Trends and Carrying Capacity of Sea Otters in Southeast Alaska

Abstract Background Reintroducing predators is a promising conservation tool to help remedy human-caused ecosystem changes. However, the growth and spread of a reintroduced population is a spatiotemporal process that is driven by a suite of factors, such as habitat change, human activity, and prey availability. Sea otters (Enhydra lutris) are apex predators of nearshore marine ecosystems that had declined nearly to extinction across much of their range by the early 20th century. In Southeast Alaska, which is comprised of a diverse matrix of nearshore habitat and managed areas, reintroduction of 413 individuals in the late 1960s initiated the growth and spread of a population that now exceeds 25,000. Methods Periodic aerial surveys in the region provide a time series of spatially-explicit data to investigate factors influencing this successful and ongoing recovery. We integrated an ecological diffusion model that accounted for spatially-variable motility and density-dependent population growth, as well as multiple population epicenters, into a Bayesian hierarchical framework to help understand the factors influencing the success of this recovery. Results Our results indicated that sea otters exhibited higher residence time as well as greater equilibrium abundance in Glacier Bay, a protected area, and in areas where there is limited or no commercial fishing. Asymptotic spread rates suggested sea otters colonized Southeast Alaska at rates of 1–8 km/yr with lower rates occurring in areas correlated with higher residence time, which primarily included areas near shore and closed to commercial fishing. Further, we found that the intrinsic growth rate of sea otters may be higher than previous estimates suggested. Conclusions This study shows how predator recolonization can occur from multiple population epicenters. Additionally, our results suggest spatial heterogeneity in the physical environment as well as human activity and management can influence recolonization processes, both in terms of movement (or motility) and density dependence.

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DIET AND FORAGING BEHAVIOR OF SEA OTTERS IN SOUTHEAST ALASKA

Marine Mammal Science ◽

10.1111/j.1748-7692.1993.tb00441.x ◽

1993 ◽

Vol 9 (2) ◽

pp. 168-181 ◽

Cited By ~ 28

Author(s):

Rikk G. Kvitek ◽

C. Edward Bowlby ◽

Michelle Staedler

Keyword(s):

Foraging Behavior ◽

Sea Otters ◽

Southeast Alaska

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Relations between red alder composition and understory vegetation in young mixed forests of southeast Alaska

Canadian Journal of Forest Research ◽

10.1139/x05-290 ◽

2006 ◽

Vol 36 (3) ◽

pp. 738-748 ◽

Cited By ~ 19

Author(s):

Thomas A Hanley ◽

Robert L Deal ◽

Ewa H Orlikowska

Keyword(s):

Carrying Capacity ◽

Basal Area ◽

Picea Sitchensis ◽

Understory Vegetation ◽

Wildlife Habitat ◽

Red Alder ◽

Southeast Alaska ◽

Net Production ◽

Understory Biomass ◽

Young Growth

Interest in mixed red alder (Alnus rubra Bong.) conifer young-growth stands has grown in southeast Alaska, USA, because they appear to provide much more productive understory vegetation and wildlife habitat than do similar-aged pure conifer stands. We studied understory vegetation in nine even-aged young-growth stands (3842 years old) comprising a gradient of red alder conifer overstory composition, with red alder ranging from 0% to 86% of stand basal area. Conifers were Sitka spruce (Picea sitchensis (Bong.) Carr.), western hemlock (Tsuga heterophylla (Raf.) Sarg.), and western redcedar (Thuja plicata Donn ex D. Don). We measured understory biomass and net production (current annual growth) in each stand by species and plant part and estimated carrying capacity for black-tailed deer (Odocoileus hemionus sitkensis Cowan) with a food-based habitat model. Highly significant positive relations (P < 0.002) were found between red alder basal area and all of the following: total understory biomass (r2 = 0.743), net production of shrubs (r2 = 0.758) and herbs (r2 = 0.855), and summer carrying capacity for deer (r2 = 0.846). The high correlation between red alder and herbaceous production is especially important, because herbs are least abundant and most difficult to maintain in young-growth conifer forests of this region. Red alder offers prospects for increasing understory vegetation biomass and its food value for deer and other wildlife when included as a hardwood overstory species in mixed hardwoodconifer young-growth forests.

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Estimating Carrying Capacity for Sea Otters in British Columbia

Journal of Wildlife Management ◽

10.2193/2006-518 ◽

2008 ◽

Vol 72 (2) ◽

pp. 382-388 ◽

Cited By ~ 21

Author(s):

Edward J. Gregr ◽

Linda M. Nichol ◽

Jane C. Watson ◽

John K. B. Ford ◽

Graeme M. Ellis

Keyword(s):

British Columbia ◽

Carrying Capacity ◽

Sea Otters

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Sea Otter Carrying Capacity in a Soft- and Mixed-sediment Benthic Habitat

10.22541/au.160996084.43475947/v1 ◽

2021 ◽

Author(s):

Ian Davis ◽

Timpthy Dellapenna ◽

Gary Maale ◽

Francis Gelwick ◽

Fred Selts ◽

...

