Swimming and Diving Energetics of Dolphins Can Help Predict the Cost of Flight Response in Wild Odontocetes

By Chelsea Black, SRC MPS student

There are many occasions when high-speed swimming might be demanded by free-ranging marine mammals. This behavior will come at an energetic cost to the animal, which is why it is usually only performed when necessary for survival of the animal. Williams et al. (2017) demonstrates the physiological consequences of oceanic noise on diving mammals, in the hopes of providing a tool for predicting the biological significance of escape responses by cetaceans facing anthropogenic disturbances.

The physiological response of fleeing marine mammals has been challenging to study due to the difficulty of simultaneously measuring both metabolic rate and swimming behavior in free-ranging cetaceans like dolphins and whales. Studies performed in lab settings can provide invaluable information to answer these unknowns. In a study by Williams et al. (2017), the energetic cost of producing a swimming stroke by exercising and diving bottlenose dolphins was measured by calculating oxygen consumption and stroking kinematics of trained bottlenose dolphins (Tursiops truncatus) and one killer whale (Orcinus orca). The animals were housed in saltwater pools at Long Marine Laboratory in Santa Cruz, where they were trained to either voluntarily rest or exercise at various levels. To measure the energetic cost of diving, the dolphins were fitted with a submersible accelerometer recorder and performed three different experimental conditions: voluntary rest at the surface, rest while submerged, and submerged swimming and diving exercises. The results show little change in oxygen consumption between rest and routine swimming speeds, most likely due to the animal’s exceptional streamlined bodies that minimize hydrodynamic resistance. In contrast, there was a marked increase in oxygen consumption during higher level performances such as high-speed swimming, which affected the total amount of oxygen utilized during the dive (Williams et al., 2017).

 

Figure 1: Dolphins breathe into a metabolic hood to analyze respiration (Williams et al., 2017).

Diving mammals must balance both speed and the duration of breath-holds, with limited available oxygen stores to minimize their energetic costs (Williams et al., 2017). High-speed swimming, increased stroke frequencies and rapid ascent from depth are commonly reported for wild tagged cetaceans following exposure to noise (Todd et al., 1996; DeRuiter et al., 2013). This particular response to noise exposure has been suggested as a cause for many marine mammal strandings, but scientists are less certain about how these responses translate into physiological costs to the animal.

The cost of flight by odontocetes is likely more complicated than counting the number of swimming strokes during a dive, therefor, the gait of the animal must also be considered. After using the calculations gathered from dolphins, Williams et al. (2017) could test the energetic cost of a dive after exposure to anthropogenic noise in the Cuvier’s beaked whale (Ziphius cavirostris), a deep diving odontocete considered to be particularly sensitive to underwater noise. In a dive without noise exposure, the whale spent over four minutes gliding on descent, however, when exposed to noise disturbance the whale did not use this energy-saving swim style, which increased its energetic cost.

Figure 2: Behavioral response of Cuvier’s beaked whale to anthropogenic noise (Williams et al., 2017).

 

Overall, the beaked whale did not exceed its dive limit by reducing its depth and duration of the dive after a noise exposure while also increasing the use of energetically costly high-speed strokes. By using this combination, the whale was able to keep the proportion of available oxygen expended below the total amount available. Conversely, long and deep dives that exceeded one hour and 1000 m that occurred after sonar exposure, exceeded the oxygen stores. A common strategy for reducing energetic costs during these extreme dives was prolonged gliding during descent, which suggests that the role of swimming style is crucial in deep-diving species.

The data gathered from bottlenose dolphins and an orca provided a basis for applying the principals to wild marine mammals, illustrating the power of integrating energetics with swimming behavior and dive characteristics to assessing the impact of anthropogenic disturbances on cetaceans. While the oxygen stores and behavioral response will differ across species, this information will allow researchers to better predict the potential physiological consequences.

Works cited

DeRuiter, S. L., Southall, B. L., Calambokidis, J., Zimmer, W. M., Sadykova, D., Falcone, E. A., Friedlaender, A. S., Joseph, J. E., Moretti, D., Schorr, G.S. et al. (2013). First direct measurements of behavioural responses by Cuvier’s beaked whales to mid-frequency active sonar. Biol. Lett. 9, 20130223.

