Foraging energetics and prey density requirements of western North Atlantic blue whales in the Estuary and Gulf of St. Lawrence, Canada

By Nicholas Martinez, SRC intern

Pelagic predators throughout the world’s oceans face the same challenge: foraging for food in an environment where much of their prey are available in clusters, centralized around specific areas of the ocean. For this reason, many pelagic predators have unique ways to find these limited resources, all the while adjusting these foraging techniques so as to maximize energy gained for every unit of energy expended.

In a world where oceanic ecosystems are facing rapid change, the need for more research and implemented protective measures is rising. Many marine animals have been documented as having shifted their foraging habits because of a rapid decline in available resources. These resources, which have supported countless generations of predators, are now facing serious threats to their population size. For this reason, studies of the foraging habits of large marine predators allows insight into the hunting grounds that still remain for these animals. Understanding how often these species forage for food allows scientists to determine the health of a specific population of that species. A 2019 paper from Guilpin and colleagues, “Foraging energetics and prey density requirements of western North Atlantic blue whales in the Estuary and Gulf of St. Lawrence, Canada”, focused on the foraging efficiency of the North Atlantic blue whale in a quickly changing oceanic environment.


Figure 1. The blue whale (Source: NOAA Photo Library/anim1754/Wikimedia Commons)

Foraging efficiency is a ratio that compares the rate of energy consumption to the rate at which energy is expelled so as to provide insight into an organism’s ability to store energy. Understanding a blue whale’s capacity to store energy is crucial because there is a direct correlation between the animal’s energy supply and its ability to reproduce. Using 10 depth-velocity tags attached to the whales, the scientists were able to monitor the foraging behaviors of blue whales in the St. Lawrence Estuary. While blue whales are the largest living organisms on the planet, their food supply consists small invertebrates called krill, which can be found in large populations throughout the study site. This food source exhibits spatial and temporal variations and thus requires a specialized foraging technique in order to maximize the whales net energy reserve.


Figure 2. “Predicted change in blue whale foraging effort with time of day in (a) feeding depth (m), (b) dive duration (s), (c) number of feeding dives, (d) number of lunges d−1, and (e) number of lunges h−1. Dark grey ribbons represent the 95% confidence intervals around the predicted response from generalized additive mixed models. Shaded areas are for nighttime (grey), dusk and dawn (light grey), and daytime (white). Points are data observations” (Source: Guilpin et al. 2019, p. 213)

Here, the researchers found that during the day, the tagged blue whales performed fewer but longer feeding dives than at other times of the day (Figure 1). This suggested that the blue whales invested in fewer but longer dives so as to maximize the amount of energy they could store by minimizing energy expenditure (Figure 2). In addition, the authors found that the whales were performing more lunges per dive (accelerating towards the surface, trapping any krill in their mouth as they momentarily breach), showing that even while the whales were not deep diving, they were still feeding.


Figure 3. “Relationship between energy expenditure during feeding dives for 3 blue whale sizes (22, 25, and 27 m length) and (a) dive duration (s) … (b) maximum dive depth (m) … and (c) number of lunges per dive” (Source: Guilpin et al. 2019, p. 214)

Although the whales were observed to feed throughout the day, this did not necessarily mean that they were consuming enough krill to achieve a neutral energetic balance. In fact, this study found that only 11.7 and 5.5% of Arctic and northern krill patches contained densities that could sustain a neutral energy balance for the blue whales. This could be due to a decline of krill populations via environmental impacts, and if so, poses a great threat to blue whale populations. This information emphasizes blue whales’ constant need to forage for high densities of krill in order to maintain neutral energy balance or maintain a healthy energy storage suitable for reproduction. The discoveries made in this paper may therefore help predict the effects of climate change on both predator/prey densities and may also offer insight on potential krill fisheries and how they may or may not affect blue whale populations.

Work cited

Guilpin M, Lesage V, McQuinn I, et al (2019) Foraging energetics and prey density requirements of western North Atlantic blue whales in the Estuary and Gulf of St. Lawrence, Canada. Mar Ecol Prog Ser 625:205–223. doi: 10.3354/meps13043

Minke Whale Genetics show Adaptations for Diving

By Jessica Wingar, RJD Intern

Minke whales, Balaenoptera acutorostrata, may not be the largest baleen whale, but they are the most abundant. These whales are about thirty five feet long, 6500kg, and are black with a white stomach (Knox, G.A., 2007). This species of whale is said to be a cosmopolitan species, since they are found in many different climates of the world. Although these whales are abundant, one of their main threats is overexploitation in fisheries. In places, such as the North Pacific, their populations have been fished so much that the International Whaling Commission, the IWC, has them listed as of concern. Overfishing is not the only threat to minke whales. They are also threatened by noise, vessel strikes, and habitat disturbance. (Minke Whale, 2014).


A minke whale.


