Ontogenetic changes in the longitudinal distribution of two species of larval fish in a turbid well‐mixed estuary

Abstract

The relationship between vertical migration, estuarine retention and species-specific patterns of longitudinal distribution of the pelagic larvae of rainbow smelt, Osmerus mordux, and tomcod, Microgadus romcod, was investigated in the upper section of the St Lawrence Middle Estuary. We hypothesized that the species-specific use of the vertical pattern of current exhibited by the two species results in the partitioning of the estuarine habitat in the longitudinal plane while assuring retention. Important differences in the longitudinal distribution of tomcod and smelt larvae were related to the ontogeny of their vertical distribution in the water column. In June, small tomcod and smelt larvae are generally associated with waters of salinities less than 5%0. As the larvae grow. their vertical distribution patterns change, leading to a horizontal separation of the two species. Tomcod juveniles migrate downstream into colder, more saline waters, whereas larger smelt larvae migrate upstream into warmer, tidal fresh waters. Ontogenetic changes in vertical distribution serve to concentrate larvae in specific conditions that may optimize physiological conditions and also permit population persistence.

Retention mechanisms of white perch (Morone americana) and striped bass (Morone saxatilis) early‐life stages in an estuarine turbidity maximum: an integrative fixed‐location and mapping approach

“…Estuarine turbidity maximum (ETM) regions are important nursery areas for larval fish, as documented in the St Lawrence River (Dodson et al. , 1989; Laprise and Dodson, 1989a; Dauvin and Dodson, 1990; Sirois and Dodson, 2000a; Winkler et al. , 2003), the upper Chesapeake Bay (Boynton et al.…”

“…Passive retention mechanisms of eggs and early‐stage larvae may depend on the depth distribution of organisms combined with net residual circulation patterns (Norcross and Shaw, 1984; Miller, 1988). Larval tomcod ( Microgadus tomcod ) used passive up‐estuary transport for retention in the St Lawrence River estuary by remaining in deep water (Laprise and Dodson, 1989a, 1990). In the Chesapeake Bay ETM region, deep landward‐flowing water down‐estuary of the salt front creates a convergence zone near the tip of the salt front (Schubel, 1968) where particles, including fish larvae and their zooplankton prey, could be passively retained.…”

“…Estuarine turbidity maximum (ETM) regions are important nursery areas for larval fish, as documented in the St Lawrence River (Dodson et al, 1989;Laprise and Dodson, 1989a;Dauvin and Dodson, 1990;Sirois and Dodson, 2000a;Winkler et al, 2003), the upper Chesapeake Bay (Boynton et al, 1997;North andHoude, 2001, 2003), and potentially the San Francisco Estuary (Jassby et al, 1995;Bennett et al, 2002). ETMs, also referred to as maximum turbidity zones or entrapment zones, are ubiquitous features of coastal plain estuaries (Schubel, 1968) and often occur near the salt front within estuarine transition zones .…”

Shallow-Water Piscivore-Prey Dynamics in California's Sacramento-San Joaquin Delta

“…First, not all small estuarine fishes are adapted to use shallow habitats like marsh creeks; many species or early life stages of species are pelagic and thus frequent the deeper habitats often used by large piscivores (Laprise and Dodson 1989;Hagan and Able 2003). These pelagic species/life stages may use turbidity, rather than water depth, as a form of cover from predators (Abrahams and Kattenfeld 1997;Utne-Palm 2002).…”

Correction: SmeltCam: Underwater Video Codend for Trawled Nets with an Application to the Distribution of the Imperiled Delta Smelt

“…As a case in point, anadromous rainbow smelt Osmerus mordax larvae are known to vertically migrate to maintain position in regions of high prey density [45,46]. The ability of young fishes to change their vertical distribution ontogenetically [47,48] or in response to varying net flow conditions [38] appears to be a common strategy for retention in favorable habitats.…”