Many of us have heard the haunting call of a whale ‘song,’ but how do the whales themselves hear sound? Similar to the way that animals see color in different ranges of the visible light spectrum, the mechanism by which … Continue reading
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The pygmy blue whale, cousin to the more well-known Antarctic blue whale, has an enigmatic history. Pygmy blue whales dwell in vast expanses of the Indian and southern Pacific oceans, and are a highly mobile species. The species was identified in 1966—although it’s likely to have been confused with its cousin the “true” blue whale prior to 1966—so it’s only in recent years that we’ve been able to catch glimpses of these elusive cetaceans during their migrations to and from breeding and feeding grounds. The researchers of a recent PLOS ONE paper tested out a new method of tracking these whales: satellite telemetry (described below). Using this method, the researchers mapped the migration of pygmy blue whales as they moved from the coast of Australia to the waters of Indonesia. We caught up with author Virginia Andrews-Goff to get some additional details on what it’s like to track these tiny giants.
How did you become interested in pygmy blue whales, and how did you get involved in mapping their migratory movements?
This research was carried out by the Australian Marine Mammal Centre, a national research centre focused on understanding, protecting and conserving whales, dolphins, seals, and dugongs in the Australian region. The work we carry out aims to provide scientific research and advice that underpins Australia’s marine mammal conservation and policy initiatives. We, therefore, have a keen interest in all whales that migrate through Australian waters including pygmy blue, right and humpback whales.
Pygmy blue whales are of particular interest, however, as so little is known in regard to their movements and population status. Large scale movements of whales are particularly hard to study and what we do know about pygmy blue whales we have mainly learnt from examining whaling records. Fortunately, pygmy blue whales were targeted by the whaling industry for only a very short period of time in the late 1950s and early 1960s just prior to the IWC banning the hunting of all blue whales in 1966.
What are the challenges of better understanding whale migration in general?
Large-scale, long-term whale movements are challenging to study as it is impractical to do so by direct observation. Therefore, we need to use devices, such as satellite tags, that can be attached to the whale to provide real-time location information.
What is satellite telemetry and how did it enable your findings?
In this case, satellite telemetry refers to the use of a satellite-linked tag attached to the whale. This tag communicates with the Argos satellite system when the antenna breaks the surface of the water. A location can then be determined when multiple Argos satellites receive the tag’s transmissions. We then receive this location data in almost real time via the Argos website, which allows us to track the movement of the tagged whale.
Based on your tracking, you found that the pygmy blue whales traveled from the west coast of Australia north to breeding grounds in Indonesia. Can you give readers a sense of why they travel this route?
Generally, whales migrate between productive feeding grounds (at high latitudes) in the summer to warmer breeding grounds (at low latitudes) during the winter. The exact reason for this general pattern is unclear, though quite a few theories exist, including to avoid predators, to assist the thermoregulatory ability of the calf, and to birth in relatively calm waters. Because of the timing of this migration, we believe these animals travel to Indonesian waters to calve. Usually it is assumed that whales fast outside of the summer when no longer located in the productive feeding grounds. Interestingly, these pygmy blue whales travel from productive feeding grounds off Western Australia to productive breeding grounds in Indonesia and therefore, probably have the opportunity to feed (and not fast) on the breeding grounds.
Satellite tag derived locations of pygmy blue whales by month.
You’ve mentioned that pygmy blue whale migratory routes correspond with shipping routes. How does this interaction impact the whales?
Baleen whales (whales that use filters to feed instead of teeth) use sound for communication and to gain information about the environment they occupy. When pygmy blue whale movements correspond to shipping routes, there is potential for the noise generated by the ships to play some role in altering calling rates associated with social encounters and feeding.
Why is it important for us to better understand pygmy blue whale migration, and how does mapping their migratory movements help conservation efforts for this endangered animal?
Our coauthor, Trevor Branch, hypothesised in 2007 that pygmy blue whales occupying Australian waters traveled into Indonesian waters. However, prior to this study, we didn’t actually know that this was the case. As such, conservation efforts relevant to the pygmy blue whales that use Australian waters are required outside of Australian waters too. We can also now gain some understanding of risks within the pygmy blue whale migratory range, such as increased ambient noise from development, shipping, and fishing, and therefore assist in mitigating these risks.
What’s next for you and your research team?
A question mark still remains over the movements of the pygmy blue whales that utilise the Bonney Upwelling feeding grounds off southern Australia. Genetic evidence indicates mixing between the animals in the feeding areas of the Perth Canyon (the animals that were tagged in this study) and the Bonney Upwelling. This indicates the potential for individuals from the Bonney Upwelling to follow a similar migration route to those animals feeding in the Perth Canyon. However, it is also thought that Bonney Upwelling animals may utilise the subtropical convergence region south of Australia. We plan to collaborate on a research project that aims to tag the pygmy blue whales of the Bonney Upwelling and ascertain whether these animals move through the same areas and are therefore exposed to the same risks as the Perth Canyon animals.
