Revealing Secrets: Understanding the Deep Dives of Ocean Predators

Recent studies using advanced electronic tagging and sonar reveal that large ocean predators such as sharks and tunas frequently venture into the deep mesopelagic zone. This zone is teeming with organisms and plays a pivotal role in both ecological balance and commercial fishing. Protecting this zone is vital to avoid irreversible ecological harm.

Data gathered from more than 300 tags on large sea predators and sonar data from ships underscore the significance of the ocean’s twilight zone.

Observing a shark leap out of the water is a rare and captivating event, but it represents only a tiny portion of their time spent at the ocean’s surface. The question arises: where do these predators usually reside?

Comprehensive New Research

A groundbreaking study reveals that sharks, tunas, and billfish frequently visit the deep sea, especially the mesopelagic zone, located 200 to 1,000 meters below the surface. This region, also known as the ocean’s twilight zone, has been underappreciated as a crucial habitat for these predators. The findings were published on November 6 in the Proceedings of the National Academy of Sciences.

Collaborative Scientific Efforts

Camrin Braun, an assistant scientist at the Woods Hole Oceanographic Institution (WHOI), led the research, combining an impressive array of data from various scientific collaborators. The study analyzed data from electronic tags, shipboard sonar, satellites, and ocean models to evaluate the ecological importance of deep diving for large oceanic predators. They highlighted the mesopelagic zone’s numerous benefits and ecosystem services for humans.

Predatory Behaviors in the Deep Ocean

Braun points out that top predators, regardless of their location in the global ocean, spend time in the deep sea. These predators, typically associated with the surface, actually utilize the deep ocean more extensively than previously thought.

The researchers used data from 344 electronic tags over 46,659 tracking days for 12 species in the North Atlantic Ocean, including various sharks and tunas.

Movements in the Deep Scattering Layer

The diving patterns of these predators, recorded by the tags, correlated with sonar data showing the daily movements of the deep scattering layer (DSL). The DSL, densely packed with small fish and marine organisms, was once mistaken for the ocean floor in early sonar readings.

During the day, DSL inhabitants stay in the mesopelagic zone. At night, they ascend to surface waters to feed, then return to the twilight zone at dawn. This pattern, known as Diel Vertical Migration, has been a subject of study at WHOI for decades.

Converging Data and Unexpected Discoveries

Alice Della Penna, co-author and acoustics expert at the University of Auckland, expressed excitement at how well different data sets aligned. The combination of diving patterns and acoustic data provided a cohesive understanding of these processes.

Feeding Behaviors and Unusual Patterns

The study offers insights into predators that track the DSL for hunting, as well as those displaying unusual diving behaviors not solely explained by feeding. For instance, swordfish follow the Diel Vertical Migration pattern predictably, but some deviations in their behavior, like diving deeper than expected, suggest other motivations.

Possible Reasons for Deep Dives

These variations imply that predators might dive for reasons beyond feeding. Previous research suggests these movements could help in predator avoidance or navigation. Nonetheless, all studied species interacted with mesopelagic organisms, suggesting significant benefits from diving into this challenging ocean environment.

Mesopelagic Zone’s Ecosystem Services

Simon Thorrold, a fish ecologist at WHOI and study co-author, notes the importance of this behavior in species as diverse as sharks and tunas. He suggests that these deep-sea excursions could play a role in moving carbon dioxide from the surface to the deep ocean, a significant but unquantified ecosystem service of the mesopelagic zone.

Conservation and Commercial Fishing Implications

Thorrold emphasizes the necessity of preserving the mesopelagic zone due to its importance to many commercially fished species. The study warns against premature exploitation of these ecosystems without thorough understanding of their dynamics.

Risks of Early Exploitation

Della Penna warns about the dangers of exploiting mesopelagic ecosystems before fully understanding them, which could lead to irreversible damage.

Key Findings

The study, integrating data from electronic tags, sonar, satellites, and ocean models, confirms the ecological significance of the mesopelagic zone for large marine predators traditionally considered surface dwellers. These predators dive deep into the twilight zone, often following dense prey layers in the DSL. The study highlights the need for further research and cautious approach to fishing and extraction activities in these deep ocean food webs.

The research, published in “Proceedings of the National Academy of Sciences,” was funded by various sources, including the Coastal Research Fund and the Investment in Science Fund at WHOI, the UK Natural Environment Research Council, the European Research Council, and others, contributing to WHOI’s Ocean

Frequently Asked Questions (FAQs) about Marine Predators Deep Diving

More about Marine Predators Deep Diving

• Marine Predators and Mesopelagic Zone
• Ecological Importance of Deep Sea Diving
• Conservation of Ocean’s Twilight Zone
• Deep Sea Behavior of Sharks and Tunas
• Mesopelagic Zone Research and Findings
• Oceanic Predator Diving Patterns
• Impact of Deep Diving on Commercial Fishing
• Marine Ecology and Predator Behavior