Peale's Dolphin (marine mammals)

 

Peale’s dolphin (Lagenorhynchus australis) is common in inshore waters of southernmost South America, but because it seldom strands, its life history is not well known. Nearly a century passed before the first descriptions of its pigmentation and skull were discovered to be of the same species.

Accounts of only five specimens had been published by 1974; many of the 80 specimens now available were beach pick-ups.

I. Taxonomy

This species was first described as Phocaena australis Peale, 1848 and Sagmatias amblodon Cope, 1866. Although lumped with Delphinus obscurus and L. cruciger at different times, the present combination Lagenorhynchus australis was proposed by Kellogg in 1941. Tursio chiloensis is a synonym. New work with DNA shows that the genus Lagenorhynchus needs revision and that the genus name of one Northern Hemisphere species and the three Southern Hemisphere species should revert to Sagmatias. Although there have been several common names in English, Peale’s dolphin is now standard. Delfin austral (southern dolphin) is the common name in Argentina and Chile, although llampa is sometimes used in the latter.

II. Diagnostic Characters

A. Pigmentation

Peale’s dolphins are dark gray or black on the dorsal surface, with two areas of lighter pigmentation on the sides (Fig. 1). A curved white-to-gray flank patch angles forward from the vent, narrowing to a single line ending below or in front of the dorsal fin. The posterior curves of the flank patch almost meet above the tail stock. The larger thoracic patch is light to medium gray, outlined with a narrow dark line on its lower surface. Both patches may be flecked with darker gray. A double black eye ring extends forward onto the snout, which is inconspicuous. The black chin or throat patch varies individually in the shape of its posterior border, usually extending backward on the sides to leave a white point in the middle. The white flipper patch is also delineated with gray and may extend onto the lower part of the flipper. The flippers and dorsal fin are dark with lighter posterior edges. Flippers in older animals may have a series of small knobs on the leading edge. The ventral surface behind the throat patch is white, with a few dark streaks in the genital area. Young animals are lighter gray than adults and have less definition between thoracic and flank patches than in adults.

Peale’s dolphins can be confused with dusk)’ dolphins, L. obscurus, through much of their range. The latter are usually a lighter gray and have white on the sides of the face and two light lines running forward from the flank patch.

B. Size and Shape

This is a stocky dolphin with the barest indication of a beak. Total length for 35 specimens ranged from 98 to 218 cm. Females (n = 20) measured 130-210 cm, males (n = 9) from 138 to 218 cm, and animals of unknown sex (n = 5) from 172 to 213 cm. The collections to date probably do not represent the total size range for the species. The heaviest animal (n = 5), a sexually mature female, weighed 115 kg.

III. Distribution

Peale’s dolphin is a southern South American species commonly found from 59°S (the Drake Passage south of Cape Horn) northward to Valdivia, Chile (about 38°S), on the west coast and Golfo San Jorge, Argentina (44°S), on the east, including the Falkland (Malvinas) Islands, with exceptional records to 33°S in the southeastern South Pacific and 38°S in the southwestern South Atlantic (Fig. 2). Sightings of animals similar to L. australis in 1988 near the Cook Islands, in tropical waters thousands of miles from its normal distribution, have been considered an anomalous occurrence by some authors or perhaps a new species by others.

IV. Ecology

A. Habitat

Peale’s dolphins occupy two major habitats; open coasts over shallow continental shelves to the north and deep, protected bays and channels to the south and west. In the channels, this is an “entrance animal” found in tide rips at the entrance to fjords. They often swim shoreward of or through channels in kelp beds (Macrocystis pyiifera). Although their distributions overlap, Peale’s dolphins are usually coast hugging, while the similarly pigmented dusky dolphin occurs a few miles seaward. There is no information on abundance, stocks, or population size.

B. Prey, Predators, and Parasites

Peale’s dolphins are noted for feeding in the kelp, where divers have observed them taking small octopus. They also feed in open waters beyond the kelp on fish, often using the “sunburst” formation for herding. Few stomachs have been examined (n = 16), and those only from the southwestern South Atlantic. About 20 prey taxa have been identified, mainly demersal and bottom fish, octopus, and squid species common over the continental shelf or in kelp beds.

Peale's dolphin, Lagenorhynchus australis.

Figure 1 Peale’s dolphin, Lagenorhynchus australis.

