Sean K. Todd

Geographic variation in northwest Atlantic fin whale (Balaenoptera physalus) song: Implications for stock structure assessment.

Passive acoustic data are increasingly being used as a tool for helping to define marine mammal populations and stocks. Fin whale (Balaenoptera physalus) songs present a unique opportunity to determine interstock differences. Their highly stereotyped interpulse interval has been shown to vary between geographic areas and to remain stable over time in some areas. In this study the structure of songs recorded at two geographically close feeding aggregations in the Gulf of St. Lawrence (GSL) and Gulf of Maine (GoM) was compared. Recordings were made from September 2005 through February 2006 in the GSL and intermittently between January 2006 and September 2007 at two locations in the GoM. 6257 pulse intervals corresponding to 19 GSL and 29 GoM songs were measured to characterize songs from both areas. Classification trees showed that GSL songs differ significantly from those in the GoM. The results are consistent with those derived from other stock structure assessment methodologies, such as chemical signature and photoidentification analysis, suggesting that fin whales in these areas may form separate management stocks. Song structure analysis could therefore provide a useful and cost-efficient tool for defining conservation units over temporal and geographical scales relevant to management objectives in fin whales.

Blast injury in humpback whale ears: Evidence and implications

To date, there is no published report of effects on marine mammal hearing from underwater explosions. External injuries consistent with inner ear damage have been found in dolphins subjected to Class C explosives, but often little change is seen in surface animal behavior near blast areas [Richardson et al., OCS MMS/90‐0093 (1991)]. In this study, temporal bones from two humpback whales, which died following a 5000‐kg explosion in Trinity Bay, Newfoundland [Lien et al., J. Acoust. Soc. Am. 94, 1849(A) (1993)], were harvested, preserved in formalin, scanned with 1‐mm‐high resolution spiral CT, decalcified, and sectioned at 20 μ. Evidence of mechanical trauma was found in all four ears: Round window rupture, ossicular chain disruption, sero‐sanguinous effusion of peribullar spaces, and dissection of the middle ear mucosa with pooled sera. In one animal, there were bilateral periotic fractures. These observations are consistent with blast injury reports in humans, particularly with damage to victims near the source who sustained massive, precipitous increases in cerebrospinal fluid pressure. There was no evidence that the pathologies found in these whales resulted from repeated barotrauma or chronic infection, and no similar abnormalities were found in control ears from humpbacks not exposed to blasts. While the results show whales, like other mammals, are subject to severe blast trauma, it remains unclear whether lower level stimuli induce temporary and/or acute threshold shifts in marine mammals. [Work supported by ONR Grant. No. N00014‐92‐J‐4000.]

Radiated noise from commercial ships in the Gulf of Maine: Implications for whale/vessel collisions

To understand mysticete acoustic-based detection of ships, radiated noise from high-speed craft, cruise ships, catamarans and fishing vessels was recorded June-September 2009. Calibrated acoustic data (<2500 Hz) from a vertical hydrophone array was combined with ship passage information. A cruise ship had the highest broadband source level, while a fishing vessel had the lowest. Ship noise radiated asymmetrically and varied with depth. Bow null-effect acoustic shadow zones were observed for all ship classes and were correlated with ship-length-to-draft-ratios. These shadow zones may reduce ship detection by near-surface mysticetes.

Rhythmic structure in humpback whale (Megaptera novaeangliae) songs: Preliminary implications for song production and perception

The hierarchical organization of the male humpback whale song has been well documented. However, it is unknown how singers keep these intricate songs intact over multiple repetitions or how they learn variations that occur sequentially during each mating season. Rather than focus on the sequence of sounds within a song, results presented here demonstrate that the individual sounds are organized into rhythmic groups that make the production and perception of the lengthy songs tractable by yielding a set of simple groups that, although arranged in rigid order, can be repeated multiple times to generate the entire song.

The reaction of humpback whales to underwater explosions: Orientation, movements, and behavior

In 1992, local fishermen reported unusually high net collision rates by humpback whales in Bull Arm, Trinity Bay, Newfoundland (47° 45’N, 53° 50’W), an area of underwater industrial activity. As part of a study to investigate this phenomenon [see also Ketten et al., this meeting], levels and types of noise—including underwater explosions—were sampled. The location and movement of a small group of humpbacks (71 individuals identified over a 19‐day period) resident in Bull Arm were monitored; when possible, behavior of individuals was recorded directly. CTD profiles and bait abundance were also noted. Explosions were of high amplitude and low frequency. Measured at 1 mile from source, levels typically reached 150 dB (re: 1 μPa at 1 m, at 350 Hz). Following explosions, residency time and location of individual humpbacks did not change. When individuals could be observed directly, no behavioral reaction to explosions (sudden dives, abrupt movements) were seen. Although not statistically significant, more anim...

Hierarchical and rhythmic organization in the songs of humpback whales (Megaptera novaeangliae)

Since the groundbreaking work of Payne and McVay (1971), humpback songs have been conceptualized in terms of the upward hierarchical organization of sound units within phrases, and phrases within themes. Songs change within each season and all whales in a geographical region detect and sing the reshaped song. Here we propose two properties that act to make relearning the evolving song possible. First, each level of the hierarchical structure constrains the others. We estimated the degree of constraint using information theory and found that the theme, phrase, and prior sound unit reduced the source entropy of the current sound unit equally. Different sound units are found in each theme and phrase; each theme and phrase ‘uses up’ some of the sound units. Second, the rhythm of the sound units acts to simplify the phrase structure. The timing between sound units often separates adjacent phrases by longer silent durations, and in spite of huge differences in the number of sound units within phrases, the overall duration of the phrases often are equal, allowing the whale to anticipate phrase repetitions. Humpback and human songs share the same hierarchical structure, but there are striking differences in the sound unit sequence.

Long-term passive acoustic recordings track the changing distribution of North Atlantic right whales (Eubalaena glacialis) from 2004 to 2014

Given new distribution patterns of the endangered North Atlantic right whale (NARW; Eubalaena glacialis) population in recent years, an improved understanding of spatio-temporal movements are imperative for the conservation of this species. While so far visual data have provided most information on NARW movements, passive acoustic monitoring (PAM) was used in this study in order to better capture year-round NARW presence. This project used PAM data from 2004 to 2014 collected by 19 organizations throughout the western North Atlantic Ocean. Overall, data from 324 recorders (35,600 days) were processed and analyzed using a classification and detection system. Results highlight almost year-round habitat use of the western North Atlantic Ocean, with a decrease in detections in waters off Cape Hatteras, North Carolina in summer and fall. Data collected post 2010 showed an increased NARW presence in the mid-Atlantic region and a simultaneous decrease in the northern Gulf of Maine. In addition, NARWs were widely distributed across most regions throughout winter months. This study demonstrates that a large-scale analysis of PAM data provides significant value to understanding and tracking shifts in large whale movements over long time scales.