05 :: Costa Rica Sharks
The fishes are divided into two classes: the Osteichthyes (bony fishes), which comprise approximately 95% of the modern ichthyofauna and Chondrichthyes (cartilaginous fishes). The latter includes two subclasses: the Elasmobranchii (sharks and rays) and Holocephalii (chimeras). Elasmobranchs are the largest group of the Chondrichthyes Class (about 1100 species), representing 96% of cartilaginous fishes.
About sharks, in the world today there are about 400 different species. They have evolved 400 million years ago, to adapt successfully to aquatic environments, being the top predators of the ecosystems where they inhabit. In order to maintain ecosystems within their natural carrying capacity, sharks have a slow growth, low reproductive rate, late maturity and low natural mortality rate. Those biological characteristics, turn the sharks particularly vulnerable to over fishing.
In Costa Rican waters live about 40 species of sharks, the Pacific Coast is the best known and studied. In the coastal fishery, stand out for their abundance the smooth hound sharks (Mustelus lunulatus and Mustelus henlei; Triakidae), followed by the whitenose shark (Nasolamia velox; Carcharhinidae), the Pacific sharpnose shark (Rhizoprionodo longurio; Carcharhinidae) and finally the scalloped hammerhead shark (Sphyrna lewini; Sphyrnidae). On the other hand, the more observed species during scuba diving is the white tip shark (Triaenodon obesus, Carcharhinidae).
Another very common coastal shark, especially in mouth`s rivers and mangrove ecosystems is the bull shark (Carcharhinus leucas, Carcharhinidae), which evolved to inhabit marine and freshwater environments. In fact, it is easy to see the bull shark in Sirena River in the Osa Peninsula and in the San Juan River along the boundary between Costa Rica and Nicaragua.
In the pelagic fishery, the longline vessels caught mainly silky shark (Carcharhinus falciformis, Carcharhinidae), which represents up to 98% of all sharks caught. Other common sharks in this fishery, but less abundant, are the pelagic thresher shark (Alopias pelagicus; Alopiidae) and hammerheads sharks (S. lewini and S. zygaena; Sphyrnidae).
Also in Costa Rican, in coastal and pelagic waters, we have the privilege of see the world's largest fish, the whale shark (Rhincodon typus; Rhincodontidae). This is a coastal pelagic species, which makes large horizontal and vertical migrations. It is common to observe it in the Golfo Dulce and in the Golfo de Papagayo, especially between December and February when the cold waters rich in nutrients move toward the surface, thereby attracting large migratory species.