 The distribution of Peale's dolphin, based on sightings and strandings from 1839 to 1997.

Figure 2 The distribution of Peale’s dolphin, based on sightings and strandings from 1839 to 1997.  

No predators but humans are known, although killer whales and leopard seals are a possibility. Parasite fauna are under study; Anisakis simplex was present in three females.

V. Behavior

A. Migration

Near Isla Chiloe and in the Strait of Magellan, resident groups have been noted throughout the year, although more animals were present during summer. In southern Tierra del Fuego, animals also seem to move inshore during summer, possibly following fish migrations. It is not known if the dolphins in different parts of the range belong to different populations or stocks.

B. Swimming and Schooling

Peale’s dolphins are most often seen swimming slowly in or near the kelp. Dive times range from 3 to 157 sec, widi an average of 28 sec (n = 723), with three short dives followed by a longer one. They commonly bow ride, with much head movement, rolling, breaching, spy hopping and spinning. They produce a wide splash when surface swimming, earning the name “plough-share” dolphins. They associate closely with other dolphins, especially Cephalorhijnchus commersonii.

Group size is usually small, from 2 to 5 animals, but aggregations of up to 100 have been seen. Little else is known of their behavior.

C. Sounds

Pulsed sounds were recorded in the Chilean channel region, revealing broadband clicks at 5-12 kHz and narrowband clicks at 1- to 2-kHz bandwidths. Whistle-like squeals were not recorded, but may have been above the limits of the recording equipment used.

VI. Internal Anatomy

The condylobasal lengths of 27 skulls ranged from 352 to 359 mm. The number of teeth is variable, with up to 37 upper and 34 lower teeth in each jaw. The mouth is unusual in having a wide lip outside the tooth line. The vertebral count is CV7 with the first two fused, T14. L13-16. Ca 31-34 for a total of 66-70, normally 67-68. The Peale’s dolphin is larger and more robust than the other two southern Lagenorhynchus, with larger vertebrae. The phalangeal number is I = 2-3, II = 6-9, III = 5-6, IV = 2-4, V = 0-2.

Few tissues have been examined. Skin thickness was 1-2 mm, and blubber thickness was 15-25 mm. The gonads and uterus of three specimens have been described, and organ weights are known for three others. Eye pigments were reported for one animal. Residues of organochlorine contaminants were found in the blubber of one animal.

VII. Life History

A. Growth and Reproduction

There is little information on reproduction. A female of 185 cm was sexually immature, one of 193 cm was pubescent, and one of 210 cm was mature. There is no information on sexual maturity in males. Calves have been reported from spring through fall, October to April.

Physical maturity, on the basis of epiphyseal fusion, has been recorded for 24 specimens. Neonates measured 98-130 cm, juveniles 138-176 cm, subadults 142-210 cm, and adults 190-199 cm. The oldest animal was a physically mature female with 13 GLGs (growth layer groups) in the teeth.

VIII. Interactions with Humans

A. Captivity and History

No Peale’s dolphins have been kept in captivity. Prehistorically, Peale’s dolphins were exploited for food by the canoe peoples of the channels of southernmost South America; remains have been found in kitchen middens dated at 2500 and 6000 years before present. More recently, a few dolphins were taken for scientific research.

B. Fisheries

1. Chile Peale’s dolphin have been heavily exploited for crab (centolla, Lithodes antarctica) bait in southern Chile since at least the early 1970s, with highest exploitation in the 1980s. Overfishing, resulting in greatly reduced populations of crabs, has led to other types of fishing that do not need bait. The full extent of the exploitation of dolphins for crab bait at present is unknown, but is thought to be less than formerly. Although common, Peale’s dolphins are rarely taken incidentally in the northern part of their range between Valdivia and San Antonio. A few dolphins have been caught in anti-pinniped nets near the salmon pens in the Isla Chiloe area.

2. Argentina A few Peale’s dolphins were taken for crab bait in eastern Beagle Channel in the late 1970s and early 1980s, but this has not continued. A small incidental take occurs in shore-set gill nets off Tierra del Fuego, but fishermen claim that Peale’s dolphins are usually strong enough to fight and release themselves from the net. Likewise, a few Peale’s dolphins die in off-shore fishing activities south of Golfo San Jorge, but not as many as other species. The extent of this exploitation is unknown; it represents a potential danger that should be monitored.

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