Document of bibliographic reference 392672

BibliographicReference record

Type

Bibliographic resource

Type of document

Book/Monograph

Type of document

Dissertation

BibLvlCode

M

Title

Abundance and biology of the southern eagle ray Myliobatis tenuicaudatus in the Swan-Canning Estuary

Abstract

The Southern Eagle Ray, Myliobatis tenuicaudatus (Hector, 1877), is the only extant myliobatid species located on the southern coast of Australia and New Zealand. Anecdotal evidence suggests that the abundance of this species has increased in the Swan-Canning Estuary in recent years, likely due to declining streamflow and marinization. As there is little information on this species, which is fished commercially within the estuary, the aim of this study was to determine key biological parameters to assist with future management. Individuals were found in the estuary year-round, with the highest catches in autumn and the lowest in winter. Similar to other myliobatids, there were strong relationships between the measures of disk width (DW) and weight, body length, and total length (P= <0.01 for all regressions). Females reached a larger size and an older age than males (DW= 1,181 vs. 816 mm; Age= 15.9 vs. 9.9 years, respectively), consistent with other members of the Myliobatidae. Females also reached a greater DW∞ value and grew at a slower rate. The estimated DW∞ was lower for M. tenuicaudatus than other myliobatids. Females matured at a larger size than males (DW50= 833 vs 595 mm). Gonadosomatic indices peaked in the summer for females and in spring for males, indicating breeding occurs in spring and females release birth young during summer. Unlike other myliobatids, both uteri were found to be fully functional in M. tenuicaudatus. As is typical for myliobatids, M. tenuicaudatus is a durophagous generalist mesopredator feeding predominantly on polychaetes, crustacean (mainly prawns and brachyurans), and molluscs. An ontogenetic shift in dietary composition was recorded with an increase of molluscs and larger crustaceans at sizes >600 mm DW. The biological data collected in this project will be used to inform future management practices of M. tenuicaudatus within Western Australian estuaries

Bibliographic citation

Taljaard, E.E. (2024). Abundance and biology of the southern eagle ray Myliobatis tenuicaudatus in the Swan-Canning Estuary. MA Thesis. Murdoch University, Centre for Sustainable Aquatic Ecosystems: Perth. 88 pp.

Topic

Marine

Access rights

open access

Is accessible for free

true