Remains of planktonic organisms in fecal material of individuals Southern Right Whale (Eubalaena australis), Peninsula Valdes, Chubut, Argentina

VALERIA C. D'AGOSTINO; MÓNICA S. HOFFMEYER; MARIANA DEGRATI

Workshop; International Whaling Commission Meeting; 2015

Península Valdés (PV) in Argentina is the austral-most nursery area for the SW Atlantic population of the southern right whale Eubalaena australis. The maximum concentration of individuals in the area occurs in both Nuevo (NG) and San José (SJG) gulfs. Recent studies indicate that E. australis often feeds in this area mainly at mid-spring. Their trophic spectrum includes euphausiids as krill, large and medium size copepods, larval and juvenile fish and other groups of micronekton. In this study we applied microscopic analysis of planktonic remains found in feces from stranded (spring 2010) and living individuals (spring 2004 and 2005). All the remains were identified and classified, detecting a clear dominance of copepod mandible gnathobases. As we expected, after a more detailed comparative analysis using scanning electron microscope and confocal laser microcopy, mandible gnathobases found in feces resulted to be equal in structure and morphometry to those obtained from dissections of Calanus australis (copepodites 4-6), a common copepod in NG and SJG. Furthermore, the significant positive lineal regression relationship, between width of C. australis mandible gnathobases edge and total length of preserved individuals, allowed us to infer the size of stages ingested by E. australis individuals analyzed. In addition, Pseudo-nitzschia spp. frustules fragments were found in all fecal samples of E. australis analyzed. All the species present in fecal samples are potentially toxic. Our findings indicate for the first time, the relevant role of C. australis copepodite 5 as main prey for E. australis in PV, as well as, the presence of Pseudo-nitzschia spp. fragments in fecal material of these whales.