Yellowfin tuna (Thunnus albacares) aggregations along the shelf break off south-eastern Australia: links between inshore and offshore processes

Abstract

In May 1996 the biological oceanography of the main yellowfin tuna longline fishing waters off southern New South Wales, Australia, was examined in relation to the catch by the fishery. A warm-core eddy was identified directly east of Eden with a temperature at 250 m depth of 15˚C. At the western edge of this eddy, relatively high levels of fluorescence (chlorophyll a) were recorded together with pigments typical of diatoms, a feature of upwelling communities. The biomass of zooplankton and micronekton was also significantly higher at the western edge of the eddy. Similarly, acoustic data showed relatively high concentrations of backscatter at the margins of the eddy, particularly at the shelf break and slope. These areas had the greatest potential prey biomass; a fact supported by the presence of shelf-and slope-associated prey species in the stomachs of yellowfin tuna caught at the same time. Fishery data for yellowfin tuna (Thunnus albacares) captures showed that catch per unit effort was highest along the shelf and shelf break. Examination of yellowfin tuna catch records from 1988 to 1998 from south-eastern Australia showed highest catches in 1996, ~75%of the catch coming from the western edge of the eddy. We conclude that the presence of a warm-core eddy in the area at this time provided a localized but productive area to which the yellowfin were attracted.

Estimation of yellowfin tuna (Thunnus albacares) habitat in waters adjacent to Australia’s East Coast: making the most of commercial catch data

“…, 2003, 2008). Chlorophyll a concentration was positively associated with the capture of YFT in the ETBF, which is consistent with the observations made in a previous ship‐based investigation in the Tasman Sea (Young et al. , 2001).…”

Modelling the oceanic habitats of two pelagic species using recreational fisheries data

“…This could be as a result of differing oceanographic upwelling processes in the studies (Cresswell, ). In the current study, the EAC retroflects eastwards between 30 °S and 34 °S (Godfrey et al ., ) leaving behind a poleward flowing eddy field (Ridgway and Godfrey, ; Everett et al ., ) that can produce productive fishing grounds (Young et al ., , ) from elevated biomass and secondary consumers such as zooplankton (Everett et al ., ) and larval fish (Mullaney and Suthers, ). The signal of productive fishing grounds may be indicated by SLA, EKE and FI, and future work could focus on examining the relationships between chlorophyll‐ a and fish intensity.…”

Pelagic cephalopods from eastern Australia: species composition, horizontal and vertical distribution determined from the diets of pelagic fishes

“…The difference in significant factors between the two predators was likely a reflection of the differing ecologies of the two predators. For example, off eastern Australia, yellowfin tuna are associated with warmer EAC waters that are mainly restricted to waters west of the Tasmantid seamount chain, whereas swordfish tolerate a far wider range of oceanic conditions in the region (Young et al 2001(Young et al , 2003, see Fig. 2).…”