Spatial and Temporal Distribution of Juvenile Steller Sea Lion (Eumetopias Jubatus) Predation Events in the Gulf of Alaska PDF Download
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Author: Norma A. Vazquez Publisher: ISBN: Category : Spatial behavior in animals Languages : en Pages : 77
Book Description
The first objective of this study was to quantify the intensity of space use of 70 juvenile (12-26 months old) Steller sea lions (SSLs) from the western Distinct Population Segment (DPS) in the Kenai Fjord(KF)/Prince William Sound (PWS) region of Alaska as derived from externally attached ARGOS satellite transmitter tags. A Bayesian state-space model (SSM) approach was used to process and interpolate the ARGOS-based locations. The resulting tracks were then used to quantify the spatio-temporal distribution of SSLs by way of a gridded utilization distribution (UD) in the study area. Each of six combined two-month UDs had an average of 24 ± 4.16 animals (range: 20-30) contributing around 5,090 ±1,879 filtered locations (range: 2,757-7,593). Results of the bimonthly UDs show juvenile SSL remained within the KF/PWS study region during the tracking period, with the exception of one individual, TJ16 (male), who crossed the 144° W Meridian separating the western and eastern DPS. Furthermore, results revealed that juveniles exhibit different spatial distributions depending on the time of year. They remain confined to a relatively smaller area (6,500-12,075 km2) in the 100% UD months of March through August compared to a larger area of 11,300-22,575 km2 in the 100% UD months September through February. In general, in winter (November-April) 90% of observations fell within 30km of the nearest haul-out, whereas in summer (May-October) 90% fell within 20km. A multifactor analysis of covariance (MANCOVA) revealed a significantly higher percent time spent at sea from November through April than May through October (n=63; age as covariate F1=3.796, p=0.056; season as factor F1=13.147, p=0.001). Thus, while age contributed to the observed variance, the main effect was clearly by season. The second objective of this study was to characterize the density effects of predator-prey interactions based on the spatial distribution of actual juvenile Steller sea lion predation events in relation to their utilization distribution. Fifteen predation events were detected from archival Life History Transmitter (LHX) tags implanted into a subset of n=36 of the 70 juvenile SSLs. A Bayesian SSM approach was used to process and interpolate the ARGOS locations received post-mortem from LHX tags. The processed tracks were then used to extrapolate the most likely locations of predation events. All 15 predation events occurred in the western DPS from 2008 through 2013. We expected predation events to occur uniformly in all areas for non-specialized predators, and more often in areas of high utilization such as near rookeries and haul-outs for predators that are specialized on SSLs and focus hunting efforts on high use areas. Results suggest the opposite, with four of the 15 predation events occurred in the 91-100% UD, or areas of the lowest relative frequency distribution of animal locations, 3 events occurred in the 81-90% UD, and only 1 event in the 21-30% UD corresponding to an area of higher relative frequency distribution of animal locations. Seven of the 15 predation events occurred outside the UD range, and therefore in areas likely of the lowest relative frequency distribution of animal locations. The winter predation rate was twice that of summer, with 10 predation events during the winter periods (November-April), and 5 events during the summer periods (May-October). Six predation events occurred in January-February. One predation event occurred in March-April, 2 events in May-June, 1 event in July-August, 2 events in September-October, and 3 events in November-December. A Rayleigh test for circular distribution showed a significant difference from uniformity with a mean ordinal date of January 6th (for n=7 animals ≤ 22 months of age), p=0.016). Studying predation in the marine environment comes with many challenges due to limitations in locating and tracking highly mobile marine predators over a long period of time and over a wide geographic range. Previous Steller sea lion studies looking at predation have inherent biases due to only sampling during the summer months and only near rookeries and haul-outs. Our study shows that we can detect predation all year round, including winter, and far away from rookeries and haul-outs. Since juvenile survival is low, and thus poses a significant risk for population-level survival, increased knowledge of the specifics of juvenile SSL space utilization patterns is of vital importance to assessing the importance of predation risk as one of the main drivers of their survivability. This is the first study to relate actual predation events to the intensity of space use of juvenile SSLs in a declining population in the KF/PWS region of Alaska.
