Squalus hawaiiensis, Daly-Engel, Toby S., Koch, Amber, Anderson, James M., Cotton, Charles F. & rubbs, R. Dean, 2018

Daly-Engel, Toby S., Koch, Amber, Anderson, James M., Cotton, Charles F. & rubbs, R. Dean, 2018, Description of a new deep-water dogfish shark from Hawaii, with comments on the Squalusmitsukurii species complex in the West Pacific, ZooKeys 798, pp. 135-157 : 135

Squalus hawaiiensis sp. n.

Diagnosis.

A large species of Squalus of the ' mitsukurii group’ with the following combination of characters: body relatively slender, trunk height 8.7-12.4% TL (mean 10.1% TL, n=8; Figure 3); snout is angular and short to moderate in length, mouth width 1.35-1.60 (1.48) times horizontal prenarial length and pre-oral length is 1.92-2.06 (1.97) times the prenarial length (Figure 4); pre-first dorsal length 30.3-31.5 (30.2)% TL; pre-second dorsal length 63.6-67.0 (65.5)% TL; interdorsal space 26.7-30.0 (28.6)% TL; pelvic-caudal space 25.2-29.3 (27.1)% TL; relatively small, upright dorsal fins; first dorsal fin length 11.4-12.8 (12.2)% TL, height 6.5-7.8 (7.3)% TL, inner margin length 4.9-5.7 (5.4)%% TL; second dorsal fin length 10.6-11.7 (11.1)% TL, height 4.0-4.6 (4.4)% TL, inner margin length 4.3-4.9 (4.6)% TL; first dorsal fin spine length 46.6-64.6 (55.6)% of first dorsal fin height; second dorsal spine length 104.5-114.5 (109.0)% of second dorsal fin height; caudal bar triangular, extending from the caudal fork nearly to the anterior edge of the lower caudal, distinct upper caudal blotch and fringe in juveniles, upper caudal blotch diffuse in adults but extending to the posterior margin of the upper caudal fin, upper and lower caudal fins white tipped; flank denticles tricuspid (Figure 5 A–C); teeth are similar in appearance in the upper and lower jaw, with numbers ranging from 26-28 in the upper jaw and 23 in the lower jaw; 41-45 monospondylous centra, 85-89 precaudal centra, 112-116 total centra; adult maximum size at least 101 cm TL.

Description.

Morphometric data are provided in Table 3. Squalus hawaiiensis sp. n. is a relatively large dogfish shark with a fusiform body, a relatively short snout, and small dorsal fins. The nape is modestly humped over the pectoral fins, particularly in large females. Head length is 21.4-23.9% TL. The snout is relatively short but angular and relatively pointed in dorsal view, with a pre-narial length that is 49-52% of the pre-oral length and 1.06-1.31 times eye length. Pre-oral length is 2.04-2.42 times the internarial space. Pre-vent length is 50.4-53.6% of the TL. Mouth width is 0.69-0.83 times the pre-oral length. Eye is large (3.9-4.9% of TL) and strongly notched posteriorly. Upper and lower labial furrows pronounced. Upper labial furrow length 1.9-2.5% TL, 24.9-33.0% of mouth width, and 19.3-24.7% of pre-oral length. Inner nostril labial furrow space is 1.89-2.27 times labial furrow length. Pre-first dorsal fin length is 30.3-31.5% of TL, pre-second dorsal space is 63.6-67.0% of TL and the interdorsal space ranges from 26.7% to 30.0% of TL. The first dorsal fin is rounded at the apex. First dorsal fin length measures 1.62-1.81 times first dorsal fin height. First dorsal fin length is 1.02-1.16 times second dorsal fin length and the height of the first dorsal fin is 1.57-1.80 times the height of the second dorsal fin. Second dorsal fin length 2.36-2.79 times the second dorsal fin height. Dorsal fin spines are stout, with the spine on the second dorsal fin typically longer (4.1-5.0%TL) than the spine on the first dorsal fin (3.6-4.6%TL). First dorsal spine length is 0.39-0.65 (mean: 0.53%) times the first dorsal fin height. Second dorsal spine length is 0.84-1.15 (mean: 1.04%) times the second dorsal fin height. The pectoral fins are well developed with an anterior margin that is 12.8-16.0% of the TL. The pectoral inner margin is 6.4-7.4% of total length and free rear tip is rounded (Figure 6 A–C).

