Bathyraja interrupta ( Gill & Townsend, 1897 )

Knuckey, James D. S. & Ebert, David A., 2022, A taxonomic revision of Northeast Pacific softnose skates (Rajiformes: Arhynchobatidae: Bathyraja Ishiyama), Zootaxa 5142 (1), pp. 1-89 : 20-25

Bathyraja interrupta ( Gill & Townsend, 1897)

Figures 11–13 ; Tables 3 , 8–9

Bering Skate

Raja interrupta Gill & Townsend, 1897: 232 [Proceedings of the Biological Society of Washington] v. 11. Lectotype: USNM 48760 (1, poor condition; designated herein). Paralectotype: USNM 48761 (1).

Raja interrupta: Gill & Townsend, 1897: 232 ; Jordan & Evermann, 1898: 2751 (compiled); Jordan & Gilbert, 1899 (listed): Berg, 1911: 96 (description, key); Garman, 1913: 345 (compiled); Fowler, 1930: 502 (listed); Jordan et al., 1930: 26 (listed); Soldatov & Lindberg, 1930: 22 (compiled); Taranetz, 1937: 51 (key); Fowler, 1941: 394 (compiled); Quast & Hall, 1972: 4 (listed); Ricker, 1973: 228 (listed); Robins et al., 1980 (listed).

Breviraja interrupta: Lindberg & Legeza, 1959: 130 , fig. 82 (compiled); Uyeno, 1965: 417 (reference); Okada & Kobayashi, 1968: 41 (description); Uyeno, 1971: 70 (listed).

Rhinoraja interrupta: Raschi & McEachran, 1991: 1902 ; Dolganov, 1999: 429; Compagno, 1999: 489 (listed); Sheiko & Fedorov, 2000: 15; Hoff, 2002: 145; Orlov, 2003: 45.

Bathyraja interrupta: Garrick & Paul, 1974: 361 ; table 5 (reference); Ishiyama & lshihara, 1977: 88, table 5 (comparison); Stehmann, 1986: 263; McAllister, 1990: 34 (listed); McEachran & Dunn, 1998: 286 (listed); Mecklenburg et al., 2002: 100 (listed); Nelson et al., 2004: 55 (listed); Spies et al., 2011: 80; Page et al., 2013: 55 (listed); Parin et al., 2014: 31 (listed); Dyldin, 2015: 63 (listed); Pietsch & Orr, 2015: 17 (listed); Weigmann, 2016: 92 (listed); Last et al., 2016: 25, 386 (figure, listed); Kells et al., 2016: 78 (figure); Ebert et al., 2017: 21, 58, 67 (description, distribution, key, listed); Ehemann et al., 2018: 24 (listed).

Diagnosis. Moderately-sized skates (825 mm TL), disc length (47.7–54.0% TL), Head length moderate (18.4– 21.4% TL), posterior lobe of pelvic fins long (10.4–23.4% TL); claspers long and robust, tip rounded and not bulbous, pseudosiphon absent, possesses a weak, but long pseudorhipidion, U-shaped cleft, projection rounded and protrudes from tip, has a very large sentina, sentinel present; teeth in 22–32 and 23–32 rows on upper and lower jaw, respectively; total vertebrae 133; dorsal surface covered in small, sandpaper-like prickles; thorns present in a noncontinuous row, mature males with strong alar thorns, malar thorns absent, middorsal thorns strong (1–8), nuchal thorns robust (2–5), tail thorns moderate (18–26), interdorsal thorns weak (0–1); dorsal coloration brown to grey, with numerous small dark spots on body; ventral coloration white, often with dark brown blotches on underside of tail.

Description. A medium-sized skate with a rhomboidal disc, 1.2–1.3 times as broad as long; anterior margin strongly concave in adult males, convex beside and just forward of eyes; apex rounded; posterior margin slightly convex; free rear tip broadly rounded. Head length moderate 18.4–21.4% TL; preorbital snout length 10.5–14.6% TL; preoral length 10.5–13.4% TL. Snout tip triangular and rounded, possessing no fleshy process at apex. A flat to moderately concave area between the eyes; interorbital width short 2.5–5.1% TL. Spiracle length 1.9–3.2% TL, oval shaped; interspiracular space short 5.5–6.8% TL; mouth width short 6.7–9.0% TL. Nasal curtain length 2.9–6.6% TL, its posterior margin fringed at the corners; anterior margin of curtain lobe-like. Internarial distance 3.2–7.4% TL. Upper jaw moderately well arched, possessing a symphysis; lower jaw convex. Teeth similar in both jaws; teeth unicuspid, with a strong, bluntly pointed posteriorly directed cusp; arranged in longitudinal rows; upper teeth and lower teeth relatively low in number (22–32 and 23–32, respectively).

