Regional Patterns in the Otolith Chemistry of Juvenile Spotted Seatrout (Cynoscion nebulosus) Differ under Contrasting Hydrological Regimes

Abstract

The value of using otolith chemistry to characterize recruitment in terms of natal source regions depends on how consistently spatio-temporal variation can be resolved. The objective of this study was to compare regional classification patterns in the otolith chemistry of juvenile Spotted Seatrout (Cynoscion nebulosus) between two years experiencing disparate hydrological regimes, and separated by a five year interlude. Spatial patterns in the whole-otolith chemistry of juveniles of this estuarine-dependent species were compared between years using five otolith elements and two stable isotopes. Consistent size-related trends in uptake and deposition were evidenced by parallel ontogenetic relationships for six otolith variables. Nine natal regions were discerned equally well in both years; and region accounted for similar overall amounts of variation in the seven otolith variables in both years. However, the otolith variables did not distinguish the nine regions in the same manner in both years, and natal regions varied in how similar they were in otolith chemistry between years. Consequently, between-year cross-classification accuracy varied widely among regions, and geographic distance per se was unimportant for explaining regional patterns in otolith chemistry. Salinity correlated significantly with regional patterns in otolith chemistry in 2001, but not at all in 2006 when conditions were much drier. Regional patterns in individual otolith variables reflected either a general trend based on hydrology, a regional-local effect whereby geographically closer regions exhibited similar otolith chemistry, or a location-specific effect for which there was either no correlation in otolith concentration among regions between years, or a significant but individualistic relationship. In addition to elucidating limitations of using otolith chemistry to identify natal source regions or for tracking fish movements, knowing more about how and why otolith chemistry varies could be used to address specific questions about early recruitment dynamics, or to aid in the development of more reliable instruments for discerning natal source contributions.

Stock discrimination of two insular populations of Diplodus annularis (Actinopterygii: Perciformes: Sparidae) along the coast of Tunisia by analysis of otolith shape

“…However, the measurements of otolith shape based on ratios of otolith radii and on the Fourier analyses in particular, had some success in distinguishing among stocks and have been assumed to be based, at least in part, on genetic differences (Capoccioni et al 2011). In some cases, reports of stock discrimination based on otoliths morphology appear to refl ect environmental differences among regions (Rakocinski et al 2015).…”

Using otolith microchemistry to assess nursery habitat contribution and function at a fine spatial scale

“…In addition, otolith signatures may vary from year to year for a given species in a particular nursery area (e.g. Clarke et al 2009, Rakocinski et al 2015, suggesting that replication for more than one cohort is required. In fact, in Puget Sound, markedly different spatial patterns in fish nursery contribution values occurred between 2 consecutive cohorts (Chittaro et al 2009).…”