Mar Biol (2012) 159:1183–1196 DOI 10.1007/s00227-012-1899-4 123 ORIGINAL PAPER The trophic ecology of two abundant mesopredators in south-east coastal waters of Tasmania, Australia Jonah L. Yick · Adam Barnett · Sean R. Tracey Received: 17 August 2011 / Accepted: 7 February 2012 / Published online: 23 February 2012  Springer-Verlag 2012 Abstract Investigating predator–prey relationships is an important component for identifying and understanding the factors that inXuence the structure and function of ecosys- tems. Mesopredators, deWned as mid-level predators, have a profound eVect on ecosystem structure by contributing an important link between apex predators and lower trophic levels. The diet of two elasmobranch mesopredators, Squalus acanthias and Mustelus antarcticus, was investi- gated in three locations in south-east Tasmania. Squalus acanthias consumed predominantly pelagic teleosts and cephalopods, while M. antarcticus predominantly con- sumed benthic crustaceans. As a result, there was low dietary and niche overlap between the two species. There was however evidence of intra-speciWc dietary variations between locations for both the species. This study has con- tributed to a better understanding of the top-down dynamics of the food web in coastal Tasmania, by providing impor- tant dietary information of two abundant mesopredators. In addition, the similar dietary patterns for S. acanthias and other Mustelus species over much of their global range suggest they may be consistent in their trophic roles across systems, with limited competition between these two sym- patric mesopredators to be expected. Introduction Investigating predator–prey relationships is an important component for identifying and understanding the factors that inXuence the structure and function of ecosystems (Heithaus et al. 2008). The key role many apex predators play in regu- lating ecosystems and sustaining biodiversity has been widely recognised (Estes et al. 1998; Heithaus et al. 2008; Baum and Worm 2009; Ritchie and Johnson 2009). However, the func- tional role of apex predators cannot be fully appreciated with- out knowing how other species within a system contribute to ecosystem dynamics. More recently, mesopredators, deWned as mid-level predators, have been receiving attention (Elmha- gen and Rushton 2007; Heithaus et al. 2008; Ritchie and Johnson 2009; Vaudo and Heithaus 2011). Mesopredators can also have profound eVects on ecosystem structure (Heithaus et al. 2008; Ritchie and Johnson 2009), and as such, trophic studies are needed to establish the prey potentially aVected by mesopredators. Information on trophic ecology is also a cru- cial component in understanding ecological interactions, such as competition and habitat partitioning, and the role of meso- predators in community dynamics. In coastal systems of southern Tasmania, the broadnose sevengill shark Notorynchus cepedianus is the dominant apex predator (Barnett et al. 2010b). However, to gain a more comprehensive understanding of ecosystem dynamics within the coastal areas of Tasmania, dietary information on the most abundant mesopredators is required. The white-spotted dogWsh Squalus acanthias and gummy shark Mustelus ant- arcticus are two abundant elasmobranchs within coastal sys- tems of Tasmania, and they are also two of the main prey of N. cepedianus (Williams and Schaap 1992; Barnett et al. 2010b). Both are elongated, relatively slender demersal spe- cies with overlapping distributions in inshore and oVshore waters of southern Australia, although S. acanthias (»1m Communicated by M. A. Peck. J. L. Yick · A. Barnett · S. R. Tracey Institute for Marine and Antarctic Studies, University of Tasmania, Private Bag 49, Hobart, TAS 7001, Australia Present Address: J. L. Yick (&) Inland Fisheries Service, PO Box 575, New Norfolk, TAS 7140, Australia e-mail: jonah.yick@dpipwe.tas.gov.au