Bioacoustics of Delphinus delphis

Status and Conservation. CITES Appendix II. Classified as Least Concern on The IUCN Red List. The subpopulation of Short-beaked Common Dolphins in the Mediterranean Sea is classified as Endangered because it has suffered a marked decline and has almost completely disappeared from large portions ofits former range (e.g. Provencal Basin, Balearic Sea, Ligurian Sea, and northern Adriatic Sea). The Black Sea Common Dolphin is classified as Vulnerable. No estimates of total abundance of the Short-beaked Common Dolphin are currently available, but there are ¢.2,963,000 individuals in the eastern tropical Pacific Ocean, ¢.352,000 individuals off western USA, ¢.63,400 individuals in European continental shelf waters, ¢.121,000 individuals in the western North Atlantic Ocean, and ¢.19,400 individuals in the western Mediterranean Sea. Several populations face local threats, but as a whole, the Short-beaked Common Dolphin is abundant and likely not declining. The population in the Mediterranean Sea, however, has been in sharp decline over the last few decades, especially in the northern Adriatic and eastern Ionian seas. Although now directly caught in only a few fisheries (mainly Japanese), the Short-beaked Common Dolphin was hunted historically until the 1980s and 1990s in Turkey, the USSR, Peru, Spain, and France.Its greatest threat currently is incidental catch. In fact, the Short-beaked Common Dolphin is one of the most common species in bycatch in pelagic purse-seine and drift-net fisheries, due to its abundance and association with large pelagic fish such as tuna. Catch limits imposed by the Inter-American Tropical Tuna Commission and resulting emphasis on dolphin release and safety gear have probably reduced mortality of Short-beaked Common Dolphins in tuna purse-seine fisheries by 97% since 1986 (incidental take was 24,307 individuals that year). This fishery killed only 325 Short-beaked Common Dolphins in 2005. Between 1990 and 2002, 21,000 Shortbeaked Common Dolphins were killed in pelagic driftnetfisheries targeting broadbill swordfish (Xiphias gladius) and common thresher shark (Alopias vulpinus) off California. Acoustic “pingers” may be effective in deterring marine mammals, including the Short-beaked Common Dolphin, from these driftnets. Large-scale driftnet fishing that targets broadbill swordfish still occurs illegally on the Mediterranean side of the Strait of Gibraltar, where 12,000-15,000 Short-beaked Common Dolphins are killed per year; most of the fleet operates from Morocco. For Short-beaked Common Dolphins, this take likely exceeds 10% of the local population size, making it unsustainable. The Short-beaked Common Dolphin is also killed incidentally in small-scale gillnet, trawl, and purse-seine fisheries throughout its distribution, including Black Sea, Mediterranean Sea, off north-western Africa, South America, New Zealand, and north Atlantic Ocean. Off northern Portugal, 52% of common dolphin strandings are due to either confirmed bycatch or harmful interactions with fishing gear, contributing to an estimated 44% of the local population’s mortality. High rates of bycatch of Short-beaked Common Dolphins also occur in UK and French pelagic pair-trawl sea bass fisheries. Although small-scale, these fisheries are estimated to have killed at least 800 dolphins in 2000-2005. The southern Australia population of the Short-beaked Common Dolphin, which appears to be genetically distinct from the nearby Tasmanian population, may be especially vulnerable to incidental catch in local purse-seine fisheries. In 2004-2005, for example, 377 Short-beaked Common Dolphins were killed in only seven months. Considering the population’s genetic distinctness, this catch rate may not be sustainable. The Short-beaked Common Dolphin is currently rare in the Adriatic Sea and has likely been steadily declining since the 1800s due to culling campaigns, which continued into the 1960s, and to more recent habitat degradation. Heavy metal and organochlorine contamination may also be a problem in some areas. For example, there are high PCB concentrations in c.40% of female Short-beaked Common Dolphins in the Atlantic Ocean off Europe. High concentrations of cadmium have also been documented in kidneys of Shortbeaked Common Dolphins off South Australia, and they have been correlated with various pathological problems such as proteinuria (excess serum proteins in urine). Overfishing of prey species (primarily anchovy and sprat) is a major threat to Shortbeaked Common Dolphins in the Black and Mediterranean seas. There is no reliable estimate of abundance for the Black Sea Common Dolphin. At least 159,000-161,000 Black Sea Common Dolphins were killed in 1962-1983 before Turkey banned small cetacean hunting. Priorto this, from the 1930s to the 1960s, the USSR, Romania, and Bulgaria took c.1-5 million Black Sea Common Dolphins before commercial hunting of small cetaceans was banned by these countries in 1966. Black Sea Common Dolphins are also threatened by habitat degradation and overfishing of prey species, which likely increased their susceptibility to infection during a morbillivirus epizootic in 1994. Decline of the Black Sea Common Dolphin has been inferred based on the combined impact of these threats.