Todd, S., Lien, J., Marques, F., Stevick, P. and Ketten, D. (1996). Behavioral effects of exposure to underwater explosions in humpback whales (Megaptera novaeangliae). Can. J. Zool. 74, 1661-1672.

 Williams, T. M., Kendall, T. L., Richter, B. P., Ribeiro-French, C. R., John, J. S., Odell, K. L., … & Stamper, M. A. (2017). Swimming and diving energetics in dolphins: a stroke-by-stroke analysis for predicting the cost of flight responses in wild odontocetes. Journal of Experimental Biology220(6), 1135-1145.

Age-specific foraging performance and reproduction in tool-using wild bottlenose dolphins

By Elana Rusnak, SRC Intern

Foraging (searching for food) is a skill that animals use to provide energy for survival, growth, and reproduction. In many animals, these skills are fully developed before reproductive age, maximizing the energy put into reproduction when sexual maturity is reached. However, female bottlenose dolphins (Tursiops aduncus) in Shark Bay, Western Australia, learn a unique foraging behavior from their mothers during development, yet continue to hone their skills long after reaching sexual maturity (at around 10 years). This complex foraging behavior includes the use of sponges as tools; the dolphin will forage for a sponge and then “wear” it on their beaks while searching for prey on the seafloor (the benthic zone). The sponge provides protection from sharp rock and shell debris, and allows “spongers” access to a unique food source. Other “non-sponger” dolphins eat fish and other prey in the water column, otherwise known as the pelagic zone. Sponge foraging (sponging) is a complex skill that takes years to develop. Researchers question why such an important skill would not be developed fully before reproductive age.

A female bottlenose dolphin with a marine sponge tool in Shark Bay, Western Australia.

A female bottlenose dolphin with a marine sponge tool in Shark Bay, Western Australia.

A study published by Patterson et al. in 2016 attempts to explore age-related changes in foraging performance. They examined three aspects of foraging efficiency: the ratio of time spent acquiring sponges to time spent foraging, the time spent foraging per tool (sponge), and the time spent traveling per tool. Their hypothesis estimated that maximum efficiency should result from shorter times acquiring the tool and longer times spent using them. They then examined how age-related changes in foraging performance relate to changes in female reproduction.

The data was collected between 1989 and 2012 and covered roughly 1800 individuals. The three stages of behavior (acquiring sponge, using sponge, travelling with sponge) were classified by the researchers and observed in the wild. Analysis included various statistical tests that modeled the three variables and percent of the population that was reproductively mature against age. It was found that sponge-acquiring behavior makes up a small percentage of an individual’s activity budget (as predicted before the study). As can be seen in Figure 2, until the age of 23.72 years, dolphins gradually learned to spend less time acquiring the sponge and more time using it (a). Until the age of 19.50 years, the time spent foraging per tool gradually increased and then remained stable (b). The model also shows that there was a gradual increase in the time spent traveling per tool as age increased up to 23.34 years of age (c). Finally, the model showed that peak foraging ability improved until roughly midlife (20-25 years), which is well after the onset of sexual maturity. This can be seen by comparing (a), (b), and (c) with (d), which shows age vs. percent of the population at different stages of reproduction.

Age specific foraging and lactation. This shows the relationship between age and the three studied variables, as well as its relationship with reproductively active females.

Age specific foraging and lactation. This shows the relationship between age and the three studied variables, as well as its relationship with reproductively active females.

What did the researchers conclude?

Overall, the data suggest that dolphins continue to improve performance in their tool-use foraging techniques long after they reach sexual and physical maturity. Females increased their foraging efficiency with age by decreasing acquisition time and increasing foraging time. By midlife, it can be concluded that they have learnt how to find the most ideal sponge for foraging, as well as figured out the best way to use it in order to avoid needing replacement. They also learn that reusing a good tool is important, and therefore are more willing to travel with it to avoid needing to find a replacement.

