Steady inter and intra-annual decrease in the vocalization frequency of Antarctic blue whales

Time averaged narrow-band noise near 27 Hz produced by vocalizations of many distant Antarctic blue whales intensifies seasonally from early February to late October in the ocean off Australia’s South West. Spectral characteristics of long term patterns in this noise band were analyzed using ambient noise data collected at the Comprehensive Nuclear-Test-Ban Treaty hydroacoustic station off Cape Leeuwin, Western Australia over 2002–2010. Within 7 day averaged noise spectra derived from 4096-point FFT (~0.06 Hz frequency resolution), the −3-dB width of the spectral peak from the upper tone of Antarctic blue whale vocalization was about 0.5 Hz. The spectral frequency peak of this tonal call was regularly but not gradually decreasing over the 9 years of observation from ~27.7 Hz in 2002 to ~26.6 Hz in 2010. The average frequency peak steadily decreased at a greater rate within a season at 0.4–0.5 Hz/season but then in the next year recovered to approximately the mean value of the previous season. A regression analysis showed that the interannual decrease rate of the peak frequency of the upper tonal call was 0.135 ± 0.003 Hz/year over 2002–2010 (R 2 ≈ 0.99). Possible causes of such a decline in the whale vocalization frequency are considered

Respiration and Heart Rate at the Surface between Dives in Northern Elephant Seals

All underwater activities of diving mammals are constrained by the need for surface gas exchange. Our aim was to measure respiratory rate (fb) and heart rate (fh) at the surface between dives in free-ranging northern elephant seals Mirounga angustirostris. We recorded fb and fh acoustically in six translocated juveniles, 1.8-2. 4 years old, and three migrating adult males from the rookery at Ano Nuevo, California, USA. To each seal, we attached a diving instrument to record the diving pattern, a satellite tag to track movements and location, a digital audio tape recorder or acoustic datalogger with an external hydrophone to record the sounds of respiration and fh at the surface, and a VHF transmitter to facilitate recovery. During surface intervals averaging 2.2+/−0.4 min, adult males breathed a mean of 32.7+/−5.4 times at a rate of 15. 3+/−1.8 breaths min(−)(1) (means +/− s.d., N=57). Mean fh at the surface was 84+/−3 beats min(−)(1). The fb of juveniles was 26 % faster than that of adult males, averaging 19.2+/−2.2 breaths min(−)(1) for a mean total of 41.2+/−5.0 breaths during surface intervals lasting 2.6+/−0.31 min. Mean fh at the surface was 106+/−3 beats min(−)(1). fb and fh did not change significantly over the course of surface intervals. Surface fb and fh were not clearly associated with levels of exertion, such as rapid horizontal transit or apparent foraging, or with measures of immediately previous or subsequent diving performance, such as diving duration, diving depth or swimming speed. Together, surface respiration rate and the duration of the preceding dive were significant predictors of surface interval duration. This implies that elephant seals minimize surface time spent loading oxygen depending on rates of oxygen uptake and previous depletion of stores

First insights into the vertical habitat use of the whitespotted eagle ray Aetobatus narinari revealed by pop‐up satellite archival tags

The whitespotted eagle ray Aetobatus narinari is a tropical to warm‐temperate benthopelagic batoid that ranges widely throughout the western Atlantic Ocean. Despite conservation concerns for the species, its vertical habitat use and diving behaviour remain unknown. Patterns and drivers in the depth distribution of A. narinari were investigated at two separate locations, the western North Atlantic (Islands of Bermuda) and the eastern Gulf of Mexico (Sarasota, Florida, U.S.A.). Between 2010 and 2014, seven pop‐up satellite archival tags were attached to A. narinari using three methods: a through‐tail suture, an external tail‐band and through‐wing attachment. Retention time ranged from 0 to 180 days, with tags attached via the through‐tail method retained longest. Tagged rays spent the majority of time (82.85 ± 12.17% S.D.) within the upper 10 m of the water column and, with one exception, no rays travelled deeper than ~26 m. One Bermuda ray recorded a maximum depth of 50.5 m, suggesting that these animals make excursions off the fore‐reef slope of the Bermuda Platform. Individuals occupied deeper depths (7.42 ± 3.99 m S.D.) during the day versus night (4.90 ± 2.89 m S.D.), which may be explained by foraging and/or predator avoidance. Each individual experienced a significant difference in depth and temperature distributions over the diel cycle. There was evidence that mean hourly depth was best described by location and individual variation using a generalized additive mixed model approach. This is the first study to compare depth distributions of A. narinari from different locations and describe the thermal habitat for this species. Our study highlights the importance of region in describing A. narinari depth use, which may be relevant when developing management plans, whilst demonstrating that diel patterns appear to hold across individuals

