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Shellfish Mariculture in Drakes Estero, Point Reyes National Seashore, California Accuracy of the Scientific Conclusions Released by NPS to the Public The Point Reyes National Seashore produced one major document on the science of Drakes Estero, including conclusions about the impacts of DBOC, for public release in four successive versions, all entitled Drakes Estero: A Sheltered Wilderness Estuary (2006b; 2007a; 2007b; 2007c). According to the Department of the Interior Inspector General’s report (DOI, 2008), Drakes Estero: A Sheltered Wilderness Estuary was prepared in part to respond to an article in the Point Reyes Light and other inquiries regarding the effects of the oyster farm on Drakes Estero and the termination of the current lease (RUO) in 2012. This document was released first as a Park News “information piece” (pdf and printed copies) in October 2006 (Box 4) and subsequent versions were posted on the Point Reyes National Seashore website. The committee received four discrete public versions of Drakes Estero: A Sheltered Wilderness Estuary. The last version released to the public was available on the Point Reyes National Seashore internet site on May 11, 2007, and was removed from the site on July 23, 2007. In addition, the Point Reyes National Seashore released one related document on July 25, 2007 (Acknowledgement of Corrections [NPS, 2007e]) and another (Clarification of Law, Policy, and Science on Drakes Estero [NPS, 2007d]) on September 18, 2007, to the Marin County Board of Supervisors that also reviewed the science on effects of DBOC on the ecosystem of Drakes Estero, which contained further modifications of NPS scientific conclusions. Whether NPS made appropriate use of available scientific information on potential impacts of the oyster culture operation on the ecosystem of Drakes Estero has been the subject of controversy, only par-
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Shellfish Mariculture in Drakes Estero, Point Reyes National Seashore, California BOX 4 Timeline for Events Related to Drakes Estero: A Sheltered Wilderness Estuary (Dates taken primarily from DOI, 2008) May 18, 2006 Point Reyes Light article claiming DBOC has little impact on estero based on the Elliot-Fisk et al. (2005) report October 28, 2006 Superintendent Neubacher gave copies of Drakes Estero: A Sheltered Wilderness Estuary (version I; NPS, 2006b) to Gordon Bennett, Sierra Club. Copies were also available to the public at this time. February 9, 2007 Drakes Estero: A Sheltered Wilderness Estuary (version II; NPS, 2007a) first posting on NPS website May 8, 2007 Drakes Estero: A Sheltered Wilderness Estuary (version III; NPS, 2007b) (date downloaded – date of posting unknown) May 8, 2007 Marin County Board of Supervisors Meeting May 11, 2007 Drakes Estero: A Sheltered Wilderness Estuary (version IV; NPS, 2007c) May 15, 2007 Letter to NPS from California Department of Fish and Game documenting NPS authority over Drakes Estero (including leased bottom) July 23, 2007 Drakes Estero: A Sheltered Wilderness Estuary removed from NPS website July 25, 2007 NPS posts “Acknowledgement of Corrections” (NPS, 2007e) September 18, 2007 NPS issues “Clarification Statement” (NPS, 2007d) November 2007 California Coastal Commission Consent Order signed by Kevin Lunny, DBOC April 22, 2008 NPS Special Use Permit signed by Kevin Lunny, DBOC tially addressed in the Inspector General’s report (DOI, 2008). Here, the committee compares its conclusions on potential impacts (the available science) to what NPS reported in their multiple versions of Drakes Estero: A Sheltered Wilderness Estuary and the “Corrections” and “Clarification” documents. While NPS in all versions of Drakes Estero: A Sheltered Wilderness Estuary accurately depicted the ecological significance and conservation value of Drakes Estero, in several instances the agency selectively presented,
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Shellfish Mariculture in Drakes Estero, Point Reyes National Seashore, California over-interpreted, or misrepresented the available scientific information on potential impacts of the oyster mariculture operation. Consequently, Drakes Estero: A Sheltered Wilderness Estuary did not present a rigorous and balanced synthesis of the mariculture impacts. Overall, the report gave an interpretation of the science that exaggerated the negative and overlooked potentially beneficial effects of the oyster culture operation. NPS has issued two documents correcting and clarifying Drakes Estero: A Sheltered Wilderness Estuary—“Acknowledgment of Corrections to Previous Versions of the Park News Document Drakes Estero: A Sheltered Wilderness Estuary,” posted on July 25, 2007 (NPS, 2007e), and the September 18, 2007 document, “National Park Service Clarification of Law, Policy, and Science on Drakes Estero” (NPS, 2007d). The Clarification document represents the most accurate NPS release of science relating to mariculture impacts, although it does not fully reflect the conclusions of this