Shellfish Mariculture in Drakes Estero, Point Reyes National Seashore, California (2009) / Chapter Skim
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V. Harbor Seals
V. Harbor Seals
Pages 41-49
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From page 41... ...
. Intertidal sand banks provide habitat for seals to give birth and suckle their pups or rest during the nonbreeding season, and other estuarine areas provide foraging habitat (Wright et al., 2007)
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From page 42... ...
, which is not sufficient to make a robust comparison with trends at other sites in the Point Reyes region with even fewer years of standardized count data. There has been one statistical modeling study that tested for potential impacts of mariculture activity on harbor seals.
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From page 43... ...
The authors attribute the departure from the previous pattern to new regulations issued by the California Coastal Commission which closed the lateral channel to the oyster farm's boats during the pupping season beginning in 2008 and further explain that this new restriction led to less disturbance of the seals and thus less displacement from their haul-out sites. However, this explanation is misleading because the previous owner of the oyster farm operated under a 1992 agreement to prohibit boat traffic in the main and lateral channels during the pupping season (DOI, 2008)
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From page 44... ...
In contrast, if seals are flushed into the water by a motor boat, underwater engine noise may result in a continued perception of risk and a stronger response by the seal. Second, the lack of definitive data on spatial and temporal variations in the precise location and behavior of the oyster farm boats prevents any scientific assessment of the authenticity of either the observations of disturbance during the seal surveys (see Box 3)
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From page 45... ...
. • etermine long-term trends in reproductive success of elephant seal D and harbor seal populations through annual estimates of productivity at [the Point Reyes National Seashore]
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From page 46... ...
The seal counts survey form includes information on the low tide level while the disturbance survey form does not. Perhaps the most important confounding factor in any monitoring database, but especially one staffed by volunteers, is the potential for simple recording errors, such as date, time, or tide level.
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From page 47... ...
C. What Effects Can Be Directly Demonstrated by Research Conducted in Drakes Estero Itself? None of the scientific research projects within Drakes Estero was designed specifically to assess whether the oyster farm operations were impacting the local harbor seal population, and this constrains attempts to draw definitive conclusions about potential impacts.
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From page 48... ...
. There has been no research conducted in similar ecosystems that has directly assessed the impact of shellfish mariculture on harbor seals or indeed any other seal populations.
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From page 49... ...
, a full assessment of potential disturbance should also consider whether disturbance during other phases of the tidal cycle affects the seals' haul-out behavior. The only study to do this was an experimental study in the Dutch Wadden Sea, in which 13 harbor seals were satellite tagged to assess the impact of recreational boat traffic passing over their haul-out sites at high tide.
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