Age, size, sex, growth, and migrations of yellow and silver phase American eels

Kenneth Oliveira, University of Rhode Island


Several aspects of the life history of the American eel Anguilla rostrata in the Annaquatucket River, RI were investigated using yellow and silver phase eels. Movements and growth rate of yellow phase eels were studied by use of mark (liquid nitrogen-cooled brands) and recapture (electrofishing) techniques. Marked yellow eels were also injected with tetracycline (75.0 mg/kg body wt.) to validate the periodicity of growth rings present on the otoliths. Migrating silver eels were collected in fyke nets in 1990 and 1991 to examine age, length, and growth rates. The effects of river location and sex on these life history parameters was also evaluated.^ Yellow eels were found to have restricted movements and it is concluded that smaller eels ($<$180 mm) conduct the majority of the upstream migration in this river. Growth of eels in the Annaquatucket River appears to occur during a 214 day growth period, when water temperatures exceed 10$\sp\circ$C. The estimated mean annual growth rate for yellow eels during this study was 23.3 mm. Examination of otoliths showed that growth rings were produced one per year and can be classified as annuli. This allowed the age of eels in this population to be determined. Among silver eels, females averaged significantly larger and older (510 mm total length, TL, and 12.8 yrs) than male eels (337 mm TL and 10.9 yrs). Female eels also had a faster mean growth rate (37.8 mm yr$\sp{-1}$) than males (30.2 mm yr$\sp{-1}$). Male eels comprised 95.6 percent of the migrating population. Upstream locations produced significantly older and slower growing eels. Female eels were only collected from upstream nets indicating a preference for the slower growth habitats. Data from this population support previous hypotheses that length and age increase with latitude. However, the sex ratio of eels in this river contradicts the hypothesis that the proportion of male eels declines at higher latitudes. ^

Subject Area

Biology, Ecology|Biology, Zoology|Agriculture, Fisheries and Aquaculture

Recommended Citation

Kenneth Oliveira, "Age, size, sex, growth, and migrations of yellow and silver phase American eels" (1994). Dissertations and Master's Theses (Campus Access). Paper AAI9513250.