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James A. Estes

Publications and source records attributed to James A. Estes.

At least 37 records · Page 2Linked to original sources
USGS2006

Sea otter mortality from the Exxon Valdez spill: Evaluation of an estimate from boat-based surveys

The Exxon Valadez oil spill killed large numbers of sea otters ( Enhydra lutris ) in Prince William Sound (PWS), Alaska, where the spill originated, as well as within the oil’s path along the coasts of the Kenai Peninsula and Kodiak Island. Sea otters attracted particular attention after the spill due to their public appeal (Batten 1990) and known vulnerability to oil (Costa and Kooyman 1982, Siniff et al. 1982, Davis et al. 1988, Williams et al. 1988). Extensive efforts were made to rescue and rehabilitate oiled otters at a resulting cost of ca. $80,000 per animal (Estes 1991). The argument that otters lost in the spill should be similarly valued made the estimate of mortality a matter of substantial concern to those involved in spill-related litigation or out-of-court settlements.

Alaska↗
USGS2006

Incorporating diverse data and realistic complexity into demographic estimation procedures for sea otters

Reliable information on historical and current population dynamics is central to understanding patterns of growth and decline in animal populations. We developed a maximum likelihood-based analysis to estimate spatial and temporal trends in age/sex-specific survival rates for the threatened southern sea otter (Enhydra lutris nereis), using annual population censuses and the age structure of salvaged carcass collections. We evaluated a wide range of possible spatial and temporal effects and used model averaging to incorporate model uncertainty into the resulting estimates of key vital rates and their variances. We compared these results to current demographic parameters estimated in a telemetry-based study conducted between 2001 and 2004. These results show that survival has decreased substantially from the early 1990s to the present and is generally lowest in the north-central portion of the population's range. The greatest temporal decrease in survival was for adult females, and variation in the survival of this age/sex class is primarily responsible for regulating population growth and driving population trends. Our results can be used to focus future research on southern sea otters by highlighting the life history stages and mortality factors most relevant to conservation. More broadly, we have illustrated how the powerful and relatively straightforward tools of information-theoretic-based model fitting can be used to sort through and parameterize quite complex demographic modeling frameworks. ?? 2006 by the Ecological Society of America.

Ecological Applications↗
USGS2006

Catastrophe, recovery and range limitation in NE Pacific kelp forests: a large-scale perspective

The 1997–98 El Niño was one of the strongest on record and resulted in widespread losses of the giant kelp Macrocystis pyrifera (Agardh) along the west coast of North America. Drawing on a rich history of studies that have shown abnormally large waves and warm nutrient-poor water associated with El Niños to negatively impact giant kelp populations at some locations in southern and Baja California, we examined (1) how these impacts scale up when considered across the species’ geographic range in the NE Pacific Ocean and (2) if these impacts are generalizable over broad spatial scales. Working at 56 sites in 14 study locations over a 3 yr period (1997 to 2000), we examined how giant kelp populations were impacted by and recovered following the 1997–98 El Niño over a ~1500 km span along the west coast of North America. Our results indicate that while nearly all giant kelp disappeared from the southern one-third of the species’ range along the coast of Baja California, Mexico, and heavy losses occurred throughout the central one-third of the species’ range in southern California, USA, only minor impacts were observed throughout the northern one-third of the species’ range in central California. Further, although highly variable among regions, these impacts were similar and generalizable among locations within each region. Our results also suggest that, as has been observed in local-scale studies, this large-scale variability in giant kelp mortality was driven by large-scale patterns in ocean temperature (nutrient concentration) and wave intensity. Recovery following El Niño, in contrast, was variable at multiple spatial scales and although not directly tested here, presumably influenced by numerous factors such as proximity to upwelling areas, competition with other algae, grazing, and propagule availability. Further, variability in the rates of recovery among locations resulted in a generally slow recovery of giant kelp throughout most of Baja California, and residual large-scale impacts of the El Niño were still evident 2 yr after the El Niño ended. As global climate change may lead to increases in the frequency and intensity of El Niños, our findings have broad implications for the ways in which ecosystems might be expected to respond to them and provide a measure by which their impacts to giant kelp ecosystems may be compared among events.

