Author: Phillipps, 1932
A white-spotted Mustelus with a broad internarial space, long upper labial furrows, dorsal fin margins not frayed, relatively large pectoral and pelvic fins, buccophryngeal denticles confined to anterior end of mouth, and 87 to 95 precaudal centra. It is the only species of Mustelus in New Zealand waters.
Body fairly slender. Head short, prepectoral length 17 to 21% of total length; snout moderately long and bluntly angular in lateral view, preoral snout 5.9 to 7.3% of total length, preorbital snout 6.6 to 8.2% of total length; internarial space moderate, 2.4 to 2.9% of total length; eyes fairly large, eye length 1.8 to 3.2 times in preorbital snout and 2.4 to 4.4% of total length; interorbital space fairly broad, 4.1 to 5.2% of total length; mouth short, subequal to eye length and 2.6 to 3.5% of total length; upper labial furrows considerably longer than lowers, upper furrows 1.9 to 2.9% of total length; teeth molariform and asymmetric, with cusp reduced to a low point; condition of buccopharyngeal denticles unknown. Interdorsal space 18 to 24% of total length; trailing edges of dorsal fins denticulate, without bare ceratotrichia; first dorsal broadly triangular, with posteroventrally sloping posterior margin, its midbase closer to pelvic bases than to pectorals; pectoral fins fairly large and broad, length of anterior margins 12 to 16% of total length, width of posterior margin 8.7 to 17% of total length; pelvic fins moderately large, anterior margin length 7.2 to 8.7% of total length; anal height 2.7 to 4.3% of total length; anal-caudal space somewhat greater than second dorsal height, 6.5 to 8.7% of total length; ventral caudal lobe not strongly falcate in adults. Crowns of lateral trunk denticles lanceolate, with longitudinal ridges possibly extending their entire length. Skeleton not hypercalcified in adults; palatoquadrates not subdivided; monospondylous precaudal centra 35 to 41, diplospondylous precaudal centra 50 to 56, precaudal centra 87 to 95. Colour grey or grey-brown, above, light below, usually with numerous white spots but lacking dark spots or dark bars. Development ovoviviparous. Size large, adults 78 to 137 cm.
Western South Pacific: New Zealand.
Habitat and Biology:
A common, temperate bottom-dwelling shark of the New Zealand insular shelves, often found close inshore but ranging to 220 m depth. It has seasonal inshore-offshore movements, retreating into deeper water in winter, as well as shorewise movements. A schooling species, with separation by size and sex: immatures form schools separate from the largely unisexual schools of adults. On the fishing grounds sex ratios of adults change as the fishing season, from September to April, progresses.
Ovoviviparous, without a placenta, number of young 2 to 23 per litter, with larger females having larger numbers of young. The sex ratio of embryos is virtually 1:1. The gestation period is about 11 months, and the period of ovulation may exceed six months. Birth is thought to occur offshore, in summer, after which time females come inshore to mate, and travel to summer feeding grounds where adults and juveniles feed heavily on bottom crustaceans. In autumn, these sharks begin to migrate back into deeper water. This may be a fast-growing species, maturing between two to four years after birth (Francis, 1981), but this needs to be confirmed by direct ageing methods such as calibrating vertebral rings.
Eats crustaceans, especially crabs.
Maximum about 137 cm; males maturing at about 78 to 89 cm and reaching about 115 cm; females maturing at about 79 to 113 cm and reaching 137 cm; size at birth about 30 to 32 cm.
Interest to Fisheries:
A shark of considerable commercial importance, comprising nearly 5% by weight of New Zealand fish landings in 1978. Commercial fisheries currently catch most of their "rig" (a South Island name for this shark) with gillnets and trawls. Utilized fresh for human consumption. Commonly taken by sports anglers with rod and reel.
Heemstra (1973) determined that all New Zealand smooth-hounds belong to one ovoviviparous species. This is particularly close to the Australian M. antarcticus, but differs in having more precaudal vertebrae and slightly larger pelvic fins.
Holotype: National Museum of New Zealand (Dominion Museum). Type locality: Wellington Harbor, Wellington, New Zealand.