between daytime and nighttime periods. Individual Swordfish behavior was characterized by occupying surface waters of less than 100m during the night and depths greater than 400m during daytime hours, vertical movements between the surface and depth occurring during crepuscular hours. The maximum depth recorded was 1,448m (one of the deepest recorded depths for the species). Daytime surfacing behavior was seen in all tagged Swordfish, a rare finding for Swordfish in tropical latitudes. A dominant diurnal period of 1 cycle/d was found from a power spectral density analysis of five of the tagged Swordfish, a novel method for determining periodicity in the behavior of tagged animals. Regression analysis indicated a significant positive relationship between depth and fraction of the moon illuminated, supporting anecdotal and vessel logbook information from local Swordfish fisheries indicating changes in depth in relation to lunar phase. Received January 17, 2012; accepted August 5, 2012

SUMMARY Data from yellowfin tuna monitored with pop-up satellite archival tags in the Gulf of Mexico were evaluated for vertical habitat use. The proportions of time spent at temperature relative to the surface temperature (Delta T) were calculated and ranked by increasing depth for periods of darkness and daylight. Percentiles were tabulated for each of the observed frequency distributions. The percentiles of mean Delta T indicated that about 25% of darkness and 4% of daylight periods were spent at surface temperature (i.e. Delta T = 0). The tabulated percentiles represent major input variables used in habitat standardization models. RESUME

Industry standard fishing hooks used prior to 2004 during Us commercial pelagic longline (Pll) fishing were the 8/0-10/0 J-hooks with a 20°-25° offset�a lateral deviation of the hook point relative to the hook shaft. However, federal regulations enacted in 2004 require the Us Pll industry to employ circle hooks allowing up to 10° offset during fishing operations. Until recently, there have been no studies directly comparing the performance of non-offset and 10° offset circle hooks in commercial Pll applications. Our study alternated non-offset and 10° offset circle hooks along the gear length on individual Pll deployments in the western north atlantic, gulf of mexico, and Windward Passage in the caribbean sea. The study compared the relative performance of both hook types in terms of: (1) catch rates, (2) percent mortality, and (3) the percentage of deep-hooked target and bycatch species. For swordfish, Xiphias gladius (linnaeus, 1758), several experiments indicate: (1) marginally higher catch rates, (2) significantly lower mortality, and (3) significantly less deep hooking on non-offset than 10° offset circle hooks. Most of the performance differences for blue marlin, Makaira nigricans lacepede, 1802, were insignificant; however, one study produced significantly higher mortality on 10° offset than non-offset circle hooks. The present study suggests that, relative to non-offset circle hooks, 10° offset circle hooks may reduce fishing efficiency and can counteract the conservation benefits commonly associated with circle hooks (e.g., lower mortality). However, additional research is required to assess the effects of offset hooks on tunas, billfishes, and elasmobranchs.

Vertical habitat use of sailfish (Istiophorus platypterus) was evaluated using pop-up satellite archival tag data from the eastern tropical Atlantic, western North Atlantic, and eastern tropical Pacific. Data included Argos transmitted depth, temperature, and light level frequency histograms binned at 1-8-h intervals, and four recovered pop-up satellite archival tags that provided high resolution archival data recorded at 30-s intervals. We tabulated the proportions of time spent within each degree of water temperature relative to the surface temperature (Delta T) and proportions of time at temperature, as these are major input variables for habitat standardization models used in stock assessment procedures. Frequency distributions were calculated for daylight, darkness, and twilight for each of the three regions and for all regions combined. Vertical habitat envelopes indicated greater use of deeper strata in the western North Atlantic, compared to the hypoxia-based habitat compressed regions of the eastern Atlantic and Pacific. However, there were no significant differences in Delta T distributions when comparing the three regions, affirming this metric for its application in habitat standardization models.

One of the impacts of ocean warming is a decrease in dissolved oxygen, with implications for valuable pelagic fish species. A study shows that the oxygenated upper ocean layer in the tropical northeast Atlantic thinned at a rate of around one metre per year between 1960 and 2010, and, by tracking individually tagged fish, demonstrates that this contraction in the oxygenated layer limited the movement of blue marlin. Climate model predictions1,2 and observations3,4 reveal regional declines in oceanic dissolved oxygen, which are probably influenced by global warming5. Studies indicate ongoing dissolved oxygen depletion and vertical expansion of the oxygen minimum zone (OMZ) in the tropical northeast Atlantic Ocean6,7. OMZ shoaling may restrict the usable habitat of billfishes and tunas to a narrow surface layer8,9. We report a decrease in the upper ocean layer exceeding 3.5 ml l−1 dissolved oxygen at a rate of ≤1 m yr−1 in the tropical northeast Atlantic (0–25° N, 12–30° W), amounting to an annual habitat loss of ∼5.95×1013 m3, or 15% for the period 1960–2010. Habitat compression and associated potential habitat loss was validated using electronic tagging data from 47 blue marlin. This phenomenon increases vulnerability to surface fishing gear for billfishes and tunas8,9, and may be associated with a 10–50% worldwide decline of pelagic predator diversity10. Further expansion of the Atlantic OMZ along with overfishing may threaten the sustainability of these valuable pelagic fisheries and marine ecosystems.

