Species Thyrsites atun

Common names: Barracouta (couta, snoek) Previous nomenclature: Leionura atun, Scomber atun

Material

Description based on otoliths of four specimens. Specimens 1-3 of 173-330 mm FL. Otolith catalogue reference 30.1351-1352, and 30.1355. Catch locality Storm Bay, Tasmania at 25 m depth. ID by RG. Specimen 4 of 840 mm FL. Otolith catalogue reference DMF52-53. Catch locality Gabo Island, Victoria, at 250 m depth. ID by DMF.

Otolith description

Otolith large, elliptic/fusiform. Dorsal margin sinuate to lobed/irregular; ventral margin rounded and sinu-ate/crenate to irregular; posterior margin notched and sharply rounded and irregular. Distal surface flat or slightly concave; proximal surface flat or slightly convex. Sulcus groove shallow, pseudo-archaesulcoid; opening ostial to ostio-caudal. Notch in posterior margin gives an impression of an ostio-caudal sulcus. Colliculum heteromorph, indistinct. Collum absent. Crista superior poorly developed along entire sulcus; crista inferior poorly developed under cauda only. Rostrum broad, elongate, sharply rounded. Antirostrum small, rounded. Pseudo-rostrum broad, moderate, sharply rounded. Excisura. moderate; notch shallow; angle varying acute to wide.

Morphometry

(Note: Data includes juvenile and adult specimens.) FL = 226.331 OW 0336 mm n = 7; Std Err Est = 0.036; R = 0.828; P<0.021 Otolith weight range = 50.0-77.0 mg (CMAR)

FL = 22.06 OL142 mm n = 25; Std Err Est = 0.073; R = 0.97;

Otolith length range = 4.2-13.5 mm (CMAR)

Distribution and ecology

Moreton Bay (Queensland) to Shark Bay (Western Australia) (Tuma 1994), and Tasmania (Last et al. 1983); also New Zealand, South America and South Africa; mesopelagic in cold waters of the southern hemisphere (Smale et al. 1995), although can be found in subtropical waters; usually in surface waters to 550 m depth (Kailola et al. 1993); exhibits schooling behaviour (Gomon et al. 1994); reaches 1500 mm in length (Nakamura and Parin 1993) (reported to 2000 mm in length by Smale et al. 1995).

Predator-prey information

Known prey of Australian fur seal (Arctocephalus pusillus doriferus) (Gales and Pemberton 1994, Hume et al. 2004), New Zealand fur seal (Arctocephalus forsterii) (Lake 1997, Fea et al. 1999), little penguin (Eudyptula minor) (Gales and Pemberton 1990), shy albatross (Thalassarche cauta) (Hedd et al. 2001), short-tailed shearwater (Puffinus tenuirostris) (Montague et al. 1984) and crested tern (Sterna bergii) (Chiaradia et al. 2002).

Mass = 2.33 X 10-6FL310 g n = 54; Std Err Est = 0.088; R = 1.00;

Fish length range = 108-1015 mm FL (TMAG)

Otolith of Thyrsites atun from fish of 330 mm and 840 mm FL, figures a and b, respectively. Two otoliths have been included to illustrate changes with otogeny.

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