North Pacific humpback whales are in crisis right now, their populations displaying distressing signs of strife. Recent studies by University of Hawaiʻi at Mānoa’s Hawaiʻi Institute of Marine Biology (HIMB) found a shocking 76.5% decrease in mother-calf sightings. This steep decline follows a disturbing pattern of declining reproduction rates. From 2013 to 2018, the crude birth rates of humpback whales in Hawaiʻi dropped by an estimated 80%. Given this lack of information, it raises alarm bells about calf humpback survival. These young whales require an incredible source of energy to survive immediately after they’re born.
The research published in the Marine Ecology Progress Series relied on drones to document spectacular, high-resolution aerial images. The study’s authors took more than 1,500 individual pictures of humpback whales in Hawaiʻi and Southeast Alaska. In comparison, researchers examined more than 12,000 measurements taken on more than 8,500 individual whales. This hampered their ability to understand what age-specific body length, mass, and energetic requirements for life inform on growth in such majestic creatures.
Energy Demands of Humpback Calves
Humpback calves are under great energy stress right from birth. Once they leave the womb, they require 38-fold increase in energy. This profound change highlights the difficulty of transitioning from life in protected bays to the open sea. In addition, during their rapid development stage, these calves need six to eight times an adult humpback whale’s daily growth energy. However, this incredible demand continues to burn their growth and attractiveness.
During their first year, humpback calves apparently reach about 30% of their potential total lifetime mass. That quick growth is key not just to their short-term survival but to long-term success back in the wild. Over 60% of a calf’s total energy requirements for growth are needed within the first 150 days of life. This pivotal time lays the groundwork for their future growth and health. That time of life is essential and often overlooked for laying the groundwork of the financial stability that will carry them through their adult years.
The energetic burden calves impose has a domino effect, influencing maternal investment strategies that govern the welfare of offspring. Humpback mothers must meet the physiological demands of lactation while fasting in Hawaii’s breeding grounds. After this, they begin a months-long trek back to their breeding grounds in Alaska.
Impacts of Population Stress on Reproduction
One impact of this population stress is seen in the decreasing numbers of mother-calf pairs we’ve all watched in recent years. The sharp decline in sightings – by an incredible 83 percent – is a warning bell that the species may be in critical danger. Adult humpback whales appear to be smaller today, averaging one to two feet shorter than their counterparts from earlier decades. This apparent shrinking may be a harbinger of other environmental factors that are impacting their overall health and reproductive success.
A mother’s success at producing a single healthy, big calf is directly tied to her energy reserves. If mothers can’t get the nutrition they need, their calves can be born smaller, weaker, or both. Consequently, these calves struggle to achieve sufficient energy intake when it is most critical during key growth phases.
Furthermore, the study’s results paint a dire picture of how these reproductive issues may contribute to an ongoing population decrease. The connection between maternal health and calf survival further highlights the need to keep strong feeding grounds available for these whales.
Research Insights and Future Directions
HIMB and the Alaska Whale Foundation collaborated on innovative research to identify individual humpback whale calls. Their efforts have uncovered the captivating complexities of humpback whale population dynamics. By employing advanced drone technology, researchers have been able to gather data on whale size and health that was previously unattainable through traditional observation methods.
Unfortunately, this research reveals some very concerning trends in humpback populations. It is a reminder of the ongoing importance of sustained scientific monitoring and targeted conservation action. The unprecedented price of birth rates and mother-calf sightings requires urgent action. Now is the time for scientists and policymakers to work together to deploy effective strategies that safeguard these powerful marine canaries.