Lissodelphis borealis (Peale, 1848)

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 : 523

32.

Northern Right-whale Dolphin

Lissodelphis borealis

French: Dauphin a dos lisse / German: Nordlicher Glattdelfin / Spanish: Delfin sin aleta septentrional

Other common names: \ White-bellied Right-whale Dolphin

Taxonomy. Delphinapterus borealis Peale, 1848 ,

“North Pacific Ocean, latitude 46° 6’ BO” N., 134° 5 W. from Greenwich,” 10° W of Astoria, Oregon, USA .

This species is monotypic.

Distribution. Temperate and subarctic waters of the N Pacific Ocean from ¢.30° N to c.50° N.

Descriptive notes. Total length 310 cm (males) and 230 cm (females); weight up to 115 kg. Neonates are typically 80- 100 cm long. The Northern Right-whale Dolphin has slender, torpedo-shaped body, with no dorsal fin and very shallow tailstock. Flippers and flukes are small and slim, and beak is short with broad base. Skin is mostly black, with white streak running along ventral body from throat all the way to fluke notch. This white streak widens to cover whole chest between flippers. There is small, white patch on chin, gray patches on upper flukes, and white patches on lower flukes. Young Northern Right-whale Dolphins have more muted color pattern than adults and dark areas tend to be paler gray. Some populations are characterized by a “swirl” morph; these individuals have more extensive white coloration that extends onto lower flanks and face and may swirl onto upper surface of flippers. There are 37-54 pairs of conical teeth in each jaw.

Habitat. Prefer cool, deep, offshore waters at or beyond continental shelves, but also areas where deep wateris close to a coast. Northern Right-whale Dolphins may move beyond their typical distribution as far south as Baja California and, in the north, as far as the Gulf of Alaska and the northern Sea ofJapan. They are most abundant at sea-surface temperatures of 8-9°C.

Food and Feeding. In the central North Pacific Ocean, lanternfish ( Myctophidae ) make up 89% of the diet of the Northern Right-whale Dolphin. In this area, it co-occurs with the Pacific White-sided Dolphin ( Lagenorhynchus obliquidens ), and they have similar diets, suggesting possible competition. Off southern California, lanternfish and California market squid ( Loligo opalescens) are the major prey of the Northern Rightwhale Dolphin. Other prey includes various cephalopods, hake ( Merlucciidae ), and sauries ( Scomberesocidae ).

Breeding. Little is known about the reproduction and life history of the Northern Rightwhale Dolphin. Males and females mature at c.10 years old. Breeding peaks during late summer in the central North Pacific Ocean, and females give birth to offspring roughly every two years. Gestation is ¢.12 months, and individuals may live up to 42 years.

Activity patterns. Northern Right-whale Dolphins are skittish and easily startled. Individuals are fairly active; breaching and tail slapping are commonly observed. They may occasionally bow-ride, but they usually avoid boats. While traveling, the Northern Right-whale Dolphin may swim up to 40 km/h—a feat aided by their sleek body form—and will regularly leap out of the water at shallow angles. Groups travel in Vshaped and “chorus line” formations. These groups may be tightly packed, or subgroup structure may be distinguished.

Movements, Home range and Social organization. The Northern Right-whale Dolphin is highly gregarious and lives in groups that average 100-200 individuals. Much larger aggregations of 2000-3000 individuals are not uncommon. They often associate with other species including the Pacific White-sided Dolphin, pilot whales ( Globicephala spp-), and Risso’s Dolphin ( Grampus griseus ). Throughout its distribution, the Northern Right Whale Dolphin is known to regularly migrate inshore and southward during winter, likely to keep within waters with preferred temperatures. Off southern California, abundance of Northern Right-whale Dolphinsis associated with peak occurrences of market squid.

Status and Conservation. CITES Appendix II. Classified as Least Concern on The [UCN Red List. Although high levels of incidental catch of Northern Right-whale Dolphins in high-sea driftnet fisheries during the 1970s and 1980slikely reduced their abundance, the decline has been estimated to be less than 30%, and high-sea driftnet fishing has since been banned. There are ¢.68,000 individuals across the North Pacific Ocean and 9000-21,000 individuals along the western USA. Incidental catch rates in squid fisheries from Japan, Taiwan, and South Korea in the North Pacific Ocean have been extremely high in the past. An estimated 15,000-24,000 Northern Right Whale Dolphins were killed per year in these fisheries during the 1980s, depleting the population to 24-73% of its abundance before exploitation. Although the 1993 United Nations’ moratorium on large-scale driftnets in the high seas has likely relieved some of the pressure, driftnets continue to be used inside exclusive economic zones (EEZ) of the North Pacific Ocean. Illegal high-sea fishing is also an issue, especially because incidental catch rates are unknown. Instances of entanglement of Northern Right-whale Dolphins continue to be reported in the western Pacific Ocean. They were once commonly taken as incidental catch in California driftnet fisheries for broadbill swordfish (Xiphias gladius) and common thresher shark (Alopias vulpinus). At least 386 individuals were caught in 1990-2002. Catch rates in Pacific US fisheries have dropped to only c.3-8 ind/year. The Northern Right-whale Dolphin was also taken directly in fisheries offJapan as far back as the 1950s, and it continues to be killed opportunistically, although the fisheries now tend to target other small cetaceans.

Bibliography. Carretta et al. (2004), Chou Liensiang et al. (1995), Ferrero & Walker (1993), Ferrero et al. (2002), Hammond et al. (2008t), Jefferson, Newcomer et al. (1994), Jefferson, Webber & Pitman (2008), Lipsky (2009), Mangel (1993).

Figures

On following pages: 33. Commerson’s Dolphin (Cephalorhynchus commersonii); 34. Chilean Dolphin (Cephalorhynchus eutropia); 35. Heaviside's Dolphin (Cephalorhynchus heavisidii); 36. Hector’s Dolphin (Cephalorhynchus hector).

Distribution. Temperate and subarctic waters of the N Pacific Ocean from ¢.30° N to c.50° N.