The most important conclusion taken from the data is that while dolphins reach sexual maturity at around 10 years of age, their peak reproductive age coincides with the peak foraging ability (20-25 years of age). It may be that it is advantageous for an individual to reach sexual maturity as soon as their foraging skills are good enough, and then continue to improve efficiency with age in order to increase reproduction. This behavior is seen in other animals, such as chimpanzees, capuchin monkeys, and sea otters. This study proves that we should not be surprised that foraging expertise after reaching adulthood has positive fitness consequences, and allows for higher rates of reproduction.

Reference

Patterson, E. M., Krzyszczyk, E., Mann, J. (2016). Age-specific foraging performance and reproduction in tool-using wild bottlenose dolphins. Behavioral Ecology, 401-410. Retrieved October 20, 2016.

Living on the Edge: Settlement Patterns by the Symbiotic Barnacle Xenobalanus globicipitis on Small Cetaceans

 

By Rachel Skubel, RJD Intern

If you were a barnacle, how would you choose your home? For X. globicipitis barnacles residing on striped dolphins, this question was ‘put under the microscope’ by Juan Carillo and colleagues at the University of Southern Mississippi and Cavanilles Institute of Biodiversity and Evolutionary Biology (Valencia, Spain).

Of all obligate barnacles studied, X. globicipitis has been found on animals that experience the most intense currents (Bearzi and Patonai, 2010). These organisms will settle on dolphins to optimize for (a) availability of passing current, to provide food, and (b) low drag from said current, to reduce physical degradation of the animal. Here, the investigators asked the following questions:

  1. Where do these barnacles choose to settle?
  2. How does this choice affect the barnacles’ recruitment (define), survival, and growth?

The researchers examined stranded striped dolphins (Stenella coerleoalba) along 556 km of the spanish mediterranean coastline (map), from 1979 to 2009. In 1990 and 2007, many of the dolphins examined had been killed by the morbillivirus (link to http://www.nmfs.noaa.gov/pr/health/mmume/midatlantic2013/morbillivirus_factsheet2013.pdf) – infected animals would have swam slower and had weaker immune systems than otherwise, making them more likely to be colonized by the barnacles. For each animal, the researchers looked at the abundance (i.e. amount), location, and size of the barnacles. Then, they used a model to investigate why barnacles were colonizing certain locations of the dolphins.

Figure 1: Barnacles were mainly found on the trailing edges of dorsal fins, flippers, and flukes, over an area ~2cm wide (Dr. Mariano Domingo, Autonomous University of Barcelona, Spain)

Figure 1: Barnacles were mainly found on the trailing edges of dorsal fins, flippers, and flukes, over an area ~2cm wide (Dr. Mariano Domingo, Autonomous University of Barcelona, Spain)

Results

Out of 242 dolphins examined, 104 had the X. globicipitis barnacles – on either their dorsal fins, flippers, and tail flukes. Of these locations, the tail flukes were by far the most common. Even if the dolphins had barnacles in multiple locations, linear density (barnacles/cm) was significantly higher on the tail. Also, the shell size of barnacles on the flukes was higher than on the flippers and dorsal fins. For these dolphins with barnacles on their tail flukes, it was more common to find them on the dorsal (top) than ventral (bottom) size of the tail.

Figure 2: When dolphins were found with X. globicipitis barnacles, they were most likely on the caudal fin.

Figure 2: When dolphins were found with X. globicipitis barnacles, they were most likely on the caudal fin.

Dolphins thought to have died from the morbillivirus did not have any significant differences in where the barnacles were located, or their size, compared to the unaffected animals.

Explaining the trends

When interpreting these results, it was important to consider that these were all pre-deceased study subjects, and the barnacles might have even settled on the carcasses. However, the finding of tail flukes being a popular settlement area for these barnacles matches with observations in the wild (see video below).

https://www.youtube.com/watch?v=8aJdW5IRZSs

 Beginning around 0:13, you can see barnacles are common on the tails of wild dolphins, supporting the findings of the present study by Carillo et al.

