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Author: Wendy Jane Schrader Publisher: ISBN: Category : Languages : en Pages :
Book Description
Relating the behavior of predators to prey density is an important aspect of foraging theory. Changes in prey accessibility may have contributed to a greater-than 80% decline in Steller sea lions (Eumetopias jubatus) throughout the western portion of their range during the last 30 years. A new method was developed for inferring prey accessibility to juveniles of this otariid, from observable features of diving and ranging behavior. Seventeen juveniles (9F, 8M) were monitored in multiple seasons and locations in the Gulf of Alaska via satellite telemetry. Twelve of the 17 had experienced 1-3 months of temporary captivity. Effects of temporary captivity on endurance, habitat use and development of diving and ranging behavior were tested. Diving and ranging patterns of previously captive juveniles were consistent with data reported for freeranging juveniles. Development in mean dive depth and duration after release was likely due to increased foraging. "Focus in time spent at depth" was tested as a proxy for prey accessibility using predictions based on foraging theory. 'Focus ... ' was defined as vertical concentration in dive distribution and was calculated by comparing the observed time spent at depth with an expected distribution. There was significantly more focus in summer than winter, and more focus at depth (>62 m) in winter. Focus at depth was significantly greater during midday for juveniles monitored in winter. Significant negative correlation between maximum focus and trip duration provided the best indication that focus may be related to prey accessibility. Short trips had significantly greater maximum focus than long trips, using a matched-pairs approach. Analysis of focus in time-at-depth data can elucidate small scale interactions between juvenile otariids and their prey. This new method of measuring the dive behavior of otariids can be applied to individual foraging trips and holds promise as a proxy for assessing seasonal, annual and developmental changes in individual prey accessibility.
Author: Wendy Jane Schrader Publisher: ISBN: Category : Languages : en Pages :
Book Description
Relating the behavior of predators to prey density is an important aspect of foraging theory. Changes in prey accessibility may have contributed to a greater-than 80% decline in Steller sea lions (Eumetopias jubatus) throughout the western portion of their range during the last 30 years. A new method was developed for inferring prey accessibility to juveniles of this otariid, from observable features of diving and ranging behavior. Seventeen juveniles (9F, 8M) were monitored in multiple seasons and locations in the Gulf of Alaska via satellite telemetry. Twelve of the 17 had experienced 1-3 months of temporary captivity. Effects of temporary captivity on endurance, habitat use and development of diving and ranging behavior were tested. Diving and ranging patterns of previously captive juveniles were consistent with data reported for freeranging juveniles. Development in mean dive depth and duration after release was likely due to increased foraging. "Focus in time spent at depth" was tested as a proxy for prey accessibility using predictions based on foraging theory. 'Focus ... ' was defined as vertical concentration in dive distribution and was calculated by comparing the observed time spent at depth with an expected distribution. There was significantly more focus in summer than winter, and more focus at depth (>62 m) in winter. Focus at depth was significantly greater during midday for juveniles monitored in winter. Significant negative correlation between maximum focus and trip duration provided the best indication that focus may be related to prey accessibility. Short trips had significantly greater maximum focus than long trips, using a matched-pairs approach. Analysis of focus in time-at-depth data can elucidate small scale interactions between juvenile otariids and their prey. This new method of measuring the dive behavior of otariids can be applied to individual foraging trips and holds promise as a proxy for assessing seasonal, annual and developmental changes in individual prey accessibility.