We look forward to seeing more from Dr. Andrews-Goff and her team in the future. In the meantime, read more about the elusive worlds of southern Pacific Ocean whales here at the EveryONE blog.
Citation: Double MC, Andrews-Goff V, Jenner KCS, Jenner M-N, Laverick SM, et al. (2014) Migratory Movements of Pygmy Blue Whales (Balaenoptera musculus brevicauda) between Australia and Indonesia as Revealed by Satellite Telemetry. PLoS ONE 9(4): e93578. doi:10.1371/journal.pone.0093578
Image 1: IA19847 Blue pygmy whale
Photograph © Mike Double/Australian Antarctic Division
Image 2: IA19850 Blue pygmy whale
Photograph © Mike Double/Australian Antarctic Division
Image 3: pone.0093578
Image 4: IA19851 Blue pygmy whale off Western Australian coast near Perth, Western Australia, Australia Photograph © Mike Double/Australian Antarctic Division
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Sharks live in the vast, deep, and dark ocean, and studying these large fish in this environment can be difficult. We may have sharks ‘tweeting’ their location, but we still know relatively little about them. Sharks have been on the planet for over 400 million years and today, there are over 400 species of sharks, but how long do they live, and how do they move? Two recent studies published in in PLOS ONE have addressed some of these basic questions for two very different species of sharks: great whites and megamouths.
The authors of the first study looked at the lifespan of the great white shark. Normally, a shark’s age is estimated by counting growth bands in their vertebrae (image 1), not unlike counting rings inside a tree trunk. But unfortunately, these bands can be difficult to 
differentiate in great whites, so the researchers dated the radiocarbon that they found in them. You might wonder where this carbon-14 (14C) came from, but believe it or not, radiocarbon was deposited in their vertebrae when thermonuclear bombs were detonated in the northwestern Atlantic Ocean during the ‘50s and ’60s. These bands therefore provide age information. Based on the ages of the sharks in the study, the researchers suggest that great whites may live much longer than previously thought. Some male great whites may even live to be over 70 years old, and this may qualify them as one of the longest-living shark species. While these new estimates are impressive, they may also help scientists understand how threats to these long-living sharks may impact the shark population.
A second shark study analyzed the structure of a megamouth shark’s pectoral fin (image 2) to understand and predict their motion through the water. Discovered 
in 1976, the megamouth is one of the rarest sharks in the world, and little is known about how they move through the water. We do know that the megamouth lives deep in the ocean and is a filter feeder, moving at very slow speeds to filter out a meal with its large mouth. But swimming slowly in the water is difficult in a similar way flying slowly in an airplane is difficult. Sharks need speed to control lift and movement.
To better understand the megamouth’s slow movement, the researchers measured the cartilage, skin histology, and skeletal structure of the pectoral fins of one female and one male megamouth shark, caught accidentally and preserved for research. The researchers found that the megamouth’s skin was highly elastic, and its cartilage was made of more ‘segments’ than any other known shark, which may provide added flexibility compared to other species. 
The authors also suggest that the joint structure (image 3) of the pectoral fin may allow forward and backward rotation, motions that are largely restricted in most sharks. The authors suggest that this flexibility and mobility of the pectoral fin may be specialized for controlling body posture and depth at slow swimming speeds. This is in contrast to the fins of fast-swimming sharks that are generally stiff and immobile.
In addition to the difficulties in exploring deep, dark seas, small sample sizes present challenges for many shark studies, including those described here. But whether studying the infamous great white shark or one of the rare megamouths, both contribute to a growing body of knowledge of these elusive fish.
Images1: doi:10.1371/journal.pone.0084006.g001
Image 2: doi:10.1371/journal.pone.0086205.g003
Image 3: doi:10.1371/journal.pone.0086205.g004
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Imagine a world where sight is limited by the extreme scattering of photons and smell is ineffective due to lethargic diffusion of molecules slowed by the density of water. In these conditions both sight and smell are limited. These conditions characterize, among other things, the ocean, where large sea mammals rely mostly on sound to communicate. The speed of sound is four times greater in water than in air at sea level. Male humpback whales have been observed communicating via ever-changing patterns of vocalization, which scientists have termed ‘song’. These whales compose their songs for the purposes of breeding, learning new songs as they come in contact with fellow crooners. Exactly how and when humpback whales learn these songs, however, remains a larger mystery.
To dive more deeply into the nebulous realms of humpback whale song sharing, researchers of a recent PLOS ONE study recorded instances of humpback whale song in the Southern Ocean.
Humpback whale song is identifiable because of its intricate pattern of structure. Songs are composed of multiple sounds types, for example, as these researchers suggest, ‘ascending cry,’ ‘moan,’ and ‘purr’. When units come together to form a pattern, these units form a phrase. Phrases repeated become a theme, and themes sung in a particular order compose a song. Researchers recorded these compositions by deploying radio-linked sonobuoys, which transmit underwater sound, and then digitized the recordings.
Here is an example of song recorded off the coast of New Caledonia in 2010:
Recordings, like the one above, reveal a possible link between three distinct breeding populations (marked D, E, and F on the map below) off the shores of eastern Australia and the island to the east of New Caledonia with a shared feeding ground in Antarctica (Area V).
