This thesis provides new information on the biology of five benthic elasmobranch species caught as bycatch in northern Australia (NAS – Gulf of Carpentaria, Arafura Sea) and north-east Australia (QTS – East Coast of Queensland and the Torres Strait); and a taxonomic review of butterfly rays (Myliobatiformes: Gymnuridae) in the Indo-West Pacific. This study also provides a description of a new catshark species, Atelomycterus marnkalha n. sp. (Carcharhiniformes: Scyliorhinidae) from north-east Australia. The primary objective of the biological analysis was to examine the life history parameters of each species including their diet, reproduction and age and growth. Species incorporated into the biological analysis included the Painted Maskray Dasyatis leylandi, the Blue Spotted Maskray D. kuhlii, the Plain Maskray
D. annotata, the Black Spotted Whipray Himantura toshi and the Australian Butterfly Ray Gymnura australis.
A total of 869 rays were collected from northern and north-east Australia from November 2003 to April 2007, of which D. leylandi (38.7%) had the highest representation, followed by G. australis (21.5%), H. toshi (19.9%), D. annotata (10.8%) and D. kuhlii (9.1%). Male to female ratios did not differ significantly (P>0.05) from unity in all four dasyatid species; at 1.56: 1 the male to female ratio for
G. australis was significant (P<0.05).
Dietary composition for each of the ray species was determined by stomach content analysis incorporating an index of relative importance (IRI); non-metric multidimensional scaling ordination (MDS) and Schoener's overlap indices. The maskrays were found to be generalist feeders, which have a high degree of interspecific dietary overlap. The major components of the maskray diet were polychaetes (72.3 %IRI) for D. kuhlii (n=120), carid shrimps (82.0 %IRI) for
D. leylandi (n=291) and a combination of carid shrimps (69.4 %IRI) and polychaetes
(25.5 %IRI) for D. annotata. The three maskrays had significantly different diets when examined by MDS (P = 0.001). Some geographical-based variability was present in the diets of D. leylandi and D. kuhlii at the genus/species level, although, this effect was not significant when data were analysed at the taxonomic level of order/infraorder.
Volumetric dietary data for NAS (n=101) and QTS (n=35) H. toshi differed significantly (ANOSIM: P<0.01) and were analysed as separate entities. Himantura toshi feeds predominantly on crustacean prey items in both NAS (99.9%) and QTS (93.9%), although polychaetes were also important in the diet of QTS specimens. In NAS, increasing body size of H. toshi was accompanied by relative shifts in prey item importance. Carid shrimps decreased from 98.3 %IRI in fish of disc width (DW) ≤225 mm to 48.0 %IRI in rays of >375 mm DW, whereas stomatopods and brachyuran prey items became more important (0.5 to 21.4 %IRI and 0.5 to 18.0 %IRI respectively).
Gymnura australis were found to be specialist feeders on teleost fishes (99.9 %IRI). It is likely that this species is an intermittent feeder, based on the high proportion of empty stomachs observed. Prey item size was large in relation to ray body size and it is suggested that G. australis (and other gymnurids) are ambush predators that use their pectoral fins to disable prey prior to ingestion.
The reproductive biology of D. leylandi (n=336), D. kuhlii (n=79),
D. annotata (n=94), H. toshi (n=173) and G. australis (187) was examined. Mature male D. leylandi, D. kuhlii, D. annotata and H. toshi comprised two functional testes, whereas mature male G. australis had one functional (left) testis. All mature female dasyatid rays had a single functional ovary and uterus on the left side of the body. In
G. australis females, there was one functional ovary (left) and two functional uteri.
The onset of sexual maturity for D. leylandi occurred at 160–190 mm DW, 180–210 mm DW for D. annotata, 250–300 mm DW for D. kuhlii and 400–470 mm DW for H. toshi. The onset of sexual maturity for male and female G. australis was 350–400 and 440–460 mm DW respectively. Fifty percent sexual maturity (DW50) for
D. leylandi occurred at 172.0 mm DW (males) and 180.7 mm DW (females); D. annotata 204.4 mm DW (males) and 190.8 mm DW (females); D. kuhlii 285.4 mm DW (males) and 266.8 mm DW (females); H. toshi 469.3 mm DW (males) and 462.7 mm DW (females); G. australis 395.1 mm DW (males) to 452.2 mm DW (females).
