Carcharhinus sealei subgroup

Carcharhinus coatesi (Whitley, 1939) is herein resurrected as a valid species of Carcharhinus occurring in northern Australia and possibly New Guinea. Although this species was previously considered to be C. dussumieri (Stevens & McLoughlin, 1991; Last & Stevens, 1994, 2009), it is closest to C. sealei of the Indo-West Pacific. Garrick (1982) in his extensive revision of the genus Carcharhinus considered this species as C. sealei, but he stated several morphological and meristic features that differed. However, Garrick only had one Australian specimen, the holotype, and in the absence of more material was unable to further assess these differences. Carcharhinus coatesi is morphologically very similar to C. sealei, but they can be distinguished by a combination of morphometric, meristic and colouration.

Carcharhinus coatesi can be most readily distinguished from C. sealei in vertebral counts, i.e. caudal vertebrae 64–73 vs. 74–81 and total vertebrae 134–147 vs. 146–163 (Table 3). Second dorsal fin colouration is also a strong differentiating character between these two species. In C. coatesi, the black apical blotch on the second dorsal fin covers the upper third to two thirds of the fin (vs. most of fin black in C. sealei), has a well defined lower edge (vs. a diffuse edge, often poorly defined from ground fin colour) and does not extend onto upper surface of the body below fin base (vs. often extending slightly onto sides below fin base). Carcharhinus coatesi also usually possesses a moderate interdorsal ridge although sometimes weak, while C. sealei usually lacks an interdorsal ridge and if present then very weak. Garrick (1982) reported that the holotype of C. coatesi possessed a wider mouth, more like C. dussumieri, than C. sealei . However, between the specimens examined in this study, there was only a slight mean difference in mouth width (6.7 vs. 7.0% TL) with considerable overlap in the ranges, i.e. 6.4–7.9 vs. 6.3– 7.0% TL. It should be noted that while this is not a consistently strong character, it is clear that C. coatesi generally has a wider mouth than C. sealei . These species did differ in length of the preventral caudal margin, 10.3–12.1 (mean 11.4) in C. coatesi vs. 11.9–13.3 (mean 12.6)% TL in C. sealei .

Since the two species are very similar morphologically, it is important to compare similar-sized specimens with each other rather than the whole size range, especially since most C. coatesi measured were large specimens (mean 680 mm TL) and most C. sealei were small (mean 527 mm TL). When comparing individuals of C. coatesi and C. sealei that were less than 600 mm TL (n = 9 for both species), a number of morphological differences were found, including: head longer in C. coatesi (direct head length 21.6–23.1 vs. 19.6–21.7% TL, prebranchial length 17.5–19.3 vs. 15.6–17.9% TL), snout longer (horizontal preorbital length 7.0–7.9 vs. 5.6–7.0% TL, preoral length 6.7–7.7 vs. 5.9–6.5% TL, direct prenarial length 5.0–5.7 vs. 3.9–4.7% TL), slightly greater interorbital width (8.7– 10.4 vs. 7.8–9.1% TL) and internarial space (4.5–5.1 vs. 3.7–4.4% TL), and a slightly longer mouth (4.6–5.3 vs. 3.8–4.7% TL).

Comparisons of larger specimens of C. coatesi and C. sealei was difficult due to the lack of adult specimens of C. sealei and only a few above 600 mm TL (n = 11 vs. 3), thus the differences listed below need to bear this in mind. In larger specimens (> 600 mm TL), the following morphometric differences were found: prepectoral length 19.3–20.5 vs. 18.2–18.6% TL, prevent length 46.4–50.4 vs. 45.6–46.3% TL, interorbital space 8.5–9.3 vs. 7.6– 8.3% TL, second dorsal-fin height 2.9–3.4 vs. 3.3–3.8% TL, and preventral caudal margin 10.3–12.1 vs. 12.2– 13.0% TL.