Correlates to survival of juvenile sea otters in Prince William Sound, Alaska, 19921993

Ballachey, Brenda E.; Bodkin, James L.; Howlin, Shay; Doroff, Angela M.; Rebar, A.H.

doi:10.1139/z03-121

Cited by 31 publications

(15 citation statements)

References 54 publications

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“…We must add the caveat that our model could not detect trends in mortality of very young juveniles because 0‐year‐old carcasses were excluded from analysis, due to known recovery bias. Thus the potential role of variation in early postweaning survival as a contributing factor to population dynamics (e.g., see Ballachey et al 2003) is impossible to directly assess with currently available data, and may be underrepresented. This uncertainty should be addressed in future field studies; however, we believe it is unlikely that survival rates of 6‐month juveniles would exhibit spatial or temporal trends that were substantially different from that of 12‐month‐old juveniles.…”

Section: Discussionmentioning

confidence: 99%

Incorporating Diverse Data and Realistic Complexity Into Demographic Estimation Procedures for Sea Otters

Tinker

Doak

Estes

et al. 2006

Ecological Applications

105

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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.

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Section: Discussionmentioning

confidence: 99%

Incorporating Diverse Data and Realistic Complexity Into Demographic Estimation Procedures for Sea Otters

Tinker

Doak

Estes

et al. 2006

Ecological Applications

105

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“…Overall, our annual survival probability estimate (Ŝ = 0·964 ± 0·022) confirms a common pattern in mammals: yearly survival after returning to the native island is higher than the first‐year post‐weaning survival (Clutton‐Brock et al . 1982; Ballachey et al . 2003).…”

Section: Discussionmentioning

confidence: 99%

Interannual variation in the post‐weaning and juvenile survival of subantarctic fur seals: influence of pup sex, growth rate and oceanographic conditions

Beauplet

Barbraud

Chambellant

et al. 2005

Journal of Animal Ecology

122

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Summary 1.A major hypothesis of life history theory is that early development conditions affect future survival and reproductive success. However, although a growing number of studies have addressed this question, many of them are taxonomically biased, thereby impeding the generalization of this hypothesis. 2. This study examines the factors influencing post-weaning survival in five weaned cohorts of subantarctic fur seal pups from Amsterdam Island, southern Indian Ocean. It used mark-recapture data from 7 consecutive years of different environmental conditions. 3. The cohort return rate varied from 45% to 74% of weaned pups, depending on the year of weaning. In each cohort, 96% of weaned pups returned between 3 and 6 years of age, and none of the factors examined seemed to influence this timing pattern. The probability of survival to this first return was negatively related to sea-surface temperature anomalies (SSTa) of the 6 months following the weaning process. It increased with pup preweaning growth rate and differed between the sexes. Females' survival rate was significantly higher than males', except during years of extreme SSTa, where no difference was detected. 4. The juvenile state represented young individuals after their first return on their native island. Annual juvenile tag loss rate was constant at 0·217 (SE = 0·027), whereas temporary emigration rate varied over cohorts and was higher in males 0·423 (SE = 0·035) than in females 0·170 (SE = 0·012). This dispersion pattern may be prolonged in some cases, as the yearly immigration probability was constant at 0·290 (SE = 0·065). 5. Taking into account tag loss and temporary emigration, the estimated yearly survival probability of juveniles was 0·964 (SE = 0·022). This value was unrelated to any tested oceanographic or individual parameter including sex. 6. Results support the hypothesis that early development traits affect short-term post-weaning survival. However, no long-term effect of maternal postnatal investment was detected after the first return to the native island. Results also indicate that the effect of early development traits on survival interacts with environmental conditions encountered shortly after independence of individuals.

