Movements and Habitat Utilization of Two Longbill Spearfish Tetrapturus pfluegeri in the Eastern Tropical South Atlantic Ocean

The longbill spearfish Tetrapturus pfleugeri Robins and de Sylva, 1963, is a small istiophorid billfish found in the Atlantic Ocean and adjacent seas that occurs as an infrequent by-catch in recreational and commercial pelagic fisheries. Although some data exist on diet and reproduction based on dead specimens, little is known of the species’ habitat preferences or individual movement patterns. In 2004, two longbill spearfish were tagged with pop-up satellite archival tags (PSATs) near Ascencion Island in the South Atlantic for 11 d and 45 d. Individual movement tracks derived from light-based geolocation estimates suggested little relationship with sea surface temperature fronts, although both animals demonstrated a clear preference away from the West African subsurface hypoxic plume. Overall temperature at depth distributions for both fish were narrow; between 22–26 °C for 97% and 82% respectively of the total time at liberty durations. Almost all of the 8-h time-at-depth periods for both day and combined periods showed that these two fish remained within 150 m of the surface. However, time at depth utilization analyses suggest a slightly bimodal distribution, with the majority of the time at depths \u3c 25 m and a secondary grouping at 50–100 m. Depth utilization data are consistent with the hypothesis that interactions between this species and deep-set pelagic longline fisheries for bigeye tuna in the eastern tropical South Atlantic occurs primarily at set and retrieval of the gear

Habitat Preferences of Istiophorid Billfishes in the Western North Atlantic: Applicability of Archival Tag Data to Habitat-Based Stock Assessment Methodologies

The Japanese pelagic longline fishery, which has a broad temporal and spatial coverage in the Atlantic Ocean, provides an important time series used in assessments of istiophorid billfishes. Past assessments of Atlantic blue marlin and white marlin by the ICCAT SCRS indicate a pronounced decrease in stock abundance of both species over the past fifty years. The current biomass of the white marlin is estimated to be 15% of that necessary for maximum sustainable yield (BMSY), while blue marlin are estimated to be at 0.4 BMSY. Over the past fifty years Japanese pelagic longline fishing operations have moved from shallow longline sets targeting yellowfin tuna to deeper longline sets targeting swordfish and bigeye tuna. As billfish are known to spend the majority of their time in surface waters, it was expected that billfish catch rates would be reduced for deeper set longlines. Coupled with the historical decrease in abundance of the stocks, the reduction of catch rates of deeper sets in recent years should be more pronounced. However, in some instances, billfish catch rates of deeper set longlines in recent years have exceeded those of shallow set longlines during times of higher billfish abundance. Such findings are enigmatic, and there are several possible explanations for the observed results (none of which are mutually exclusive): (1) the assessments may not be correct (billfish abundance may not be as low as it is currently estimated to be); (2) deep set longline hooks may fish at shallower depths than estimated; (3) the majority of billfish may be taken as deep set longlines are deployed and retrieved (a longer time for the bait to be moving through the water column); or (4) billfish may preferentially feed at depth. In this paper we provide detailed time-at-depth information for two blue marlin released alive from pelagic longline gear with pop-up archival satellite tags (PSATs) programmed to release from the animals after 30 days. Both blue marlin made several dives each day. The fish moved quickly to depth, and the times at depth were greater than those spent in descent or ascent. The depth of dives was greater during daylight hours. These data are suggestive of feeding excursions to deeper waters, movements for which these fish are well adapted with large eyes and a brain (eye) heating organ. If billfish undertake specific feeding movements to depth, then one would expect increased catch rates for deeply set longline gear. Researchers have recently attempted to standardize catch rates of billfish on pelagic longline for the time fish spend at depth (habitat-based models). However, if feeding motivation is not the same for an animal at all depths, then such standardizations will significantly bias catch rates and lead to errors in assessment

A novel method for transient detection in high-cadence optical surveys: Its application for a systematic search for novae in M31