Pacific Ocean↗
USGS2005

Re-wilding North America

A plan to restore animals that disappeared 13,000 years ago from Pleistocene North America offers an alternative conservation strategy for the twenty-first century, argue Josh Donlan and colleagues.

Nature↗
USGS2005

Response from Soulé and Estes

The letter from Kimberly Heiman points out the applicability of our framework to nonnative invasive species. Indeed, many alien species are changing the sign and increasing the amplitude of strong interactions in contemporary ecosystems, in some cases catastrophically. Invasive exotic species require much more attention at the policy and administrative levels.

BioScience↗
USGS2004

Determinants of reproductive costs in the long-lived Black-legged Kittiwake: A multiyear experiment

We studied reproductive costs of Black-legged Kittiwakes ( Rissa tridactyla ) in Prince William Sound, Alaska (USA) by removing entire clutches from randomly selected nests over four successive years, and then contrasting survival and fecundity of adults from manipulated and unmanipulated nests in each subsequent year. To elucidate mechanisms that lead to the expression of reproductive costs, we simultaneously characterized several behavioral and physiological parameters among adults in the two treatment groups. We also examined naturally nonbreeding adults that previously bred to determine their survival and future nonbreeding probabilities. Food availability varied during the study, being generally poor at the onset, and improving in later years. Adult nest attendance and body condition (assessed late in the chick- rearing period) varied accordingly among years, and between adults raising chicks and adults that had their eggs removed. Adults from unmanipulated nests incurred significant survival costs in all years, although fecundity costs were strongly expressed in only one of four years. Neither survival nor fecundity costs were strongly influenced by body condition or food availability, and no difference in reproductive costs was detected between the sexes. Although unmanipulated breeders survived at lower rates than manipulated breeders due to costs of reproduction, their survival rates were elevated compared to those of natural nonbreeders, presumably due to differences in individual ability. These findings indicate that models of adult survival must consider not only an organism's reproductive state, but also the factors that lead to that state. Although body condition appeared to be weakly related to survival, it was insufficient to explain the full magnitude of survival costs observed. We suggest that other parameters that were found to differ between treatment groups (e.g., rates of energy turnover, baseline levels of stress, and patterns of allocating body reserves) may be important mechanistic determinants of reproductive costs in kittiwakes, and potentially other long-lived species. Future efforts should move beyond simple assessments of body condition and toward more integrated measures of physiological condition when attempting to identify factors that influence how long-lived species balance the costs and benefits of reproduction.