committee. It appears that hasty responses to local stakeholder concerns by NPS led to the publication of inaccuracies and a subsequent series of retractions and clarifications during this process from 2007–2008, which cast doubt on the agency’s credibility and motivation. A lack of coordination among the multiple agencies regulating the mariculture operation also gave mixed messages to stakeholders, fueling the controversy. For example, the extension in 2004 of the DBOC shellfish leases until 2029 by the California Fish and Game Commission sent a message that could be construed as conflicting with the Department of the Interior Office of the Solicitor’s interpretation of the congressional mandate for designating Wilderness in the Point Reyes National Seashore, which would prohibit the extension of the lease beyond 2012. The California Fish and Game Commission did, however, stipulate termination of the leases if the RUO was not extended. The committee describes below the major scientific conclusions presented by NPS and how these conclusions change among the various NPS public releases. Version I (released in October 2006) of Drakes Estero: A Sheltered Wilderness Estuary reports that Anima (1990) “documented substantial sediment inputs of the pseudo-feces from the oysters.” All four of the public versions of Drakes Estero: A Sheltered Wilderness Estuary make similar statements, with the last (version IV downloaded on May 11, 2007) stating that Anima (1990) “identified pseudo feces of oysters as the primary source of sediment fill.” In fact, Anima (1990, 1991) does not report any direct observations of oyster pseudofeces or feces in the sediments. The Acknowledgment of Corrections (July 2007) and Clarification (September 2007) documents admit the error in the characterization of Anima’s studies in Drakes Estero: A Sheltered Wilderness Estuary and retracts those claims. In the Clarification document, NPS uses scientific literature on effects of
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Shellfish Mariculture in Drakes Estero, Point Reyes National Seashore, California oyster biodeposition into sediments and quotes from independent scientific experts to reach reasonably substantiated conclusions about sedimentation effects that match those reached by this committee. Specifically, NPS concludes that any biodeposits from feeding oysters must necessarily fall to the estuarine bottom and to some undocumented extent become incorporated into the bottom sediments with a potential for inducing sedimentary anoxia under conditions of high shellfish stocking densities. The Clarification notes that the sediment cores taken under the racks in a subsequent study (Harbin-Ireland, 2004; Elliott-Fiske et al., 2005) did not show evidence of hypoxia, but NPS also suggests that these results from 2003 may not be representative of current conditions given the steady and substantial increase in oyster culturing activities from 2000 to 2007 (see Figure 6). All versions of Drakes Estero: A Sheltered Wilderness Estuary cite Anima (1990) in support of the conclusion that “pseudofeces of oysters are the primary source of sediment fill.” In fact, Anima (1990, 1991) does not make any observations on rate of sedimentation from oyster pseudofeces or compare those rates to other sources of sedimentation. Erosion of sediments from grazed pastures and deposition of eelgrass detritus represent potentially important additional sources of sedimentation. The Clarification document correctly states that Anima did not make any measurements of sedimentation rate from oyster biodeposits and further qualifies Anima’s (1990, 1991) statement as expert opinion that fine sediments deposited by oysters beneath the racks were likely resistant to erosion because tidal action would be limited in the upper reaches of the estero. In contradiction to Anima’s opinion, Harbin-Ireland (2004) demonstrated that sediments underneath oyster culture racks are slightly coarser not finer than those at distance from the racks. This potentially conflicting observation is not presented by NPS in discussing the sedimentation issue in the Clarification document. Each version of Drakes Estero: A Sheltered Wilderness Estuary cites Harbin-Ireland (2004) and Elliott-Fisk et al. (2005) in support of the claim that “eelgrass growth is severely restricted under active oyster racks.” While observations on eelgrass in Drakes Estero do imply some localized reduction in areal cover underneath oyster culture racks, affecting about eight acres in total (1% of eelgrass habitat in 2007), this statement does not place the relatively small effect of the oyster racks on eelgrass coverage in the appropriate context. NPS’s Clarification document provides a more balanced assessment, explicitly characterizing the observed pattern of eelgrass distribution around culture racks and placing it into the context of an approximate doubling of eelgrass coverage in Drake Estero from 1991 to 2007. Another inconsistency between all four versions of Drakes Estero: A Sheltered Wilderness Estuary and the actual data relates to
