Scientists at the Woods Hole Oceanographic Institution (WHOI) discovered that mid-sized fish, such as the bigscale pomfret, serve as a crucial link between the deep ocean and surface food webs, explaining why large predators like sharks spend significant time in the ocean's twilight zone. Researchers tracked these fish, which inhabit the mesopelagic zone (200 to 1,000 meters deep) during the day and ascend to feed at night, using satellite tags for the first time.

The study revealed that the movements of these mid-sized fish are influenced by water clarity, potentially impacting entire ocean food chains. Danny Mears, who provided the image of the tagged big-scale pomfret, noted the significance of understanding these previously hidden behaviors. The research highlights the importance of the mesopelagic zone, a dimly lit region often referred to as the twilight zone, in sustaining larger marine predators.

The mesopelagic zone has long been recognized as a challenging environment to study due to its depth and darkness. Traditional methods of observation, such as nets and sonar, can be disruptive and provide limited insight into the natural behavior of its inhabitants. The use of satellite tags allowed researchers to track the movements of individual fish over extended periods, providing a more comprehensive understanding of their role in the marine ecosystem.

The findings have implications for understanding the impact of climate change and human activities on ocean food webs. Changes in water clarity, driven by factors such as pollution and algal blooms, could alter the behavior of mid-sized fish and disrupt the flow of energy from the deep ocean to surface waters. This could, in turn, affect the populations of larger predators and the overall health of the marine ecosystem.

Researchers plan to continue studying the movements and behavior of mid-sized fish in the mesopelagic zone to further refine our understanding of their role in the ocean food web. Future studies may also explore the impact of plastic pollution and other stressors on these important species. The WHOI team hopes their work will inform conservation efforts and promote sustainable management of ocean resources.