Keyword(s):

Population Density ◽

Carrying Capacity ◽

Standing Stock ◽

Food Resources ◽

Equilibrium Density ◽

Benthic Habitat ◽

Sea Otter ◽

Replacement Rate ◽

Sea Otters ◽

The Mean

Identifying factors that influence sea otter (Enhydra lutris) population density can provide insight into why it varies spatially and temporally and when a recovering population has reached an equilibrium density because of food resources (i.e., carrying capacity K). Although food availability is widely recognized as an important extrinsic factor affecting sea otter density, how do we determine when a population has reached K? The goal of this study was to estimate K for Simpson Bay, Alaska by measuring the abundance of edible bivalves, the primary prey for sea otters for over 40 years. We then compared prey abundance and estimated replacement rate (i.e., the mean age of bivalves predated by sea otters) to estimated annual prey consumption based on the mean population density for the past 18 years. On average, 110 adult sea otters (5.2 km−2) have occupied Simpson Bay annually since 2001 consuming an estimated 176,660 kg of bivalves. The total mass (standing stock) of the major bivalves (predominately butter clams and stained macomas) was 785,730 kg, so adult sea otters consumed about 22% annually. Based on these observations and calculations, the estimated annual number of sea otters occupying Simpson Bay appears to be at or near K based on the replacement rate of food resources. However, other intrinsic (e.g., male territoriality and emigration) and extrinsic (e.g., predation, disease, human-related mortality) factors may influence equilibrium density, which varies spatially and temporally, resulting in a mosaic of subpopulations with different densities, rates of growth and discontinuous distributions. Understanding the balance among these factors may be one of the most challenging ecological questions for sea otter conservation and management as populations recover from their range-wide decimation during the Maritime Fur Trade in the late 18th and 19th centuries

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Did Tlingit Ancestors Eat Sea Otters? Addressing Intellectual Property and Cultural Heritage through Zooarchaeology

American Antiquity ◽

10.1017/aaq.2019.101 ◽

2020 ◽

Vol 85 (2) ◽

pp. 202-221

Author(s):

Madonna L. Moss

Keyword(s):

Alaska Native ◽

Marine Ecosystem ◽

Keystone Species ◽

Sea Otter ◽

Sea Otters ◽

Southeast Alaska ◽

The North ◽

Commercially Important ◽

The 1960S ◽

The North Pacific

The maritime fur trade caused the extirpation of sea otters from southeast Alaska. In the 1960s, sea otters were reintroduced, and their numbers have increased. Now, sea otters are competing with people for what have become commercially important invertebrates. After having been absent for more than a century, the reentry of this keystone species has unsettled people. Although some communities perceive sea otters as a threat to their livelihoods, others view their return as restoration of the marine ecosystem. The federal Marine Mammal Protection Act authorizes any Alaska Native to harvest sea otters for subsistence provided that the harvest is not wasteful. Some people are seeking to define “traditional” Tlingit use of sea otters as not only using their pelts but consuming them as food, but some Tlingit maintain they never ate sea otters. This project analyzes the largest precontact archaeological assemblage of sea otter bones in southeast Alaska, with the benefit of insights gained from observing a Tlingit hunter skin a sea otter to infer that Tlingit ancestors hunted sea otters primarily for pelts. The extent to which other Indigenous peoples of the North Pacific consumed sea otters as food deserves investigation, especially as sea otters recolonize their historic range.

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Impacts of sea otter (Enhydra lutris) predation on commercially important sea cucumbers (Parastichopus californicus) in southeast Alaska

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/cjfas-2013-0025 ◽

2013 ◽

Vol 70 (10) ◽

pp. 1498-1507 ◽

Cited By ~ 15

Author(s):

Sean D. Larson ◽

Zachary N. Hoyt ◽

Ginny L. Eckert ◽

Verena A. Gill

Keyword(s):

Sea Cucumber ◽

Inverse Relationship ◽

Population Survey ◽

Fishery Management ◽

Sea Otter ◽

Enhydra Lutris ◽

Sea Otters ◽

Sea Cucumbers ◽

Southeast Alaska ◽

Commercially Important

Sea cucumbers (Parastichopus californicus), which are an important commercial, subsistence, and ecological resource, are negatively affected by an expanding sea otter (Enhydra lutris) population in southeast Alaska. A few hundred sea otters were reintroduced into southeast Alaska in the late 1960s after their extirpation during the 18th and 19th century fur trade. In the ensuing decades after recolonization, the sea otter population grew exponentially in number and distribution, and sea cucumbers declined in density in areas with otters, suggesting an inverse relationship between sea otter numbers and sea cucumber density. We evaluated the interaction and effects of sea otters on sea cucumbers using sea otter foraging observations, sea otter population survey data, and sea cucumber density data. Our results indicate that sea cucumber density declined with and without sea otter presence and that the extent of the decline depends on the duration and magnitude of sea otter presence, with 100% decline in areas occupied by sea otters since 1994. Sea otter predation should be included in sea cucumber fishery management as a step toward ecosystem-based management.