How do the barnacles choose where to dig in? The researchers propose that once they’ve used chemical cues to recognize the dolphins as proper hosts, a two-pronged mechanism follows.

  • First, attachment success: those that choose the tail to latch onto will be less likely to fall off in the process because there is some shelter from strong currents. And once one barnacle settles, it actually becomes easier for more to do the same because they will be ‘sheltered’ by this first individual.
  • Second, there is less early cyprid mortality, which means that once fully attached, it is easier to stay attached.

Lastly, the authors considered why there were more barnacles on the dorsal sides of the tails. This could be due to an asymmetrical swimming style by the dolphins, which means that their ‘downstroke’ is stronger than their ‘upstroke’, so there is less force on the settled barnacles if they settle on the top of the tail. However, whether the swimming style of these dolphins is symmetrical or assymetrical is not conclusively known.

 

References

Bearzi M, Patonai K (2010). Occurrence of the barnacle (Xenobalanus globicipitis) on coastal and offshore common bottlenose dolphins (Tursiops truncatus) in Santa Monica Bay and adjacent areas, California. Bull South Calif Acad Sci. 109: 37–44. DOI: 10.3160/0038-3872-109.2.37

Carrillo JM, Overstreet RM, Raga JA, Aznar FJ (2015) Living on the Edge: Settlement Patterns by the Symbiotic Barnacle Xenobalanus globicipitis on Small Cetaceans. PLoS ONE 10(6): e0127367. DOI: 10.1371/journal.pone.0127367

 

 

Investigating the Intellectual and Emotional Lives of Cetaceans

By Heather Alberro, RJD Intern

The question of intelligence in animals other than human beings and perhaps some species of primates is a provocative and widely contested one. However, there is a growing body of evidence suggesting that cetaceans, the mammalian order that includes whales and dolphins, may possess many of the “intelligence markers” we typically ascribe to intelligent beings such as primates, including language, a sense of self, culture, and displays of emotional complexities. Despite having evolved along quite different evolutionary paths that were shaped by vastly different physical environments, both cetaceans and primates evolved the two largest brains in the animal kingdom. Consequently, as a large body of literature suggests, cetaceans display many of the signs of intelligence often exclusively attributed to the order of primates while even surpassing them in areas such as brain-to-body-size ratio. From living in tight-nit and highly structured social groups to their displays of emotional complexity and self-awareness, cetaceans are indeed evolutionary marvels that appear to be close to primates, particularly humans, in terms of the cognitive and behavioral complexities they exhibit.

Having originated from a hoofed land mammal turned aquatic inhabitant from the Paleocene nearly 50 to 60 million years ago, and despite the radically different physical environment that gave way to a different neuroanatomical structure, cetaceans have nonetheless undergone a similar brain size evolution, known as encephalization, to that of its terrestrial counterpart, the primate brain (Marino, 25). In fact, primates and cetaceans possess the highest encephalization levels in the animal kingdom. The common dolphin, a member of the cetacean sub-order odontoceti that also includes toothed whales, is known to have even higher encephalization levels than non-human primates such as chimpanzees, coming in second only to humans (Marino, 25).  In terms of EQ or “emotional intelligence value”, many modern odontoceti species have a value of 4.5, the highest in the animal kingdom apart from the average 7.0 for humans. Despite variations in neuroanatomical organization and the stark differences in the physical environments that shaped the evolutionary trajectories of primates and cetaceans, it is remarkable that encephalization levels between the two mammalian orders are in fact so similar in terms of size and complexity.

800px-Tursiops_truncatus_brain_size_modified

Comparison of the brains of a wild pig, bottle nose dolphin, and modern human.

