Abstract
Despite the demonstrated benefits of marine protected areas, there has been relatively little dialogue about freshwater protected areas (FPAs) even though some have been established to protect freshwater species from recreational and commercial fishers. After populations recover from fishing pressure, abundances and densities of formerly fished species increase, and we should therefore expect changes in demographic traits compared to those in exploited populations. To test this, we used capture-mark-recapture data for 10 Galaxias maculatus populations across a density gradient mediated by different degrees of fishery closure. We examined the extent to which density-dependent (DD) and density-independent (DI) effects interact to affect specific growth rates in post-recruit populations. We found that population density, stream temperature and individual size interact to affect growth rates. When population densities were high, compensatory responses of far slower growth rates were strongest, indicating that DD growth is a key mechanism regulating post-recruit populations of G. maculatus. This study emphasizes the importance of understanding DD and DI processes, their interactions, function and effectiveness for freshwater fisheries management. For FPAs to be effective, the extent and quality of target species' habitats must serve as key criteria for protection to alleviate competition for limited resources that underpins DD processes.
Highlights
The last century has seen an expansion of protected areas (PAs) worldwide [1]
We examined the additive and interactive effects of individual size, population density, benthic biomass, canopy closure, stream temperature and stream discharge on specific individual growth rates of G. maculatus across a density gradient mediated by areas closed to fishing [26]
Galaxias maculatus population density patterns matched expectations based on stream type, with closed streams (Sites 6, 7 and 9) having greater population densities than partially closed and open streams (Sites 1, 2, 3, 4, 5, 8 and 10; table 1)
Summary
The last century has seen an expansion of protected areas (PAs) worldwide [1]. Marine protected areas (MPAs), in particular, have been embraced as management tools for biodiversity conservation and fisheries enhancement. The reserve effects that typically occur after the establishment of MPAs, when compared with unprotected areas, include increased average ages and sizes of individuals within fish populations, increased abundances and densities, enhanced reproductive output, increased biodiversity, improved habitat complexity and shifts in ecosystem function [6,7] These types of responses to protection are expected, but subsequent biological and ecological processes. Post-recruit demography may inherently reflect the demography of early life stages [29] and their survival to adulthood
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