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Sherley RB, Botha P, Underhill LG, Ryan PG, van Zyl D, Cockcroft AC, Crawford RJ, Dyer BM, Cook TR.2016. Defining ecologically-relevant scales for spatial protection using long-term data on an endangered seabird and local prey availability. PeerJ Preprints4:e2122v1https://doi.org/10.7287/peerj.preprints.2122v1
Human activities are important drivers of marine ecosystem functioning. However, teasing apart the synergistic effects of fishing and environmental variability on the prey base of non-target predators is difficult, often because estimates of prey availability on appropriate scales are lacking. Hence, understanding the links between direct measures of prey abundance and population change can help integrate the needs of non-target predators into fisheries management. Here we investigated the local population response (number of breeders) of bank cormorants Phalacrocorax neglectus, an Endangered seabird, to the availability of its prey, the heavily-fished West Coast rock lobster Jasus lalandii. Using Bayesian state-space modelled counts of cormorants at three colonies, 22 years of fisheries-independent data on local lobster abundance and generalized additive modelling, we determined the spatial-scale pertinent to these relationships in areas of differing lobster abundance. Cormorant numbers responded positively to rock lobster availability in the regions of intermediate and high abundance, but not where regime shifts and fishing pressure have made rock lobster scarce. However, the spatial scale (30 km) at which the relationships were strongest was greater than the cormorants’ foraging range when breeding. Prey availability in the non-breeding season, prey switching and prey ecology can all influence neritic seabirds and should be considered in marine spatial planning. Crucially, though, our results highlight the potential for small-scale marine protected areas (MPAs) to benefit top predators over their full-life cycle by protecting their prey. Precautionary implementation of MPAs, with robust assessment and adaptive-management, could protect predators and their prey without negatively impacting dependent fisheries.
This is a preprint submission to PeerJ Preprints. The manuscript is to be submitted to Conservation Biology.