Shannon Rankin

A tool for real-time acoustic species identification of delphinid whistles

The ability to identify delphinid vocalizations to species in real-time would be an asset during shipboard surveys. An automated system, Real-time Odontocete Call Classification Algorithm (ROCCA), is being developed to allow real-time acoustic species identification in the field. This Matlab-based tool automatically extracts ten variables (beginning, end, minimum and maximum frequencies, duration, slope of the beginning and end sweep, number of inflection points, number of steps, and presence/absence of harmonics) from whistles selected from a real-time scrolling spectrograph (ISHMAEL). It uses classification and regression tree analysis (CART) and discriminant function analysis (DFA) to identify whistles to species. Schools are classified based on running tallies of individual whistle classifications. Overall, 46% of schools were correctly classified for seven species and one genus (Tursiops truncatus, Stenella attenuata, S. longirostris, S. coeruleoalba, Steno bredanensis, Delphinus species, Pseudorca crassidens, and Globicephala macrorhynchus), with correct classification as high as 80% for some species. If classification success can be increased, this tool will provide a method for identifying schools that are difficult to approach and observe, will allow species distribution data to be collected when visual efforts are compromised, and will reduce the time necessary for post-cruise data analysis.

Acoustic detection and satellite-tracking leads to discovery of rare concentration of endangered North Pacific right whales

The North Pacific right whale, Eubalaena japonica, is one of the most endangered species of whale in the world. On 10 August 2004, two right whales were located in the Bering Sea using headings to right whale calls provided by directional sonobuoys. A satellite-monitored radio tag attached to one of these whales functioned for 40 days. Over the 40-day period, this whale moved throughout a large part of the southeast Bering Sea shelf, including areas of the outer-shelf where right whales have not been seen in decades. In September, multiple right whales were acoustically located and subsequently sighted by another survey vessel approaching a near-real-time position from the tag. An analysis of photographs confirmed at least 17 individual whales (not including the tagged whales). Genetic analysis of biopsy samples identified 17 individuals: 10 males and 7 females. The discovery of seven females was significant, as only one female had been identified in the past. Genetics also confirmed the presence of at least two calves. Although the future of this population is highly uncertain, the discovery of additional females and calves gives some hope that this most critically endangered of all whale populations may still possess the capacity to recover.

The effect of recording and analysis bandwidth on acoustic identification of delphinid species

Because many cetacean species produce characteristic calls that propagate well under water, acoustic techniques can be used to detect and identify them. The ability to identify cetaceans to species using acoustic methods varies and may be affected by recording and analysis bandwidth. To examine the effect of bandwidth on species identification, whistles were recorded from four delphinid species (Delphinus delphis, Stenella attenuata, S. coeruleoalba, and S. longirostris) in the eastern tropical Pacific ocean. Four spectrograms, each with a different upper frequency limit (20, 24, 30, and 40 kHz), were created for each whistle (n = 484). Eight variables (beginning, ending, minimum, and maximum frequency; duration; number of inflection points; number of steps; and presence/absence of harmonics) were measured from the fundamental frequency of each whistle. The whistle repertoires of all four species contained fundamental frequencies extending above 20 kHz. Overall correct classification using discriminant function analysis ranged from 30% for the 20-kHz upper frequency limit data to 37% for the 40-kHz upper frequency limit data. For the four species included in this study, an upper bandwidth limit of at least 24 kHz is required for an accurate representation of fundamental whistle contours.

Species-specific beaked whale echolocation signals

Beaked whale echolocation signals are mostly frequency-modulated (FM) upsweep pulses and appear to be species specific. Evolutionary processes of niche separation may have driven differentiation of beaked whale signals used for spatial orientation and foraging. FM pulses of eight species of beaked whales were identified, as well as five distinct pulse types of unknown species, but presumed to be from beaked whales. Current evidence suggests these five distinct but unidentified FM pulse types are also species-specific and are each produced by a separate species. There may be a relationship between adult body length and center frequency with smaller whales producing higher frequency signals. This could be due to anatomical and physiological restraints or it could be an evolutionary adaption for detection of smaller prey for smaller whales with higher resolution using higher frequencies. The disadvantage of higher frequencies is a shorter detection range. Whales echolocating with the highest frequencies, or broadband, likely lower source level signals also use a higher repetition rate, which might compensate for the shorter detection range. Habitat modeling with acoustic detections should give further insights into how niches and prey may have shaped species-specific FM pulse types.

Patterned burst-pulse vocalizations of the northern right whale dolphin, Lissodelphis borealis

Vocalizations from the northern right whale dolphin, Lissodelphis borealis, were recorded during a combined visual and acoustic shipboard survey of cetacean populations off the west coast of the United States. Seven of twenty single-species schools of L. borealis produced click and pulsed vocalizations. No whistles were detected during any of the encounters. Clicks associated with burst-pulse vocalizations were lower in frequency and shorter in duration than clicks associated with echolocation. All burst-pulse sounds were produced in a series containing 6-18 individual burst-pulses. These burst-pulse series were stereotyped and repeated. A total of eight unique burst-pulse series were detected. Variation in the temporal characteristics of like units compared across repeated series was less than variation among all burst-pulses. These stereotyped burst-pulse series may play a similar communicative role as do stereotyped whistles found in other delphinid species.