[abridged] In large-scale time-domain surveys, the processing of data, from procurement up to the detection of sources, is generally automated. One of the main challenges is contamination by artifacts, especially in regions of strong unresolved emission. We present a novel method for identifying candidates for variables and transients from the outputs of such surveys' data pipelines. We use the method to systematically search for novae in iPTF observations of the bulge of M31. We demonstrate that most artifacts produced by the iPTF pipeline form a locally uniform background of false detections approximately obeying Poissonian statistics, whereas genuine variables and transients as well as artifacts associated with bright stars result in clusters of detections, whose spread is determined by the source localization accuracy. This makes the problem analogous to source detection on images produced by X-ray telescopes, enabling one to utilize tools developed in X-ray astronomy. In particular, we use a wavelet-based source detection algorithm from the Chandra data analysis package CIAO. Starting from ~2.5x10^5 raw detections made by the iPTF data pipeline, we obtain ~4000 unique source candidates. Cross-matching these candidates with the source-catalog of a deep reference image, we find counterparts for ~90% of them. These are either artifacts due to imperfect PSF matching or genuine variable sources. The remaining ~400 detections are transient sources. We identify novae among these candidates by applying selection cuts based on the expected properties of nova lightcurves. Thus, we recovered all 12 known novae registered during the time span of the survey and discovered three nova candidates. Our method is generic and can be applied for mining any target out of the artifacts in optical time-domain data. As it is fully automated, its incompleteness can be accurately computed and corrected for.Comment: 16 pages, 8 figures, accepted to A&

Habitat Standardization of CPUE Indices: Research Needs

Habitat standardization for billfish CPUE offers a potentially useful alternative to the statistical procedures used in the past. However, most of the assumptions of the current habitatstandardization methodology remain untested and some are not consistent with current knowledge about the behavior of billfish. This paper outlines research required to ensure the methods for habitat standardization produce robust estimates of CPUE

Swordfish Vertical Distribution and Habitat Use in Relation to Diel and Lunar Cycles in the Western North Atlantic

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 100 m during the night and depths greater than 400 m during daytime hours, vertical movements between the surface and depth occurring during crepuscular hours. The maximum depth recorded was 1,448 m (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

Validity, Identification, and Distribution of the Roundscale Spearfish, Tetrapturus georgii (Teleostei: Istiophoridae): Morphological and Molecular Evidence

The roundscale spearfish, Tetrapturus georgii Lowe, 1840, is known only from four specimens from the Mediterranean and eastern North Atlantic. Additional specimens have not been identified since 1961, making the validity and distribution of this species unclear. Analysis of 16 billfish specimens from the western North Atlantic on the basis of scale morphology, anus position, and mitochondrial DNA confirms the validity of this species and extends its distribution. Mid-lateral scales are soft, notably rounded anteriorly, and bear 2–3 points distinct from those of the sympatric longbill spearfish (Tetrapturus pfluegeri Robins and de Sylva, 1963) and white marlin (Tetrapturus albidus Poey, 1860). Position of anus relative to first anal fin and a related morphometric ratio (distance from anus to first anal fin origin: height of first anal fin) are intermediate between T. pfluegeri and T. albidus. These characteristics match those described by Robins (1974) from the four eastern North Atlantic specimens of T. georgii. The mitochondrial ND4L, ND4, and cyt b gene sequences strongly support reciprocal monophyly of the western North Atlantic specimens relative to other Atlantic istiophorids. The difficulty in distinguishing between morphologically similar T. georgii and T. albidus in the field and the previously unrecognized presence of T. georgii in the western North Atlantic has implications for stock assessments of T. albidus, a species that is severely overfished

Phylogenetic Relationships of Monocots Based on the Highly Informative Plastid Gene ndhF

We used ndhF sequence variation to reconstruct relationships across 282 taxa representing 78 monocot families and all 12 orders. The resulting tree is highly resolved and places commelinids sister to Asparagales, with both sister to Liliales—Pandanales in the strict consensus; Pandanales are sister to Dioscoreales in the bootstrap majority-rule tree, just above Petrosaviales. Acorales are sister to all other monocots, with Alismatales sister to all but Acorales. Relationships among the four major clades of commelinids remain unresolved. Relationships within orders are consistent with those based on rbcL, alone or in combination with atpB and 18S nrDNA, and generally better supported: ndhF contributes more than twice as many informative characters as rbcL, and nearly as many as rbcL, atpB, and 18S nrDNA combined. Based on functional arguments, we hypothesized that net venation and fleshy fruits should both evolve—and thus undergo concerted convergence—in shaded habitats, and revert to parallel venation and dry, passively dispersed fruits in open, sunny habitats. Our data show that net venation arose at least 26 times and disappeared 9 times, whereas fleshy fruits arose 22 times and disappeared 11 times. Both traits arose together at least 15 times and disappeared together 5 times. They thus show a highly significant pattern of concerted convergence (P \u3c 10-9) and are each even more strongly associated with shaded habitats (P \u3c 10-10 to 10-23); net venation is also associated, as predicted, with broad-leaved aquatic plants. Exceptions to this pattern illustrate the importance of other selective constraints and phylogenetic inertia