Chilean Devil Ray

The 🇨🇱 Chilean devil ray (Mobula tarapacana), also referred to as the box ray, greater Guinean mobula, sicklefin devil ray, or the spiny mobula, is a distinguished species within the Mobulidae family. This ray is frequently observed worldwide, often positioned just below the ocean surface in tropical, subtropical, and warm temperate seas, with occasional appearances near coastal areas. It is notable for its impressive disc width, reaching up to 3.7 meters (12 feet), and can weigh up to 400 kilograms. Although the exact lifespan is unknown, it is estimated to be at least 15 years.

The species is characterized by an olive-green or brown dorsal surface, with grey ventral shading on the posterior margin of its pectoral fins, transitioning to white anteriorly. A distinctive zigzag margin separates these two colors. The tail is notably shorter than the disc width and is covered in scales. A pronounced ridge along the dorsal midline is a defining feature, as are the medium to large gill plates featuring fused lobes and a rounded terminal lobe with a pronounced midline ridge. These plates exhibit a distinctive bicoloration at the midpoint, with white inner lobes and black outer lobes.

Initially thought to reside primarily at the surface, the Mobula tarapacana has been found to forage at depths reaching 1,896 meters (6,220 feet), making it one of the deepest-diving oceanic animals. This deep diving typically follows a stepwise pattern, wherein the ray descends deeply before progressively resurfacing through a series of incremental ascents. Sonar observations indicate that these levels correlate with denser prey layers, suggesting a foraging strategy.

The ray exhibits two specific deep-dive behaviors: one involves a stepwise descent to maximum depths, resurfacing after 60 to 90 minutes, typically performed once every 24 hours, while the other, less frequent, entails dives reaching up to 1,000 meters for as long as 11 hours, potentially linked to travel rather than feeding.

The diving behavior of the ray may be facilitated by an organ known as the retia mirabilia, found in rays and deep-diving great white sharks. This network of blood vessels aids in maintaining brain temperature at colder depths. Observations reveal that rays linger near warmer surface waters for a minimum of an hour before and after deep dives, indicating a period of thermal preparation and recovery from the cooler sub-surface temperatures.