Alaska↗
USGS2003

Kelp forest ecosystems: Biodiversity, stability, resilience and future

Kelp forests are phyletically diverse, structurally complex and highly productive components of coldwater rocky marine coastlines. This paper reviews the conditions in which kelp forests develop globally and where, why and at what rate they become deforested. The ecology and long archaeological history of kelp forests are examined through case studies from southern California, the Aleutian Islands and the western North Atlantic, well-studied locations that represent the widest possible range in kelp forest biodiversity. Global distribution of kelp forests is physiologically constrained by light at high latitudes and by nutrients, warm temperatures and other macrophytes at low latitudes. Within mid-latitude belts (roughly 40–60° latitude in both hemispheres) well-developed kelp forests are most threatened by herbivory, usually from sea urchins. Overfishing and extirpation of highly valued vertebrate apex predators often triggered herbivore population increases, leading to widespread kelp deforestation. Such deforestations have the most profound and lasting impacts on species-depauperate systems, such as those in Alaska and the western North Atlantic. Globally urchin-induced deforestation has been increasing over the past 2–3 decades. Continued fishing down of coastal food webs has resulted in shifting harvesting targets from apex predators to their invertebrate prey, including kelp-grazing herbivores. The recent global expansion of sea urchin harvesting has led to the widespread extirpation of this herbivore, and kelp forests have returned in some locations but, for the first time, these forests are devoid of vertebrate apex predators. In the western North Atlantic, large predatory crabs have recently filled this void and they have become the new apex predator in this system. Similar shifts from fish- to crab-dominance may have occurred in coastal zones of the United Kingdom and Japan, where large predatory finfish were extirpated long ago. Three North American case studies of kelp forests were examined to determine their long history with humans and project the status of future kelp forests to the year 2025. Fishing impacts on kelp forest systems have been both profound and much longer in duration than previously thought. Archaeological data suggest that coastal peoples exploited kelp forest organisms for thousands of years, occasionally resulting in localized losses of apex predators, outbreaks of sea urchin populations and probably small-scale deforestation. Over the past two centuries, commercial exploitation for export led to the extirpation of sea urchin predators, such as the sea otter in the North Pacific and predatory fishes like the cod in the North Atlantic. The large-scale removal of predators for export markets increased sea urchin abundances and promoted the decline of kelp forests over vast areas. Despite southern California having one of the longest known associations with coastal kelp forests, widespread deforestation is rare. It is possible that functional redundancies among predators and herbivores make this most diverse system most stable. Such biodiverse kelp forests may also resist invasion from non-native species. In the species-depauperate western North Atlantic, introduced algal competitors carpet the benthos and threaten future kelp dominance. There, other non-native herbivores and predators have become established and dominant components of this system. Climate changes have had measurable impacts on kelp forest ecosystems and efforts to control the emission of greenhouse gasses should be a global priority. However, overfishing appears to be the greatest manageable threat to kelp forest ecosystems over the 2025 time horizon. Management should focus on minimizing fishing impacts and restoring populations of functionally important species in these systems.

Environmental Conservation↗
USGS2003

Clinical pathology and assessment of pathogen exposure in southern and Alaskan sea otters

The southern sea otter ( Enhydra lutris nereis ) population in California (USA) and the Alaskan sea otter ( E. lutris kenyoni ) population in the Aleutian Islands (USA) chain have recently declined. In order to evaluate disease as a contributing factor to the declines, health assessments of these two sea otter populations were conducted by evaluating hematologic and/or serum biochemical values and exposure to six marine and terrestrial pathogens using blood collected during ongoing studies from 1995 through 2000. Samples from 72 free-ranging Alaskan, 78 free-ranging southern, and (for pathogen exposure only) 41 debilitated southern sea otters in rehabilitation facilities were evaluated and compared to investigate regional differences. Serum chemistry and hematology values did not indicate a specific disease process as a cause for the declines. Statistically significant differences were found between free-ranging adult southern and Alaskan population mean serum levels of creatinine kinase, alkaline phosphatase, alanine aminotransferase, aspartate aminotransferase, calcium, cholesterol, creatinine, glucose, phosphorous, total bilirubin, blood urea nitrogen, and sodium. These were likely due to varying parasite loads, contaminant exposures, and physiologic or nutrition statuses. No free-ranging sea otters had signs of disease at capture, and prevalences of exposure to calicivirus, Brucella spp., and Leptospira spp. were low. The high prevalence (35%) of antibodies to Toxoplasma gondii in free-ranging southern sea otters, lack of antibodies to this parasite in Alaskan sea otters, and the pathogen's propensity to cause mortality in southern sea otters suggests that this parasite may be important to sea otter population dynamics in California but not in Alaska. The evidence for exposure to pathogens of public health importance (e.g., Leptospira spp., T. gondii ) in the southern sea otter population, and the naïveté of both populations to other pathogens (e.g., morbillivirus and Coccidiodes immitis ) may have important implications for their management and recovery.

Journal of Wildlife Diseases↗
USGS2002

Activity patterns and time budgets of the declining sea otter population at Amchitka Island, Alaska

