Cephalorhynchus hectori

Hector's Dolphin

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Hector's Dolphin Hector's Dolphin

 

Description

Hector's dolphin, one of the rarest and smallest of marine dolphins, has a short, stocky torpedo-shaped body, which becomes narrow towards the tail. The beak is short and the rounded snout lacks a melon. The sides and back are light grey, there is a darker stripe along the middle, and the underside is whitish. The large tail flukes, flippers and characteristically rounded dorsal fin are all black. A black marking extends from the snout back around the eye reaching to the flipper. Males and females are generally similar in appearance, but females tend to be slightly longer than males. Calves have the same markings as adults but pale lines can be seen on darker areas, and the underside has a yellowish tint. The common name of this dolphin refers to the New Zealand zoologist Sir James Hector, who first collected the species in 1869.

Geography

Hector’s dolphin is endemic to New Zealand, and it has one of the most restricted distributions of any cetacean (Dawson and Slooten 1988; Dawson 2002). They are most common off the South Island and the west coast of the North Island. There are at least three genetically separate populations in the South Island, and a single small North Island population (C. h. maui - Baker et al. 2002).

Ecosystem

The habits and biology of Hector's dolphin have been well studied in the last couple of decades, and this is undoubtedly the best-known species of the genus (Dawson 2002). It is found in shallow coastal waters, almost always within about 15 km of shore and <100 m deep, strongly concentrated in shallow, turbid waters close to shore in summer months and dispersing more widely in winter (Slooten et al. 2006a). Photo-identification studies have demonstrated that at least some individuals are resident in small areas (about 30 km of coastline) year-round (Slooten et al. 1993). No two sightings of an individual have been more than 106 km apart (Bräger et al. 2002).

Hector's dolphins feed on several species of small fish and squid (Dawson 2002). The diet is more varied on the east coast of the South Island (8 species make up 80% of the diet) than on the west coast (only 4 species make up 80%).

Conservation

This species is considered to be Endangered A4d due to an ongoing and projected decline of greater than 50% over 3 generations (approx. 39 years, Slooten et al. 2000) considering both the past and the future. It is also important to consider that although its extent of occurrence and area of occupancy likely exceed the thresholds for criteria B1, B2 and D2, Hector’s dolphin has the most limited range of any marine cetacean other than the vaquita (Phocoena sinus). In a population viability analysis, the estimated rate of decline was 74% over 3 generations where the time period under consideration was from 1970-2009 (Slooten 2007). The main cause of population decline is ongoing bycatch in fisheries.

 

Threats

Hector’s dolphin faces serious pressures from human activities given its limited coastal distribution. The main threat to the species in general is entanglement in gillnets (Dawson 1991; Slooten and Lad 1991; Dawson and Slooten 1993; Martien et al. 1999; Secchi 2006; Slooten 2007; DOC and Mfish 2007), with trawl fisheries also causing some mortality. Amateur gillnetting (as opposed to commercial gillnetting) is a significant part of the problem (Dawson and Slooten 2005). Sixty percent of all dead Hector’s dolphins for which cause of death could be determined, had died as a result of gillnet entanglement (DOC and Mfish 2007). Risk analyses for Hector’s and Maui’s dolphins indicate that recent levels of mortality are unsustainable (Slooten and Lad 1991; Martien et al. 1999; Slooten et al. 2000; Burkhart and Slooten 2003; Slooten 2007; DOC and Mfish 2007). This conclusion is robust to the uncertainty in abundance, mortality, and vital rates (Slooten et al. 2000; Slooten 2007). The most recent population viability analysis indicates continued population declines (Slooten 2007). Additional threats include pollution, disease, vessel traffic, and habitat modification (Stone and Yoshinaga 2000).

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