Newswise — The pygmy right whale remains a captivating mystery within the whale community. It stands out not only as the tiniest among the typically large filter-feeding baleen whales but also due to its infrequent sightings and limited research conducted on it. One of the reasons for this lack of attention is its inconspicuous appearance, often being mistaken for minke whales.
However, recent investigations, spearheaded by UNSW Sydney, have shed light on this enigmatic creature. By analyzing hidden chemical indicators in the jawlines of pygmy right whales, researchers have confirmed what they had long suspected – these graceful marine mammals exhibit distinct behaviors when compared to their larger whale counterparts. The findings, published in Frontiers in Marine Science, suggest that the pygmy right whale is among the rare whale species that do not undertake long-distance migrations to Antarctic waters. Instead, they choose to inhabit the temperate waters near Australia throughout the year.
According to Adelaide Dedden, the study's lead author and a marine ecologist at UNSW Science, when you search for information about the pygmy right whale, one of the primary questions that surfaces is whether they are extinct. This highlights the limited knowledge we possess about these creatures and how little attention they have received.
Professor Tracey Rogers, a marine ecologist at UNSW Science and senior author of the study, adds that the discoveries are particularly astonishing because the pygmy right whales seem to be resident species, choosing to remain in Australian waters throughout the year. They exhibit a preference for staying close to home, never venturing far from the comforts of continental waters. This behavior is intriguing as it mirrors the habits of ancestral baleen whales, which also did not undertake extensive journeys between their feeding and breeding grounds. The resemblance in behavior adds to the fascination surrounding these small whales.
Uncovering the chemical clues in their bristles
Conducting laboratory studies on whales, even on a relatively small species like the pygmy right whale, presents significant challenges due to their massive size. However, scientists have found an alternative approach by analyzing the composition of smaller tissues that hold detailed records of the animal's activities.
In the case of filter-feeding whales like the pygmy right whale, they possess long, slender keratin bristles known as baleen plates, which extend from their upper jaw. These baleen plates not only enable them to consume numerous small prey like krill, but they also contain chemical indicators known as stable isotopes. These stable isotopes offer valuable clues to researchers about the behavior and habits of these whales.
According to Prof. Rogers, as the baleen of pygmy right whales grows, it traps biochemical signals from their food known as stable isotopes. These signals act as a historical record of their behavior, providing insights into their diet and the general areas they inhabited over time. It's like delving into a history book that reveals valuable information about the whales' past activities.
For the study, the researchers examined the stable isotopes present in the baleen plates of 14 Australian pygmy right whales. Borrowed from the South Australian Museum, each baleen plate contained data spanning three to four years, enabling the researchers to piece together a comprehensive picture of the pygmy right whale's diet and movements over almost four decades. This investigation represents the most extensive study to date on the diet and movements of the pygmy right whale.
According to Ms. Dedden, the isotopic record reveals that the pygmy right whales stay in mid-latitude waters off southern Australia throughout the year, where they primarily feed on krill and copepods (small crustaceans). Interestingly, there is no indication of them feeding in Antarctic waters. This suggests that the waters off Southern Australia can adequately meet their dietary requirements year-round.
Prof. Rogers explains that this behavior aligns with the slender structure of their baleen plates relative to their body size. To sustain themselves in these less productive waters around Australia, they need to maximize their intake of food, which allows them to remain in the region throughout the year.
Additionally, the researchers discovered intriguing evidence indicating that the pygmy right whales' feeding patterns correlated with oceanic changes affecting food web dynamics in the region, particularly related to upwelling events. These natural cycles bring nutrient-rich water to the surface, leading to an increase in the availability of krill in Australian waters.
Ms. Dedden explains that the signals found in the baleen, which corresponded to Australian krill, coincided with times of upwelling in the summer, which is when krill is most abundant. This observation aligns logically with the increased availability of krill during upwelling periods. Conversely, during winter when downwelling occurs and krill availability decreases, the signal in the baleen reflecting Australian krill was not as pronounced, further supporting the overall findings of the study.
A potential indicator of ecosystem health
The research outcomes provide a crucial groundwork for further investigations aimed at enhancing our knowledge of the pygmy right whale.
Ms. Dedden suggests that with the increased evidence of their mid-latitude distribution, conducting satellite tagging could offer valuable insights into their movements, allowing us to closely monitor their travels within the region.
Prof. Rogers points out that since they were never targeted for whaling, their population is likely stable at present. However, due to the lack of sufficient data, we cannot be certain about their current status and whether they are in a favorable condition. More research is essential to address this data deficiency and ensure a better understanding of the species' well-being.
While the pygmy right whale is currently listed as least concern in terms of conservation status, there remains uncertainty regarding its population trend. Researchers emphasize that this species might be vulnerable to emerging threats, particularly the warming of oceans and other environmental changes.
Nevertheless, the pygmy right whale holds value as an indicator species for scientists to study and monitor the marine environment. Their position as consumers at the base of the food chain and their apparent reliance on specific regions make them sensitive to any significant alterations in the marine ecosystem.
Ms. Dedden notes that potential future challenges could arise if there are substantial changes in the marine environment, affecting the whale's habitat and food sources. However, conducting further research on these whales provides an opportunity to improve our ability to forecast potential risks. This knowledge would allow us to safeguard not only the well-being of the pygmy right whales but also protect the entire ecosystem they inhabit.
The study also involved co-authors Gary Truong and Dr Matthew McCurry from UNSW, Dr Catherine Kemper from the South Australia Museum and Dr Paul van Ruth from the University of Tasmania.
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