Time budgets of predators may reflect population status if time spent foraging varies with local prey abun- dance. We assumed that the sea otter (Enhydra lutris) population at Amchitka Island, Alaska, USA, had been at equilibrium since the early 1960s and collected time budgets of otters to be used to represent future conditions of currently expanding sea otter populations. We used radiotelemetry to monitor activity-time budgets of otters from August 1992 to March 1994. Sea otter activity was directly linked to sex, age, weather condition, season, and time of day. Sea otters differed in percent time foraging among cohorts but not within cohorts. Percent time foraging ranged from 21% for females with very young (≤ 3weeks of age) dependent pups to 52% for females with old (≥10 weeks of age) pups. Otters foraged more and hauled out more as local sea conditions worsened. Adult males spent less time foraging during winter and spring, consistent with seasonal changes in prey selection. Time spent for- aging was similar to that reported for otters in California and an established population in Prince William Sound, Alaska, but greater than that of otters in recently established populations in Oregon and Alaska. Despite current evidence indicating that the population was in decline during our study, we were unable to recognize this change using time budgets. Our results illustrate the importance of stratifying analyses of activity patterns by age and sex cohorts and the complexity inherent in comparisons of behavioral data between different populations relying on distinct prey bases.

Journal of Wildlife Management↗
USGS2002

Otters

The otters (Mustelidae; Lutrinae) provide a unique look into the evolution of marine living by mammals. This is because most extant marine mammals have been so highly modified by long periods of selection for life in the sea that they bare little resemblance to their terrestrial ancestors. Marine otters, by contrast, are recent expatriates from terrestrial and freshwater habitats, and some species still live in both environments. Contrasts within this group, and among the otters, terrestrial mammals, and the more highly adapted pinnipeds and cetaceans potentially offer deep insight into mammalian adaptations to life in the sea. Among the marine mammals, sea otters also provide the clearest understanding of predation and ocean ecosystem function. This is due in part to serendipitous opportunities provided by history and in part by the relative ease with which shallow coastal systems where sea otters live can be observed and studied. These two qualities of the otters are what make them interesting to marine mammalogy. Thus, our contribution to this volume on the marine mammals is built around these themes.

Book chapter↗
USGS2001

Survival costs of chick rearing in black-legged kittiwakes

1. We tested for costs of chick rearing in the black-legged kittiwake Rissa tridactyla (Linnaeus) by removing entire clutches from 149 of 405 randomly selected nests, in which one or both mates was colour-banded. After the manipulation, we monitored adult nest attendance and body condition at unmanipulated and manipulated nests, and measured the survival and fecundity of these adults the following year. 2. Late in the chick-rearing period, adults from unmanipulated nests (i.e. with chicks) went on significantly longer foraging trips, and were significantly lighter for their size, than adults from manipulated nests (i.e. without chicks). 3. Adults from unmanipulated nests also survived to the following nesting season at a significantly lower rate than those from the manipulated nests (0·898 vs. 0·953), suggesting that attempting to raise chicks can reduce life expectancy by 55%. 4. There was a tendency for adults from nests that were unmanipulated in year one to have lower reproductive success in year two, primarily because of reduced fledging success, and a higher incidence of non-breeding. 5. These findings suggest that mass loss in kittiwakes during chick rearing may not be adaptive. Raising chicks can lead to reproductive costs, and the causal mechanism appears to be a reduction in body condition. 6. We compare our results with previous brood (or clutch) size manipulation experiments that have measured adult body condition, survival and/or future fecundity. Although the empirical evidence suggests that long-lived species are more likely to experience survival costs than short-lived species, we believe the opposite may be true. We suggest that shifting the experimental protocol of cost of reproduction studies from brood enlargements (an approach taken in most prior studies) to brood reductions will provide more accurate quantifications of naturally occurring costs. 7. The cost of reproduction is one mechanism proposed to explain the reduced survival rates reported for kittiwake populations in the North Atlantic relative to those in the North Pacific ocean. Oceanographic data, however, suggest that lower food availability may limit survival of kittiwakes in the North Atlantic where a deeper mixed layer and reduced primary production combine to make conditions less favourable for this seabird during the winter months.

