![]() Using electronic tags, scientists have tracked blue and white sharks using eddies as a fast-track to the feast. ![]() Some sharks access the deep ocean by taking advantage of warm-core eddies - large, swirling ocean currents that draw warm water deep into the twilight zone where temperatures are normally colder. Nearly all species of sharks have a specialized, reflective tissue in their eyes (tapetum lucidum) that increases photosensitivity, helping them to navigate the pitch-black waters. Bioluminescence is the predominant source of light in the deep ocean, and sharks may detect it as point-source flashes or as shadows against the extended, dim background light it produces. Very little sunlight makes its way into the TZ, imposing the need for adaptations to enhance vision or alternative senses. How do sharks persevere in these deep depths if the conditions are much different than their surface water habitats? The ability for sharks and other LMPs to access the mesopelagic has evolved over time. Some whale sharks migrate vast distances and seem to time their visits around annual phytoplankton blooms or fish spawning events off continental shelves. Unlike other large filter-feeders (like the basking shark), the whale shark actively vacuums up water by rapidly opening and closing its mouth and expelling water through its gills. They venture to the mesopelagic to feed during migrations, and research suggests that whale sharks may also visit the middle ocean to cool down, remove parasites, save energy, or even to calibrate their internal navigation. Take the whale shark, for instance. Whale sharks aren’t really sharks at all, but the largest fish in the ocean, yet feed on the smallest of critters in surface waters, mainly zooplankton and fish eggs. There could be reasons other than food that marine animals visit the twilight zone. Basking sharks are known as “ram feeders”, swimming through dense patches of zooplankton with their mouths open, passively filtering food through its gill rakers. ![]() It averages 8 meters (26 feet), but some individuals have been recorded as large as 12 meters (40 feet). Though the “Biggest Fish in the Ocean” title goes to the whale shark, which is about as big as a school bus, the basking shark is a worthy contender. Blue sharks spend up to an hour hunting for a meal whale sharks can spend a few hours and basking sharks take it to the extreme, spending up to four months feasting on TZ creatures before reemerging to the sunlit surface waters. Many shark species venture from surface waters to the deep ocean between 2 meters (656 to 3280 feet) and experts believe the main purpose is to hunt for prey when food is scarce in surface waters.ĭifferent shark species spend varying lengths of time in the TZ. The ocean’s TZ is home to some of the largest fish biomass on Earth, making it a unique feeding ground for the ocean’s largest predators. Woods Hole, MA (July 9, 2021) - Sharks are some of the largest fish in the ocean, known as apex predators, that steal the show in films, television and of course - shark week! For decades, Woods Hole Oceanographic Institution (WHOI) has studied the ways large marine predators (LMPs), like sharks, use the mesopelagic zone or middle layer of the ocean, better known as the ocean’s twilight zone (TZ). ![]()
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