Diel Vertical Movements of a Scalloped Hammerhead, \u3ci\u3eSphyrna lewini\u3c/i\u3e, in the Northern Gulf of Mexico

Despite the circumglobal distribution of scalloped hammerheads, Sphyrna lewini (Griffith and Smith, 1834), little information is available regarding fine-scale movement and habitat use patterns for this species. Over a 27-d period, data were collected on diel habitat use and environmental preferences of a 240 cm (total length) female S. lewini. The shark exhibited a consistent and repeated diel vertical movement pattern, making more than 76 deep nighttime dives; the maximum depth reached was 964 m, where the temperature was 5.8 degrees C. The purpose of the nightly oscillatory deep diving pattern is unknown but could possibly represent feeding behavior. These findings represent the first detailed account of S. lewini diel vertical behavior and habitat utilization in the western North Atlantic Ocean

First Record of a Sleeper Shark in the Western Gulf of Mexico and Comments on Taxonomic Uncertainty Within Somniosus (Somniosus)

A sleeper shark, Somniosus (Somniosus) sp., is reported from Alaminos Canyon in the western Gulf of Mexico at a depth of about 2647 m based on observations made using a remotely operated vehicle. This is the first record of a sleeper shark (Somniosus, Somniosidae) from the western Gulf of Mexico and deepest record of any shark from the Gulf of Mexico. Despite claims to the contrary in the literature, no taxonomic character has been identified to date that can be used to unequivocally identify all representatives of Somniosus (Somniosus), and as a result, some species records must be considered dubious

Observation of a potential future sensitivity limitation from ground motion at LIGO Hanford

A first detection of terrestrial gravity noise in gravitational-wave detectors is a formidable challenge. With the help of environmental sensors, it can in principle be achieved before the noise becomes dominant by estimating correlations between environmental sensors and the detector. The main complication is to disentangle different coupling mechanisms between the environment and the detector. In this paper, we analyze the relations between physical couplings and correlations that involve ground motion and LIGO strain data h(t) recorded during its second science run in 2016 and 2017. We find that all noise correlated with ground motion was more than an order of magnitude lower than dominant low-frequency instrument noise, and the dominant coupling over part of the spectrum between ground and h(t) was residual coupling through the seismic-isolation system. We also present the most accurate gravitational coupling model so far based on a detailed analysis of data from a seismic array. Despite our best efforts, we were not able to unambiguously identify gravitational coupling in the data, but our improved models confirm previous predictions that gravitational coupling might already dominate linear ground-to-h(t) coupling over parts of the low-frequency, gravitational-wave observation band

Short-term post release mortality of skates (family Rajidae) discarded in a western North Atlantic commercial otter trawl fishery

a b s t r a c t Due to market and regulatory factors, Rajidae skates are routinely discarded by commercial otter trawlers in the western North Atlantic. Accounting for post-release mortality is therefore essential to total fishing mortality estimates, stock status and management of this group of fishes. However, despite a presumed species-specific range in tolerance, few studies have investigated the short-term post-release mortality among skates indigenous to the western North Atlantic following capture by mobile fishing gears, and never in the Gulf of Maine. This study addresses this shortfall for the prohibited thorny skate, Amblyraja radiate and smooth skate, Malacoraja senta, and the targeted winter skate, Leucoraja ocellata, and little skate, Leucoraja erinacea. Of 1288 skates evaluated, negligible immediate mortality was observed at the time of capture, even in relation to the largest catches and/or most prolonged tows. However, injury frequency was moderate, with highest levels in the smooth (60%) and thorny (52%) skates. Aside from the smooth skate (59%), 72 h mortality rates were low overall (19% across all species when accounting tow durations indicative of the fishery), with the winter skate (8%) exhibiting the lowest levels. Logistic regression modeling revealed tow duration as the most universal predictor of condition and 72 h mortality, while catch biomass, sex, temperature changes, and animal size also held influence in certain species. Although in general the studied species appear more resilient to trawl capture and handling than previously estimated, interspecific differences must be accounted for when managing this group

Implications of Dedicated Seismometer Measurements on Newtonian-Noise Cancellation for Advanced LIGO

Newtonian gravitational noise from seismic fields will become a limiting noise source at low frequency for second-generation, gravitational-wave detectors. It is planned to use seismic sensors surrounding the detectors’ test masses to coherently subtract Newtonian noise using Wiener filters derived from the correlations between the sensors and detector data. In this Letter, we use data from a seismometer array deployed at the corner station of the Laser Interferometer Gravitational Wave Observatory (LIGO) Hanford detector combined with a tiltmeter for a detailed characterization of the seismic field and to predict achievable Newtonian-noise subtraction levels. As was shown previously, cancellation of the tiltmeter signal using seismometer data serves as the best available proxy of Newtonian-noise cancellation. According to our results, a relatively small number of seismometers is likely sufficient to perform the noise cancellation due to an almost ideal two-point spatial correlation of seismic surface displacement at the corner station, or alternatively, a tiltmeter deployed under each of the two test masses of the corner station at Hanford will be able to efficiently cancel Newtonian noise. Furthermore, we show that the ground tilt to differential arm-length coupling observed during LIGO’s second science run is consistent with gravitational coupling