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Shellfish Mariculture in Drakes Estero, Point Reyes National Seashore, California results of a study by Applied Marine Sciences (AMS, 2002). NPS wrote: “Eelgrass, for example, in Estero de Limantour where there is no oyster farming, had higher indicators of standing stock, as measured by the numbers of turions and blades, compared to Drakes Estero (AMS 2002)”. Actually, AMS (2002) reports just the opposite—that both sites in Drakes Estero exhibited higher counts of eelgrass blades and turions than the one site sampled four times over 18 months in Estero de Limantour. Furthermore, AMS notes that this contrast is unreliable because elevation differences confound the site comparison. NPS also fails to include the demonstration by AMS (2002) that eelgrass disappeared over those 18 months from 5 of 6 plots in Estero de Limantour while persisting at all 6 plots at both sites in Drakes Estero. Later versions of Drakes Estero: A Sheltered Wilderness Estuary and the Clarification document appropriately include the observation that approximately 50 acres of eelgrass habitat show propeller scars leading to and from oyster culture racks that can be reasonably attributed to boats associated with oyster operations. A more complete overview of how eelgrass and oyster culturing may functionally interact would also mention the potential for oyster filtration to depress turbidity and thereby locally enhance light penetration and extension of eelgrass habitat into deeper water and would note the potential for oyster biodeposits and ammonium excretion to fertilize eelgrass. Each of these effects has been demonstrated experimentally for modest densities (16 per square meter) of hard clams (Mercenaria mercenaria) in a relatively oligotrophic Long Island estuary: the authors argued that positive effects of modest numbers of suspension-feeding bivalves are more likely to benefit eelgrass in relatively oligotrophic water bodies where massive additions of filtering capacity are not required to achieve meaningful enhancement of light reaching the bottom (Carroll et al., 2008). These potential positive contributions of oysters to seagrasses are not mentioned in any of the NPS public releases of information on effects of oyster mariculture in Drakes Estero. Based on research of Wechsler (2004), also summarized in Elliott-Fisk et al. (2005), the first version (October 2006) of Drakes Estero: A Sheltered Wilderness Estuary maintained that “Schooner Bay … supported an entirely different fish community than that in the Estero de Limantour.” In fact, the only quantitative study of the fishes in Drakes Estero (Wechsler, 2004), based on limited sampling, failed to demonstrate substantial or statistically significant differences in the fish community composition between these two arms of the estero. There is some suggestion that the guild of fishes associated with hard substrates, a pattern driven by kelp surfperch, has enhanced abundances in close proximity to the oyster racks, but the spatial scope of any such signal is limited and not statistically significant (Wechsler, 2004). The later versions III and IV (May 8 and
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Shellfish Mariculture in Drakes Estero, Point Reyes National Seashore, California May 11, 2007, respectively) of Drakes Estero: A Sheltered Wilderness Estuary removed the reference to changes in the fish community associated with the oyster racks. The Clarification document provides a rigorous overview of Wechsler’s (2004) fish sampling data, admitting that there is inadequate evidence to reach conclusions about whether oyster culturing in Drakes Estero has any impact, positive or negative, on fishes. This NPS release also correctly identifies the suggestion of elevated abundance or attraction of fish species associated with hard substrates, while noting the lack of any statistical significance of this pattern despite a logical mechanistic basis that could explain it. Version I of the Drakes Estero: A Sheltered Wilderness Estuary (October 2006) asserted that the “marine invertebrate fouling community could be properly characterized as ‘introduced’ or ‘invasive’ due to lack of hard substrata in Drakes Estero,” citing Elliott-Fisk et al. (2005) as the source. The dominant occupier of space on the culture racks and oysters hung over them appears to be the nonnative tunicate, Didemnum vexillum, and three other nonnative fouling species are documented in Elliott-Fisk et al. (2005). Nevertheless, the assertion that hard substrates are absent in Drakes Estero is false (Bull Point contains some natural rocks), and insufficient sampling data exist to characterize the entire fouling community as nonnative. Furthermore, none of the versions of Drakes Estero: A Sheltered Wilderness Estuary acknowledges that hard substrate in the form of the native Olympia oyster shells likely existed in abundance within Drakes Estero in the past. Fouling organisms introduced into the estero would have found suitable hard substrate for attachment