Despite their size, whales are threatened by human activity such as fishing, ship traffic, and pollution. These stressors can overlap and compound effects on whale populations. In California, the protection policies that are currently in place do not address these factors.
In a new study from UC Davis, researchers set out to better understand the main causes of death among nine whale species. This includes humpback, gray, blue, fin, minke, sei, sperm, North Pacific right, and killer whales in the California Current Ecosystem, which stretches from British Columbia, Canada to Baja California, Mexico.
“We found that oftentimes, people single out fishing or ship strike for their roles in whale mortality,” said study co-author Eliza Oldach. “But a whole slew of human activities have collided to make the modern ocean a really tough environment for whales to survive. We’re excited about efforts that look broadly to rebuild healthy oceans.”
The experts identified five main contributors to whale mortality that are currently targeted by policy instruments. These include entanglements, vessel strikes, noise, water quality and marine debris. But three other threats – nutritional stress, disease and predation – were also identified and are not included in policy responses. Researchers argue these threats must also be considered to provide a holistic approach to managing whale deaths.
“Gray whales migrate over 5,000 miles between their foraging and breeding grounds at either end of the California Current,” said study co-author Helen Killeen. “Throughout their journey, they must pass through a gauntlet of human activities, all while contending with changes to their environment precipitated by climate change. The best conservation approach for these whales is one that addresses overlapping and interacting stressors that span geographic and jurisdictional boundaries.”
The results are timely and align with the goals of the California Ocean Protection Council to develop a plan for zero mortality for whales in the California Current Ecosystem. This would require a strong understanding of threats to whales as well as the opportunity for policy change and ecosystem management.
On the bright side, the research team found some cases where agencies are already working to develop policies that tackle multiple stressors for whales. “Our paper is intended to highlight that approach and urge other policymakers to think along similar lines.” said Oldach.
The study was funded by the UC Davis Sustainable Oceans: From Policy to Science to Decisions program, a National Science Foundation Research Traineeship. The research is published in the journal Marine Policy.