A Case Study of Beluga Whales (Delphinapterus leucas)

Beluga_Whales.jpgBeluga whales are gentle beautiful creatures. The word beluga means "white one" in Russia.

Scientists have found that there has been no increase in the Beluga Whale population in the St. Lawrence River in the last 50 years. By reading various passages and answering questions based on these passages in a sequential manner, piece together the scientists’ inquiry and analyze both the process and product of the investigation to find the answer to this question.
In order to ensure that you go through the inquiry process step-by-step please DO NOT be tempted to search for the answers online. Whatever information that is needed to deduce the answers on your own will be provided.

I hope that you will follow the guidelines in order to make your learning experience a meaningful and exciting one. In other words, NO SHORTCUT, don't be tempted to cheat.
(This case study is based on a May 1996 article from Scientific American titled “The Beluga Whales of the St. Lawrence River” by Pierre Béland. The activity is adapted from BSCS and NSTA.)



Answer the following questions WITHOUT going online to look for the answers. Make intelligent guesses by applying whatever Biological knowledge you have.
  • Where do you think a scientist might find whales to study? Why did you guess that they found are there?
  • Mark on this map to indicate those locations. (Try out Google map and let see if we could have all 3 classes' predictions drawn on one map).
  • List three things that a scientist might study about whales in those locations. (Enter your answers by keying in your guesses HERE in a shared Google document.)

The scientists in the following case study are investigating populations of beluga whales. This case study took place in the St. Lawrence River where a population of beluga whales resides.

Read the passage below, then discuss your answers to the questions. You may discuss in a group of not more than 3.
Remember to think of yourself as scientists as you read and answer the questions.

Passage One

Beluga Whales in the St. Lawrence River

The Arctic beluga whales are, at maturity, pure white and highly intelligent organisms. They have lived in the St. Lawrence Seaway for millennia. As a resource, beluga whales provided traders, fisheries, and settlers with a livelihood for centuries. But, times change. Scientists estimate that the population of belugas must have been 5,000 to 10,000 near the turn of the 20th century and about 500 in the second half of the century. As the demand for whale products decreased, the beluga were increasingly ignored and almost forgotten.
One would assume that the populations would increase. However, by the 1970s the population still was estimated at 500. In 1979 the Canadian government provided the whales complete protection from hunting. Despite this twenty-year protection, the population has not increased.

  1. Why do you think the number of whales has not increased?
  2. What is the question that would best guide a scientific investigation about why the population of whales does not increase?

Share your responses and explain why you chose these responses. Remember to click SUBMIT after you have filled in your responses.

View your friends' choices HERE .

Are they different from yours?
Use the back button of your browser to get back on this page.

As more experiments are carried out your decision may have changed based on new data. Read the second passage and answer the questions.
Concentrate on the final question, What would be the best approach to design and conduct a scientific investigation that would demonstrate a cause-and-effect relationship? Record your responses.

Passage Two

Beluga Whales in the St. Lawrence River

A team of marine biologists headed by Pierre Béland began a series of investigations with one dead beluga beached on the St. Lawrence. Laboratory work showed that the whale died from renal failure. Tissue samples revealed that the whale was heavily contaminated with mercury, lead, PCBs, DDT, MIREX, and other pesticides. Investigations of two other dead belugas revealed similar results.

Still curious about why the population remained low, the biologists continued their investigations. During a 15-year period the team recorded 179 deaths and examined 73 carcasses. The entire sample was highly contaminated with an array of chemicals.

Results of the study included the following.
  • 40% of the organisms bore tumors, 14 of which were cancerous.
  • The whales had a high incidence of stomach ulcers, including three perforated ulcers.
  • 45% of females produced smaller than normal amounts of milk due to infections or tumors in their mammary glands.
  • Lesions of the thyroid and adrenal glands were common.
  • Some whales had compromised immune systems.

In comparison, Arctic beluga in other locations did not display any of these conditions, nor did other species of whales or seals living in the St. Lawrence. Both of the latter groups contained the same toxic substances as the belugas, but in lesser amounts. Finally the scientists also found that the toxins were not confined to the fat in blubber. Small amounts were found in other tissues, which might have contributed more readily to the injury of vital organs. In answering the original questions the scientists proposed that the whales were victims of pollution.

When the scientists presented their evidence and explanation suggesting that pollution was the cause of the low numbers and lack of increase in the beluga population, other marine biologists maintained that toxins were not at fault. The skeptical scientists argued that although the diseases and lesions observed in belugas matched the known effects of toxic chemicals, the original investigations had not demonstrated a cause-and-effect relationship.

