Freshwater reserves for fisheries conservation and enhancement of a widespread migratory fish.
As management tools, freshwater reserves are under-represented in protected area networks for fisheries conservation and enhancement. This is surprising considering that freshwater ecosystems, and the biodiversity they support, are among the most threatened worldwide. We compared freshwater reserve types established to prevent overexploitation of migratory galaxiids (mostly īnanga Galaxias maculatus) from fishing and evaluated their performance as reproductive reservoirs. We studied 10 streams classified into three a priori types: (a) closed, (b) partially closed and (c) open streams. Closed streams had greater abundances, biomasses and egg production of G. maculatus despite having a greater proportion of smaller fish compared to partially closed and open streams. Community-level analyses indicated differences in fish assemblages between closure types. Large, native, predatory fish (longfin eel Anguilla dieffenbachii, shortfin eel Anguilla australis and giant kōkopu Galaxias argenteus) were more common in closed streams. Overall, there were notable reserve effects related to closed streams. There was slight evidence that partially closed streams conferred some fisheries benefits compared to streams open to fishing. While the limited number of reserve streams warrants some caution in conclusions, partial closures may still be worthwhile as a management tool where complete closure to fishing is not feasible. Closures can be effective in increasing fish numbers, albeit at a cost of smaller sized individuals, most likely because of density-dependent processes relating to food and habitat. Despite clear benefits in total egg production of populations in closed streams, it remains unclear how these benefits may translate across the full life history of the annual G. maculatus. Synthesis and applications. We demonstrate that freshwater reserves have many of the 'reserve effects' observed in more common marine reserves, but there are also important differences. Stream closure should be considered as one potential management tool that is unlikely to be effective unless stream habitats are returned to more pristine states. Our effort to evaluate the explicit effects of different reserve types across different spatial scales is the first we know of for migratory freshwater fishes, providing useful insights for adjusting the current reserve network and establishing new reserves.