Using otolith microchemistry to reconstruct habitat use of American eels Anguilla rostrata in the St. Lawrence River–Lake Ontario system

Abstract

Catadromy among freshwater eels is increasingly recognised as being facultative, with some individuals carrying out growth exclusively in brackish or coastal marine waters, or switching between brackish or marine waters and freshwater habitats. In an attempt to reconstruct habitat use of yellow-stage American eels in a large river-lake ecosystem, trace element line scans were obtained, using LA-ICP-MS, from the otoliths of 110 eels sampled at various locations throughout the St. Lawrence River-Lake Ontario (SLRLO) system. Elemental profiles for strontium (Sr), barium (Ba), manganese (Mn) and magnesium (Mg) enabled us to distinguish three chemical signatures that appear to represent three distinct habitats within the SLRLO. Of these, one was shown to likely correspond to the brackish estuary (high strontium values). The other two signatures, characterised by low strontium but variable concentrations of barium and manganese, may correspond to habitats within the main-stem St. Lawrence River and one or more of its tributaries. Most (78%) of the switches among habitats occurred within the first four years after recruitment suggesting an increasing likelihood for eels to maintain residence in one habitat as they grow older. This suggests that tributaries may provide important habitats for American eels during the first several years after recruiting to the SLRLO. In addition, our results suggest that a small proportion American eels in the SLRLO can undertake movements on the order of at least 200 km during the early growth stage. This information has important implications for the management and conservation of this species in the system.

Freshwater eels: A symbol of the effects of global change

“…During their first year in continental waters, eels display an active migratory behaviour and then shift to a resident behaviour (Benchetrit et al, 2017;Imbert et al, 2010). Resident behaviour does not exclude habitat shifts (Daverat & Tomás, 2006) although these types of movement correspond more to ranging than strict migration (Dingle & Drake, 2007).…”

Underutilized biogeochemical tracers distinguish invertebrate populations in a complex river system

“…Clarke et al () found significant relationships between Sr and Ba between otoliths and the water, and was able to use these relationships to trace fish back to specific rivers. Similarly, Benchetrit et al () established temporally explicit elemental profiles of American eel Anguilla rostrata otoliths in the St. Lawrence River and Lake Ontario, Canada using Sr, Ba, Mn, and Mg. Benchetrit et al () identified three chemical signatures that appeared to represent three different habitats within the system (i.e., brackish estuary, main channel, and a tributary), and subsequently used these signatures to identify habitat switching events for individual eels. As the number of studies which use biogeochemical tracing increases, and researchers attempt to examine population connectivity and movement at smaller scales, the need for more accurate tracers will also increase.…”

Age determination for whitespotted conger Conger myriaster through somatic and otolith morphometrics

“…Katayama introduced a new age method for the C. myriaster using UV light observation of burnt otoliths to make the annuli relatively easy to read [8], which is also applicable to other eel species, such as Conger conger [9] and Anguilla rostrata [10]. However, eels’ otoliths require more complex preparations prior to age determination, which is time-consuming.…”