(Adapted from “Beluga Whales in the St. Lawrence River” published in The Scientific American, May 1996)

  1. Based on your understanding, were the original investigations adequate? Why or why not?
  2. Did the scientists use appropriate tools and techniques to gather, analyze, and interpret data? How do you know?
  3. What evidence did the scientists use to develop an explanation that the whales died because of pollutants?
  4. What would be the best approach to design and conduct a scientific investigation that would demonstrate a cause-and-effect relationship?

Remember to click SUBMIT after you have filled in your responses.

View the responses from your classmates HERE.

Read the final passage and compare the case study results with your previous responses. How have you fare?

Passage Three

Beluga Whales in the St. Lawrence River

At first, the scientist turned their attention to the most striking disorder – cancer. The incidence of cancer in belugas is twice as high as in humans and higher than in horses and cats. Restricting the comparison to gastrointestinal organs, those most affected in whales, makes this comparison even more striking. In the latter comparison the only animals that exceed whales were sheep in Australia and New Zealand. The high disease rate in the sheep populations has been attributed to carcinogenic herbicides. The sheep graze in pastures contaminated with carcinogenic chemicals. This observation eventually provided a model that applied to whales because sediments in portions of the St. Lawrence contain an extremely potent carcinogen that collects in invertebrates. Although able to detect the carcinogen in belugas, the scientists were not certain how it entered the animals’ systems until they discovered that, in addition to eating fish, belugas dig into sediments to feed on bottom-dwelling invertebrates. This seemed like a good model and likely explanation for how a specific, potent carcinogen entered the belugas.

In the end, however, the cancer data were confounding. Exposure to a certain carcinogen usually harms a specific tissue, but in the belugas a variety of organs were affected. So, the investigations moved to organohalogens, the chemicals that were most abundant in the whales. Other research has demonstrated that in many animals’ organohalogens impede the activity of killer cells, the immune cells that ordinarily destroy malignant tumor cells. When given to experimental animals in embryonic, fetal, and early postnatal stages, these chemicals caused defects in the nervous, endocrine, and reproductive systems. In addition, other research indicated that organohalogens stunted the production of immune cells. This line of research led to investigations that
  • Examined blood samples from contaminated whales to determine the levels of organo- halogens in the plasma and the numbers and responses of immune cells, and
  • Determined the minimum levels at which the ill effects of organohalogens arise.

As a result of these investigations, the biologist determined that beluga whales were in fact more contaminated than expected. The researchers found the observation puzzling because larger animals typically have lower levels of toxins. There are two reasons that larger animals have lower levels of toxins: 1) smaller whales require more food per pound of body weight than do larger whales, and 2) some larger whales consume base-level plankton while other smaller whales such as the harbor porpoise consume fish that are higher in food chain, where organo- halogens accrete. Application of the model developed in this line of research provided an explanation. The belugas feed on eels, which have high levels of MIREX (a chemical produced in a plant near Lake Ontario), and adult eels migrate to the Atlantic through the beluga habitat. During the course of 15 years of eating migrating eels the beluga whales would have taken in the amounts of MIREX found in dead belugas and half the amounts of other chemicals such a PCBs and DDT. The investigations continued and the evidence was helping scientists form cause-effect explanations. But as the senior scientist indicated, “At this juncture I felt like a naïve detective who had been trying to figure out how packages move between cities by searching highway vehicles at random. I got nowhere until I chanced on a mail truck” (p.63).

In this statement the scientist was referring to an alternative explanation. The investigators noticed that organohalogen levels were often higher in very young animals, which contradicted another common explanation – toxins accumulate during the animals’ lifetime. Also, they found that adult females were consistently less contaminated than the males. These observations suggested the explanation that the females passed significant amount of chemicals on to their calves. When the team examined several females that had died shortly after giving birth, they found evidence for this explanation. The milk provided the evidence. The suckling calf ingests food that is far more contaminated than its mother’s food. In ecological terms, the calves feed at a higher echelon in the food chain where the toxins have been concentrated. Every new wave of calves begins life with higher levels of toxins than those of their mothers. They then take in fish that also contain higher levels of toxins each year. So, each new generation begins at a less advantageous position than prior generations.

The scientists proposed an answer to the original question – What explains the lack of increase of the beluga population? All the evidence indicates that the belugas have failed to increase in number due to the long-term exposure to a complex mixture of toxic chemicals.
  1. Can you outline the feeding habits of beluga whale? Draw a food chain to illustrate this.
  2. Explain the important ecological phenomenon that is mentioned in the passage that caused the accumulation of toxin in animals feeding on the higher trophic level.

For more readings about the Beluga Whales please refer to:
  1. Beluga Whales
  2. Diseases of Beluga Whales in Saint Lawrence Estuary
  3. The Saint-Lawrence Beluga Whale