When assessing the relative intelligence and cognitive capacities of cetaceans, particularly those of the odontoceti sub-order that include highly social species such as the common dolphin and the orca, various lines of enquiry have been pursued, such as whether or not these animals are self-aware. One test typically employed by researchers to test for advanced cognitive developments such as self-awareness is the mirror test. In her article, Convergence of Complex Cognitive Abilities in Cetaceans and Primates, Lori Marino describes a mirror test that she and a fellow researcher conducted with two bottlenose dolphins, whereby they placed marks on their bodies and allowed them to observe themselves in a mirror. Lori notes that, “both dolphins in our study used a mirror to investigate parts of their bodies that were marked [Reiss and Marino, 2001]” and that the findings of the study “open up the possibility that the emergence of self-recognition, and perhaps other forms of self-awareness, are not byproducts of factors unique to humans and great apes (29).” Indeed, the possibility that cetaceans may possess a sense of self, an attribute originally thought to be exclusively human, suggests that there is some level of cognitive complexity that warrants further research.

dolphins-mirror

Dolphin mirror test (Reiss and Marino, 2001)

Another marker of intelligence originally believed to be exclusive to humans and some non-human primates such as macaques and chimpanzees is the presence of “culture”, which is defined as the information or behavior that is shared by a population or subpopulation, and which is acquired from conspecifics through some form of social learning (Rendall and Whitehead, 2001).  As Lori Marino elucidates, “Recently, enough data has been amassed on wild cetaceans to show that many species possess cultural traditions with regard to dialects, tool use among some wild dolphin populations, methods of prey capture in killer whales, and other related social behaviors (28).” Similarly, populations of wild orcas off the west coast of Canada have been known to display various hierarchical divisions, much of which seems cultural as the primary division is between resident and transient orcas (Baird, 2000). Such displays of complex social behavior and organization bear a striking resemblance to those of primates, suggesting continuities in their intellectual lives, despite disparities in the outward physical appearance of the two orders.

The idea that cetaceans experience emotional states such as grief, joy, fear, and the like, while difficult to corroborate for the simple reason that cetaceans cannot express any feelings they may have vocally, is nonetheless frequently maintained by many researchers who have spent a number of years working with these animals. In Into the Brains of Whales, Mark Peter Simmonds cites examples such as the “prolonged grief” displayed by Orcas upon losing an infant or other family member. One case involves two male orcas that, after encountering the body of an older female they had grown up with in mind November, 1990, spent the rest of their lives isolated from other orcas and visiting old places that the female had visited when she was alive (Rose 2000a)(Simmonds 108). Simmonds also notes the prominent field biologist Denise L. Herzing’s remarks on the “joy” often expressed by her long-studied Atlantic bottlenose dolphins. Such examples, while undoubtedly inconclusive, still warrant further examination, as they suggest that cetaceans may be as emotionally complex as humans and non-human primates.

Cetaceans have been known to display remarkable behaviors such as rudimentary forms of “culture” for the transfer of information and outward displays of emotionally complex behavior such as grief and excitement. Indeed, they appear to be rather close to humans and above many non-human primates in terms of cognitive, social, and emotional complexity. In terms of the size and anatomical complexity of their brains, many members of the odontoceti sub-order come in second only to modern humans. Further research should aim at gaining a closer look at the lives of these fascinating and intelligent animals, as there is much we have yet to learn, such as whether they indeed experience emotion, whether they can develop significant emotional attachments to members of their group like humans and non-primates do, and just what exactly they are capable of, cognitively.  Such questions lead to the issue of conservation: if these animals are indeed as intelligent and self-aware as they appear to be, should they therefore be granted increased protection from pollution, habitat destruction, hunting, and other man-made dangers? As fellow sentient beings with advanced emotional and intellectual lives, do we owe them the sort of consideration often awarded to members of our own species?

 

Bibliography:

  1. Marino, Lori. “Convergence of complex cognitive abilities in cetaceans and primates.” Brain, Behavior and Evolution 59.1-2 (2002): 21-32.
  2. Rose, N.A., 2000a. A death in the family. In: Berkoff, M. (Ed.), The Smile of the Dolphin. Discovery Books, London.
  3. Simmonds, Mark Peter. “Into the brains of whales.” Applied Animal Behaviour Science 100.1 (2006): 103-116.
  4. Rendell, Luke, and Hal Whitehead. “Culture in whales and dolphins.” Behavioral and Brain Sciences 24.02 (2001): 309-324.