Author: Leslie Anne Cornick Publisher: ISBN: Category : Steller's sea lion Languages : en Pages : 210
Book Description
"The western stock of the Steller sea lion (Eumetopias jubatus) (SSL) along the Aleutian Islands and in the Gulf of Alaska (GOA) has continuously declined over the past three decades, and is now listed as endangered. While the causes of this decline are not well understood, nutritional stress, resulting in excessive juvenile mortality, is the leading hypothesis. Optimal foraging theory predicts that predators should change their dive behavior (foraging strategy) as prey availability changes. Relative prey accessibility (RPA, the ability of an individual SSL to access prey during a dive cycle) is likely a crucial causal link between hypothesized reduced prey biomass resulting from commercial fishing activity and depressed foraging efficiency of SSL, but cannot be controlled in the wild, and is impossible to accurately quantify at the individual level. This study, for the first time, experimentally validates prey availability-foraging behavior relationships previously hypothesized by optimality and foraging theory, but never before experimentally tested for a diving mammal. I employed a combined approach of predictive model development and controlled experiments. Testable predictions were determined by developing a bioenergetics-based model of individual dive behavior for aerobic dives of otariids. To determine the relationship between RPA and dive behavior, I examined how dive duration, foraging time, surface interval, percent time foraging, submerged, surface time, dive efficiency, and foraging efficiency varied with changes in simulated RPA in optimal foraging experiments performed with three seven, year-old SSL (two females, one male) held captive at the Alaska Sea life Center in Seward, AK. RPA had a significant positive effect on dive duration, foraging time, percent time foraging, and relative foraging efficiency. The dive model accurately predicted the observed effect of changing RPA on dive behavior and foraging efficiency. A population-based model was also developed in order to predict the effects of varying regimes of commercial fisheries activity on SSL population trends, based upon an estimate of annual SSL energetic requirements. The model accurately portrayed SSL abundance trends predicted by published projections, but failed to implicate competition with the commercial groundfish fishery in Alaska as a cause of the decline of SSL"--Leaves iii-iv.
Author: Stephen R. Meck Publisher: ISBN: Category : Steller's sea lion Languages : en Pages : 104
Book Description
Range, areas of concentrated activity, and dispersal characteristics for juvenile Steller sea lions Eumetopias jubatus in the endangered western population (west of 144° W in the Gulf of Alaska) are poorly understood. This study quantified space use by analyzing post-release telemetric tracking data from satellite transmitters externally attached to n = 65 juvenile (12-25 months; 72.5 to 197.6 kg) Steller sea lions (SSLs) captured in Prince William Sound (60°38'N -147°8'W) or Resurrection Bay (60°2'N -149°22'W), Alaska, from 2003-2011. The analysis divided the sample population into 3 separate groups to quantify differences in distribution and movement. These groups included sex, the season when collected, and the release type (free ranging animals which were released immediately at the site of capture, and transient juveniles which were kept in captivity for up to 12 weeks as part of a larger ongoing research program). Range-use was first estimated by using the minimum convex polygon (MCP) approach, and then followed with a probabilistic kernel density estimation (KDE) to evaluate both individual and group utilization distributions (UDs). The LCV method was chosen as the smoothing algorithm for the KDE analysis as it provided biologically meaningful results pertaining to areas of concentrated activity (generally, haulout locations). The average distance traveled by study juveniles was 2,131 ± 424 km. The animals mass at release (F[subscript 1, 63] = 1.17, p = 0.28) and age (F[subscript 1, 63] = 0.033, p = 0.86) were not significant predictors of travel distance. Initial MCP results indicated the total area encompassed by all study SSLs was 92,017 km2, excluding land mass. This area was heavily influenced by the only individual that crossed over the 144°W Meridian, the dividing line between the two distinct population segments. Without this individual, the remainder of the population (n = 64) fell into an area of 58,898 km2. The MCP area was highly variable, with a geometric average of 1,623.6 km2. Only the groups differentiated by season displayed any significant difference in area size, with the Spring/Summer (SS) groups MCP area (Mdn = 869.7 km2) being significantly less than that of the Fall/Winter (FW) group (Mdn = 3,202.2 km2), U = 330, p = 0.012, r = -0.31. This result was not related to the length of time the tag transmitted (H(2) = 49.65, p = 0.527), nor to the number