Black Oystercatchers
Resource Brief - March 2009
Importance/Issues
The black oystercatcher was selected as a SWAN marine nearshore vital sign because: 1) it is a common and conspicuous member of the rocky and gravel intertidal communities along marine shorelines; 2) it is completely dependent on nearshore marine habitats for all critical life history components including foraging, breeding, chick-rearing, and resting; 3) it serves as "keystone" species that it important in structuring nearshore systems, largely as a consequence of its' preference for preying on species such as mussels and limpets; and 4) it is highly susceptible to human disturbance. Because of their complete reliance on intertidal invertebrates as forage, the black oystercatcher provides a unique opportunity to view the nearshore zone from the perspective of an avian predator, as well as allowing the use of recognized relations between black oystercatchers and their prey to allow inferences between oystercatcher populations and their prey. Specifically, over the long-term the sampling design will facilitate inferences relating density and productivity of oystercatchers to their diet (as reflected by prey brought to provision chicks) and to they prey populations.
Sampling Design
Collection of black oystercatcher nest density/occupancy and diet data will be collected annually along a 20-km transect centered on each randomly-selected intensive intertidal invertebrate and algal sample site. Identification of all nests within each transect will allow estimation of nest density, and visits to all nest sites in subsequent years will allow estimation of nest abandonment and establishment rates. Shell remains of prey captured and transported to the nest site to provision chicks will be collected and used to estimate the species composition and size distributions of prey. The sampling design will allow contrasts of black oystercatcher nest density, nest occupancy rates, and size and species composition among sites within a park, among different regions in the Gulf of Alaska, and among years.
Progress and Current Efforts
In 2006, five 20-km transects were surveyed along the Katmai NP coastline corresponding to each of the five rocky intertidal intensive sampling locations. One additional transect was established at Ninagiak Island, associated with the establishment of a selected intertidal site there. In 2006 we located 17 black oystercatcher nests, 15 that were classified as active and 2 as failed. The number of nests ranged from 1 to 5/transect. Eleven eggs and 13 chicks were located and two active nests were located but chicks were not detected. We recovered dietary prey remains from 10 of the 17 nest sites, or 10 of 12 nests where chicks were present. More than 500 prey items were identified to species and measured. Limpets (Tectura persona, T. scutum, and Lottia sp.) and mussels (Mytilus trossulus) dominated the dietary remains. These same transects were sampled again at Katmai in 2007. In 2007 we located 20 active nests that included 27 eggs and 10 chicks. More than 1000 prey remains were collected from eight nests and again were dominated by limpets and mussels. In 2007 we implemented the same sampling of black oystercatchers and their diet at Kenai Fjords NP.
USGS and SWAN biologists examine a Black Oystercatcher nest site and collect prey remains, Katmai National Park and Preserve 2006.
