Marine Mammals

Overview of Marine Mammals

Focus Areas

• Diving adaptations

• Nitrogen management

• Echolocation

• Migration patterns

Diving Adaptations

• Diving behaviors: Marine mammals show diverse diving behaviors:

  • Toothed whales (e.g., sperm whales, dolphins) are deep divers capable of reaching significant depths (over 1,000 meters) for prolonged periods in search of prey, while

  • Baleen whales (e.g., blue whales, humpback whales) typically perform shallower dives, generally ranging from 20-100 meters to feed on small organisms such as krill and plankton.

• Respiration: Before diving, toothed whales inhale rapidly, increasing lung capacity to maximize oxygen intake, and perform a large exhalation to expel excess CO2 and prepare for the dive.

• Myoglobin in muscles: Toothed whales possess high levels of myoglobin in their muscles, enabling them to store significant amounts of oxygen (up to 10 times more than in human muscles) for extended dives.

• Anaerobic metabolism: During long dives, marine mammals can switch to anaerobic metabolism due to the lack of oxygen, which leads to lactic acid production. Despite this, marine mammals have evolved mechanisms to tolerate higher levels of lactic acid without incurring damage to their tissues.

• Bradycardia: This physiological response involves a slowed heart rate, allowing marine mammals to conserve oxygen during dives. Conversely, research indicates that in humans, bradycardia often occurs in cold water and during certain athletic activities to preserve stamina.

• Blood flow restrictions: During dives, blood is redirected away from non-essential organs (like limbs) to vital organs (brain and heart), ensuring they function optimally under pressure.

Understanding the Bends (Decompression Sickness)

• Definition: The bends, clinically known as decompression sickness, occurs when nitrogen gas forms bubbles in the bloodstream due to rapid ascent from deep dives. These bubbles can cause severe pain and other symptoms, including paralysis or death if untreated.

• Human effects: For scuba divers, adhering to safety protocols such as performing safety stops at various depths during ascent is crucial to allow nitrogen to be safely released from their bodies, thus avoiding painful and potentially life-threatening consequences.

• Marine mammals' adaptations: Uniquely, marine mammals generally do not suffer from bends due to several physiological adaptations:

  • Their flexible ribcages compress under pressure, effectively expelling air from lungs and minimizing nitrogen uptake.

  • Additionally, they have centralized gas storage in their lungs (unlike humans) which significantly decreases nitrogen absorption into the bloodstream during dives, preventing bubbles from forming upon ascent.

Echolocation

• Definition: Echolocation is a sophisticated biological sonar system employed by many marine mammals to navigate through murky waters and locate prey effectively.

• Mechanism: Marine mammals generate sounds by storing air in specialized air sacs, which vibrate to produce sound waves. These sound waves travel through water and bounce back upon hitting an object, allowing the animal to determine the object's size, distance, and even texture.

• Frequency of clicks:

  • Low-frequency clicks travel long distances and are utilized to stun fish and other prey.

  • High-frequency clicks are used for probing nearby objects with precision detailing, aiding in navigation and hunting.

• Communication vs. echolocation: While clicks primarily serve hunting purposes, the distinct whistles emitted by whales often facilitate communication among individuals, forming social bonds within species.

Migration Patterns

• General trends: Marine mammals typically exhibit migratory behavior between feeding grounds (usually in colder, nutrient-rich higher latitudes) and breeding grounds (warmer, lower latitudes).

• Gray whales: An illustrative example, gray whales embark on a long migration in the fall towards breeding grounds in warm lagoons along the Baja California Peninsula, then return in the summer to northern feeding grounds in the Bering Sea full of nutrients.

• Humpback whales: Humpbacks exhibit similar migration patterns, with populations in both the Northern and Southern Hemispheres undertaking extensive travel to optimize feeding and breeding opportunities throughout the year.

Reproductive Biology

• Live birth: All marine mammals give birth to live young, which can occur at sea or on land, depending on the species' reproductive adaptations and habitat needs.

• Delayed implantation: A noteworthy reproductive strategy among certain species is delayed implantation, allowing marine mammals to time the births of their young with optimal environmental conditions for survival, a strategy particularly helpful in changing climates.

• Calving position: Cetaceans (such as whales and dolphins) often give birth tail-first; this ensures that the newborn calf can immediately take its first breath upon entering the water, which is critical for survival.

Life Expectancy Trends

• Metabolism and size relation: Generally, there is an inverse relationship to life expectancy where smaller marine mammals (e.g., sea otters) have shorter lifespans (around 15-20 years), while larger species (e.g., bowhead whales) exhibit remarkable longevity, often living over 50 years or more.

• Comparison with terrestrial mammals: There are notable similarities and differences in longevity trends observed between marine mammals and terrestrial mammals concerning body size; for example, larger terrestrial mammals tend to have longer lifespans as well, prompting research into its underlying biological mechanics.