of location fixes (H(2) = 62.77, p = 0.449). The KDE UD was less variable, with 50% of the population within a range of 324-1,387 km2 (mean=690.6 km2). There were no significant differences in area use associated with sex or release type (seasonally adjusted U = 124, p = 0.205, r = -0.16 and U = 87, p = 0.285, r = -0.13, respectively). However, there were significant differences in seasonal area use: U = 328, p = 0.011, r = -0.31. There was no relationship between the UD area and the amount of time the tag remained deployed (H(2) = 45.30, p = 0.698). The kernel home range (defined as 95% of space use) represented about 52.1% of the MCP range use, with areas designated as "core" (areas where the sea lions spent fully 50% of their time) making up only about 6.27% of the entire MCP range and about 11.8% of the entire kernel home range. Area use was relatively limited - at the population level, there were a total of 6 core areas which comprised 479 km2. Core areas spanned a distance of less than 200 km from the most western point at the Chiswell Islands (59°35'N -149°36'W) to the most eastern point at Glacier Island (60°54'N -147°6'W). The observed differences in area use between seasons suggest a disparity in how juvenile SSLs utilize space and distribute themselves over the course of the year. Due to their age, this variation is less likely due to reproductive considerations and may reflect localized depletion of prey near preferred haul-out sites and/or changes in predation risk. Currently, management of the endangered western and threatened eastern population segments of the Steller sea lion are largely based on population trends derived from aerial survey counts and terrestrial-based count data. The likelihood of individuals to be detected during aerial surveys, and resulting correction factors to calculate overall population size from counts of hauled-out animals remain unknown. A kernel density estimation (KDE) analysis was performed to delineate boundaries around surveyed haulout locations within Prince William Sound-Kenai Fjords (PWS-KF). To closely approximate the time in which population abundance counts are conducted, only sea lions tracked during the spring/summer (SS) months (May 10-August 10) were chosen (n = 35). A multiple state model was constructed treating the satellite location data, if it fell within a specified spatiotemporal context, as a re-encounter within a mark-recapture framework. Information to determine a dry state was obtained from the tags time-at-depth (TAD) histograms. To generate an overall terrestrial detection probability 1) The animal must have been within a KDE derived core-area that coincided with a surveyed haulout site 2) it must have been dry and 3) it must have provided at least one position during the summer months, from roughly 11:00 AM-5:00 PM AKDT. A total of 10 transition states were selected from the data. Nine states corresponded to specific surveyed land locations, with the 10th, an "at-sea" location (> 3 km from land) included as a proxy for foraging behavior. A MLogit constraint was used to aid interpretation of the multi-modal likelihood surface, and a systematic model selection process employed as outlined by Lebreton & Pradel (2002). At the individual level, the juveniles released in the spring/summer months (n = 35) had 85.3% of the surveyed haulouts within PWS-KF encompass KDE-derived core areas (defined as 50% of space use). There was no difference in the number of surveyed haulouts encompassed by core areas between sexes (F[subscript 1, 33] “0.001, p = 0.98). For animals held captive for up to 12 weeks, 33.3% returned to the original capture site. The majority of encounter probabilities (p) fell between 0.42 and 0.78 for the selected haulouts within PWS, with the exceptions being Grotto Island and Aialik Cape, which were lower (between 0.00-0.17). The at-sea (foraging) encounter probability was 0.66 (± 1 S.E. range 0.55-0.77). Most dry state probabilities fell between 0.08-0.38, with Glacier Island higher at 0.52, ± 1 S.E. range 0.49-0.55. The combined detection probability for hauled-out animals (the product of at haul-out and dry state probabilities), fell mostly between 0.08-0.28, with a distinct group (which included Grotto Island, Aialik Cape, and Procession Rocks) having values that averaged 0.01, with a cumulative range of H"0.00-0.02 (± 1 S.E.). Due to gaps present within the mark-recapture data, it was not possible to run a goodness-of-fit test to validate model fit. Therefore, actual errors probably slightly exceed the reported standard errors and provide an approximation of uncertainties. Overall, the combined detection probabilities represent an effort to combine satellite location and wet-dry state telemetry and a kernel density analysis to quantify the terrestrial detection probability of a marine mammal within a multistate modeling framework, with the ultimate goal of developing a correction factor to account for haulout behavior at each of the surveyed locations included in the study.