A new way of assessing the strength of a figure-ground cue

Methods to assess the strength of figure-ground cues generally fall into two categories: (1) Subjective reports about which part of a display is seen as figure. (2) Reaction time measures to stimuli that probe a part of a display. Both methods have drawbacks. Subjective reporting manipulates the process under investigation. Studies with probes can superimpose a new figure on the figure-ground display, possibly changing the representation, or fail to control what subjects do during the presentation of figure-ground displays (when probes follow the display). In our approach we try to increase control over the behaviour of subjects using a visual short term matching task (Driver and Baylis, 1996), while refraining from explicit figure-ground instructions. We biased figure-ground assignment by presenting the first half of an ambiguous figure-ground display before adding the second half. The first half will initially become figure, since it is presented on a large background. If the first half contains a strong figure cue, it should be resistent against the distraction caused by the onset of the second half, 100 msec later. If, however, the second half contains a strong figure cue it self, this may cancel the initial figure assignment to the first half. Figure assignment was probed afterwards and subjects decided which of two mirror images was part of the figure-ground display. In our experiment, we used the lower-region cue (Vecera, Vogel and Woodman, 2002). We report an interaction between region presented first, and whether this region is subsequently probed. For upper regions presented first and probed, reaction times are slower than for lower regions presented first and probed. This illustrates the viability of our approach: a strong figure cue will overcome the disadvantage of being presented second, whilst also holding on to the advantage of being presented first

The time course of figure-ground reversal.

We report the results from five experiments employing a modified version of the short-term visual matching (STVM) method introduced by Driver and Baylis (1996). In STVM, participants see a study display with ambiguous figure-ground relations. After the study display, participants have to decide which of two shapes in a match display was seen before in the study display. STVM has been used by Vecera, Vogel, and Woodman (2002) to demonstrate that the lower region is a figure-ground cue. In our modified version of STVM, the study stimulus was preceded by a brief prime. This caused a biasing of the figural interpretation of the ambiguous figure-ground displays that contained the lower region cue. We show that 100-msec priming with an unambiguous display is enough to affect the subsequent interpretation of the ambiguous figure-ground display. It takes maximally 350 msec to complete a transition from the nondominant interpretation to the dominant interpretation of an ambiguous figure-ground display that contains the lower region cue

Towards collective circum-antarctic passive acoustic monitoring:the southern ocean hydrophone network (SOHN)

The Southern Ocean Research Partnership (SORP) is an international research program initiated within the International Whaling Commission (IWC) in 2009 to promote collaborative cetacean research, develop nov el research techniques, and conduct non-lethal research on whales in the Southern Ocean (CHILDERHOUSE 2009). One of the original research projects of the SORP is the Blue and Fin Whale Acoustic Trends Project, which aims to implement a long term passive acoustic research program to examine trends in Antarctic blue (Balaenoptera musculus intermedia) and fin whale (B. physalus) abundance, distribution, and seasonal presence in the Southern Ocean through the use of a network of passive acoustic recorders: the Southern Ocean Hydrophone Network (SOHN). Networks of widely spaced passive acoustic recorders can provide insights in spatio-temporal patterns of the presence and properties of whale calls as well as the potential to monitor trends in Antarctic blue and fin whale abundance. The SOHN will consist of a network of autonomous underwater acoustic re cording stations surrounding the Antarctic continent with each site remaining active throughout the 10-year duration of the project. In addition to circum polar coverage, high priority will be given towards achieving simultaneous temporal coverage, especially in the early years of the project. While logis tical constraints may prevent uniform distribution of SOHN recording sites around the continent, the Acoustic Trends Working group (ATW) aims to have at least one recording site in each of the six IWC management areas (i.e., one per 60° longitudinal wedge). International collaboration and coordination are imperative to achieve the project goals due to the high cost of Antarctic research as well as the broad spatial and temporal scales over which the SOHN will span. Furthermore, standardization of data is paramount for accurate and efficient analysis and interpretation of SOHN data. To facilitate international participation in the SOHN, this document provides practical recommendations to guide and support passive acoustic data of project as well as technical and logistic information and recommendations regarding standardization of recording locations is provided here for a diverse collection in Antarctic waters. This whitepaper addresses a wide audience, ranging from scientists from different disciplines with access to instrumenttation and/or infrastructure to collect passive acoustic data in the Southern Ocean, to ship operators or other parties that can provide logistic support to make the SOHN a reality. Background information and an outline of the sci entific aims of project as well as technical and logistic information and re commendations regarding standardization of recording locations is provided here for a diverse audience coming from different backgrounds with widely differing levels of experience with the applications and use of passive acoustic instrumentation. By providing the information relevant for SOHN from the ground up, we aim that this document contributes to increase aware ness and participation by a broad range of partner nations and organizations in the SOHN and Acoustic Trends Projects