Pelvic fins large overall; anterior lobe 7.7–11.6% TL, posterior lobe very large 10.4–23.4% TL and similar between sexes and maturities, inner margin deeply incised. Tail length 39.4–60.2% TL, relatively short and stout; wider at base, tapering to the first dorsal fin origin, not expanded in the middle. Precaudal length short 44.5–51.1% TL. Dorsal fins moderate in size and shape, the first dorsal fin displays a wider range than second dorsal fin, 1.7–5.2% TL and 2.1–2.9% TL, respectively; bases of both dorsal fins similar in size and length, 3.8–5.2% TL and 3.4–4.6% TL, respectively; anterior margins of both fins concave, apices rounded; free rear tip rounded; interdorsal space relatively short 0.2–1.8% TL, with larger individuals having a shorter interdorsal space, rear tip of first dorsal fin not overlapping base of second dorsal fin. Caudal fin height 0.6–1.1% TL; its dorsal margin weakly concave; not connected to second dorsal fin by a small membranous ridge.

Dorsal surface covered in uniform, small, sandpaper-like prickles. Scapular, middorsal, nuchal, interdorsal, and tail thorns present, males with a well-developed set of alar thorns; malar thorns absent; thorns vary slightly in size, from short to well-developed. Middorsal thorns range from low to high in number (1–8); nuchal thorns well-developed and average in number (2–5); tail thorns moderate in number (18–26); scapular thorns absent in some specimens and present in others (0–2); interdorsal thorns weakly developed (0–1). Thorns in a single, noncontinuous row; no multiple rows of thorns on body. Alar thorn patches range between 4–6 rows and 8–22 columns on both pectoral fins.

Mature claspers relatively long and robust, base length 1.8–2.8% TL, inner length 25.5–26.0% TL, tip of clasper rounded and not bulbous ( Figure 14 ). Clasper inner length 46.5–47.0% of tail length; pseudosiphon is absent; inner surface of dorsal lobe with a relatively weak, but long pseudorhipidion and a U-shaped cleft; inner surface of ventral lobe possesses a rounded projection that conspicuously protrudes from the tip of the clasper; a very large sentina; sentinel present; clasper relatively robust overall.

Clasper skeleton consists of 3 dorsal terminal, 1 accessory terminal, ventral terminal and axial cartilages; dorsal terminal 1 shaped like a long, rounded leaf, and possessing a long shaft; unlike most bathyrajids in the ENP the dorsal terminal 1 does not form an external pseudosiphon; the tip of the dorsal marginal is pointed, and forms a long, thin pseudorhipidion externally; ventral terminal curved, possessing a blunt tip that forms the exposed projection; accessory terminal 1 nearly as long as the ventral terminal; tip of accessory terminal 1 is rounded; very large sentina located above the projection; sentinel present next to the sentina.

Dermal denticles possess 3–5 base points and are moderately developed on the posterior third of the dorsal surface; denticles on the first dorsal fin not curved, posterior-oriented, found in low densities across surface ( Figure 15 ).

Length of rostral cartilage 46.6% of cranial length; prefontanelle rostral length 47.2%; cranial width 78.9%; least interorbital width 20.1%; length of anterior prefontanelle 19.5%; length of posterior prefontanelle 26.5%; length of rostral appendices 18.9%. Rostral cartilage nearly straight; fontanelles rectangular in shape; the posterior fontanelle larger ( Figure 16 ).

Coloration. Dorsal coloration dark brown to brown grey, with numerous small dark spots on body. Snout and edges of fins usually darker than the rest of the body. Ventral coloration white, usually with small to large dark brown blotches on underside of tail. Coloration after preservation is similar to fresh specimens; however, the dark spots on dorsal surface tend to disappear.

Egg case description. Egg cases small (78–79 mm TL), golden brown in color, and covered with small, coarse prickles that form longitudinal rows. Cases possess lateral keels that are very wide. Horns taper and become thin and filamentous at their ends, with the anterior horn being more robust ( Ebert, 2005).

Distribution. Bathyraja interrupta has been confirmed as occurring in the eastern North Pacific, specifically from the Bering Sea, Alaska south to British Columbia, Canada ( Kyne et al. 2012). This species is most common on the continental shelf-slope break at around 200–500 m, but is possibly found down to 1,372 m ( Mecklenburg et al., 2002, Bizzarro et al., 2014).

Biological notes. Size at maturity for males is 69–70 cm TL and 71–72 cm TL for females, with a maximum size of at least 89 cm TL ( Ainsley, 2009; Ainsley et al., 2014). The age of maturity was found to be 62 cm for males and 61for females ( Bizzarro & Vaughn, 2009). As with other skates, B. interrupta are a late maturing species ( Ainsley et al., 2011). The species feeds on benthic invertebrates, including euphausiids, crabs, and various shrimps (e.g., pandalids, hippolytids, crangonids) and bony fishes ( Brown, 2010).

Habitat. Inhabits deep waters, on the outer continental shelf and upper slope, often being found on fine sediment ( Ebert, 2003).

Etymology. The species name comes from the interrupted row of thorns down the middorsal and tail.

