|Seabird Distribution and Abundance|
Final Report to CIAP and BOEM:
Pham, A. C., and Kuletz, K. J. 2015. Seabird Distribution and Abundance in the northeastern Bering Sea and Chukchi Sea. US Dept. of the Interior, Bureau of Ocean Energy Management, Alaska OCS Region. OCS Study BOEM 2010-AK-10-10 to U.S. Fish and Wildlife Service, as part of 2011-AK-11-08 a/b. 58 pp. – DRAFT REPORT
This study seeks to improve our knowledge of arctic seabird ecology by examining distributional and community changes in response to interannual changes in marine habitats and prey. To this end, we used data from the Arctic Eis to examine the prey and oceanographic factors that influenced seabird community structure within and between the two study years. First, we defined seabird communities and their associations with habitats and prey using a nonmetric multidimensional ordination. The ordination identified three habitats based on associated seabird communities. These habitats were most strongly correlated with latitude, longitude, salinity, chlorophyll-a, slope, and fish catch-per-unit-effort. A multi-response permutation procedure grouped by year and geographic region revealed differences between years in seabird community structure. These results suggest that seabird communities are structured by ecotones that may change in location interannually, with oceanographic properties being slightly stronger predictors than prey abundance. We will examine these correlations on a coarse scale by using generalized additive models to determine the most important factors that influence the distribution of seabird foraging guilds and numerically dominant species.
Manuscripts which include Seabird Arctic Eis data:
|Major Players – Species Ecology|
Auklets are planktivorous seabirds which mainly feed upon copepods and some euphausiids. They are small-bodied diving alcids and are the most abundant seabirds in the study area. Their nest sites are in Aleutian Islands and the other large islands of the Bering Sea (including the Diomede Islands). However, they do not have colonies in the Chukchi Sea. Surveys suggest non-breeders and post-breeders feed in the Chukchi Sea in late summer/fall. Crested auklets may be molting and flightless in the greater Hanna Shoal area (pers. obs.), and would require high densities of high-quality prey. In collaboration with Arctic Eis oceanographers and zooplankton ecologists, it appears auklet distributions generally overlap the higher salinity, lower temperature oceanic/Bering Sea water in areas of high zooplankton biomass.
Murres are primarily piscivores, or fish eaters. Though, thick-billed murres also consume some pelagic euphausiids and amphipods. They are large-bodied, deep-diving birds. They nest throughout the Bering Sea, as well as at Cape Lisburne and Cape Thompson in the Chukchi Sea.
Shearwaters are omnivores and mainly forage at the surface, but can dive 20-plus meters for prey. They breed in the southern hemisphere and migrate to Alaska to feed in summer. They can be locally abundant and their numbers in the Chukchi Sea may have increased recently.
Ancient and Kittlitz’s murrelets consume small fish, zooplankton, euphausiids, amphipods. They are small-bodied diving alcids. Ancient murrelets nest near Japan or Aleutian islands and B.C., so these must migrate to N. Bering/Chukchi post-breeding. Ancient murrelets are a recent phenomena in the Arctic Eis study area. Kittlitz’s murrelets nest in low numbers along the western AK/Chukchi coast, but satellite tagged birds traveled from Gulf of Alaska breeding areas to the Chukchi. They are an ice-associated species.
There were several other species seen in 2012 and 2013. These include (various families, genera, and additional species): loons, fulmars, shearwater spp., storm petrels, cormorants, mergansers, all 4 species of eiders, ducks, pharalopes, jaegers, terns, gulls, kittiwakes, guillemots, and puffins.
|2012 and 2013 Preliminary Results|
Although we encountered 35 species of marine birds in the northern Bering and Chukchi seas during the Arctic Eis cruises, relatively few species comprised the majority of seabirds we encountered in the study area. The most abundant species included crested and least auklets (Aethia cristatella and A. pusilla), short-tailed shearwaters (Puffinus tenuirostris), red and red-necked phalaropes (Phalaropus fulicarius and P. lobatus), common and thick-billed murres (Uria aalge and U. lomvia), and black-legged kittiwakes (Rissa tridactyla) (Figure 1, 2).
Based on a preliminary review of density maps (Figure 3), the seabird community within the Arctic Eis study area appears to have shifted southward from 2012 to 2013. The community was highly aggregated both years, but birds were more dispersed in 2013.
Planktivorous seabirds, which eat primarily copepods, euphausiids, and other large zooplankton, appeared to drive a large proportion of the changes in relative abundance and distribution observed between 2012 and 2013 (Figure 4, 5, 6). In particular, in 2012 Aethia auklets were more abundant overall, especially in the Chukchi Sea, whereas they had shifted southwards in 2013 (Figure 7). While they were less abundant overall in 2013 compared to 2012, they were more densely aggregated in 2013 than in 2012. These changes in auklet distribution may have been related to warmer sea surface temperatures, fresher sea surface salinities, and decreased zooplankton biomass observed in 2013 by other Arctic Eis researchers. In contrast, phalaropes (Phalaropus sp.), which breed on the Arctic tundra and winter at sea throughout the North Pacific Ocean, were more abundant in 2013 but slightly less aggregated compared to 2012 (Figure 8). In 2012, these birds were sighted primarily in the south-central Chukchi Sea in association with feeding gray whales (Eschrichtius robustus), whereas in 2013, they were also sighted in association with the ice edge in the northern Chukchi Sea. However, because phalaropes are migrating at this time of the year (late summer-early fall) and are patchily distributed in flocks, apparent differences in distribution are difficult to interpret.
Omnivorous seabirds consume zooplankton, squid, and small fish, and in the Arctic Eis study area, the most abundant omnivores were short-tailed shearwaters. Shearwaters were more
Piscivores, which eat primarily fish, were found in inshore waters in 2013 more than they were in 2012 (Figure 11). The main species driving observed changes in piscivorous seabirds were thick-billed and common murres (Figure 12), but shifts were also observed in black-legged kittiwakes (Rissa tridactyla) (Figure 13). The changes in distribution may have been related to increases in biomass of juvenile Arctic cod (Arctogadus glacialis), capelin (Mallotus villosus), and juvenile Pacific herring (Clupea pallasii) observed in 2013 by Arctic Eis researchers. In 2013, piscivorous seabirds were both less abundant and less clustered compared to 2012 (Figure 4, 5).
Benthic-feeding seabirds (which eat benthic crustacea and worms) consisted primarily of eiders (common, king, and spectacled eiders). These species nest on the tundra, but during migration are typically found in shallow coastal waters, thus they were poorly sampled during the more pelagic Arctic Eis surveys. In general, compared to 2012, they were found further south and were less densely aggregated in 2013 (Figure 14).
Although we are just beginning to examine the relationships between seabirds and their environment in the Arctic Eis study area, the differences we observed between 2012 and 2013 show how dynamic the northern Bering Sea – Chukchi Sea ecosystem can be (Figure 15). The differences also highlight the importance of surveying large areas over multiple years to determine how seabirds respond to changes in physical and biological conditions.
|2012 / 2013 Opportunistic Marine Mammal Observations|