Swordfish are highly specialized top-level predators that have been challenging to study. In this paper, data from 31 pop-up satellite archival tags attached to swordfish from (i) the eastern Pacific, (ii) central Pacific, and (iii) western North Atlantic-Caribbean were analyzed. Common across locations was a pronounced diel vertical pattern with daytime hours spent primarily below the thermocline and nighttime hours spent in warmer waters, close to the surface. One exception to this pattern was periodic daytime basking events which were most common in cooler waters off California. Maximum daytime depths were significantly correlated with light penetration as measured by the diffuse attenuation coefficient at 490 nm. Temperature did not appear to influence daytime depths, and swordfish tolerated both extremely low temperatures (4 degrees C) and rapid and dramatic temperature changes (> 20 degrees C). Temperature did appear to influence the nighttime depths in the Pacific where fish typically remained in the surface mixed layer. In contrast, in the warm tropical Atlantic this was not the case, and nighttime depths were much deeper. In all areas, nighttime depth increased around the full moon. Given the parallels between the vertical movement patterns of swordfish and those of the deep sound scattering layer we suggest that swordfish vertical distribution patterns, especially during daytime, are influenced largely by resource availability. At night, when swordfish are typically targeted by fisheries, both ambient light and temperature influence movements. Understanding vertical movement patterns of swordfish can help evaluate gear vulnerability, improve population assessments, and potentially reduce fisheries bycatch.

Post-release behaviour modification, possibly a result of capture and handling stress, was evaluated using empirical eigenfunction analysis to detect changes in vertical movement patterns recorded by 183 pop-up satellite archival tags (PSATs) deployed on large pelagic fish. Argos-transmitted summary, timed interval, and some archival data were included. Scoring of irregular post-release behaviour was based on a separation of plotted eigenfunction coefficient values by their mean, with the transection across the mean reference line denoting the duration of irregular behaviour. In all, 67 (36.6%) individual fish exhibited irregular behaviour, lasting from 3 to 60 d (mean = 15.8, s.d. = 10.4). An additional 27 (14.8%) displayed patterns suggestive of irregular behaviour. Data quality and quantity were important criteria for revealing behaviour patterns. Irregular behaviour was detected in 32.6% of Argos-transmitted dataseries, increasing to 60.6% in the higher-resolution archival series. Decreased vertical movement characterized the irregular behaviour of blue sharks (Prionace glauca) and porbeagles (Lamna nasus), whereas all other species showed increased vertical activity. The approach described provides a useful method of revealing behavioural modification during the post-release recovery period of PSAT-tagged large pelagic fish, although the extent of influence on normal behaviour is not fully understood.

The use of habitat modeling is becoming a common approach for standardization of CPUE allowing one to incorporate environmental influences on the distribution of fishes (ICCAT 2004). We propose to model the habitat of Atlantic blue marlin using an approach developed for a Spatial Ecosystem and Populations Dynamics Model (SEAPODYM). The model will be calibrated and evaluated using fishing data and electronic tagging data. While the results will be useful for CPUE standardization, they will also provide the first step toward a full application of SEAPODYM to investigate spatial population dynamics of blue marlin and to develop stock assessment studies.

SUMMARY The U.S. conventional tagging data base for Atlantic sailfish (1955-2008), Istiophorus platypterus, consists of data from the NOAA Southeast Fishery Science Center’s Cooperative Tagging Center (CTC) and The Billfish Foundation (TBF). We examined the patterns of sailfish tag release and recapture results in the Atlantic Ocean using a composite analysis from both agencies. In addition, we discuss tagging results and other data that might provide insight into Atlantic sailfish stock structure. RESUME

Stable carbon (delta C-13) and oxygen (delta O-18) 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 delta C-13 and delta O-18 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 US Atlantic (58%) Variability in otolith delta O-18 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 delta O-18 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 delta O-18 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 Published by Elsevier B V