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Yellow Eel Ecology Post-Metamorphosis: Habitat Use, Activity, Diet, Demographics, and Morphological Changes

Explore the ecology of yellow eels post-metamorphosis, including their habitat use in estuaries and rivers, variable activity levels, opportunistic diet, demographics related to distance inland, and morphological transformations from yellow to silver. Gain insights into their movements, survival rates, growth patterns, and physiological adaptations.

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Yellow Eel Ecology Post-Metamorphosis: Habitat Use, Activity, Diet, Demographics, and Morphological Changes

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  1. Yellow eel ecology

  2. After Metamorphosis • Staging in estuaries/river mouths • Later by increasing latitude (March-May) • Size 50-70 mm (increases with latitude) • Movement upstream related to tidal height, temperature(10-12) and temperature differential (river and bay), and discharge • Upstream movement • up to 2.3 km/day (St Lawrence River) • ‘many years’ (Atlantic coast drainages)

  3. Size • Recently metamorphosed • TLx~61 mm (range 50-70 mm) • TL increases with increasing latitude • Max • > 1m (large migratory females) • Males typically smaller than females

  4. Habitat Use • Brackish (estuarine) • Freshwater (lakes, rivers, streams) • Multimodal (FW then estuarine, growth advantage?)

  5. Habitat use • Highly variable • Leaf packs, debris, undercut banks in rivers • Small mountain streams, ‘trout habitat’ (pools with structure) • Sheltering in winter (large cobbles, under stream banks)

  6. Home range High site fidelity - short time (GA, VA, NE); multi years (VA) Range Size – greater in FW than brackish (GA), seasonal migrations in FW; VA mountain year-round residents may vary with food availability, habitat type, density of conspecifics

  7. Activity • Varies by season, time of day • Spring, summer, early fall longer periods of activity in mountain streams (crepuscular/night) • Winter (VA) largely inactive except for brief periods late night/early morning

  8. Diet Top predator individuals often largest predators and eels comprise significant proportion of total fish biomass in a community Diet opportunistic, related to availability and eel size - larger eels, larger prey • Small eels FW: insects • Large eels FW: crayfish and fish • Small eels Brackish: microcrustaceans

  9. Survival/mortality • From Anguilla anguilla: • Age related, age 1-2 increase 35-80% then approaches 90% through age 10 • Predation presumed • Fisheries (all life stages), Hydro facilities, diversions, pollution

  10. Growth • ME • 18-31 mm/yr • RI • Coastal streams 23-33 mm/yr • GA • Coastal plain 67-62 mm/yr • VA • Mountains 19-26 mm/yr

  11. Demographics • Related to distance inland • Density declines with distance • Riverine eels longer than estuarine (GA, VA, NE) • Further inland more likely to be female (NE, GA, SC, VA) • Closer to coast sex ratios disparate but males often predominate • Lacustrine habitats greater proportions of females

  12. Demographics (con.) • Southern eels > 300km inland (e.g. Shenandoah) similar to northern eels (Lakes Ontario and Champlain) • Females, max size > 1m • Far upstream eels take 2+ years longer to mature • 15% increase in maturation time yields 65-93% increase in fecundity

  13. Demographics (con.) • Distribution & abundance: Scale dependant • Large scale predictive models based on local habitat features highly variable, not transferable. Habitat relations a function of distance from ocean • Density not related to habitat type, substrate, etc. NC, SC, NE, VA • Large scale (physiographic or river-basin) patterns better described by random upstream dispersal (diffusion) model

  14. Yellow to Silver • Morphology • Change in skin color from yellow to silver or bronze • Thickening of integument • Increased length and weight • Relative lengthening of pectoral fins • Increased eye diameter • Physiology • Change in gill structure/cell composition • Degeneration of alimentary canal • Increased oocyte diameter and developmental stages • Increased gonadal weight • Changes in muscle properties

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