Like many other marine mammals, minke whales have multiple techniques to catch their prey. Minke whales feed on a variety of food. These varieties are crustaceans, plankton, and small schooling fish. In order to eat some of these food types they must dive. This species can dive for up to fifteen minutes at a time. Some of the techniques that they use while diving include landing on their side on top of the prey and ingesting a significant amount of water while feeding. By side lunging they can stun their prey and by gulping a lot of water they can collect a lot of plankton that they can then sift through (Minke Whale, 2014). Once they have the food, minke whales then swallow their food whole (Know, G.A., 2007). Diving for their prey requires a lot of adaptations.

When a whale dives, a lot of changes occur internally. There are three steps that occur when marine mammals hold their breath. The first step is called hypoxia, which is the decrease in oxygen in the whale’s body. The second step is hypercapnia when the body experiences an increase in carbon dioxide. And the final step occurs when there is a build up of lactic acid in the body. All of these stages add up and prevent the animal from suffocating because they tell the body that it needs air. Thus, the whale then returns to the surface to breathe (Richardson, 2013). One of the main behaviors of minke whales is diving, and a recent study on their genetics shows how their genes are adapted for this behavior.


Minke whales provide a good specimen for genome sequencing because they are such a widely distributed marine mammal. This study is the first of its kind to complete a high depth genetic analysis of a marine mammal. From the study, the researchers found that there were many whale specific genes. One of the most interesting gene that was found to be expanded in minke whales was the peroxiredoxin (PRDX) family. This family is related with stress resistance. The fact that this gene family is expanded could show that these animals are prone to stress, whether from humans or from diving, and have evolved to have more stress combating genes. Another interesting finding also involved their diving physiology. O-linked N-acetylglucasominylation in many proteins has been found to multiply the response to stress. Stress occurs when a minke whale dives and experiences hypoxia. In minke whales, this gene is expanded three times. This gene is just an example of one of the many genes they found expanded that are related to dealing with hypoxia. In addition, as mentioned above, lactate can build up in the body after prolonged diving. The researchers found that the enzyme, lactate dehydrogenase, which converts pyruvate to lactate to be expanded in animals, such as minke whales. Therefore, many different objects in the minke whale genome have expanded in order to account for the behaviors most exhibited by this animal. This study was very ground breaking and will lead the way for many other marine mammal genomes to be completely sequenced (Yim, H et al, 2014).

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Expanded PRDX gene in minke whales and some other organisms.


Knox, G. (2007). Biology of the southern ocean. (2nd ed.). Boca Raton, FL: CRC Press.

Minke whale. (2014, January 09). Retrieved from

Richardson, Jill. “Anatomy and Physiology Part II.” MSC 350. University of Miami, Coral Gables. Mar. 2013. Lecture.

Yim, H, Cho, Y.S., Guang, X, Kang, S.G., Jeong, J, Cha, s, Oh, H, Lee, J, Yang, E.C., Kwon, K. K., Kim, Y.J., Kim, T.W., Kim, W, Jeon, J.H., Kim, S, Choi, D.H., Jho, S, Kim, H, Ko, J, Kim, H, Shin, Y, Jung, H, Zheng, Y, Wang, Z, Chen, Y, Chen, M, Jiang, A, Li, E, Zhang, S, Hou, H, Kim, T.H., Yu, L, Liu, S, Ahn, K, Cooper, J, Park, S, Hong, C.P., Jin, W, Kim, H, Park, C, Lee, K, Chun, S, Morin, P.A., O’Brien, S.J., Lee, H, Kimura, J, Moon, D.Y., Manica, A, Edwards, J, Kim, B.C., Kim, S, Wang, J, Bhak, J, Lee, H.S. and Lee, J. 2014. Minke whale genome and aquatic adaptation in cetaceans. Nature Genetics, 46 (1): 88-94.



Anthropogenic Noise Pollution and Cetaceans

Brittany Bartlett, RJD Intern

It is no secret that our oceans and the species within them face a wide range of anthropogenic, human induced threats. And, as a result, the health of the ocean is rapidly declining. Among these threats is that of pollution; plastics, oil, runoff, etc. One form of pollution that tends to be overlooked is noise pollution, specifically the use of Navy Sonar.

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Assessing Management Efforts for Large Whales

by Fiona Graham, RJD Intern

Sometimes imposing a regulatory action alone is not enough. Implementing a new policy aimed at reducing the mortality of a species or group of species requires scientific studies to gather the information necessary to enact that policy. Some important questions to be asked are which species need protecting? Where are they most vulnerable, both spatially and temporally within their life cycle? What threats are they faced with? Once a clear idea of how and why a species needs protected is formed, regulations can be put into place using that information to conserve that species. While this may be a great start, following up with an assessment of the management that has been put into place can be just as important. Maximum effectiveness depends upon strong science from beginning to end.

A recent study by Julie Van Der Hoop and colleagues provides one such assessment of management attempting to mitigate human induced mortalities of large whales in the Northwest Atlantic. To do this, the team complied reports of strandings, mortalities and necropsies from 1970 to 2009 for 8 species of large whales, and determined temporal and spatial trends. They found that 66.9% of mortalities were related to human activities, and that the leading cause of death was entanglement in fishing gear.

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