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“…Other data on sea otter characteristics were derived from the literature, including sea otter energetics (Dean et al 2002), sea otter body mass (Dean et al 2002; Rotterman and Monnett 2002; Ballachey et al 2003), surface area of sea otter fur (Kenyon 1969; Davis et al 1988), paw size (Tarasloff 1973), and other model parameters (e.g., energy density of each prey category [Dean et al 2002]). The PAH concentrations and distributions of prey, sediments, and seawater were derived from chemical analyses conducted on samples taken in oiled and unoiled areas (Boehm et al 2004, 2007; Neff et al 2006; Brannon et al 2007).…”

Section: Individual-based Modelsmentioning

confidence: 99%

Quantifying population‐level risks using an individual‐based model: Sea otters, Harlequin Ducks, and the Exxon Valdez oil spill

Harwell¹,

Gentile

Parker

2012

Integr Envir Assess & Manag

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Ecological risk assessments need to advance beyond evaluating risks to individuals that are largely based on toxicity studies conducted on a few species under laboratory conditions, to assessing population-level risks to the environment, including considerations of variability and uncertainty. Two individual-based models (IBMs), recently developed to assess current risks to sea otters and seaducks in Prince William Sound more than 2 decades after the Exxon Valdez oil spill (EVOS), are used to explore population-level risks. In each case, the models had previously shown that there were essentially no remaining risks to individuals from polycyclic aromatic hydrocarbons (PAHs) derived from the EVOS. New sensitivity analyses are reported here in which hypothetical environmental exposures to PAHs were heuristically increased until assimilated doses reached toxicity reference values (TRVs) derived at the no-observed-adverse-effects and lowest-observed-adverse-effects levels (NOAEL and LOAEL, respectively). For the sea otters, this was accomplished by artificially increasing the number of sea otter pits that would intersect remaining patches of subsurface oil residues by orders of magnitude over actual estimated rates. Similarly, in the seaduck assessment, the PAH concentrations in the constituents of diet, sediments, and seawater were increased in proportion to their relative contributions to the assimilated doses by orders of magnitude over measured environmental concentrations, to reach the NOAEL and LOAEL thresholds. The stochastic IBMs simulated millions of individuals. From these outputs, frequency distributions were derived of assimilated doses for populations of 500 000 sea otters or seaducks in each of 7 or 8 classes, respectively. Doses to several selected quantiles were analyzed, ranging from the 1-in-1000th most-exposed individuals (99.9% quantile) to the median-exposed individuals (50% quantile). The resulting families of quantile curves provide the basis for characterizing the environmental thresholds below which no population-level effects could be detected and above which population-level effects would be expected to become manifest. This approach provides risk managers an enhanced understanding of the risks to populations under various conditions and assumptions, whether under hypothetically increased exposure regimes, as demonstrated here, or in situations in which actual exposures are near toxic effects levels. This study shows that individual-based models are especially amenable and appropriate for conducting population-level risk assessments, and that they can readily be used to answer questions about the risks to individuals and populations across a variety of exposure conditions. Integr Environ Assess Manag 2012; 8: 503–522. © 2012 SETAC

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Correlates to survival of juvenile sea otters in Prince William Sound, Alaska, 19921993

Cited by 31 publications

References 54 publications

Incorporating Diverse Data and Realistic Complexity Into Demographic Estimation Procedures for Sea Otters

Incorporating Diverse Data and Realistic Complexity Into Demographic Estimation Procedures for Sea Otters

Interannual variation in the post‐weaning and juvenile survival of subantarctic fur seals: influence of pup sex, growth rate and oceanographic conditions

Quantifying population‐level risks using an individual‐based model: Sea otters, Harlequin Ducks, and the Exxon Valdez oil spill

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Correlates to survival of juvenile sea otters in Prince William Sound, Alaska, 19921993

Cited by 31 publications

References 54 publications

Incorporating Diverse Data and Realistic Complexity Into Demographic Estimation Procedures for Sea Otters

Incorporating Diverse Data and Realistic Complexity Into Demographic Estimation Procedures for Sea Otters

Interannual variation in the post‐weaning and juvenile survival of subantarctic fur seals: influence of pup sex, growth rate and oceanographic conditions

Quantifying population‐level risks using an individual‐based model: Sea otters, Harlequin Ducks, and the Exxon Valdez oil spill

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Correlates to survival of juvenile sea otters in Prince William Sound, Alaska, 19921993