Application of otolith analysis for elucidation of life-history and demographic parameters in pejerre

YOKOCHI H; OKAJIMA H; KAKUTA N; YAMAMOTO Y; STRÜSSMANN CA; MIRANDA LA; COLAUTTI DC; BERASAIN GE

Buenos Aires

Jornada; XX Jornadas de la Sociedad Argentina de Biología; 2018

SAB

The pejerrey Odontesthesbonariensis is one of the most important inland water fisheries resourcesin the Pampa region. Pejerrey populations inhabit an extensive network ofrivers and shallow lakes where environmental conditions may vary fromhyposaline to hypersaline and with temperature fluctuations sometimes in excessof 25ºC. This area is also characterized by decadal cycles of droughts andinundations that impart marked changes in the water bodies? levels,connectivity, physico-chemical parameters, nutrients, primary production andtrophic structure. In this environment, natural pejerrey populations showmarked fluctuations in abundance, from hyper abundance and dominance over otherspecies to mass mortality and even complete disappearance in some years, butthe causes are still not clear. Analyzes of otolith microstructure andchemistry can provide information useful for the estimation of age, birth date,past growth rates, migration, and even the past environment experience ofindividual fish, and hence for the study and management of natural pejerreyresources. In this study, we used Electron Probe Micro Analysis (EPMA) to examinethe chemical composition of the otoliths of juvenile and young-of-the-year pejerreyspecimens collected in Chascomúslake in 2016 in relation to environmental variables. We applied a novel methodto equate the EPMA results, which are usually referred in terms of distance fromthe otolith nucleus, to calendar dates, and which facilitates the examinationof causal relationships between otolith chemistry and environmental factors inwild populations. The EPMA results, combined to birth date estimation based onotolith increment counting, revealed that both salinity and temperature affect otolithSr content. Fish with different birth dates or sizes generally had similarotolith Sr composition, but some minor differences noted could reflect size- orcohort-dependent habitat segregation. The results also allowed clear discriminationof native, resident individuals and immigrants. Otolith analyzes may providecrucial insight on the biology of natural pejerrey populations.