Impact of climate on eel populations of the Northern Hemisphere

Abstract

Glass eel abundances are declining worldwide. This has mostly been attributed to direct impacts of human activities such as overfishing or habitat loss and degradation, whilst the potential influence of changes in oceanic conditions has received less attention. Eel are characterized by a complex and still enigmatic life cycle that includes a trans-oceanic spawning and larval migration. The apparent synchrony in the decline of eel populations worldwide suggests that the oceanic mechanisms involved are similar for all populations. We analyse the relationships between oceanic conditions in eel spawning areas and glass eel recruitment success of the 3 most commercially important species of the genus Anguilla: A. anguilla, A. rostrata, and A. japonica. We provide evidence that the survival of eel larvae is strongly correlated with food availability during their early life stages. Over the last 4 decades, changes in the marine production related to global warming may have led to the decline of European, American and Japanese eel populations. In the Pacific and Atlantic Oceans, the shifts in the temperature regime detected in the late 1970s were followed by shifts in the recruitment regime of glass eel for the 3 species. The decrease in primary production through climate-driven processes has therefore affected the recruitment of eel populations.

LENGTH WEIGHT RELATIONSHIPS OF THE EUROPEAN EEL Anguilla anguilla (Linnaeus, 1758) FROM SIX KARST CATCHMENTS OF THE ADRIATIC BASIN, CROATIA

“…In the Rivers Jadro and Žrnovnica, the overall CPUE (g 100 m rapidly declined in time during the sampling period (Fig 3. ), probably due to environmental changes, but also due to the global disappearance of this species (Behrmann-Godel and Eckmann, 2003;Bonhommeau et al, 2008). Eel population from the Hutovo Blato Wetland showed a similar trend (Glamuzina et al, 2008).…”

Changes in the fish community of Loch Leven: untangling anthropogenic pressures

“…The above local anthropogenic pressures together with more widespread factors (Bonhommeau et al, 2008) are also likely to have contributed to a decline in the eel population of Loch Leven. The catches of commercial eel fishings at the outflow from the loch declined through the nineteenth century and these operations finally came to an end in 1901 (Munro, 1994).…”

Habitat residence during continental life of the European eel Anguilla anguilla investigated using linear discriminant analysis applied to otolith Sr:Ca ratios

“…Despite the existence of many studies documenting eel movements between marine, brackish and freshwater environments (Tzeng et al 1997, Tsukamoto et al 1998, Bonhommeau et al 2008, Bureau du Colombier et al 2008, Aarestrup et al 2009), little is known about the dominant migratory strategies during continental life in A. anguilla. After entering freshwater, European eels are assumed to be primarily resident in freshwater habitats (Laffaille et al 2005, Lin et al 2011), but inter-habitat migrations be tween fresh and brackish waters and residence in brackish waters have been observed for this species and its close relatives (Arai et al 2004, Daverat et al 2005, 2006, Jessop et al 2008).…”

“…Investigating Anguilla anguilla movements during continental life and its variation at both local and global scales is of paramount importance for the conservation of this endangered species (Bonhommeau et al 2008, Belpaire et al 2009), especially within the context of littoral habitat alteration due to anthropogenic activities and climate change. Because the abiotic and biotic conditions experienced by the eels within their continental habitats can induce strong differences in growth rate, age at maturity, sex ratio and lifetime reproductive success (Panfili & Ximenes 1994, Jessop et al 2004, Walsh et al 2004, Bevacqua et al 2006, Daverat & Tomas 2006, Melia et al 2006a, habitat loss during continental life can also threaten the maintenance of eel stocks in the future through a loss in reproductive success (Bonhommeau et al 2008, Belpaire et al 2009). In this regard, most of the investigations have focused on the continental habitats identified along the west European coasts (Daverat et al 2005, Laffaille et al 2005, Daverat & Tomas 2006, and nothing is known about the migratory behaviour of A. anguilla within its Mediterranean coastland habitats.…”