Alaska↗
USGS1998

Human influences on trophic cascades along rocky shores

A three-trophic-level interaction among American Black Oystercatchers ( Haematopus bachmani ), limpets ( Lottia spp.), and erect fleshy algae in rocky intertidal communities of central and southern California was documented via manipulative and “natural” experiments. Removal of the territorial limpet ( Lottia gigantea ) initially caused large increases in the percent cover of erect fleshy algae, followed by a more gradual increase in density of small limpets ( Lottia spp.) and a decline in algal cover. Algal cover increased following the removal of small limpets at the sites from which L. gigantea had been removed earlier, thus demonstrating that the large and small limpets had similar inhibitory effects on plant populations. A comparison of sites with and without oystercatchers showed that L. gigantea occupied substrate inclinations in proportion to their availability at sites where oystercatchers were rare, whereas the distribution of L. gigantea was skewed toward vertically inclined substrates where oystercatchers were common. Survival rates of limpets translocated to horizontal and vertical substrates were similar in sites lacking oystercatcher predation, but were much lower on horizontal substrates where oystercatchers were common. Our results are consistent with those from several prior studies in demonstrating that shorelines frequented by humans typically lack oystercatchers. Humans also exploit L. gigantea and reduce populations to low densities of small individuals. These findings may explain why the midlittoral zone of rocky intertidal communities in western North America are so often dominated by high population densities of small limpets.

Ecological Applications↗
USGS1996

Comparative demography of sea otter populations

Population trends are poorly documented and demographic information is typically lacking for many carnivorous mammals. The sea otter ( Enhydru lutris ) has a well known history of decline and recovery, and while many other species have declined as precipitously, few have recovered so spectacularly. Generally speaking, northern populations (remnants within the range of E. l. lutris and E. l. kenyoni ) have recovered at high rates while recovery of the southern sea olter ( E. I. nereis ), which is listed as legally threatened under the Endangered Species Act (ESA), has progressed more slowly. Our purpose is to contrast trends in abundance and demographic patterns between Southern California and northern (Washington, British Columbia, Alaska, and Asia) sea otter populations. Specifically, we provide (1) a brief review of the main findings to date: (2) a summary of ongoing and planned studies; and (3) recommendations for future research. A more detailed account of these and other issues concerning the conservation and management of sea otters is provided in the U.S. Fish and Wildlife Service's Recovery Plan for the Califomia Sea Otter (U.S. Fish and Wildlife Service 1996).

Endangered Species UPDATE↗
USGS1995

Sea otters in the northern Pacific Ocean

About 250 years ago sea otters ( Enhydra lutris ) were distributed continuously from central Baja California, north and west along the Pacific Rim to Machatka Peninsula in Russia, and south along the Kuril Island to northern Japan (Kenyon 1969; Fig. 1a). Several hundred thousand sea otters may have occurred in the north Pacific region when commercial hunting began in the 18th century (Riedman and Estes 1990). At least two attributes of the sea otter have influenced humans, likely for as long as they have resided together along the coast of the north Pacific Ocean. First, sea otters rely on a dense fur, among the finest in the world, for insulation in the cold waters of the Pacific Ocean. The demand for sea otter fur led to their near extinction in the 19th century. The fur harvest, begun about 1740 and halted by international treaty in 1911, left surviving colonies, each likely numbering less than a few hundred animals, in California, south-central Alaska, and the Aleutian, Medney, and Kuril Islands (Fig. 1a). These individuals provided the nucleus for the recovery of the species. Today more than 100,000 sea otters occur throughout about 75% of their original range (fig. 1b). Immigration has resulted in near-complete occupation of the Aleutian and Kuril archipelagos and the Alaska peninsula. Successful translocations have resulted in viable populations in southeast Alaska, Washington, and British Columbia. Large amounts of unoccupied habitat remain along the coasts of Russia, Canada, the United States, and Mexico. The second potential source of conflict between sea otters and humans is that sea otters prey on and often limit some benthic invertebrate populations. Because some of these invertebrates are aso used by humans (Estes and VanBlaricom 1985), human perceptions about the effects of sea otter foraging on invertebrates sometimes differ. By limiting populations of herbivorous invertebrates ( e.g. , sea urchins [Echinoidea]) otters help maintain the integrity of kelp forest communities. At the same time, sea otter predation on other marine invertebrates can lead to direct competition with humans for resources. These interactions add complex dimensions to the conservation and management of sea otters, in large part because of wide-ranging social, ecological, and economic consequences of sea otter foraging. Long-term data on abundance and distribution are available for relatively few sea otter populations. Here we summarize such data from three populations: Being Island, Russia; Prince William Sound, Alaska; and Olympic Peninsula, Washington. The Bering Island population resulted from natural emigration and represents complete recovery. Prince William Sounds represents near recovery of a remnant population, whereas the Washington population was established via translocations from Alaska and is just beginning to recover. We will compare growth rates and current status among these populations. Because of its unique status and growth characteristics, the California sea otter is not treated in this article.

