Geology topics

Gerard J. McChesney

Publications and source records attributed to Gerard J. McChesney.

4 recordsLinked to original sources

USGS2022

Spatial effects in relation to reproductive performance of Common Murres (Uria aalge) at a re-established colony

A main goal of seabird colony restoration is for the colony to become self-sustaining. To do so, elevated rates must be attained in (1) reproductive success and (2) recruitment by immigrants and birds produced at the colony. Thus, an understanding of the factors affecting reproductive success and recruitment at restoration sites is vital. We examined how spatial features at the colony level affected reproductive success of Common Murres Uria aalge (hereafter, murres) over a six-year period at Devil's Slide Rock, California, a colony re-established using social attraction techniques. Clusters of sites with similar egg-laying dates, as well as high hatching and breeding success, occurred in the densest portion of the colony, which was also the last area occupied by murres at the time of extirpation and the first area to be re-colonized. Clusters of sites with low success occurred in outlying, low-density portions of the colony. Breeding success, influenced largely by high fledging success, averaged > 60% most years. Reproductive success was greatest at breeding sites with earlier egg-laying dates, those in closest proximity to the breeding sites of other murres and the Brandt's Cormorant Urile penicillatus , and those outside Brown Pelican Pelecanus occidentalis disturbance zones. Based on our findings, for future murre restoration projects in the California Current System, we suggest (1) placing social attraction equipment in the area(s) last utilized by murres prior to extirpation, (2) attempting to establish two dense breeding groups, (3) targeting sites already utilized regularly by nesting Brandt's Cormorants, and (4) avoiding sites or habitats prone to disturbance by larger and aggressive species such as Brown Pelicans, Bald Eagles Haliaeetus leucocephalus , or Common Ravens Corvus corax .

California↗

USGS2020

Extreme mortality and reproductive failure of common murres resulting from the northeast Pacific marine heatwave of 2014-2016

About 62,000 dead or dying common murres ( Uria aalge ), the trophically dominant fish-eating seabird of the North Pacific, washed ashore between summer 2015 and spring 2016 on beaches from California to Alaska. Most birds were severely emaciated and, so far, no evidence for anything other than starvation was found to explain this mass mortality. Three-quarters of murres were found in the Gulf of Alaska and the remainder along the West Coast. Studies show that only a fraction of birds that die at sea typically wash ashore, and we estimate that total mortality approached 1 million birds. About two-thirds of murres killed were adults, a substantial blow to breeding populations. Additionally, 22 complete reproductive failures were observed at multiple colonies region-wide during (2015) and after (2016–2017) the mass mortality event. Die-offs and breeding failures occur sporadically in murres, but the magnitude, duration and spatial extent of this die-off, associated with multi-colony and multi-year reproductive failures, is unprecedented and astonishing. These events co-occurred with the most powerful marine heatwave on record that persisted through 2014–2016 and created an enormous volume of ocean water (the “Blob”) from California to Alaska with temperatures that exceeded average by 2–3 standard deviations. Other studies indicate that this prolonged heatwave reduced phytoplankton biomass and restructured zooplankton communities in favor of lower-calorie species, while it simultaneously increased metabolically driven food demands of ectothermic forage fish. In response, forage fish quality and quantity diminished. Similarly, large ectothermic groundfish were thought to have increased their demand for forage fish, resulting in greater top-predator demands for diminished forage fish resources. We hypothesize that these bottom-up and top-down forces created an “ectothermic vise” on forage species leading to their system-wide scarcity and resulting in mass mortality of murres and many other fish, bird and mammal species in the region during 2014–2017.

PLoS ONE↗

USGS2019

Changes in breeding population sizes of double-crested Cormorants Phalacrocorax auritus in the Humboldt Bay area, California, 1924–2017

To better understand recent population growth of the Double-crested Cormorant Phalacrocorax auritus along the Pacific coast of North America, we assessed long-term breeding population trends in the Humboldt Bay area, California, using aerial photographic survey data collected since 1989 as well as available prior data. The earliest documentations of breeding (but without nest counts) are from 1924, 1943, and 1947 on the outer coast near Trinidad, and from 1959 in Humboldt Bay at Old Arcata Wharf. The breeding population increased from 188 nests (376 breeding birds) at one colony in 1961 to ~ 350 nests (700 breeding birds) at four colonies by 1980, and then to peaks of nearly 1,700 nests (3,400 breeding birds) in 1997 and 2004 at eight colonies. Breeding was documented at 13 coastal colonies through 2017. The population increased 100% (9 % per annum) from 1989 to 1997, decreased during the strong 1998 El Niño, and rebounded by 2004. After the 2004 peak, three years of available data indicated slight population decline. For the entire 1989–2017 period, the population increased by 91% (2% per annum). Artificial habitats in Humboldt Bay allowed most of the population growth, especially Teal Island, which was colonized in 1993 and became the largest colony in all but one year thereafter. Nest totals on the outer coast decreased, likely because of movements to the Humboldt Bay colonies, which are closer to main foraging areas, and because of competition for nesting space with Common Murres Uria aalge at one colony (False Cape Rocks). Future growth of the population in the Humboldt Bay area appears limited by the availability of disturbance-free breeding habitat. Declines may occur if artificial habitats are lost.

California↗

USGS1995

Population size, trends, and conservation problems of the Double-Crested Cormorant on the Pacific Coast of North America

Population size, trends and conservation problems of the Double-crested Cormorant ( Phalacrocorax auritus ) were collated for the Pacific coast of North America using available data up to 1992. About 54,942 birds currently breed there, including roughly 5,848 (5,622 at 90 coastal colonies and at least 226 at 5 interior colonies) and 49,094 (43,358 at 126 coastal colonies and at least 5,736 at 22 interior colonies) for subspecies P. a. cincinatus in Alaska and P. a. albociliatus , from British Columbia to Sinaloa (Mexico), respectively. In addition, 51 and 22 inactive colonies have been documented in coastal and interior regions, respectively. Major historical declines (in the 1800s and early 1900s) occurred in much of Alaska, California, and Mexico, followed by increases in British Columbia, Washington, Oregon and California from the 1920s to 1980s. Recent declines are occurring in British Columbia, Washington, and Baja California. Trends are affected by apparent movements of nesting birds during El Niño oceanographic conditions and due to habitat loss at interior colonies, as well as recent use of artificial nesting habitats in some areas. Conservation problems have included various forms of human disturbance and persecution, marine pollutants, and high levels of predation owing to introduced and natural predators.

Alaska, California, Oregon, Washington↗