No 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

Latitudinal variability in length and age at maturity and annual growth rate for the American eel ( Anguilla rostrata ) along the Atlantic coast of North America was examined with respect to life history strategies and theory. Maturing (silver phase) female lengths and ages increased with increasing latitude (and distance) from the Sargasso Sea spawning site, as did male ages but not lengths. Growth rates for females (and males) declined with increasing latitude south of 44°N latitude, approximately the entrance to the Cabot Strait, but were constant or increased within the Gulf of St. Lawrence and St. Lawrence River, depending on the analysis method. The growing season and the number of degree-days ≥ 10 °C declined with increasing latitude. Female growth rates adjusted for the number of degree-days were approximately constant south of 44°N but increased further north, suggesting countergradient variation in growth. The temperature–size rule (increase in body size at lower temperatures) evidently applies to American eel females, but not males. No current life history model provides a satisfactory explanatory mechanism for the temperature–size rule and for anguillid life history strategies. A genetic link is proposed between increasing age (length) at elver and silver eel stages with increasing distance from the spawning area.

American eel (Anguilla rostrata) recruitment has declined dramatically, in parallel with that of European eel (Anguilla anguilla). Since both species spawn in the Sargasso Sea and migrate as larvae to continental waters, the coincidence in recruitment failure implies an Atlantic‐wide cause, due perhaps to ocean climate. There is indirect evidence that the Gulf Stream has weakened in the 1980s. A slower Gulf Stream could interfere with larval transport and generate observed patterns of declining abundance of American eel only in northern North America and relatively uniform declines of European eel throughout Europe. While specific causes are still unclear, these data indicate a threat to both species and to their commercial fisheries.