In early 2010, the researchers identified four songs near Antarctica that matched themes from eastern Australia in 2009. By July, 2010, all four songs were then also identified in the group from New Caledonia. The themes recognized in New Caledonia in 2010 were entirely different than the themes of 2009, suggesting a movement of new songs eastward from eastern Australia to New Caledonia.
Consequently, the shared feeding grounds in Antarctica used by both the eastern Australia and New Caledonia groups in early 2010 may be the point at which these populations’ songs diverged.
By capturing sonobuoy recordings near feeding grounds off the Balleny Islands, researchers recorded the first instances of humpback whale song in Area V of Antarctica.
In addition, the inclusion of feeding grounds into the dynamic pattern of humpback whale song sharing helps shed new light on overall patterns of song learning and transmission from one breeding group to another.
Sound recording off the Balleny Islands near Antarctica, however, is challenging, and the sample of whale singers from this area remains relatively small. Regardless, the song documented here suggests Antarctica (Area V) as an emerging location for future study, and highlights the importance of feeding grounds in the transmission of humpback whale song. Through a better understanding of how and where these dynamic compositions radiate across the Southern Ocean, we can begin to understand humpback whale population connectivity and one of the best examples of non-human, large-scale learning demonstrated throughout the Southern Hemisphere.
To listen to more of the whale song recorded by these researchers, check out the Supporting Information of their article. For more on humpback whales, check out these PLOS ONE papers.
Citation: Garland EC, Gedamke J, Rekdahl ML, Noad MJ, Garrigue C, et al. (2013) Humpback Whale Song on the Southern Ocean Feeding Grounds: Implications for Cultural Transmission. PLoS ONE 8(11): e79422. doi:10.1371/journal.pone.0079422
Images and Acoustic Files:
Image 1: Humpback Whale Tail by Natalie Tapson
Acoustic File: doi:10.1371/journal.pone.0079422
Image 2: doi:10.1371/journal.pone.0079422
Image 3: doi:10.1371/journal.pone.0079422
When you think about tropical paradise, Hawaii is often at the top of the list. Waikiki is one of the most iconic Hawaiian beaches on Oahu and is a popular swimming and surfing spot. However, it is also a popular stop for the box jellyfish, one of the most venomous animals in the world. Once a month, about 8 to 12 days after the full moon, the shallow waters of Waikiki beach are temporarily flooded with box jellyfish. They are not coming in for a mai tai under the waning moon; rather, scientists believe that jellyfish reproduce in these waters. This monthly influx creates a hazard to swimmers due to the jellyfish’s painful—and even lethal—stings.
The environmental factors that affect these influxes are not well understood, and learning more about them may help us predict and mitigate the risk that box jellyfish pose to swimmers. Several scientists from Hawaiian institutions published the first long-term (14-year) assessment of the environmental conditions that potentially correlate with box jellyfish population changes in the North Pacific Sub-tropical Gyre.
The researchers surveyed a 400-m section of Waikiki beach during the days jellyfish were present. They counted more than 66,000 jellyfish over 14 years and compared the data to 3 measures of how the climate changes over time, called climate indices; 13 physical and biological variables, such as sea surface temperature and plankton; and seven weather measurements, including wind speed, air temperature, and rainfall.
They confirmed that box jellyfish arrive at Waikiki monthly after each full moon and stay for 2- 4 days. They counted on average 400 jellyfish each month, but the range was quite wide at 5-2,365 individuals. Rather than seeing a net population change over 14 years, researchers observed approximately 4-year periods of increased population count followed by 4-year periods of decreased population count, which coincided with fluctuations in three main environmental factors: oceanic changes in salinity and nutrient availability, called the North Pacific Gyre Oscillation, small organisms’ ability to access nutrients, called primary production, and abundance of small zooplankton.
The researchers suggest that the relationship between environmental fluctuations and jellyfish population changes at Waikiki may result from changes in the availability of food for jellyfish in the ocean around Hawaii, brought about by the North Pacific Gyre Oscillation. During an increase in nutrient availability, phytoplankton populations also increase, meaning more food for jellyfish, allowing them to grow faster and increase their rate of reproduction.
Previous studies have shown that jellyfish populations change due to human-caused disturbances, but this is one of the first long-term studies showing that large-scale climate patterns may also impact box jellyfish populations. Understanding long-term climate and oceanic trends and their effects on jellyfish populations may provide information to develop strategies for avoiding mass stinging events and beach closures at Waikiki and other popular recreation sites in the Pacific.
Citation: Chiaverano LM, Holland BS, Crow GL, Blair L, Yanagihara AA (2013) Long-Term Fluctuations in Circalunar Beach Aggregations of the Box Jellyfish Alatina moseri in Hawaii, with Links to Environmental Variability. PLoS ONE 8(10): e77039. doi:10.1371/journal.pone.0077039
Image Credit: Jellyfish by James Brennan Molokai Hawaii