Thursday, March 10, 2016

[Ichthyology • 2016] Pegasus tetrabelos • Integrated Taxonomy Reveals Hidden Diversity in Northern Australian Fishes: A New Species of Seamoth (Genus Pegasus)

Short-spined Seamoth | Pegasus tetrabelos  
 Osterhage, Pogonoski, Appleyard & White, 2016


Fishes are one of the most intensively studied marine taxonomic groups yet cryptic species are still being discovered. An integrated taxonomic approach is used herein to delineate and describe a new cryptic seamoth (genus Pegasus) from what was previously a wide-ranging species. Preliminary mitochondrial DNA barcoding indicated possible speciation in Pegasus volitans specimens collected in surveys of the Torres Strait and Great Barrier Reef off Queensland in Australia. Morphological and meristic investigations found key differences in a number of characters between P. volitans and the new species, Pegasus tetrabelos. Further mt DNA barcoding of both the COI and the slower mutating 16S genes of additional specimens provided strong support for two separate species. Pegasus tetrabelos and P. volitans are sympatric in northern Australia and were frequently caught together in trawls at the same depths.

Diagnosis and Description

Pegasus tetrabelos Osterhage, Pogonoski, Appleyard and White sp. nov.

Fig 2. Holotype of Pegasus tetrabelos (CSIRO H 6553–03, 110 mm PCL). (A) dorsal; (B) lateral; and (C) ventral views.

Diagnosis: Tail rings 12, anteriormost 9 mobile, articulating laterally, remaining 3 fused together, attenuated and dorsoventrally flattened; terminodorsal-lateral (tdl) and terminoventral-lateral (tvl) plates each with an anteriorly and posteriorly directed spine; terminal-lateral plates (tl) absent; interpectoral plate (ip) present; single ventral preopercular notch present; rostrum spatulate; carapace with three small posteriorly directed tubercles along each dorsal ridge, one at the centre of each dorsal plate; scales not present on orbit; pectoral fin composed of 9–10 (usually 10) soft rays, 5th ray stouter than other rays; abdominal centra 7, caudal centra 14, total centra 21; tail with 4 dark saddles, no dark saddle on tail ring XI.

Distribution: Pegasus tetrabelos is known from the east coast of Queensland and Torres Strait between latitudes 9°15’ S and 22°01’ S, and in the Northern Territory from the Beagle Gulf to off Darwin (Fig 8). Specimens collected during the Torres Strait and Great Barrier Reef trawl surveys formed three distinct clusters (Fig 9). The first cluster was located in the Torres Strait between latitudes 9°15’ S and 10°51’ S; the second cluster in Princess Charlotte Bay (~14°15’ S); and the third from Bowling Green Bay (19°26’ S) south to Broad Sound (22°01’ S). Despite intensive trawling, no specimens of the new species (or P. volitans) were caught between these clusters in the trawl survey. This likely reflects specific habitat preferences. There are currently no records of this species from the Gulf of Carpentaria or Western Australia.

Specimens of P. tetrabelos were collected at depths of 8–45 m, mostly in depths less than 30 m. Although the trawling surveys of the Great Barrier Reef and Torres Strait were conducted to depths of 100 m, P. tetrabelos was not collected in depths greater than 40 m.

Etymology: The species name tetrabelos is a combination of the Greek ‘tetra’ meaning four and ‘belos’ meaning dart or arrow in allusion to the four backward pointing spines on the terminal tail ring (two on each side). The name is treated as a noun in apposition.

Vernacular names: Short-spined Seamoth.

Conservation and management implications: 

This study has delineated and described a new cryptic species, Pegasus tetrabelos, from what was previously a commonly-recognised, wide-ranging species. This has been strongly supported by multiple taxonomic tools through an integrated taxonomy approach, and will provide a basis for scientific studies, and informed management and conservation efforts into the future.

A consequence of having a single wide-ranging species split into two, with one species having a much more restricted range, is that there is a need to reassess management or impacts relevant to each species. Pegasus species are caught as bycatch in northern Australian commercial prawn trawl fisheries, where they are discarded. The abundance of ‘P. volitans’ was reported to have declined in the southeast Gulf of Carpentaria after 20 years of prawn trawl fishing, with demersal fish surveys recording a reduction in catches of 32%. In the East Coast Trawl Fishery and Torres Strait Prawn Fishery, ‘P. volitans’ were found to be caught in ~24 and 41% of prawn trawls, respectively. Although it is not possible to determine the relative contribution of P. volitans and P. tetrabelos from this data, it is likely both species are encountered in these two fisheries.

Although pegasids are not utilised in large quantities in Australian waters, there is evidence of far greater exploitation of pegasids in some Asian countries. In a single Philippine province, it is estimated 43,000–62,000 seamoths/year (predominantly P. volitans) are caught live for the aquarium trade, with an additional 130,000–620,000 P. volitans/year caught incidentally by fishers and sold to traditional Chinese medicine markets. Sales of P. volitans for traditional medicine in China are estimated to be in the millions each year, provided by suppliers throughout Southeast Asia. This highlights the need for further taxonomic work on this group outside of Australia. If the wide-ranging P. volitans is found to be a complex of species with more restricted ranges, such localised heavy exploitation could be a more significant threat than currently recognised.

Deborah Osterhage, John J. Pogonoski, Sharon A. Appleyard and William T. White. 2016. Integrated Taxonomy Reveals Hidden Diversity in Northern Australian Fishes: A New Species of Seamoth (Genus Pegasus). PLoS ONE. 11(3): e0149415.   DOI: 10.1371/journal.pone.0149415