NATURALIST'S 



NOTEBOOK 



Gene Helfm, 



55? 



An eel's skin and thick epidermis 

 protect it from changes in water salinity. 



young larva, the eel has little or no 

 pigmentation, is virtually transparent 

 and is called a "glass eel." 



When half-grown, it darkens to 

 blackish-yellow and is called a "yellow 

 eel." At adulthood, the burnished bronze 

 fish is called a "silver eel." 



The catadromous American eel 

 migrates from fresh to salt waters to 

 spawn, unlike the anadromous salmon. 

 It is found from Iceland to Venezuela 

 wherever rivers flow into the sea. Many 

 scientists believe the eel's slick, slimy 

 coating and thick epidermis provide 

 double protection against the osmosis of 

 toxic saline levels when it returns to salt 

 water from fresh water. In its lifetime, 

 an eel travels from the cool waters of the 

 Sargasso Sea, located in the middle of 

 the Atlantic Ocean, to the fresh inland 



waters of North America and then back 

 again with no signs of toxicity. 



Life for eels begins in the deep, 

 dark heart of the Sargasso, which 

 averages more than 3 miles deep. As 

 tiny larvae, they hatch and begin to 

 slowly ascend the water column. 

 Gradually, the newborns join micro- 

 plankton at the water's surface to ride 

 the currents bound for land. 



Only the fortunate eels survive this 

 yearlong swim. Those that make it have 

 yet another expedition ahead of them — 

 a swim along freshwater rivers, canals 

 and streams. Unlike the more acrobatic 

 adult salmon, which can be seen leaping 

 waterfalls on their upstream migration to 

 spawn, young eels move deeply and 

 silently, preferring cool, dark waters to 

 warm, sunny ones. 



Obstructions pose a challenge — 

 but not a blockade — to creatures so 

 forwardly inclined. In the evenings, 

 when the eels prefer to move, they have 

 been spotted scaling moist bridges or 

 wet dams, even shimmying over dewy 

 grasses to resume their journey on the 

 other side. 



This remarkable pioneer eventually 

 makes its "home away from home" in 

 cool lakes, ponds, tranquil reservoirs or 

 estuaries where it remains and matures 

 for up to 10 years. In these habitats, it 

 begins to eat heavily, taking on a heavy 

 mantle of flesh and fat as stored energy 

 for a future journey. 



Its mucus thickens, and its blood 

 becomes toxic — systemic defenses that 

 help boost resistance to starvation, 

 asphyxiation and infections. Eventually, 

 its digestive tract degenerates, and it 

 ceases to feed. 



From late August to mid-Novem- 

 ber, changes in the environment, such as 

 higher water levels and dimmer light 

 intensities, signal the eel to begin its last 

 journey. It turns seaward to the Sar- 

 gasso, where it will mate. 



The events surrounding eel 

 spawning are shrouded in mystery. 

 Many scientists believe that adult eels 

 die soon after spawning. Helfman 

 agrees. "Female fishes that have 

 spawned have very characteristic 

 ovaries with a few leftover eggs," he 

 says. "No eels have ever been found in 

 that spent condition." Also, he adds, 

 "large, ripe eels are found migrating out 

 of rivers, but none have ever been found 

 migrating back into rivers." 



Perhaps the eels tire and sink to the 

 ocean floor. Perhaps, in a defenseless 

 state, they are eaten by predators. One 

 thing is certain. As many as 15 million 

 to 20 million eggs per female spill onto 

 the waves, spiraling gently across them. 

 Soon, in the warm sunlight of a prime, 

 vernal season, the waves begin to pulse 

 with the rhythm of the young. □ 



COASTWATCH 23 



