Large Pelagic Predators Found Lurking in Deep Ocean for Unknown Reasons

Large pelagic predators, that include great white sharks, have been discovered by researchers lurking in the deep ocean for unknown reasons, according to a new study led by an international scientific team. The research paper states that these ocean predators are hanging out in the ocean's twilight zone and midnight zone, at depths thousands of meters below the sea surface. Reasons relating to food or climate change could cause these movements, but scientists are still baffled by the phenomenon.

Pelagic marine animals are organisms found living in the open sea as opposed to benthic organisms, creatures that live on and in the bottom of the ocean. In this context, the discovery made in the recent study shows that even large members of the swimming and floating organisms in the pelagic zone can also dwell in the deep ocean, which is not their natural habitat.

Large Pelagic Predators in Deep Ocean

Marine scientists have long considered the deep ocean to be a place with many ecosystems available for different marine animals but it remains largely inaccessible for most sea creatures that live on the surface and even along coastal areas. Aside from water pressure and lack of sunlight, the ocean's twilight and midnight zones are relatively remote compared to the waters on the surface.

In the study published in the journal PNAS, researchers confirmed that multiple species of large pelagic predators spend their time in the twilight and midnight zones of the deep ocean where they feed and engage in other potential activities, a discovery that left scientists scratching their heads. These findings came after the scientific team detected vertical movements of the predators in the open ocean.

The ocean predators in question include not only great white sharks but also tiger sharks, whale sharks, yellowfin tuna, and swordfish, which were tagged with an electronic tracking device. The team used shipboard sonar to monitor the marine predators for a cumulative period of 46,659 days to determine which of the species regularly dive into the twilight and midnight zones.

Twilight and Midnight Zones

The deep ocean regions mentioned in the study is part of the ocean zones that consists of five parts as follows:

• Sunlight zone (epipelagic)
• Twilight zone (mesopelagic)
• Midnight zone (bathypelagic)
• Abyssal zone (abyssopelagic)
• Hadal zone (trenches)

The PNAS study emphasizes the mesopelagic and bathypelagic zones, with the twilight zone having a depth of 200 to 1,000 meters and the midnight zone extending to about 4,000 meters, according to the Woods Hole Oceanographic Institution (WHOI).

Despite the remoteness of the deep ocean zones, it is also filled with bizarre-looking creatures such as microscopic bacteria, zooplankton, squid, fish, large crustaceans, and other gelatinous animals, the WHOI adds. Furthermore, the midnight zone is also host to animals outside of this world like vampire squids, eels, and anglerfish.