Common Dolphin – Delphinus delphis
Habitat: Correlated with prominent undersea topography such as seamounts and sea escarpments, and continental slope waters.
Description: Slender, torpedo-shaped body. Beak is long and dark with 41 – 56 pairs of small, sharp teeth in each jaw. Chevron-shaped groove separates beak from low, receding forehead. Dorsal fin is centrally placed, slender, sickle-shaped to erect. Colouration is variable both within and between populations. Best identifying mark is hourglass or crisscross colour pattern formed by other markings. Black ‘cape’ covers head and back, to about half way down the tail stock, lower margin dipping to a point about half way along the side of the animal. Cream or dirty yellow patch runs from front of head to point of cape. Grey stripe runs from point of cape back to tail. White marking runs along abdomen. Dorsal fin black, but often with large cream coloured central patch. Flippers variable, black to light grey. Flukes dark grey or black with distinct median notch. Males have prominent black blaze above genital opening; in females, blaze is narrower, black and grey.
Size: 240 – 250 cm, males larger, most individuals < 230 cm. Prior to 1980s average lengths were 250 – 270 cm.
Weight: 135 kg.
Lifespan: Maximum recorded age 28 years.
Distribution: Worldwide in temperate and tropical waters. On GB continental shlef, common in western half of English Channel and south Irish Sea, particularly around Celtic Deep, in smaller numbers north to Sea of Hebrides and southern part of Minch. Also common south and west of Ireland. In some years since around 2000, occurs further north and east in shelf areas – north Hebrides, Shetland, Orkney, north North Sea – probably due to stronger North Atlantic current.
Diet & Feeding: Variety of fish and squid. Reported to be an opportunistic feeder, but in north-east Atlantic, diet predominately consists of a few species which vary depending on season and region. Food-herding behaviour frequently observed with cooperation between individuals.
Breeding: Reproduction seasonal. in NE Atlantic, mating and calving occurs May – September. Gestation period 11.5 months, lactation period 10 months (although calves from the age of 3 months may take solid food), calving interval 42.5 months. Average age at sexual maturity 11.86 years for males, 9 to 10 years for females.
Conservation Status & Population: Listed by IUCN as lower risk / least concern. Several surveys using line transect methods have estimated population abundance levels in north east Atlantic:
MICA, summer 1993 – 61,888 individuals in Bay of Biscay, continental shelf W to c.20° W, S to c.43°N.
SCANS I, July 1994 – 75,450 individuals, Celtic shelf to c. 11°W and 48°S.
SCANS II, 2005, same area as SCANS II but increased to include Irish Sea, waters off W and N Ireland, W Scotland, continental shelf waters off France, Spain, Portugal, estimated 63,400 individuals.
Current main cause of concern for NE Atlantic population is large scale but poorly documented incidental capture in fishing gear. In 1990s, extensive bycatch by western European tuna driftnet fisheries led to closure of fisheries in 2002. Numerous contaminants investigated in NE Atlantic population; 40% of D. delphinus sample exceeded level where PCBs known to have reproductive impact on botttlenose dolphin.
Small, swift dolphin with long slender beak. Often attracted to vessels. Frequestly leaps clear of water revealing distinctive hourglass pattern on flanks.
Vocalisations: Include whistles 1 – 50 kHz, duration 0.05 – 2.02 s; echolocation clicks, not well described but may reach 150 kHz at repetition rates of 30 – 200 clicks /s; pulsed calls (buzzes and barks). Clicks and whistles may be produced simultaneously.