Why are we monitoring?

The black oystercatcher is a conspicuous member of rocky intertidal marine communities in the north Pacific. Black oystercatchers are completely dependent on nearshore marine habitats for all critical parts of their life cycle including foraging, breeding, chick-rearing, and resting. As such, they are useful indicators of nearshore ecosystem health and therefore particularly amenable to long-term monitoring. However, this same reliance on coastal ecosystems makes the black oystercatcher highly susceptible to human disturbance and other forms of nearshore habitat change. The black oystercatcher is considered a Management Indicator Species by the Chugach National Forest and a species of concern by the Alaska Shorebird Working Group.

We monitor several aspects of black oystercatcher populations, including diet through collection of prey remains brought back to the nests to feed the chicks, nest density, nesting phenology, nest productivity, nest density, and overall density.

Where are we monitoring?

We monitor black oystercatchers across a broad swath of the northern Gulf of Alaska within the area affected by the Exxon Valdez oil spill. Study regions include western Prince William Sound (WPWS), Kenai Fjords National Park (KEFJ), Kachemak Bay (KBAY), and Katmai National Park and Preserve (KATM). 

How are we sampling?

There are five different ways black oystercatcher data are collected:

1. 1. Black oystercatcher specific boat-based nearshore surveys to estimate nest density and distribution. These surveys are conducted in early summer.
   2. Once a nest is located, the area is searched on foot to determine nest productivity (the number of eggs and chicks per nest).
   3. During the same nest search, if chicks are present, prey remains are collected (food brought back to the nest to feed the chicks) to determine species composition and size distribution.
   4. If eggs are present during the nest search, they are floated in fresh water to determine the stage of embryo development and estimate the hatch date.
   5. Marine bird and mammal boat-based nearshore surveys to estimate overall density and distribution for a variety of species, including black oystercatchers (see Marine Birds).

What are we finding?

Black Oystercatcher Nest Density

Long-term monitoring of black oystercatchers across the northern Gulf of Alaska shows variable but generally stable trends in nest density, with notable regional differences. Following the Pacific marine heatwave, nest density increased in some regions, including Kenai Fjords National Park and Kachemak Bay, with elevated or stable levels persisting through recent years. In contrast, trends in other regions, such as Prince William Sound, have been more variable, including a decline in 2025.

Black oystercatcher nest density estimates across all four Gulf Watch Alaska regions: Katmai National Park and Preserve (KATM), Kachemak Bay (KBAY), Kenai Fjords National Park (KEFJ), and western Prince William Sound (WPWS). Error bars indicate ±1SE

Black Oystercatcher Chick Diet

Diet observations indicate that black oystercatchers continue to rely primarily on intertidal invertebrates, with limpets consistently comprising the majority of prey remains across regions. Mussels are typically the second most common prey item, although their contribution to chick diet varies by region and year. In some cases, shifts in prey use, including increased consumption of other invertebrates, have been observed.

Species composition of prey remains collected at black oystercatcher nests across all four Gulf Watch Alaska regions: Katmai National Park and Preserve (KATM), Kachemak Bay (KBAY), Kenai Fjords National Park (KEFJ), and western Prince William Sound (WPWS).

Black Oystercatcher Density and Mussel Abundance

Overall, there is little evidence that black oystercatcher diet or productivity was negatively affected by recent marine heatwave conditions. In some regions, increased availability of benthic prey, such as mussels, may have supported stable or increasing nest densities. These observations suggest that black oystercatchers remain a useful indicator of nearshore ecosystem conditions, reflecting changes in prey availability and broader ecosystem dynamics across the Gulf of Alaska.