Keith D. Mullin

Distribution and abundance of large floating plastic in the north-central Gulf of Mexico☆

Aerial surveys were conducted in the north-central Gulf of Mexico from June 1988 to May 1989. Sightings of marine debris and specifically large floating plastics were recorded during these surveys. Five study areas off the Louisiana coast were monitored and seasonal distribution and densities were estimated. Each study area contained plastic throughout the year. The estimated densities of plastic were largest in the offshore areas (4 & 5) and smallest in the inshore areas (1 & 3). Seasonally, density of plastic was smallest in the summer and largest in the fall. The reasons for the differences in seasons and study areas are not apparent but the amount of plastic in each area and season could be affected by variations in currents, winds, discharge from rivers, and human activity.

Eddy Forced Variations in On‐ and off‐Margin Summertime Circulation Along the 1000‐m Isobath of the Northern Gulf of Mexico, 2000–2003, and Links with Sperm Whale Distributions Along the Middle Slope

In summers 2000-2003, NOAA Ship Gordon Gunter and TAMU R/V Gyre dropped XBTs and logged ADCP data while carrying out visual and passive-acoustic surveys for sperm whales along the 1000-m isobath of the northern Gulf of Mexico. The ships also made CTD casts, particularly when/where the XBT and ADCP data indicated the ships were passing into or out of anticyclonic and/or cyclonic slope eddies. The fine-scale resolution of the ship surveys, when combined with the meso-scale resolution of remote sensing surveys of sea surface height and ocean color, document the summer-to-summer variability in the intensity and geographic location of Loop Current eddies, warm slope eddies, and areas of cyclonic circulation over this middle slope region of the northern Gulf of Mexico. These variations forced striking year-to-year differences in the locations along the 1000-m isobath where there was on-margin and off-margin flow, and in locations where sperm whales were encountered along the 1000-m isobath. For example, when there was on-margin flow into the Mississippi Canyon region in early summer 2003, sperm whales were very rarely seen or heard there. In contrast, later that summer and during other summers when flow was along-margin or off-margin there, sperm whales were locally abundant. In this report we describe how eddy-forced variations in on-margin and off-margin flow changed the meso-scale circulation along the 1000-m isobath, and we show that most sperm whales were encountered in regions of negative SSH and/or higher-than-average surface chlorophyll.

U.S. Atlantic and Gulf of Mexico marine mammal stock assessments, 2013

1National Marine Fisheries Service, 166 Water St., Woods Hole, MA 02543 2National Marine Fisheries Service, 75 Virginia Beach Dr., Miami, FL 33149 3National Marine Fisheries Service, 219 Ft. Johnson Rd., Charleston, SC 29412 4National Marine Fisheries Service, 3209 Frederic St., Pascagoula, MS 39567 5Mote Marine Laboratory, 1600 Ken Thompson Pkwy., Sarasota, FL 34236 6Sea World, Inc., 7007 Sea World Dr., Orlando, FL 32821

Density, abundance, survival, and ranging patterns of common bottlenose dolphins (Tursiops truncatus) in Mississippi Sound following the Deepwater Horizon oil spill

After the Deepwater Horizon (DWH) oil spill began in April 2010, studies were initiated on northern Gulf of Mexico common bottlenose dolphins (Tursiops truncatus) in Mississippi Sound (MSS) to determine density, abundance, and survival, during and after the oil spill, and to compare these results to previous research in this region. Seasonal boat-based photo-identification surveys (2010–2012) were conducted in a section of MSS to estimate dolphin density and survival, and satellite-linked telemetry (2013) was used to determine ranging patterns. Telemetry suggested two different ranging patterns in MSS: (1) inshore waters with seasonal movements into mid-MSS, and (2) around the barrier islands exclusively. Based upon these data, dolphin density was estimated in two strata (Inshore and Island) using a spatially-explicit robust-design capture-recapture model. Inshore and Island density varied between 0.77–1.61 dolphins km−2 (x¯ = 1.42, 95% CI: 1.28–1.53) and 3.32–5.74 dolphins km−2 (x¯ = 4.43, 95% CI: 2.70–5.63), respectively. The estimated annual survival rate for dolphins with distinctive fins was very low in the year following the spill, 0.73 (95% CI: 0.67–0.78), and consistent with the occurrence of a large scale cetacean unusual mortality event that was in part attributed to the DWH oil spill. Fluctuations in density were not as large or seasonally consistent as previously reported. Total abundance for MSS extrapolated from density results ranged from 4,610 in July 2011 to 3,046 in January 2012 (x¯ = 3,469, 95% CI: 3,113–3,725).

Analysis of frequency structure of sperm whale clicks as a function of dive depth and animal orientation

During overnight tracking of a pod of sperm whales in the Gulf of Mexico in July 2000, the NOAA ship GORDON GUNTER recorded their characteristic ‘‘click’’ sounds on a five‐element towed hydrophone array. Multiple reflections from the surface and ocean bottom were also recorded. Analysis of the arrival times and bearings of the reflections allowed the computation of three dimensional dive profiles for several animals. By assuming the orientation of the animal was aligned with its velocity, the relative orientation of the animals relative to the array could also be estimated. A visual examination of the frequency content of the received clicks versus dive time suggested that the double resonances in the 1.2 and 2.2 kHz band increased 20%–30% during depth changes of 1000 m. In this presentation the possible relationship between click structure and whale depth and orientation is rigorously analyzed, and the observed relationships are compared with predictions from various sound production and resonator models...

Three‐dimensional localization of diving sperm whales using a short‐aperture towed horizontal array

Three‐dimensional sperm whale localizations are typically obtained via recording their ‘‘clicks’’ on widely distributed hydrophones. Here, an alternative 3D localization method is investigated, using data collected by an 8‐m aperture, five‐element horizontal towed array deployed from the NOAA ship Gordon Gunter in the Gulf of Mexico, as part of a recent sperm whale pilot study. During the night of 3 July 2000, the Gunter towed the array at a steady 1‐kn speed and 60‐m depth through a pod of sperm whales, in 1000‐m‐deep water. During that time, surface and bottom reflections from a single sperm whale click were often recorded. By measuring the bearings and relative arrival times of the direct arrival and reflections, the whale location, array depth, and array tilt could be computed. The latter results were checked against measurements obtained from a time‐depth recorder attached to the array. Assuming that the speed of the ship remained fixed and the prevailing currents did not change, subsequent positions...

Acoustic detection distances of sperm whales in the Gulf of Mexico

During a cruise in June–July 2000 in the north‐central Gulf of Mexico, sperm whales were acoustically detected, located, and tracked using a small‐aperture hydrophone array towed at a depth of 20–100 m. Water depth was 800–2000 m. Detection ranges to groups of sperm whales were estimated on several occasions by determining the location of a calling whale or group of whales, then moving away in a straight line until the group was undetectable. The range at which sperm whales could no longer be detected, either aurally with headphones or visually in a spectrogram, was found to be 4–6 km, significantly less than the 11 km that had been estimated previously in the Gulf [Norris et al., Minerals Management Service Report 1996‐0027]. To investigate this result, acoustic propagation models were run. Results from the models are shown and are used to explain the short detection distances present. In addition, propagation models are used to evaluate the effects of water depth, sensor depth, and bottom composition on...