why do orcas have collapsed dorsal fins in the wild
Captive killer whales Collapsed or collapsing dorsal fins are rare in most wild populations and usually result from a serious injury to the fin, such as from being shot or colliding with a vessel.[72] After the 1989 Exxon Valdez oil spill, the dorsal fins of two male resident killer whales who had been exposed to the oil collapsed, and the animals subsequently died. In 2002, the dorsal fin of a stranded killer whale showed signs of collapse after three days but regained its natural upright appearance as soon as the orca resumed strong normal swimming upon release.[72]
Gill slit Most sharks and rays have five pairs of gill slits, but a few species have 6 or 7 pairs. Shark gill slits lie in a row behind the head. The anterior edge of a gill slit is motile, moving outward to allow water to exit, but closing to prevent reverse flow. A modified slit, called a spiracle, lies just behind the eye, which assists the shark with taking in water during respiration and plays a major role in bottomâ€“dwelling sharks. Spiracles are reduced or missing in active pelagic sharks.[1] While the shark is moving, water passes through the mouth and over the gills in a process known as "ram ventilation"[2]. While at rest, most sharks pump water over their gills to ensure a constant supply of oxygenated water. A small number of species have lost the ability to pump water through their gills and must swim without rest. These species are obligate ram ventilators and would presumably asphyxiate if unable to move. Obligate ram ventilation is also true of some pelagic bony fish species.[3]