Decadal Changes in the Abundance and Length of Snapper (Chrysophrys auratus) in Subtropical Marine Sanctuaries

RESEARCH ARTICLE Decadal Changes in the Abundance and Length of Snapper (Chrysophrys auratus) in Subtropical Marine Sanctuaries Hamish A. Malcolm1*, Arthur L. Schultz2, Patrick Sachs3, Nicola Johnstone4, Alan Jordan5 1 Marine Ecosystems Research, NSW Department of Primary Industries, PO Box 4297, Coffs Harbour, NSW, 2450, Australia, 2 Southswell Marine, 204 Schnapper Beach Road, Urunga, NSW, 2455, Australia, 3 Australian Fisheries Management Authority, Box 7051, Canberra, ACT, 2610, Australia, 4 Solitary Islands Marine Park, NSW Department of Primary Industries, PO Box 4297, Coffs Harbour, NSW, 2450, Australia, 5 Marine Ecosystems Research, NSW Department of Primary Industries, Private Bag 1, Nelson Bay, NSW, 2315, Australia * Abstract OPEN ACCESS Citation: Malcolm HA, Schultz AL, Sachs P, Johnstone N, Jordan A (2015) Decadal Changes in the Abundance and Length of Snapper (Chrysophrys auratus) in Subtropical Marine Sanctuaries. PLoS ONE 10(6): e0127616. doi:10.1371/journal. pone.0127616 Academic Editor: Dennis M. Higgs, University of Windsor, CANADA Received: November 5, 2014 Accepted: March 27, 2015 Published: June 10, 2015 Copyright: © 2015 Malcolm et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability Statement: All relevant data are within the paper and its Supporting Information file. Funding: The authors received no specific funding for this work. It was undertaken as part of core funding for marine parks research by the NSW Government. Abundance and length of the highly-targeted snapper Chysophrys auratus were compared between sites in 'no take' areas (Sanctuary Zones: SZ), partial protected areas which are fished (Habitat Protection Zones: HPZ), and areas outside (Outside) the Solitary Islands Marine Park (SIMP), Australia. Baited Remote Underwater Video (BRUV) sampling on shallow rocky reef (15 - 25 m) was conducted annually from 2002 until 2014 in the Austral-winter, covering the decade after these marine park zones were established (2002). Additional deeper sites (25 - 40 m) were sampled in 2010-2011 to assess if findings were more-broadly applicable. Lengths were measured using stereo-BRUVs from 2011-2014. Snapper were significantly more abundant in SZ overall and in most years compared with the other two management types, which did not significantly differ. Snapper rapidly increased after 2 - 3 years protection in all management types, especially SZ. Snapper were present on more SZ deployments than HPZ and Outside after the same period. The positive SZ response in snapper abundance on shallower reef was also found at a broader spatial scale on deeper sites. Again the two fished management types did not show significant differences among each other. There was considerable variation in snapper abundance between years, with strong peaks in 2005, 2009 and 2014 especially in SZ. Abundances remained higher in SZ in the year or two following a strong peak, but decreased to similar abundances to fished areas before the next peak. Snapper length frequency distribution significantly differed between SZ and both fished management types, with more larger snapper within SZ including a higher proportion (58%) that were legal-sized (>25.7 cm FL). HPZ and Outside did not significantly differ from each other, and were dominated by individuals below legal size. Overall, SZ's have positively influenced abundance and length of snapper on these subtropical rocky reefs. Competing Interests: The authors have declared that no competing interests exist. PLOS ONE | DOI:10.1371/journal.pone.0127616 June 10, 2015 1 / 18 Increased Snapper Abundance and Length in Sanctuaries Introduction With the implementation of marine protected areas globally, there is increasing need to assess the ecological changes resulting from such spatial management arrangements. Overall, no-take areas (marine sanctuaries) can result in increases in the density and/or biomass of target species [1–3], but this response can be highly variable spatially and temporally due to inherent variability in physical, environmental, ecological and social factors [4–8]. Additionally, evaluating the effects of marine sanctuaries can be difficult as abundance data is often over-dispersed or zero-inflated reflecting biotic patterns, combined with sampling constraints in the marine environment [9]. However, key target species for fishers sampled at suitable scales can be important indicators on which to examine marine sanctuary effects [9]. A significant response to protection on abundance of targeted species can occur over a range of time-scales, but often within the decadal scale [6, 7, 10], a time-scale relevant to applied and adaptive management [8, 11]. Therefore, a spatial comparison around the decadal time-scale is useful for appraisal of management arrangements [12], although increases of target species can occur over longer periods [13–15]. Unlike marine sanctuaries, there may be no differences in abundance between partial protected areas, which are areas still fished by some methods (e.g. fishing-allowed zones in multiple-use marine parks), and adjacent fished areas outside marine parks where only fishing input and output regulations apply (e.g. bag and size limits, gear restrictions) [16, 17]. Likewise, abundances may be similar between marine park zones with different levels of partial protection (e.g. differing restrictions in the types of fishing gears allowed, although both still fished) [18]. This indicates that a response gradient decreasing from marine sanctuaries to partial protected areas and then to fished areas should not necessarily be expected, although there is potential that proximity to a marine sanctuary may increase abundance and/or size relative to areas further away [19]. This proximal increase may occur through movement of fish with a home range greater than a marine sanctuary or through density dependent interactions [19– 21]. However, this movement can be spatially constrained with distance from a sanctuary boundary [22, 23], and will depend strongly on the taxa [24] and habitat continuity across zone boundaries [25]. A species often found to have higher abundances within no-take areas compared to adjacent fished areas is snapper (Chrysophrys auratus) [9, 26, 27], an opportunistic and generalist predator in the family Sparidae. Snapper is found in temperate and subtropical continental shelf waters of southern Australia and New Zealand, with a sister species in Japan and Indonesia [28– 30]. In Australia, adult snapper prefer rocky reef habitat at depths of 20 to 200 m, while juvenile snapper are most abundant in shallower inshore habitats [28, 31]. Snapper are one of the most important target species in the subtropical and temperate waters of the east coast of Australia [32–34] with (...truncated)