What otolith microchemistry and stable isotope analysis reveal and conceal about anguillid eel movements across salinity boundaries

Abstract

Otolith microchemistry studies indicate that growth-phase (yellow stage) anguillid eels commonly shift at irregular intervals between fresh and saline waters, but this technique has not detected regular seasonal migrations across salinity zones. We tested the ability of otolith microchemistry and stable isotope analysis to detect migrations of American eels (Anguilla rostrata) between salinity boundaries in two small stream-estuary systems in Canada's Bay of Fundy. Although the two methods showed concordant classifications of recent residence history, most eels caught in fresh water in spring (68.8-89.7%) and fall (78.8-83.3%) showed microchemical and isotopic signatures that reflected occupancy of saline waters. These eels were classified as migrants which had summered in saline waters and then migrated to freshwater wintering grounds where they retained their saline signatures. In summer, most eels (85.0-100.0%) captured in fresh and saline water had recent microchemical and isotopic signatures matching the habitat of capture. Our results suggest that lifetime otolith microchemistry profiles are unable to detect eel wintering migrations, a failure that is likely due to winter depression of otolith accretion. Elucidation of seasonal eel movements requires cross-seasonal and cross-site sampling for the microchemistry and stable isotope methods, or tagging studies. Seasonal saline-fresh eel migrations may be more common than previously appreciated, underlining the need for conservation of both habitats, and connectivity between the two.

Trophic structure of a coastal fish community determined with diet and stable isotope analyses

“…The enriched signals exhibited by A. sapidissima and A. pseudoharengus may reflect their anadromous life histories or recent estuarine foraging, as 15 N increases markedly in coastal environments where the enriched 15 N signal of human sewage and other nutrient sources is persistent throughout the food web (Cabana & Rasmussen, 1996;Hansson et al, 1997;McKinney et al, 2010). In general, the isotopic signatures of migratory species often reflect feeding in multiple areas and habitats (Clément et al, 2014;Dixon et al, 2015). As such, the isotopic signatures of highly mobile species, which integrate multiple months of feeding behaviour, must be interpreted with care (Hobson, 1999;Abrantes & Barnett, 2011).…”

Identification of potential fish stocks and lifetime movement patterns of Mugil liza Valenciennes 1836 in the Southwestern Atlantic Ocean

“…Different methods have been used to study displacements and identify fish stocks such as mark-recapture, parasites, genetics and the analysis of calcified structures like scales and otoliths (Avigliano et al, 2014;Clément et al, 2014;Kerr and Campana, 2014;Sturrock et al, 2012). The research on otolith (complex calcium carbonate structures located in the inner ear (Campana, 1999)) has widen the knowledge of fish movements and migrations and stock identification of important commercial species (Avigliano et al, 2014;Avigliano et al, 2015a;Gillanders, 2005;Tabouret et al, 2010;Tracey et al, 2012).…”

White mullet Mugil curema population structure from Mexico and Brazil revealed by otolith chemistry

“…Different methods have been used to identify fish stocks and nursery areas such as mark‐recapture, parasites and the analysis of otolith features, such as morphometry and chemical composition (Avigliano et al ., 2014; Clément et al ., 2014; MacKenzie et al ., 2008; Sturrock et al ., 2012). Otolith microchemistry has been a good alternative for the study of fisheries because it reflects both exogenous ( e.g ., environment) and endogenous ( e.g ., genetics) factors, which can contribute to detecting differences in chemical signatures between different stocks (Hüssy et al ., 2020; Tzadik et al ., 2017).…”