Lagenorhynchus cruciger (Quoy & Gaimard, 1824)

Russell A. Mittermeier & Don E. Wilson, 2014, Delphinidae, Handbook of the Mammals of the World – Volume 4 Sea Mammals, Barcelona: Lynx Edicions, pp. 410-526 : 490-491

4.

Hourglass Dolphin

Lagenorhynchus cruciger

French: Dauphin sablier / German: Sanduhrdelfin / Spanish: Delfin cruzado

Other common names: Sea Skunk, Springer, Wilson's Dolphin

Taxonomy. Delphinus cruciger Quoy & Gaimard, 1824 ,

“entre la Nouvelle-Hollande et le cap Horn [= between Australia and Cape Horn]...par 49 [S] de latitude,” southern Pacific Ocean.

Taxonomy of Lagenorhynchus is currently in dispute; recent molecular analyses have revealed that the genus is not monophyletic. L. australis and L. cruciger appear to be most closely related to species of Cephalorhynchus and may be reassigned to this or another genus ( Sagmatias ) in the near future. Monotypic.

Distribution. Circumpolar in subantarctic and Antarctic waters, primarily between 45° S and 65° S, but occasionally recorded N up to 33° S off Chile.

Descriptive notes. Total length 160-190 cm (males) and 140-180 cm (females); weight up to 94 kg (males) and up to 88 kg (females). Neonates are ¢.100 cm long. The Hourglass Dolphin has robust body shape with short but well-defined beak. Dorsal fin is medium-sized and characteristically hooked in shape. In some individuals, mostly adult males, dorsal fin’s leading edge is bent backward. Males also have more keeled tailstock. Back and flanks are black, and belly and throat are white. Flanks are marked by wide white streaks that extend from base of flukes, arch over upper onehalf of body, and descend along sides of head to mouth in front of eyes, converging with white lower jaw and throat. Flank streaks taper into a thin white line mid-body just below dorsal fin, creating characteristic hourglass shape. Just in front of urogenital area, white belly pigmentation intrudesslightly into black pigmentation of lower lateral tailstock in the shape of a small hook. Dorsal fin, flippers, and flukes are black on both sides. Immature individuals have less pronounced hooks in dorsal fins and have more muted color pattern. There are 26-34 pairs of slender, conical teeth in upper jaw and 27-35 pairs in lower jaw.

Habitat. Deep offshore waters, but sometimes in water less than 200 m deep around islands and banks off southern South America and the Antarctic Peninsula. The Hourglass Dolphin is the only small delphinid regularly observed south of the Antarctic Convergence. They may be observed within 160 km of the ice edge in some parts of Antarctica. In the Drake Passage, the Hourglass Dolphin seems to be most abundant at the southern boundary of the Antarctic Circumpolar Current and is often seen in areas with turbulent water. Preferred sea-surface temperatures seem to be 0-6-13°C.

Food and Feeding. The Hourglass Dolphin preys on fish, squid, and crustaceans. Preferred prey includes Myctophidae (e.g. Krefftichthys anderssoni ), hooked squid ( Onychoteuthidae ), lesser shining bobtail squid ( Semirossia tenera ), Patagonian squid ( Doryteuthis gah), and juvenile Argentine hake ( Merluccius hubbsi ). The Hourglass Dolphin is primarily a surface species. They often forage in mixed-species aggregations with other cetaceans and seabirds. They sometimes feed among plankton swarms.

Breeding. Very little is known about reproductive biology and life history of the Hourglass Dolphin. Females appear to reach sexual maturity at 180-185 cm in length, and males at 174 cm. Breeding seems to peak in January-February. Testes of mature males are large relative to body length, which may imply a promiscuous mating system and sperm competition.

Activity patterns. The Hourglass Dolphin can swim at speeds of up to 22 km/h. They have been known to bow-ride and surf in stern wakes, and they are attracted to large ships. They may approach such ships even from long distances and remain with them for up to 30 minutes. The Hourglass Dolphin is also known to surf in high-sea waves. They can be acrobatic when leaping, sometimes spinning on their longitudinal axes. When traveling, they may also leap at long, low angles in a fashion similar to swimming penguins. Vocalizations are narrow-banded and high frequency, characteristic of species of Cephalorhynchus —perhaps suggesting a close evolutionary relationship between the Hourglass Dolphin and this genus.

Movements, Home range and Social organization. Group sizes of Hourglass Dolphins are usually 1-14 individuals, but groups of up to 100 individuals have been observed. These are unusually small groups sizes for an oceanic delphinid. The Hourglass Dolphin often associates with the Fin Whale (Balaenoptera physalus), the Sei Whale ( Balaenoptera borealis ), the Southern Bottlenose Whale (Hyperoodon planifrons), Arnoux’s Beaked Whale (Berardius arnuxii), the Killer Whale ( Orcinus orca ), the Long-finned Pilot Whale ( Globicephala melas ), and the Southern Right-whale Dolphin ( Lissodelphis peronii ). There are currently no documented migrations, but in some areas, there may be seasonal north-south shifts. For example, abundance of Hourglass Dolphins around the Falkland Islands appears to decrease during winter (July-August), which may reflect movement into near-shore and subantarctic waters.

Status and Conservation. CITES Appendix II. Classified as Least Concern on The [UCN Red List. Abundance of the Hourglass Dolphin is ¢.144,300 individuals south of the Antarctic Convergence. There is no known systematic exploitation of the Hourglass Dolphin. There are few reports of incidental catches, and it has never been taken for captivity. Overall, there are no known major threats to the Hourglass Dolphin.

Bibliography. Brownell & Donahue (1999), Fernandez et al. (2003), Goodall (2009b), Hammond et al. (2008d), Jefferson et al. (2008), LeDuc et al. (1999), May-Collado & Agnarsson (2006), Santora (2012), Tougaard & Kyhn (2010).

Figures

On following pages: 3. Peale’s Dolphin (Lagenorhynchus australis); 4. Hourglass Dolphin (Lagenorhynchus crucigen; 5. Pacific White-sided Dolphin (Lagenorhynchus obliquidens); 6. Dusky Dolphin (Lagenorhynchus obscurus); 7. Irrawaddy Dolphin (Orcaella brevirostris); 8. Australian Snubfin Dolphin (Orcaella heinsohni).

Distribution. Circumpolar in subantarctic and Antarctic waters, primarily between 45° S and 65° S, but occasionally recorded N up to 33° S off Chile.