Squalus hawaiiensis is morphologically similar to other species in the " mitsukurii " group. It is distinguished morphologically by a very long inter-dorsal space which ranges from 26.7% to 30.0% of TL compared to 18.7-25.5% in Squalus mitsukurii ( Last et al. 2007a) and 23.5-24.6% in Squalus formosus ( White and Iglésias 2011), both from Taiwan and southern Japan, and to 23.5-25.6 in S. edmundsi , 20.6-23.8% in S. grahami ( White et al. 2007), 21.7-25.9% in S. montalbani ( Last et al. 2007b), all from Australia and 22.6-26.0% in S. griffini ( Duffy and Last 2007) from New Zealand, but overlaps with S. chloroculus (23.7-27.5%) from Australia ( Last et al. 2007b), S. nasutus (24.4-28.0%) from Australia, Indonesia, and the Philippines ( Last et al. 2007a) and S. japonicus from Japan (28.0-29.5%TL) ( Chen et al. 1979). Squalus hawaiiensis is further distinguished from S. mitsukurii by having smaller first and second dorsal fin lengths and anterior margins and a longer body or torso (longer pre-caudal and pre-second dorsal lengths but shorter dorsal caudal margin; Table 3). The longer torso is reflected in differences in the ranges of the following ratios between S. mitsukurii type specimens (reported in Last et al. 2007) and all S. mitsukurii measured here (N=8): pre-first dorsal length 1.45-1.73 vs. 1.01-1.16 times interdorsal space; prepectoral length 1.09-1.28 vs. 0.74-0.86 times interdorsal space; prepectoral length 1.02-1.07 vs. 0.78-0.89 times pelvic-caudal space. Based on data from Chen et al. (1979), S. mitsukurii has higher vertebral meristic counts (45-51 monospondylous centra, 87-93 precaudal centra, 118-127 total centra) than S. hawaiiensis (41-45 monospondylous centra, 85-89 precaudal centra, 112-116 total centra). Squalus chloroculus has a caudal bar that extends much higher on the upper caudal fin and lacks the upper caudal blotch characteristic of S. hawaiiensis (Figure 7 A–C). Squalus chloroculus also has much shorter first dorsal fin spines (2.3-3.3%TL) and second dorsal fin spines (2.5-3.9%TL) than S. hawaiiensis . Squalus nasutus has a much longer snout with pre-narial lengths of 5.9-7.5%TL and pre-oral lengths of 11.1-12.7%TL compared to 4.8-5.4%TL and 9.6-10.4%TL respectively for S. hawaiiensis . Based on the morphometrics from Chen et al. (1979), the closely related S. japonicus differs from S. hawaiiensis in having a smaller mouth (6.4-6.9%TL compared to 7.0-8.1%TL) and shorter first and second dorsal fin lengths. First dorsal fin length in S. japonicus is 10.1-11.0%TL compared to 11.4-12.8%TL in S. hawaiiensis . Second dorsal fin length is 7.9-8.4%TL S. japonicus compared to 10.6-11.7%TL in S. hawaiiensis .

Color. In life (based on many captured specimens): dorsal surface uniformly dark gray to brown, light gray to white ventrally. Dorsal fins uniformly gray to brown with think black tips that narrow with age, free rear tips slightly paler. Caudal fin mostly dusky with a broken white trailing edge, dark caudal bar triangular, extending from the caudal fork nearly to the anterior edge of the lower caudal (Figure 8 A–B). Upper caudal blotch diffuse in adults, extending to a short length of the posterior margin of the upper caudal fin, upper and lower caudal fins white tipped; pectoral and pelvic fins greyish dorsally, darker in the middle and with well-defined white posterior margin; Juveniles with much more pronounced fin markings; dorsal fins with black fringes, dark blotch in pectoral fins, caudal bar distinct on lower caudal from the fork to the anterior edge, well-defined and separated black upper caudal blotch and upper caudal fringe with upper caudal blotch not reaching the posterior margin of the upper caudal fin. In juvenile S. mitsukurii the upper caudal blotch is smaller and indistinct from the upper caudal fringe and the caudal bar is diagonal rather than triangular and does not reach the posterior edge of the lower caudal fin. In preservative: holotype similar, dark markings on fins faint but evident; caudal bar faint; broad, pale posterior margins on pectoral and pelvic fins well-defined. Eyes bright green in life (Figure 8C).

Size. Based on 197 Hawaii specimens surveyed, 156 females and 41 males ( Daly-Engel et al. 2010; Cotton et al. 2011), the maximum observed length of females and males was 101 cm TL and 78 cm TL respectively. Cotton et al. (2011) reported that females reach maturity at ~64 cm TL and males reach maturity at ~47 cm TL.

Etymology. Derived from the type locality in the Hawaiian Archipelago

Vernacular. Hawaiian Spurdog