2026/07/01 by Simon D. Stewart, Robin Holmes, Robin P. Holmes +5
Biochemistry, Genetics and Molecular Biology · Environmental Science · Agricultural and Biological Sciences · #Reproductive biology and impacts on aquatic species #Fish Ecology and Management Studies #Aquaculture Nutrition and Growth
paper · doi:10.1111/1365-2664.70489
Abstract Despite multiple calls to adopt new food web‐based restoration approaches, habitat enhancement remains the most widely used strategy. Habitat enhancement is premised on the ‘field of dreams’ concept (build it and they will come), assuming that restoring degraded systems by adding or improving habitat will increase the carrying capacity and thus increase target species populations. However, exothermic apex predators are commonly limited by food availability, not solely by access to habitat. Rebuilding structure without increasing food availability is a hidden constraint on restoration success which will be accentuated by higher ambient temperatures with resultant elevated metabolic rates. Here, using a catchment‐scale natural experiment in which prey availability for predators is controlled by stochastic variability in coastal lagoon morphology, we demonstrate that the annual production of a threatened freshwater apex predator, the longfin eel ( Anguilla dieffenbachii ), increases through restoration of small‐bodied diadromous upstream fish migrations. By supplying freshwater systems with trophic subsidies—that is, food—apex predator production increases even within highly modified agricultural river catchments where longfin eels are habitat‐limited. We found that longfin eels in our study system were near carrying capacity and migratory prey fish enhanced growth of longfin eels by ~350%, with no compensatory reduction in biomass observed, as otherwise assumed within a habitat‐constrained population. The trophic subsidy translated into higher eel production. These results demonstrate that a diet‐based conservation approach which enhances cross‐ecosystem food subsidies is a viable approach to top predator conservation. Synthesis and applications . Our study shows that, ‘If you build it, they will come—but only if they can meet their energetic demands’. Given the ubiquity of diadromous fish globally, coupled with the threatened status of many freshwater predators, our findings highlight the significant potential of lowland freshwater ecosystems to support predatory fish conservation through restoring cross‐ecosystem food web connections.