Author: United States. National Marine Fisheries Service. Office of Protected Resources. Permits Division Publisher: ISBN: Category : Northern fur seal Languages : en Pages : 1124
Author: Douglas P. DeMaster Publisher: ISBN: Category : Nature Languages : en Pages : 86
Book Description
The most likely cause of the moderate decline of western Alaska Steller sea lions, in the 1990s, is poor recruitment (reproduction and survival of young). Also implicated are nutritional stress, predation, and disease. In contrast, nutritional stress alone was the leading hypothesis for a steep decline in sea lions the 1980s. This book has 13 extended abstracts presented at a May 2001 workshop. Attendees included the nation's leading authorities on Alaska's Steller sea lions.
Author: National Research Council Publisher: National Academies Press ISBN: 0309086329 Category : Science Languages : en Pages : 217
Book Description
For an unknown reason, the Steller sea lion population in Alaska has declined by 80% over the past three decades. In 2001, the National Research Council began a study to assess the many hypotheses proposed to explain the sea lion decline including insufficient food due to fishing or the late 1970s climate/regime shift, a disease epidemic, pollution, illegal shooting, subsistence harvest, and predation by killer whales or sharks. The report's analysis indicates that the population decline cannot be explained only by a decreased availability of food; hence other factors, such as predation and illegal shooting, deserve further study. The report recommends a management strategy that could help determine the impact of fisheries on sea lion survival-establishing open and closed fishing areas around sea lion rookeries. This strategy would allow researchers to study sea lions in relatively controlled, contrasting environments. Experimental area closures will help fill some short-term data gaps, but long-term monitoring will be required to understand why sea lions are at a fraction of their former abundance.
Author: Holly Beth Briggs Publisher: ISBN: Category : Languages : en Pages :
Book Description
Recent studies indicate a 70% decrease in the Alaskan Steller sea lion (SSL) population (ca. 5% per year) since the early 1980's. In accordance with a 1997 status classification of the Western Steller sea lion (WSSL) stock as endangered, the "critical habitat" for the species was to be defined. This habitat has now been designated to include 10-20 nautical mile buffer zones around most rookeries and haulouts in the Gulf of Alaska (GOA) and Aleutian Islands. However, these zones were based on limited, summer, foraging data. The primary objective of this study was to characterize juvenile SSL diving behaviorand habitat use along the Kenai Peninsula and Prince William Sound (PWS) from winter to spring. Fifteen free ranging, subadult SSL of both sexes were captured and equipped with satellite telemeters at five haulout sites in PWS and Resurrection Bay, Alaska. Telemeters transmitted for an average of 122 days (range 38-181 days). A total of 11,692 locations were received and 217,419 dives recorded. All sea lions exhibited localized movements parallel or close to shore (3-15 kmoffshore). Young of the year (YOY) exhibited high site fidelity. Older juvenile sea lion lions were less restricted in their movements and traveled greater distances (200-400km) visiting avariety of islands, buoys, and other locations in PWS. Most dives were short (mean duration = 1.1 min) and shallow (mean depth = 10.8 m), with animals diving to an average maximum depth of 193 m. During winter (January and February), many dives (>̲40%) occurred during the daytime (0900-1500 LT). However, by April and May this pattern shifted and the animals made most of their dives (>̲40%) during the night (2100-0300 LT). This relationship was more pronounced for dives deeper than 20 m and coincided with the seasonal increase in photoperiod. Subadult SSL, especially YOY, remained within the 20 nautical mile coastal zone during winter and spring. Shallow, nearshore waters provide important habitat during this critical period of transition to nutritional independence. However, more conclusive data on SSL foraging ecology is necessary to better understand locations and depths preferred by the species.
Author: Wendy Jane Schrader
Author: Wendy Jane Schrader
Author: Leslie Anne Cornick
Author: Richard Merrick
Author: Stephen R. Meck
Author: Earl F. Becker
Author: 
Author: United States. National Marine Fisheries Service. Office of Protected Resources. Permits Division
Author: Douglas P. DeMaster
Author: National Research Council
Author: Holly Beth Briggs