Comparisons. Bathyraja interrupta is a medium-bodied skate that can be separated relatively easily from its congeners based on coloration, size, thorn counts, and distribution. Bathyraja abyssicola , B. aleutica , B. spinosissima and B. trachura all display markedly different colorations. Bathyraja microtrachys has a geographic range that is much further south and does not possess middorsal, nuchal, and scapular thorns, whereas B. interrupta does. Posterior pelvic lobe significantly longer than all of its congeners (F 6,104 = 25.5, p <0.0001). Additionally, precaudal length significantly shorter than its conspecifics (F 6,104 = 86.7, p <0.0001).

Bathyraja interrupta is very closely related to B. kincaidii , which is a smaller-bodied species found in a more southern geographic range than B. interrupta . The two species may form a larger species complex that ranges from northern Mexico to the Bering Sea.

Bathyraja interrupta differs from its congener in that it possesses a shorter interdorsal space than B. kincaidii (0.2–1.8% TL and 0.6–3.3% TL, respectively). The pelvic fins are a useful separator of the two species, as B. interrupta has a much larger posterior lobe length (10.4–23.4% TL) and inner anterior pelvic lobe length (2.7– 9.3% TL) than B. kincaidii does (8.1–14.9% TL and 5.5–8.5% TL, respectively). The mature claspers of both species differ, as B. interrupta has more robust, stockier claspers than B. kincaidii . Furthermore, B. interrupta has a pointed projection that conspicuously protrudes out past the tip of the clasper, whereas B. kincaidii has a rounded projection that does not protrude past the tip. The cleft of B. interrupta is V-shaped and the cleft is U-shaped and curved in B. kincaidii . The sentina on the mature clasper is very large in B. interrupta , but average in B. kincaidii .

Remarks. Bathyraja interrupta is one of the most common skate species in its range. It occurs in two of the largest marine ecosystems in Alaska, the Eastern Bering Sea and the Gulf of Alaska ( Ainsley et al., 2011). It is included in this study due to its relationship with B. kincaidii , in that the two may form a species complex. Nursery regions have been identified for this species on the upper continental slope in the eastern Bering Sea ( Hoff 2010). The species has been shown to exhibit hermaphroditism, with a hermaphroditic specimen being collected in the Gulf of Alaska ( Haas & Ebert, 2008).

Figures

FIGURE 11. Bathyraja interrupta, PSRC BSPP-A 01, 710 mm TL, mature male, dorsal view, fresh. Photo by Diane Haas (MLML). Scale bar = 70 mm.

FIGURE 12. Bathyraja interrupta, PSRC BSPP-A 01, 710 mm TL, mature male, ventral view, fresh. Photo by Diane Haas (MLML). Scale bar = 70 mm.

FIGURE 13. Bathyraja interrupta, lectotype, USNM 48760, mature male, ventral view, preserved. Photo by D.A. Ebert.

FIGURE 14. Components of the clasper for Bathyraja interrupta, UW 046450-2, 768 mm TL, mature male. CL- cleft, PJ- projection, PR- pseudorhipidion, SN- sentina, ST- sentinel. Photo by J.D.S. Knuckey.

FIGURE 15. Scanning electron microscope images of the dermal denticles of Bathyraja interrupta, UW 046450-2, 768 mm TL, mature male, from A. the first dorsal fin and B. the head region, behind the eyes. Photos by Justin Cordova (MLML).

FIGURE 16. Ventral view X-radiograph of Bathyraja interrupta, CAS 243647, mature male. X-radiograph by Jon Fong (CAS).

Tables

TABLE 3. Morphometrics for Bathyraja interrupta expressed as % of total length (n = 16).

Total length (mm)	289–768
Disc length (%)	47.7–54.0
Disc width	61.2–67.0
Snout to maximum disc width	28.1–33.6
Head length	18.4–21.4
Preorbital snout length	10.5–14.6
Interorbital width	2.5–5.1
Spiracle length	1.9–3.2
Interspiracular width	5.5–6.8
D1 origin to tail tip	10.1–16.0
D1 base length	3.8–5.2
D1 vertical height	1.7–5.2
D2 base length	3.4–4.6
D2 vertical height	2.1–2.9
Interdorsal space	0.2–1.8
Caudal base length	1.9–4.2
Caudal vertical height	0.6–1.1
Lateral tail fold length	16.6
Preoral snout length	10.5–13.4
Mouth width	6.7–9.0
Prenarial snout length	8.5–11.8
Internarial width	3.2–7.4
Nasal curtain length	2.9–6.6
Snout to 1st gill slit	17.7–21.4
Pelvic posterior lobe length	10.4–23.4
Pelvic anterior lobe length	7.7–11.6
Inner anterior lobe length	2.7–9.3
Clasper inner length	5.5–26.0
Clasper outer length	2.8–17.7
Clasper base length	1.0–2.8
Precaudal length	44.5–51.1
Tail length	39.4–60.2