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UC Santa Cruz’s Long-Term Study on Northern Elephant Seals Reveals New Insights into Ocean Ecosystems
For the last six decades, marine biologists at the University of California, Santa Cruz have been closely observing the northern elephant seals at Año Nuevo Natural Reserve. This notable research effort has resulted in over 350,000 individual observations spanning more than 50,000 seals as they gather in large numbers to breed and molt along the beach.
This extensive project, bolstered by advanced technologies and dedicated fieldwork, has yielded both historical and real-time data regarding seal fitness, foraging behavior, and population dynamics. Researchers have been able to weigh, tag, and observe these robust marine mammals, providing a rare glimpse into their lives.
Roxanne Beltran, who is set to take over the project’s leadership, highlights the significance of seals as “smart sensors” in her new study. Published on February 14 in Science, the study focuses on how northern elephant seals can provide critical data regarding fish populations inhabiting the twilight zone of the ocean, which is situated between 200 and 1,000 meters deep where sunlight fails to penetrate effectively.
This twilight zone is essential for fish biomass and is where these seals hunt for food. By tracking the foraging success of the seals, researchers are offered a novel method of estimating the availability of fish populations over vast ocean areas. Beltran warns that as global demand for protein-rich food increases, this capability becomes increasingly important.
Insights from an Urgent Need
Beltran emphasized the urgency of monitoring marine ecosystems: “Given the importance of the ocean for carbon sequestration, climate regulation, oxygen production, and as a food source for billions, we need to urgently measure changes in these ecosystems.” The study illustrates how the extensive range of foraging activities and the vast number of feeding attempts by the seals make them excellent indicators of ecosystem health, particularly for fish populations and apex predators in open waters.
Each seal undertakes around 75,000 foraging attempts during an impressive seven-month journey spanning approximately 6,000 miles across the Pacific Ocean. This means that by simply tracking 14 seals each year, researchers can gather vast estimates of fish availability across an incredible volume of ocean.
Additionally, tracking the weight of the seals aids in understanding long-term changes in prey populations. This information is crucial as fish stocks face increased pressure from commercial fishing activities that strive to meet rising public demand, making sustainable management practices essential.
Fostering Student Involvement in Research
In a notable facet of this research, the recent paper features contributions from 14 undergraduate students who participated in a hands-on field course taught by Beltran and Año Nuevo Reserve Director Patrick Robinson. Within this immersive program, students analyzed data accumulated over six decades of seal research while engaging in real-world scientific exploration.
Teaching assistant Allison Payne noted the importance of fostering a scientific community among students: “This collaborative experience not only benefits students but also enhances instructors’ engagement in meaningful scientific inquiry.” The collaborative nature of this program empowers students and increases their confidence in navigating the complexities of scientific research.
In their course, which continues to be offered, participants devised research topics, delving into the long-term data on seal health and behavior, including investigations into how environmental factors affect seal reproductive success.
Undergraduate student Madi Reed investigated how varying ocean conditions impact the survival rates of seal pups, revealing significant correlations between environmental changes and the reproductive outcomes of elephant seals. “This was an invaluable experience that connected our classroom learning to practical research and has fueled my aspirations for a career in biological oceanography,” Reed shared.
Understanding the Twilight Zone
The twilight zone is vital for the survival of various species, including those that humans depend on for food. However, scientists have limited knowledge about the populations residing in these deeper waters. Current estimates of fish abundance in this region carry significant uncertainty, which could result in dire consequences for broader marine ecosystems.
The latest research combines decades of data, including contributions from previous program leaders Burney LeBoeuf and Dan Costa. Costa noted the breakthrough of linking seal behaviors across vast distances to their breeding outcomes on land, a feat made possible by a comprehensive and multidisciplinary research approach.
Earlier findings from this ongoing research have established the extensive foraging migrations of the seals, their frequent hunting of smaller fish, and the relationship between the quality of seal pups and ocean health, based on their mothers’ foraging success.
The new findings confirm a direct relationship between the seals’ foraging successes and broader oceanographic measures obtainable via satellites, allowing researchers to track oceanic patterns over extended periods. “Our results offer ecological baselines essential for sustainable fisheries and assessments of human impacts on marine life across entire ocean basins,” Beltran added.
The research team also included contributors from UC Santa Cruz and NOAA, and the project received support from multiple organizations, such as the National Science Foundation and the Arnold and Mabel Beckman Foundation.
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