VOCALIZATIONS OF THE SEI WHALE BALAENOPTERA BOREALIS OFF THE HAWAIIAN ISLANDS

ABSTRACT Little is known about the sounds produced by the Sei Whale Balaenoptera borealis and no recordings have been made in their presence in the Pacific Ocean. This research presents sounds recorded in the presence of Sei whales near the Hawaiian Islands in November, 2002. A total of 107 vocalizations, including two variations of low-frequency downswept calls, were measured. Two of these calls were sweeps from 100 Hz to 44 Hz, over 1.0 seconds. The second call type (n=105) consisted of low- frequency calls which swept from 39 Hz to 21 Hz over 1.3 seconds. These calls are different from sounds attributed to Sei whales in the Atlantic and Southern Oceans, where recordings were made only in the summer months. These sounds are similar, however, to sounds attributed to fin whales in Hawaiian waters. Additional studies are needed in order to understand the spatial and temporal variation in the vocal repertoire of Sei and Fin whales in the Pacific Ocean.

Description of sounds recorded from Longman's beaked whale, Indopacetus pacificus.

Sounds from Longmans beaked whale, Indopacetus pacificus, were recorded during shipboard surveys of cetaceans surrounding the Hawaiian Islands archipelago; this represents the first known recording of this species. Sounds included echolocation clicks and burst pulses. Echolocation clicks were grouped into three categories, a 15 kHz click (n = 106), a 25 kHz click (n = 136), and a 25 kHz pulse with a frequency-modulated upsweep (n = 70). The 15 and 25 kHz clicks were relatively short (181 and 144 ms, respectively); the longer 25 kHz upswept pulse was 288 ms. Burst pulses were long (0.5 s) click trains with approximately 240 clicks/s.

To Whistle or Not to Whistle? Geographic Variation in the Whistling Behavior of Small Odontocetes

Whistles are used by odontocetes to varying degrees. During a visual and acoustic survey of dolphin abundance in the eastern tropical Pacific Ocean (ETP), whistles were heard from 66% of single species schools and from 98% of mixed species schools. In contrast, whistles were heard from only 24% of single species schools and 23% of mixed species schools during a survey of temperate waters off the western United States. The most common species encountered in the ETP were Stenella coeruleoalba, S. attenuata, and Tursiops truncatus, all of which whistled frequently. The most common species encountered in the temperate study area were Delphinus delphis, Phocoenoides dalli, Lissodelphis borealis, and Phocoena phocoena, only one of which whistled (D. delphis). Why do small odontocete species living in the ETP whistle more frequently than those living in colder waters farther north? Six hypotheses are explored: (1) predator avoidance, (2) group size, (3) school composition, (4) behavior state, (5) temporal variation, and (6) anatomical differences. Multivariate logistic regression with whistling as the dependent variable and group size, school composition, time of day, presence of a beak, and study area as independent variables showed that all variables were significant (p < 0.001). An explanation of the aggregation of whistling species in the tropical study area and nonwhistling species in the temperate study area is likely found in some combination of the hypotheses discussed.

Integration of real‐time odontocete call classification algorithm into PAMGUARD signal processing software.

Real‐time odontocete call classification algorithm (ROCCA) is a tool for real‐time acoustic species identification of delphinid whistles. Introduced in 2006 as MATLAB‐based software, ROCCA is currently being incorporated into PAMGUARD, a freely‐available, open source software package. ROCCA provides automated extraction of whistle contours from a spectrogram. It measures 54 whistle contour features including frequencies, slopes, duration, and variables related to the positions of inflection points and steps. ROCCA currently classifies whistles of seven species and one genus: Globicephala macrorhynchus, Pseudorca crassidens, Steno bredanensis, Stenella attenuata, S. coeruleoalba, S. longirostris, Tursiops truncatus, and Delphinus species. The classifier is a Random Forest trained on 2231 whistles collected over six cruises and 7 years in the eastern tropical Pacific Ocean. The original ROCCA classifier used a combination of discriminant function analysis and CART algorithms on 13 whistle contour features f...

Effect of low‐frequency seismic exploration signals on the cetaceans of the Gulf of Mexico

The increasing use of seismic exploration has created a need to understand effects that intense low‐frequency sounds have on the distribution, abundance, and behavior of cetaceans. The goal of this study is to determine possible effects of seismic exploration on cetaceans in the northern Gulf of Mexico. Low‐frequency sounds originating from seismic exploration were compared with the presence/absence of cetaceans as determined by acoustic and visual methods of detection. The recordings were collected via a towed passive hydrophone array during seasonal GulfCet research cruises from 1992–1997. The study area consisted of 14 north–south transects ranging from the 100–2000 m isobath in the northern Gulf of Mexico. For odontocetes, with the exception of sperm whales, no relationship between presence of low‐ and medium‐frequency seismic noise was found on a relatively large spatial scale of hundreds of kilometers. For mysticetes, results were inconclusive due to small sample size. These findings suggest that th...