had the historical abundance of the Olympia oyster been sustained, assuming that its distribution extended into the subtidal zone as it does in British Columbia and elsewhere on the Pacific coast. The Clarification document provides a more accurate overview of the risks of enhancing populations of the nonnative tunicate, D. vexillum, by the provision of hard substrates in the form of oyster racks and oysters. Specifically, NPS identifies the concern that abundant populations of such an invasive species might change the biological environment in ways that lead to promoting successful invasion of other nonnatives—a process known as invasional meltdown (Grosholz, 2005). In addition, the Clarification document correctly identifies the risk that high populations of D. vexillum pose to enhancing the potential dispersal to other sites. Consequently, the Clarification document provides a rigorous summary of the issues relating to D. vexillum and other invertebrates occupying hard substrates, including oyster culture racks and the oyster shells. The only substantive difference between what NPS reported in the Clarification document and the findings of the committee is the failure of NPS to acknowledge the likely historical presence of common hard substrates in the form of shells of the native Olympia oyster.
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Shellfish Mariculture in Drakes Estero, Point Reyes National Seashore, California The first version also maintained that the “… oyster operation is a source for many invasive species.…” Credible arguments support the inference that successful introductions of nonnative species into Drakes Estero are the consequence of historic oyster farming practices in Drakes Estero. Specifically, the introduced salt marsh snail, Batillaria attramentaria, has been associated with oyster farming (Byers, 1999) and introduction of a nonnative haplosporidian oyster parasite into Drakes Estero is also associated with importation of Pacific oysters (Burreson et al., 2000). The Pacific oyster now cultured in Drakes Estero, Crassostrea gigas, is itself a nonnative species and has potential to escape culture and establish a self-replicating population as does the nonnative Manila clam (V. philippinarum). However, historic oyster mariculture practices that involved transport of nonnative oysters in juvenile or partially grown forms on cultch (large shell) have ended. This practice has been replaced by the transport of eyed larvae for remote setting in the nurseries of DBOC in a fashion similar to current practice at other mariculture operations. Consequently, the oyster operation is not now likely to be a source for further introductions of nonnative species. The only types of species that now could conceivably be introduced along with importation of oyster larvae are microbes, including notably oyster herpes viruses. None of the NPS review documents describe this change in mariculture methods and the great reduction in risk of new introductions that is achieved by transferring larvae from hatcheries inspected by High Health criteria (see Appendix E) instead of juvenile oysters on cultch. Versions III and IV of Drakes Estero: A Sheltered Wilderness Estuary state that oyster culture operations have resulted in an 80% decline in harbor seals “at one area” in Drakes Estero. This description is misleading because it implies that there has been a decline in the seal population at Drakes Estero whereas what has been observed is a reduction in the use of some of the haul-out subsites during the breeding season. In addition, the 80% value represents a selective presentation of subsite use that does not place this information into context with the spatially replicated and longer-term count data throughout the Drakes Estero colony and the Point Reyes region. The paper by Becker et al. (2009) improves on this simplistic description by analyzing the use of three haul-out subsites over a decade and relating it to local mariculture activities and changes in oceanic conditions from the 1998 ENSO climatic event. The conclusions reached by the authors of the paper are generally consistent with the results of the analysis, but the limitations of the analysis and hence tenuous nature of the conclusions may not be obvious to the non-expert. First, it is important to recognize that the analysis showing a relationship between mariculture activities and a decline in the mean seal attendance at two of three haul-out subsites in Drakes Estero does not demonstrate