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Archaeological and Contemporary Evidence Indicates Low Sea Otter Prevalence on the Pacific Northwest Coast During the Late Holocene

Ecosystems ◽

10.1007/s10021-021-00671-3 ◽

2021 ◽

Author(s):

Erin Slade ◽

Iain McKechnie ◽

Anne K. Salomon

Keyword(s):

Pacific Northwest ◽

Carrying Capacity ◽

Late Holocene ◽

Northwest Coast ◽

Sea Otter ◽

Size Distributions ◽

Sea Otters ◽

Pacific Northwest Coast ◽

Social Ecological ◽

The Pacific

AbstractThe historic extirpation and subsequent recovery of sea otters (Enhydra lutris) have profoundly changed coastal social-ecological systems across the northeastern Pacific. Today, the conservation status of sea otters is informed by estimates of population carrying capacity or growth rates independent of human impacts. However, archaeological and ethnographic evidence suggests that for millennia, complex hunting and management protocols by Indigenous communities limited sea otter abundance near human settlements to reduce the negative impacts of this keystone predator on shared shellfish prey. To assess relative sea otter prevalence in the Holocene, we compared the size structure of ancient California mussels (Mytilus californianus) from six archaeological sites in two regions on the Pacific Northwest Coast, to modern California mussels at locations with and without sea otters. We also quantified modern mussel size distributions from eight locations on the Central Coast of British Columbia, Canada, varying in sea otter occupation time. Comparisons of mussel size spectra revealed that ancient mussel size distributions are consistently more similar to modern size distributions at locations with a prolonged absence of sea otters. This indicates that late Holocene sea otters were maintained well below carrying capacity near human settlements as a result of human intervention. These findings illuminate the conditions under which sea otters and humans persisted over millennia prior to the Pacific maritime fur trade and raise important questions about contemporary conservation objectives for an iconic marine mammal and the social-ecological system in which it is embedded.

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Carrying Capacity and Pre-Decline Abundance of Sea Otters (Enhydra lutris kenyoni) in the Aleutian Islands

Northwestern Naturalist ◽

10.2307/3536541 ◽

2003 ◽

Vol 84 (3) ◽

pp. 145 ◽

Cited By ~ 5

Author(s):

Douglas M. Burn ◽

Angela M. Doroff ◽

M. Tim Tinker

Keyword(s):

Carrying Capacity ◽

Aleutian Islands ◽

Enhydra Lutris ◽

Sea Otters

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Diffusion modeling reveals effects of multiple release sites and human activity on a recolonizing apex predator

10.21203/rs.3.rs-341528/v1 ◽

2021 ◽

Author(s):

Joseph Eisaguirre ◽

Perry Williams ◽

Xinyi Lu ◽

Michelle Kissling ◽

William Beatty ◽

...

Keyword(s):

Human Activity ◽

Residence Time ◽

Prey Availability ◽

Commercial Fishing ◽

Apex Predators ◽

Sea Otters ◽

Southeast Alaska ◽

Bayesian Hierarchical ◽

Factors Influencing ◽

Multiple Population

Abstract Background: Reintroducing predators is a promising conservation tool to help remedy human-caused ecosystem changes. However, the growth and spread of a reintroduced population is a spatiotemporal process that is driven by a suite of factors, such as habitat change, human activity, and prey availability. Sea otters (Enhydra lutris) are apex predators of nearshore marine ecosystems that had declined nearly to extinction across much of their range by the early 20th century. In Southeast Alaska, which is comprised of a diverse matrix of nearshore habitat and managed areas, reintroduction of 413 individuals in the late 1960s initiated the growth and spread of a population that now exceeds 25,000. Methods: Periodic aerial surveys in the region provide a time series of spatially-explicit data to investigate factors influencing this successful and ongoing recovery. We integrated an ecological diffusion model that accounted for spatially-variable motility and density-dependent population growth, as well as multiple population epicenters, into a Bayesian hierarchical framework to help understand the factors influencing the success of this recovery. Results: Our results indicated that sea otters exhibited higher residence time as well as greater equilibrium abundance in Glacier Bay, a protected area, and in areas where there is limited or no commercial fishing. Asymptotic spread rates suggested sea otters colonized Southeast Alaska at rates of 1-8 km/yr with lower rates occurring in areas correlated with higher residence time, which primarily included areas near shore and closed to commercial fishing. Further, we found that the intrinsic growth rate of sea otters may be higher than previous estimates suggested. Conclusions: This study shows how predator recolonization can occur from multiple population epicenters. Additionally, our results suggest spatial heterogeneity in the physical environment as well as human activity and management can influence recolonization processes, both in terms of movement (or motility) and density dependence.

Download Full-text