Book chapter↗
USGS1994

Breeding patterns and reproductive success of California sea otters

Following commercial exploitation in the eighteenth and nineteenth centuries, sea otter ( Enhydra lutris ) populations in Alaska, British Columbia, and Washington recovered at 17-20% a year, yet the California population increased at only 5% a year. This slow rate of increase is perplexing, given that unoccupied and apparently favorable habitats occur throughout the sea otter's California range, and higher growth rates occurred among northern sea otter populations. Better knowledge of the demography of the California population is important in understanding these disparate population growth rates. We studied the reproductive biology and behavior of 53 tagged female sea otters from 1985 to 1991 in Monterey Bay, California. During the study, 136 pups were born to these females. Observations of each female enabled us to determine exact or estimated pup birth dates, which we used to calculate lengths of gestation, pup dependency, and reproductive cycle. Seasonal trends in pupping, in the proportion of adult females with pups, and in pup separations from their mothers were relatively uniform throughout the year. The average interval between separation from pup and subsequent birth was 198 days, the interbirth interval was 407 days, and estimated birth rate was 0.90/year for all adult females. For females that pupped annually (did not lose undetected newborns), the average interbirth interval was 342 days, given an estimated birth rate of 1.07/year. Length of the reproductive cycle increased with increasing length of prior pup dependency. However, the interval between separation from pup and subsequent birth was delayed among females that prematurely lost their pups. The average length of dependency for pups that survived to weaning was 166 days, but ranged from 120 to 280 days. The maximum preweaning survival rate was 0.60-0.65, less than values measured or inferred for some Alaskan populations. Most pups that did not survive to weaning were lost within a month of birth. The probability of successfully weaning pups and the length of dependency increased ( P = 0.077) with mothers' ages, thus indicating that reproductive success may increase among females with greater mothering experience. The high preweaning pup mortality we observed probably accounts for much of the relatively slow growth rate of the California sea otter population.

California↗
USGS1992

Experimental evidence for the effects of polyphenolic compounds from Dictyoneurum californicum Ruprecht (Phaeophyta: Laminariales) on feeding rate and growth in the red abalone Haliotus rufescens Swainson

The effects of polyphenolic compounds from brown algae on grazing and growth rate of the California red abalone Haliotis rufescens Swainson were examined. Abalone consumed three phenolic-poor algal species, Laminaria sinclarii (Harvey) Farlow, Macrocystis pyrifera Agardh, and Nereocystis luetkeana Postels et Ruprecht (mean phenolic content = 0.52% dry mass), at a greater rate than two phenolic-rich species, Dictyoneurum californicum Ruprecht and Cystoseira osmundacea Agardh (mean phenolic content = 4.60% dry mass). This inverse relationship between phenolic content and consumption rate also existed after the algae were macerated and the liquid portion of the blended slurry incorporated in agar discs. However, the correlation between grazing rate and phenolic content imprpve d in this latter experiment, thus suggesting that abalone grazing was deterred significantly by the morphology of L. sinclarii and, to a lesser extent, of M. pyrifera . Polyphenolics extracted from D. californicum reduced abalone grazing rates by 90% when incorporated into agar discs at a concentration of 6 mg·ml −1 . Although abalone were unable to maintain body mass when fed ad libitum on macerated M. pyrifera incorporated into agar discs, polyphenolics from D. californicum further inhibited shell growth when added to the discs at 5 mg·ml −1 . The abalone ate less of the phenol-containing discs than of the discs lacking phenolics. Our results support findings of several prior studies that polyphenolic compounds from brown algae deter grazing by coastal zone herbivores in the northeast Pacific Ocean.

Journal of Experimental Marine Biology and Ecology↗