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Shellfish Mariculture in Drakes Estero, Point Reyes National Seashore, California cause and effect. Second, the use of oyster production level as a proxy for mariculture activities that displace or disturb seals may be confounded by changes in culture methods or management practices. Third, demonstrating changes in mean attendance at seal haul-out subsites is not equivalent to demonstrating a decline in the seal population at Drakes Estero. The entire estero should be considered as one unit for population analyses for comparison to trends at other nearby locations occupied by harbor seals. For these reasons, the Becker et al. (2009) paper has limited value for understanding the long-term trends in seal counts in Drakes Estero. The NPS 2007 Pacific Harbor Seal monitoring annual report recognizes the need to look at these longer-term trends: “Inclusion of all survey years (2000–2007) in the average calculation accounts for the inherent inter-annual variability in the harbor seal population and reproductive output. Declines below one standard deviation from the mean, especially over the course of a few years, may merit further analysis of the data for statistical significance, additional research, or management actions.” (Truchinski, et al. 2008). The 2007 annual report shows that although the adult counts for 2007 are within one standard deviation of the 2000–2007 average, pup counts in Marin County colonies as a whole have declined to below one standard deviation for 2006 and 2007, which is a cause of concern that merits more detailed analysis. With regard to disturbance, we note that the 100 yd (91 m) buffer between mariculture activities and seal haul-out locations, while consistent with the National Marine Fisheries Service guidelines under the Marine Mammal Protection Act and Allen et al.’s (1984) observations of threshold disturbance distances for hauled-out seals in Bolinas Lagoon, is not as large as the 500–1,500 m buffers employed at two European locations to protect seals from human disturbance. Interpretation of the disturbance data is limited by the lack of critical information on how individual fitness and population consequences may vary with disturbance type. Hence, the disturbance monitoring conducted by NPS is inadequate for rigorous inferences on the impacts of mariculture on harbor seals. Version IV (May 11, 2007) of Drakes Estero: A Sheltered Wilderness Estuary highlights a quote from Dr. Janet Thompson of the U.S. Geological Survey, who inferred “a shift in the carbon from the pelagic food web to the benthic food web.” Elsewhere, this document reports that “… in Drakes Estero, ecological function has been degraded and altered over the past several decades due to activities associated with oyster farming and ranching.” Our review of available scientific information fails to demonstrate any empirical evidence of food web shifts in response to oyster farming in Drakes Estero. The scientific literature on the effects of culturing oysters and other suspension-feeding bivalves does not support a broad characterization of degradation of function, especially in physically
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Shellfish Mariculture in Drakes Estero, Point Reyes National Seashore, California well flushed estuaries and where stocking densities are relatively low, as in Drakes Estero. Furthermore, while some shift from pelagic to benthic food webs is a reasonable inference, there is no acknowledgement of the historical baselines of the natural ecosystem in Drakes Estero. Humans caused the depletion of the native Olympia oyster in California’s coastal bays and estuaries during the mid 1800s to early 1900s (Barrett, 1963; Baker, 1995; Kirby, 2004). The presence of shells of living, albeit cultured, oysters re-introduces biogenic hard substrates for fouling organisms, although differing in location by including elevated rack and surface plastic mesh culture structures, and the maintenance of feeding cultured oysters represents re-introduction of ecological filtering and biodeposition functions that prevailed before the native oysters were overharvested. Characterizing these changes as a degradation of ecological function ignores the perspective of history by selecting as a baseline for contrast only the recent anthropogenically modified status of the estero, and ignoring the historical baseline conditions (e.g., Jackson, J.B.C. et al., 2001; Lotze et al., 2006). Likewise, the historic presence and ecological roles of Olympia oysters in the estero is not mentioned in the Clarification document, which reports instead: “The presence of a reported nine million oysters and one million clams within an area that would not have these resources naturally is itself enough to demonstrate an alteration of natural conditions.” (NPS, 2007d). The literature on estuarine ecosystems and restoration identifies oysters as a major contributor to maintaining or restoring water quality and as important biogenic habitat for demersal fishes and mobile crustaceans (Lenihan and Peterson, 1998; Newell, 2004; Hosack et al., 2006; Coen et al., 2007; Grabowski and Peterson, 2007). Although there is a dearth of research on the extent to which the cultured Pacific oyster restores the ecological contribution of the native Olympia oyster in Drakes Estero, none of the NPS documents released to the public acknowledges that oysters were part of the historical baseline ecosystem before substantial human intervention and that oysters typically have largely beneficial biogeochemical functions in estuarine and lagoonal ecosystems.