What’s the deal with eels? – Lucy Porter, David Righton and Caroline Durif

What It Covers

European eels undertake an 8,000 kilometer migration from European rivers to the Sargasso Sea to spawn once and die, yet scientists have never observed spawning or found eggs in the wild despite centuries of research.

Key Questions Answered

• •Magnetic navigation system: Eels navigate across the Atlantic using Earth's magnetic field by sensing both direction (magnetic north) and intensity (which varies from poles to equator), creating a biological GPS that guides them to spawning grounds without visual landmarks.
• •Vertical migration behavior: During ocean migration, eels dive to 1,000 meters depth during daylight and rise to 500 meters at night, timing their movements precisely with dawn and dusk despite extreme pressure changes of 50 atmospheres, likely for navigation calibration.
• •Critical endangerment factors: European eels face population collapse because they live decades before reproducing once, bioaccumulate pollutants throughout their lifespan, encounter barriers like dams, and cannot be farmed because scientists cannot identify what to feed larvae in captivity.
• •Delayed sexual maturation: Eels remain sexually immature adolescents for 15 to 90 years in freshwater habitats, only developing reproductive organs during their final ocean migration when they stop eating entirely and rely on stored energy for the 5,000 kilometer journey.