A switch in species dominance of a recovering pelagic ecosystem

Abstract

Although many marine ecosystems have been adversely impacted by human activities,1 some are now recovering due to reductions in fishing pressure.2-4 Here, we document the recovery of an ecosystem subjected to intense anthropogenic activity for over 200 years, the Clyde Sea.5 This region once had productive fisheries for herring (Clupea harengus) and other fish, but these disappeared at the turn of the century.6,7 Using acoustic surveys of the pelagic ecosystem, we found that the Clyde Sea supports 100 times as many forage fish as in the late 1980s. However, herring has now been replaced by sprat (Sprattus sprattus), despite virtually no fishing on herring for 20 years. A combination of a warming sea,6 bycatch of herring in the prawn (Nephrops norvegicus) fishery,8,9 and susceptibility of herring to poor recruitment may have contributed to this unexpected recovery. We compare this to similar unexpected "recoveries" involving unforeseen ecosystem effects, such as the return of hake (Merluccius merluccius) to the North Sea;10,11 the recent expansion of the pelagic squat lobster, "munida," (Pleuroncodes monodon) off Peru;12 and the increase in scallop (Placopecten magellanicus) numbers on Georges Bank.13 The lack of a current sprat fishery in the Clyde presents a unique opportunity to develop an alternative industry for its seafaring community: ecotourism. Charismatic megafauna (whales, dolphins, and seabirds) that people will pay to see14 will, in time-if not already15,16-be drawn in by the abundance of forage fish now present, further restoring the biodiversity of the region after centuries of overexploitation.