Did a “Perfect Storm” of Oceanic Changes and Continental Anthropogenic Impacts Cause Northern Hemisphere Anguillid Recruitment Reductions?

Attention has focused on two primary possible causes of the declines of anguillid eels in the Northern Hemisphere that include anthropogenic impacts on eels in their growth habitats, such as overfishing, dams, filling wetlands, revetment/channelization of rivers, pollution, and introduction of parasites.  The cumulative effects of dams/river alterations and reaching a peak in industrial pollution must have greatly affected eel production in many areas, and contamination by metallic and organic compounds may have contributed to shifts in eel life history traits.  Secondly, various ocean-atmospheric changes might reduce feeding success of larvae or disrupt adult spawning or larval transport.  Recent research indicates that leptocephali feed on marine snow particles, so if regime shifts such as NAO reduce the production of marine snow, it may affect larval survival.  This could be important if the critical time-window is larval first-feeding that requires a specific size range of marine snow particles, because this could result in density-dependent early larval survival for each spawning event.  Reduction of spawners from species-range margins that might spawn outside of peak periods could reduce recruitment further.  The possibility that both types of impacts, oceanic and anthropogenic, impacted eel populations simultaneously is discussed along with issues related to population recovery.