Vertebral band formation analysis was used to compare the age and growth characteristics of the four Dasyatidae species. Age estimates were obtained from 312
D. leylandi, 94 D. annotata, 74 D. kuhlii and 173 H. toshi vertebrae samples. Annual band deposition was verified using two semi-direct methods; centrum edge analysis (CEA) and marginal increment ratio analysis (MIR). A traditional three-parameter von Bertalanffy growth function (VBGF), two-parameter von Bertalanffy growth function (2VBGF) and the Gompertz growth function (GGF) was fitted to disc width (DW)-at-age data. Each models fit to the DW-at-age data was assessed using the coefficient of determination (r2), Akaike's information criterion, Akaike weight (ωi) and suitability of biological estimates. Based on the goodness-of-fit criteria, the traditional VBGF produced the most appropriate fit for maskray DW-at-age data and the GGF for H. toshi DW-at-age data.
Overall, all four species exhibited relatively slow growth characteristics when compared to other myliobatoid age and growth analyses: D. leylandi VBGF (males, DW50 = 271 mm, k = 0.12, t0 = -5.0, DW0 = 124.9 mm; females, DW50 = 360.5 mm, k = 0.08, t0 = -5.0, DW0 = 123.7 mm); D. annotata VBGF (males, DW50 = 230.4 mm, k = 0.31, t0 = -2.7, DW0 = 130.6 mm; females, DW50 = 360.5 mm, k = 0.08, t0 = -5.0, DW0 = 138.4 mm); D. kuhlii VBGF (males, DW50 = 438.6 mm, k = 0.08, t0 = -5.3, DW0 = 147.6 mm; females, DW50 = 440.6 mm, k = 0.08, t0 = -5.3, DW0 = 119.8 mm);
H. toshi GGF (males, DW50 = 639.9 mm, k = 0.13, t0 = -1.9, DW0 = 180.4 mm; females, DW50 = 763.8 mm, k = 0.09, t0 = -3.4, DW0 = 202.0 mm). Growth coefficient
(k) estimates derived from the GGF however, were more consistent with previous myliobatoid age and growth analyses.
The taxonomy of G. australis was examined as part of a wider review of Indo-West Pacific Gymnuridae species. The study revealed two distinct morphological variants: G. australis var eastern Australia and G. australis var northern Australia. Principally defined by tail colouration and morphology, G. australis var eastern has ≤3 complete or partially complete white tail bands and may or may not have a dorsal fin. In comparison, G. australis var northern Australia has ≥4 predominantly complete white tail bands and always has a dorsal fin. Genetically, the two morphological variants had a 1.22% gap difference, which was considered to be intraspecific variation. Gymnurids have historically been separated into two genera Aetoplatea with a dorsal fin and Gymnura without. The present study indicates Aetoplatea is an invalid genus and provides substantial support for the incorporation of all species into the genus Gymnura.
A new atelomycterine catshark species (Scyliorhinidae: Atelomycterinae), Atelomycterus marnkalha n.sp., is described from north-east Australia (Great Barrier Reef Marine Park, Torres Strait and Gulf of Carpentaria). It differs from A. baliensis,
A. marmoratus and A. macleayi in having posteroventally sloping dorsal fins, a lower precaudal vertebrae count and smaller adult size. Most similar to the Western Australian catshark species A. fasciatus, A. marnkalha differs from this species in having a larger anal fin, lateral denticles with prominent shallow depressions, claspers of adult males with a cover rhipidion lacking an obvious notch and its colour pattern with prominent white spots and fewer, smaller black spots.