Geographic effects on American eel (Anguilla rostrata) life history characteristics and strategies

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 degrees 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 degrees C declined with increasing latitude. Female growth rates adjusted for the number of degree-days were approximately constant south of 44 degrees 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.