PONE-D-19-27751

Early conservation benefits of a de facto marine protected area at San Clemente Island, California

PLOS ONE

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Reviewers' comments:

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Reviewer #1: Yes

Reviewer #2: Partly

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Reviewer #1: Yes

Reviewer #2: Yes

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Reviewer #1: Yes

Reviewer #2: No

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Reviewer #1: Yes

Reviewer #2: Yes

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5. Review Comments to the Author

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Reviewer #1: This is a clear and compelling paper that evaluates some of the effects of restricted use in a de facto marine protected area (DFMPA) off the California coast. The subject is of particular interest as countries look for ways to ramp up the percent protected area coverage of their maritime jurisdictions. Military restrictions around San Clemente Island present an opportunity to study a controlled area and compare biomass and community structure with adjacent fished areas. The paper is technically sound, extremely well-written, and presents the data that were used in the analysis.

However, regarding whether the data can be said to support the conclusions, this is the paper’s greatest weakness. The authors claim that the lack of differentiation in biodiversity metrics between the DFMPA and fished sites for most species surveyed is due to longer trajectories of recovery for species other than sheephead and ocean whitefish – but does what we know about the life histories the other species support this contention? An alternative hypothesis might be that fishing pressure in the fished area is spread across many species, and therefore does not alter the community ecology (therefore not presenting a condition from which recovery can be measured). Or perhaps microhabitats do vary between fished and DFMPA sites – these were not assessed and as the authors themselves state, may be a bigger factor in determining condition (biomass and diversity) than fishing pressure. Differential spillover is unlikely, unless the authors can point to some aspect of reproductive ecology or larval dispersion of the sheephead and whitefish not shared by the other species. Since the data collected and the time since closure are both limited, it may be too early and too much of a stretch to speculate as to why the DFMPA has bigger specimens and higher densities of sheephead and whitefish and not the other species.

I believe the paper would also benefit from an expanded discussion around Other Effective Conservation Measures (OECMs). The authors are undoubtedly aware of the very fluid (and sometimes highly contentious) debates around what constitutes OECMs, and the fact that there is a lot of pressure to make the definition as wide as possible so that contracting parties to the Convention on Biological Diversity can claim to be approaching Aichi Target 11, thereby keeping to their commitments. However, the draft decision of the SBBSTA (CBD/SBSTTA/22/L.2 6 July 2018) does say that the definition of OECM covers considerations of governance, including equity issues, which military bases and restricted areas could not be said to fulfill. Furthermore, while the DFMPA studied does demonstrate tangible conservation benefits for two heavily fished species, no assessment was made of how routine military operations or periodic exercises affect all species in the area, including marine mammals. ‘Effective conservation’ within the OECM means conservation of all species, not only a select few. The paper should be forthright about mentioning these limitations.

Another area where the paper could be strengthened is in the discussion of future research – in particular how to overcome the design flaw that the current study has in that it had no reference points in fished areas other than those adjacent to the DFMPA. Spillover could confound the existing comparison, as could any perception issues among fishers that would limit their fishing in the areas adjacent to the restricted area (if, for instance, fishers were wary of accidentally entering the restricted area). If any information is currently available on the recreational fisheries taking place in the vicinity of the DFMPA, it would be useful to include this. The specific characteristics of the fishery(ies) may also pertain to trying to surmise why the reserve effect is measurable for sheephead and whitefish – perhaps recreational fishers target primarily these two species? And getting back to the next steps part of the discussion, the authors could provide more detail on how an expanded sampling design could overcome some of the weaknesses of the original limited research.

One might argue that it would be necessary to conduct this additional research and feed the additional data into the analysis, before the paper could be ready for publication. However, even though the findings are limited and the implications circumscribed, this paper is pioneering and merits publication. With a more robust discussion of what constitutes OECM and how DFMPAs can add value alongside proper MPAs, the paper will provide valuable guidance to MPA planners and to marine spatial planners looking at wider scale marine management and conservation.

One very minor point: in Line 61, recommend substituting ‘very little research’ with ‘very few published studies’ – no one knows how much research is going on, especially if the research is not yielding significant results.

Reviewer #2: In this study, the authors used ROV surveys to compare the density, size structure, and biomass of fishes between a de facto marine protected area (DFMPA) and a fished site on San Clemente Island, California, in the 2-3 years following full closure of the DFMPA. The authors report differences in the density and biomass of one fish species (California sheephead) and biomass of another fish species (ocean whitefish), but no differences in diversity, community structure, or the abundance and biomass of any other species. Below are specific comments for the authors to consider.

- How long has the DFMPA been in place in Zone G? When were the 8 naval safety zones established? What fraction of the time are the other zones closed to human activities, such as fishing? It sounds like the other zones can serve as partial DFMPAs, depending on the frequency with which they are closed due to military activities. OK… I see that in the methods the timing of implementation of the DFMPA was 2010. This should be mentioned in the abstract and probably earlier in the intro as well. If the surveys occurred in 2012 and 2013, then it appears that the area was only closed for 3 years. If that is the case, it’s not surprising that few significant differences were detected, especially if fishing pressure in zone F isn’t too intense.

- Line 133. I think maybe the wrong citation is used for fishing pressure at San Clemente. I think this should be reference 23, not 24. In addition, more detail is needed to quantify how much fishing pressure occurs in zone F, as opposed to more generally at San Clemente Island. Zone F is on the windward side and far from the most popular anchorage, so how much fishing pressure actually occurs there? If not all that much, that could explain why differences between the DFMPA and fished zone were not great for most species.

- One of the major challenges with this study is that it only compares 1 DFMPA to 1 fished area outside the DFMPA. This needs to be discussed in more detail, because the differences or lack of differences observed could be due to this design. The authors include some simple comparisons of habitat between the two areas, suggesting that habitat is similar. However, that analysis used simple metrics of percent rocky habitat and depth. What is not shown is whether the habitat quality is similar or not. How does the rugosity and complexity of the rocky habitat compare between the two zones? If one has mainly flat rock and the other has much more complex 3-dimensional habitat with higher relief, that could explain the differences in sheephead and ocean whitefish density and biomass, irrespective of fishing pressure. The size distribution comparison for sheephead shows that not only are larger fish present in the DFMPA, but also new recruits and small juvenile size classes are present as well. That could be an indicator of better habitat quality for all size classes of this species in the DFMPA. Lastly, Zone G is located at the northern tip of the island. Many studies show higher densities and biomass of fishes at the tips of islands, reefs, and atolls, due to stronger currents, productivity, and prey availability at the tips. This oceanographically-driven phenomenon could be another explanation for higher sheephead density and biomass, that should be discussed.

- More description is needed of the video imagery analysis section. How do you define a non-overlapping video quadrat? What are the dimensions of the quadrat? How many quadrats per transect?

- Even though the community structure was similar in the multivariate analysis, it would still be useful to include the nMDS figure to show the reader how the sites overlap. Where the community structure analyses done using density or biomass and the response variable. Are the results the same for both metrics?

- The analysis comparing size distributions between the DFMPA and fished site should be placed in the results section and not saved for the discussion. Size frequency distribution comparisons should also be shown for some of the other common species sampled.

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Reviewer #1: No

Reviewer #2: No

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Early conservation benefits of a de facto marine protected area at San Clemente Island, California

PONE-D-19-27751R1

Dear Dr. Esgro,

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Heather M. Patterson, Ph.D.

Academic Editor

PLOS ONE

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