Big Skate, Beringraja binoculata
Big Skate, Beringraja binoculata, Female. Fish caught from coastal waters off Sitka, Alaska, May 2022. Weight: 38 kg (84 lbs). Catch, photograph and identification courtesy of Chris Wheaton, Fullerton, California.
The Big Skate, Beringraja binoculata, is a member of the Skate or Rajidae Family, that is known in Mexico as raya bruja gigante. Globally, there are six species in the genus Beringraja (a new Genus created in 2012), of which five are found in Mexican waters of the Pacific Ocean.
The Big Skate is very large in stature with a flattened, diamond-shaped disk that is slightly wider than it is long. They are mottled on the dorsal surface in brown, reddish-brown, dark gray and black. They may have small pale spots and scattered dark blotches on the dorsal surface. They have two large black spots, with a pale border and a dark center on the dorsal surface of the pectoral fins. The ventral side varies from white to off white and some have dark blotches. Their snout is long and tapers to a blunt point. They have small eyes that are just in front of the large spiracles. Their gill slits and mouth are on the ventral side. Their mouth is equipped with small, raised cusps arranged in 24 to 48 rows in the upper jaw and 22 to 45 rows in the lower jaw. They do not have an anal fin; their caudal fin is a simple fold; they have two small dorsal fins that are set well back on the tail, their pectoral fins are broad and attached to the snout and incorporated with the body and have concave margins, and, their pelvic fins are large, moderately concave, and have a week notch. Their tail is long and narrow and has a small fleshy keel on both sides. The dorsal surface and the underside of the snout and the abdomen are covered with small prickles. Their back has an irregular row of 33 middorsal thorns that extend down the back and tail to the first dorsal fin. They have a middorsal thorn just behind the orbits and orbital thorns between the eyes which surface with maturity. They have a limited number of small, placoid scales on the body, tail, and rear of the head.
The Big Skate is a demersal species that is found at depths up to 800 m (2,600 feet) within coastal bays, estuaries and over the continental shelf over sandy and muddy substrate. They are normally found half submerged lying motionless on the bottom floor with only their eyes protruding. They are the largest skate in North American that reach a maximum of 2.44 m (8 feet 0 inches) in length and 91 kg (200 lbs) in weight. They swim via a graceful sweeping motion appearing to fly rather than swim through the water. They feed on small fishes and a wide variety of invertebrates including clams, various crustaceans, mollusks, shrimp, and worms. In turn they are preyed upon by large predatory bony fishes and sharks. Their egg capsules are consumed by elephant seals. They utilize camouflage for protection, and they have the ability to bury themselves partially or completely in the substrate. Reproduction of the Big Skate is oviparous with internal fertilization and the females deposit large, leathery, oblong egg cases with horns at each corner that are known as Mermaid Purses, on the sea floor over sandy or muddy substrate. They are the largest egg capsule in the Rajidae Family, each measuring up to 30 cm (12 inches) in length. The egg cases contain between one to seven embryos, which has drawn the attention of the scientific community, that feed solely on the yolk that develop in six to twenty months. Each female can deposit over 350 egg cases per year indicative that the Big Skate may be one of the most fecund elasmobranchs. The young, that appear as miniature adults are between 18 cm (7.1 inches) and 23 cm (9.1 inches) in length. They are generally sedentary but have been documented to migrate between 20 km and 1,000 km in some areas. The Big Skate is poorly studied with very limited information available about their lifestyle and behavioral patterns including specific details on age, growth, longevity, movement patterns, diet, habitat use, and reproduction. They have life spans of up to twenty-six years.
The Big Skate can be confused with other skates found in Mexican waters including the Artic Skate, Amblyraja hyperboprea, the California Skate, Beringraja inornata, the Equatorial Skate, Rostroraja equatorialis, the Longnose Skate, Beringraja rhina, the Rasptail Skate, Rostroraja velezi, and the Starry Skate, Beringraja stellulata. However, their size, dark eye spots on the pectoral fins, and overall body shape allow them to be easily identified.
In Mexican waters the Big Skate are not abundant but found from Guerrero Negro, Baja California, northward along the central and northwest coasts of Baja and within the northern portions of the Sea of Cortez.
From a conservation perspective the Big Skate is currently considered to be of Least Concern with stable, widely distributed populations. They are caught as an incidental bycatch by long lines and bottom trawlers, but they are only of minor commercial importance as their mean not highly regarded of human consumption. They are slow maturing (males at least seven years, females twelve years), slow growing and have low reproductive rates making them vulnerable to overfishing with noted reductions in landing rates in certain regions. Their population trends are poorly monitored. With the increasing demands for fresh fish more and more pressure is being put on this fishery with decreasing size and landing rates stilling interests in conservationist with new catch and gear limitations being put into effect. They are caught occasionally by recreational angler and normally discarded. They can be found in large public aquariums as they readily adapt to captivity. They are harmless to humans.