The importance of the Subtropical Convergence Zone south of Australia as a feeding area to the pygmy blue whale of the eastern Indian Ocean was investigated to better understand migration patterns and habitat use. A combination of satellite tagging studies during 2003-2005 and acoustic and visual surveys during the austral summer of 2013 confirmed the presence of pygmy blue whales in the Subtropical Convergence Zone and provided evidence for feeding throughout the region. Of the 67 pygmy blue whales acoustically detected, many were localized in proximity to sea surface temperature fronts and high chlorophyll concentrations, which could be a behavioral strategy to attract conspecifics to good feeding sites. Aggregations of up to four pygmy blue whales, along with decreased call rates during the day, may suggest feeding despite no direct observations of pygmy blue whales consuming euphausiids. The oceanographic features present throughout the Subtropical Convergence Zone continue to create an environment productive enough to support the world's largest living mammals during their migratory foraging movements between the Southern Ocean and Indonesia.

8The Leeuwin Current is an anomalous eastern boundary current which transports warm, low salinity water poleward off 9Western Australia. This study investigated epi-pelagic euphausiids in the Leeuwin Current system from 22°S -34°S 10focusing on the latitudinal gradient in species richness and whether variability in euphausiid assemblages was associated 11with an increase in seawater density across latitude. Twenty-eight species of euphausiids (including five new records) were 12 identified from the study area. Species richness remained relatively constant across latitude as the distribution of seven

In the eastern Indian Ocean, the Kimberley region off northwestern Australia is characterised by a wide continental shelf, complex coastal topography and very large tides (>10 m). Diversity of fishes is high although little is known about the distribution of their larvae in this dynamic region. This study investigated spatial variation in ichthyoplankton assemblages along four coastal-oceanic transects and related the results to tidal cycles and other environmental variables. Larvae representing 92 neritic and 21 mesopelagic teleost families were collected; this far exceeds the diversity described for other comparable tropical continental shelf and oceanic systems. Distinct ichthyoplankton assemblages characterised inner shelf (Engraulidae and Gobiidae were dominant families), outer shelf / slope (mixed neritic and mesopelagic taxa) and oceanic waters (mesopelagic taxa, particularly Myctophidae, Gonostomatidae and Phosichthyidae), and were correlated with changes in environmental variables (water depth, seawater density, mixed layer depth and zooplankton). The spring-neap tidal cycle and subsequent tides (same stations sampled 12 h apart) had no significant influence on larval fish assemblages. Coastal waters were delineated by a density front and larval fish assemblages were significantly different from offshore assemblages. This study provides new insights into the pelagic ecosystem in the tropical eastern Indian Ocean and contributes to the understanding of the role of environmental variables and physical forcing in the structuring of larval fish assemblages.

The north-west marine bioregion of Australia, which includes the waters adjacent to the Kimberley and Ningaloo coasts, is influenced by both the Indian and Pacific oceans and has high tropical biodiversity, some of which is conserved in a suite of Marine Protected Areas. In the present study, the epipelagic euphausiid assemblages of this bioregion were investigated and related to the physical and biogeochemical properties of the water column, as well as food availability. Twenty-five euphausiid species were identified, including three new records for Australian waters. Pseudeuphausia latifrons was the most abundant species, dominating the shelf waters across both study areas. Stylocheiron carinatum replaced P. latifrons in the deeper waters where species richness was greater. Off Ningaloo, there were higher concentrations of euphausiids, and this may be linked to the bathymetry, the narrowness of the shelf and the resultant effects of these features on oceanography and biogeochemistry. Assemblages were primarily structured by depth, but mean seawater density, dissolved oxygen, fluorescence and mesozooplankton abundance also significantly explained some of the variation in euphausiid assemblages. The present study has confirmed that the physical and biogeochemical properties of the water column and food availability are recurrent factors affecting euphausiid assemblage variation in the eastern Indian Ocean.

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