Tope, Galeorhinus galeus
The Tope, Galeorhinus galeus, whose Spanish common name is tiburón aceitoso, is a species in the Hound Shark or Triakidae Family, known collectively as cazónes in Mexico. This fish is also known as the Soupfin Shark. Globally, this is only species in the genus Galeorhinus, and it is found in Mexican waters of the Pacific.
The Topes have elongated slender bodies and long snouts. They are gray or brown on their backs and sides transitioning to white ventrally. The underside of their snout tip is translucent. Their fins have no distinguishing marks with the exception of their pectoral fins, which have pale edges. Some fish have scattered pale spots on their flanks. Their head has a rounded mouth, very small front nasal flaps, and horizontal oval eyes. They have small teeth of equal size on both jaws; these are broadly triangular with serrations on one side. Their anal fin is the same size as the second dorsal fin and its origin is behind the origin of the second dorsal fin. Their caudal fin is strongly asymmetrical with a long upper lobe and a well-developed lower lobe (a key to identification). Their first dorsal fin is much larger than the second dorsal fin and is inserted well behind the pectoral fins. They have five gill slits with the last two being over the pectoral fins.
The Topes are a coastal schooling pelagic species found demersal over the continental shelf at depths up to 470 meters (1,545 feet). They reach a maximum length of 2.0 meters (6 feet 6 inches), with females being slightly larger than males, making them the largest member of the Hound Shark family. They feed on crabs, isopods, polychaetes worms, shrimp, squid, and a wide variety of small fish. In turn they are preyed upon by larger predatory bony fish including the Great White Shark, Carcharadon carcharias, the Sevengill Shark, Notorynchus cepedianus, and large marine mammals. They are a highly migratory species having both winter and summer grounds and can travel up to 2,500 km between sites. Reproduction is via aplacental viviparity with embryos being nourished by yolk-sac placenta. Litters range from twenty to thirty-five pups born live and measuring 26 cm (10 inch) to 40 cm (16 inch). They have a lifespan of up to sixty years. They are a poorly studied species and very little is known about their behavioral patterns.
In Mexican water they are found in all waters of the Pacific with the exception that they are absent from Mazatlán southward along the coast of the mainland south to Guatemala.
Due to the shape of its tail, the Tope cannot easily be confused with any other species.
The Topes have a wide global distribution in temperate waters. From a conservation perspective, they are considered of Least Concern in Mexican waters but Vulnerable globally with decreasing populations. Major factors affecting their long-term survival include unregulated targeted fishing with gillnets and longlines, habitat destruction in nursery areas, and a very low reproduction rate due to females requiring ten years to reach sexual maturity. They have known pupping areas in shallow protected bays and estuaries which makes them easy targets for commercial fishermen. They are an important recreational species in some parts of the world. In the Eastern Pacific they were a focused species between 1936 and 1944 as a source of Vitamin A but with the production of synthetic Vitamin A, their demand has been eliminated and they have had a chance to recover. Globally a modest demand exists for their liver oil, meat, and fins. In general, their meat is considered of marginal quality and not of economic significance. Over the last year all sharks have become protected species in Mexico. This species is considered to be harmless to humans.
Tope, Galeorhinus galeus, female. Fish caught at night from the beach, Encinitas, California, November 2016. Length: 1.75 meters (69 inches). Catch, photo, and identification courtesy of Ben Cantrell, Peoria, IL.