Defining ecologically-relevant scales for spatial protection using long-term data on an endangered seabird and local prey availability
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Abstract
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.
Cite this as
2016. Defining ecologically-relevant scales for spatial protection using long-term data on an endangered seabird and local prey availability. PeerJ Preprints 4:e2122v1 https://doi.org/10.7287/peerj.preprints.2122v1note This preprint is not peer-reviewed. You may wish to reference the subsequent peer-reviewed version of this article.
Author comment
This is a preprint submission to PeerJ Preprints. The manuscript is to be submitted to Conservation Biology.
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Supplemental Information
Appendix S3: Full candidate model set and model selection results
Additional Information
Competing Interests
The authors declare that they have no competing interests.
Author Contributions
Richard B Sherley conceived and designed the experiments, analyzed the data, wrote the paper, prepared figures and/or tables, reviewed drafts of the paper.
Philna Botha analyzed the data, wrote the paper, reviewed drafts of the paper.
Les G Underhill analyzed the data, reviewed drafts of the paper.
Peter G Ryan reviewed drafts of the paper.
Danie van Zyl performed the experiments, reviewed drafts of the paper.
Andrew C Cockcroft performed the experiments, reviewed drafts of the paper.
Robert JM Crawford performed the experiments, reviewed drafts of the paper.
Bruce M Dyer performed the experiments, reviewed drafts of the paper.
Timothée R Cook conceived and designed the experiments, analyzed the data, wrote the paper, prepared figures and/or tables, reviewed drafts of the paper.
Animal Ethics
The following information was supplied relating to ethical approvals (i.e., approving body and any reference numbers):
The work involving vertebrate animals (counts of birds) was conducted by staff of the South African Government's Department of Environmental Affairs (the relevant permitting authority) and approved by their Animal Ethics Board.
Field Study Permissions
The following information was supplied relating to field study approvals (i.e., approving body and any reference numbers):
The field data were collected by the co-authors from the South African Government's Department of Environmental Affairs and Department of Agriculture, Forestry and Fisheries (the relevant permitting authorities).
Data Deposition
The following information was supplied regarding data availability:
Plots of the bank cormorant count data and rock lobster data are including in the manuscript. Code to fit the state-space model is included in the supplementary materials. All raw data are held in repositories of the South African government and are free-available upon request.
Funding
Funding was provided by the National Research Foundation (NRF), through its SEAChange Programme (Grant Number: 79735) and an incentive grant to RJMC, the Leiden Conservation Foundation (RBS), the Claude Leon Foundation (TRC). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
