Variation in the annual growth, by sex and migration history, of silver American eels Anguilla rostrata

Abstract

Silver American eels Anguilla rostrata from the East River, Chester, on the Atlantic coast of Nova Scotia, as evaluated by the temporal pattern of Sr:Ca ratios in their otoliths, showed variable patterns of migration between river and estuarine/marine waters during their yellow eel stage. Eels with a history of primarily estuarine residence were longer (total length) at migration and had higher annual growth rates than did eels with a primarily freshwater residence. Female eels were longer at migration and had higher annual growth rates than did males. The percentage (64%) of silver eels with a history of estuarine residence and their larger size at age, size at migration, and higher growth rate relative to freshwater resident eels may result from higher productivity in oceanic than freshwaters at higher latitudes, as modified by regional environmental conditions. Environmental conditions change with increasing latitude in a different pattern for American and Japanese eels than for European eels.KEY WORDS: Anguilla rostrata · American eel · Otolith microchemistry · Strontium:calcium ratios · Migratory history Resale or republication not permitted without written consent of the publisher

A synthesis of the ecological processes influencing variation in life history and movement patterns of American eel: towards a global assessment

“…Female eel become sexually mature at larger sizes and older ages than males from a particular region (Helfman et al 1987;Oliveira 1999;Oliveira and McCleave 2002) and, as a result, male size at seaward migration is significantly smaller than female size (Jessop et al 2004). Males also approach their theoretical maximum length more quickly than females (Jessop et al 2004), reflecting a negative relationship between growth rate and age at maturity consistent with life history theory (Stearns and Crandall 1984) and generally observed in eels (Vollestad 1992;Jellyman 2001;Oliveira and McCleave 2002).…”

“…Males also approach their theoretical maximum length more quickly than females (Jessop et al 2004), reflecting a negative relationship between growth rate and age at maturity consistent with life history theory (Stearns and Crandall 1984) and generally observed in eels (Vollestad 1992;Jellyman 2001;Oliveira and McCleave 2002).…”

“…Although, on average, growth rates of yellow and silver female eel are higher than males (Oliveira 1999;Oliveira and McCleave 2002;Tzeng et al 2003;Jessop et al 2004), some studies have found higher growth rates for males than females (Poole and Reynolds 1996;Holmgren et al 1997). One potential reason for this inconsistency may be an inability to accurately determine sex in young eel.…”

“…Arguably, existing evidence supports the hypothesis that eels evolved a migratory behaviour in response to the relative habitat productivity prevailing in their geographical range (Edeline 2007)-temperate eels living at higher latitudes with higher oceanic productivity exhibit a greater probability of remaining in lower reaches in brackish water than eels living at lower latitudes ) with higher freshwater productivity. But other factors must be involved since general patterns defining the variation in life history traits and movement patterns as functions of latitude (Helfman et al 1987;Tesch 2003) or ocean-freshwater productivity gradients (Jessop et al 2004) show some inconsistencies across the entire geographical range of the species (e.g., Hansen and Eversole 1984;Krueger and Oliveira 1999;Oliveira et al 2001). Since panmixis would preclude the segregation of genotypes, local differences in life history patterns would be most likely phenotypic in origin (Jessop et al 2004) and triggered by biotic and abiotic factors associated with local habitats.…”

“…But other factors must be involved since general patterns defining the variation in life history traits and movement patterns as functions of latitude (Helfman et al 1987;Tesch 2003) or ocean-freshwater productivity gradients (Jessop et al 2004) show some inconsistencies across the entire geographical range of the species (e.g., Hansen and Eversole 1984;Krueger and Oliveira 1999;Oliveira et al 2001). Since panmixis would preclude the segregation of genotypes, local differences in life history patterns would be most likely phenotypic in origin (Jessop et al 2004) and triggered by biotic and abiotic factors associated with local habitats.…”