Geology topics

Research about Kodiak Archipelago

Source-linked reports with geographic coverage including Kodiak Archipelago.

4 recordsLinked to original sources

USGS2025

Factors influencing daily nest survival rates of Aleutian terns in the Kodiak Archipelago, Alaska

The Aleutian tern ( Onychoprion aleuticus ) is a species of high conservation concern in Alaska, USA, owing to large declines at known breeding locations since the 1960s. The small population size and ephemeral behavior of this species have limited the collection of basic biological information and hindered the identification of potential drivers of this decline. Significant unknowns include the factors, and their relative importance, influencing nest survival. To investigate these questions, we estimated daily nest survival (DNS) for 148 nests from 5 breeding colonies during 2017 to 2020 in the Kodiak Archipelago, Alaska with 105 monitored using remote cameras. We used the nest survival model in program MARK to estimate DNS rates as a function of colony location, year, within-season time trends, vegetation cover and height, and 6 daily weather covariates. Our top model suggested that DNS rates increased with vegetation height, decreased as the season progressed, and included a significant interaction between year and colony. Average nest success (i.e., percent chance that a nest survived to hatch) over the 22-day incubation period varied by colony but was generally very low, averaging 1.2% (95% CI = 0–11%) in 2017–2018 to 14% (95% CI = 0.1–38%) in 2019–2020 across all colonies. The importance of year in the model suggests that a large-scale annual driver, like food availability, may have played an important role in this species' breeding success. A severe marine heatwave was present in the Gulf of Alaska during 2014–2016 and our results suggest that some effects of this anomalous event, such as reduced prey availability, lingered even after temperatures returned to normal. Additionally, the variation in DNS across colony locations indicated that local factors, such as predation pressure, may also drive significant variation in Aleutian tern productivity. These findings suggest that a combination of local factors and climate change may be important drivers of the >90% decline in Alaska's breeding population of Aleutian terns.

Alaska↗

USGS2016

Techniques for monitoring Brachyramphus murrelets: A comparison of radar, autonomous acoustic recording and audio‐visual surveys

Conditions in Alaska, USA, pose a challenge for monitoring populations of Brachyramphus murrelets using standard survey methods, because of strong winds, 2 sympatric species, short nights, and variable nesting habitat. We tested 3 methods for monitoring Brachyramphus murrelets breeding in the Kodiak Archipelago, Alaska, in 2010–2012. In addition to standard audio‐visual and radar methods, we tested—for the first time with murrelets in Alaska—the application of autonomous acoustic recorders for monitoring vocal activity. We completed 74 radar, 124 audio‐visual, and 134 autonomous acoustic surveys, focused on presunrise activity peaks; this yielded 26,375 murrelet detections. Marbled ( B. marmoratus ) and Kittlitz's murrelets ( B. brevirostris ) could not be distinguished using combinations of radar and acoustic recordings; therefore, at‐sea surveys will be required to determine localized species proportions. Of the 3 methods, radar sampled the largest area and detected silently flying murrelets, providing the most reliable data on local populations; however, radar identification of murrelets was unreliable in winds exceeding 18 km/hr. Audio‐visual surveys were useful for species identification and to document behaviors associated with local nesting, whereas autonomous acoustic recorders allowed season‐long monitoring of murrelet vocal activity. Within potential forest‐nesting habitat of marbled murrelets, all 3 methods gave similar measures of presunrise murrelet activity, but only radar reliably sampled murrelets commuting between nest and ocean. Because of their low cost and flexible programming, automated sound recorders offer an affordable way to sample vocal activity prior to more intensive or expensive radar and audio‐visual surveys. We recommend that population monitoring and habitat studies of Brachyramphus murrelets in Alaska include combinations of all 3 methods.

Alaska↗

USGS2006

Genetic characterization of brown bears of the Kodiak Archipelago

Here we examine genetic characteristics of brown bears of Kodiak and Afognak islands, using 14 variable nuclear microsatellite loci and nucleotide sequence information including the hypervariable domain I of the mtDNA control region (Wakely 1993). Because these markers, or a subset of them, have been used to characterize brown bears of the Kenai Peninsula (Jackson et al. 2005), Katmai National Park, Seward Peninsula, and nine other populations in Alaska (Talbot, unpublished data), we compared levels of genetic diversity and relationships among populations when possible. In addition, we obtained preliminary comparative information from class II DQA and DQB genes of the brown bear MHC, to examine levels of variation at this important immunology-mediating supergene. These data were used to answer the following questions: 1) are earlier findings of extremely low levels of variability at nuclear (biparentallyinherited) microsatellite loci from a small geographic area (Paetkau et al. 1998b) representative of Kodiak Archipelago populations as a whole? 2) Is the level and type of variation at the maternally-inherited mtDNA lower, or similar to, levels found in other populations in Alaska? 3) Is there concordance between low levels of genetic variation observed at neutral markers with levels of variation observed at functional genes? 4) Is there population substructuring within Kodiak and Afognak islands? 5) What is the connectivity between populations on Afognak Island and Kodiak Island? 6) What are the phylogeographic relationships between bears of the Kodiak Archipelago with brown bears on mainland Alaskan and other western Beringian populations? We also test whether these markers will provide an appropriate baseline for designing genetic tagging studies for use in future research and management activities, such as mark-recapture efforts, on the Refuge.

Alaska↗

USGS1992

Changes in Alaskan soft-bottom prey communities along a gradient in sea otter predation

Sea Otter ( Enhydra lutris ), well documented as "keystone" predators in rocky marine communities, were found to exert a strong influence on infaunal prey communities in soft-sediment habitats. Direct and indirect effects of sea otter predation on subtidal soft-bottom prey communities were evaluated along a temporal gradient of sea otter occupancy around the Kodiak Archipelago. The results indicate that Kodiak otters forage primarily on bivalve prey and dramatically reduce infaunal bivalve and green sea urchin ( Strongylocentrotus droebachiensis ) prey populations. Bivalve prey abundance, biomass, and size were inversely related to duration of sea otter occupancy. The relative conditions of shells discarded by otters in shallow (<10 m) vs. deep (> 20 m) water at the same sites indicate that otters first exploited Saxidomus in shallow-water feeding areas, and later switched to Macoma spp. in deeper water. Otter-cracked shells of the deep-burrowing clam Tresus capax were rarely found, even at otter foraging sites where the clam accounted for the majority of available prey biomass, suggesting that it has a partial depth refuge from otter predation. The indirect effects of otter predation included substratum disturbance and the facilitation of sea star predation on infaunal prey. Sea stars, Pycnopodia helianthoides , were attracted to experimentally dug excavations as well as natural sea otter foraging pits, where the sea stars foraged on smaller size classes of infaunal bivalves than those eaten by otters. Otters also discard clam shells on the sediment surface and expose old, buried shells during excavation. Surface shells were found to provide attachment sites for large anemones and kelp. Our study shows that sea otters can affect soft-sediment communities, not only through predation, as in rocky habitats, but also through disturbance, and thus retain a high degree of influence in two very different habitat types.

Alaska↗