Author: Norma A. Vazquez Publisher: ISBN: Category : Spatial behavior in animals Languages : en Pages : 77
Book Description
The first objective of this study was to quantify the intensity of space use of 70 juvenile (12-26 months old) Steller sea lions (SSLs) from the western Distinct Population Segment (DPS) in the Kenai Fjord(KF)/Prince William Sound (PWS) region of Alaska as derived from externally attached ARGOS satellite transmitter tags. A Bayesian state-space model (SSM) approach was used to process and interpolate the ARGOS-based locations. The resulting tracks were then used to quantify the spatio-temporal distribution of SSLs by way of a gridded utilization distribution (UD) in the study area. Each of six combined two-month UDs had an average of 24 ± 4.16 animals (range: 20-30) contributing around 5,090 ±1,879 filtered locations (range: 2,757-7,593). Results of the bimonthly UDs show juvenile SSL remained within the KF/PWS study region during the tracking period, with the exception of one individual, TJ16 (male), who crossed the 144° W Meridian separating the western and eastern DPS. Furthermore, results revealed that juveniles exhibit different spatial distributions depending on the time of year. They remain confined to a relatively smaller area (6,500-12,075 km2) in the 100% UD months of March through August compared to a larger area of 11,300-22,575 km2 in the 100% UD months September through February. In general, in winter (November-April) 90% of observations fell within 30km of the nearest haul-out, whereas in summer (May-October) 90% fell within 20km. A multifactor analysis of covariance (MANCOVA) revealed a significantly higher percent time spent at sea from November through April than May through October (n=63; age as covariate F1=3.796, p=0.056; season as factor F1=13.147, p=0.001). Thus, while age contributed to the observed variance, the main effect was clearly by season. The second objective of this study was to characterize the density effects of predator-prey interactions based on the spatial distribution of actual juvenile Steller sea lion predation events in relation to their utilization distribution. Fifteen predation events were detected from archival Life History Transmitter (LHX) tags implanted into a subset of n=36 of the 70 juvenile SSLs. A Bayesian SSM approach was used to process and interpolate the ARGOS locations received post-mortem from LHX tags. The processed tracks were then used to extrapolate the most likely locations of predation events. All 15 predation events occurred in the western DPS from 2008 through 2013. We expected predation events to occur uniformly in all areas for non-specialized predators, and more often in areas of high utilization such as near rookeries and haul-outs for predators that are specialized on SSLs and focus hunting efforts on high use areas. Results suggest the opposite, with four of the 15 predation events occurred in the 91-100% UD, or areas of the lowest relative frequency distribution of animal locations, 3 events occurred in the 81-90% UD, and only 1 event in the 21-30% UD corresponding to an area of higher relative frequency distribution of animal locations. Seven of the 15 predation events occurred outside the UD range, and therefore in areas likely of the lowest relative frequency distribution of animal locations. The winter predation rate was twice that of summer, with 10 predation events during the winter periods (November-April), and 5 events during the summer periods (May-October). Six predation events occurred in January-February. One predation event occurred in March-April, 2 events in May-June, 1 event in July-August, 2 events in September-October, and 3 events in November-December. A Rayleigh test for circular distribution showed a significant difference from uniformity with a mean ordinal date of January 6th (for n=7 animals ≤ 22 months of age), p=0.016). Studying predation in the marine environment comes with many challenges due to limitations in locating and tracking highly mobile marine predators over a long period of time and over a wide geographic range. Previous Steller sea lion studies looking at predation have inherent biases due to only sampling during the summer months and only near rookeries and haul-outs. Our study shows that we can detect predation all year round, including winter, and far away from rookeries and haul-outs. Since juvenile survival is low, and thus poses a significant risk for population-level survival, increased knowledge of the specifics of juvenile SSL space utilization patterns is of vital importance to assessing the importance of predation risk as one of the main drivers of their survivability. This is the first study to relate actual predation events to the intensity of space use of juvenile SSLs in a declining population in the KF/PWS region of Alaska.
Author: Claudio Campagna Publisher: Springer Nature ISBN: 3030591840 Category : Nature Languages : en Pages : 667
Book Description
This book is focused on the marine mammalian groups the Otariidae and the Odobenidae, otherwise known as fur seals, sea lions and the walrus. In 30 chapters, more than 60 authors from 30 institutions and 13 nationalities, discuss a broad suite of topics from maternal care and mating behavior, through play, cognition and personality, to adaptation to life in the Anthropocene. The authors explore the behaviors that have allowed these semi-aquatic mammals to thrive in the marine realm. Many populations have recovered following historical decimation, with interesting evolutionary consequences which are explored. Detailed, selected, individual species descriptions are also provided, showcasing the behavioral diversity of this engaging, adaptive and highly successful group of marine mammals.
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: 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: 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: National Research Council Publisher: National Academies Press ISBN: 0309168724 Category : Science Languages : en Pages : 216
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: Norma A. Vazquez
Author: Norma A. Vazquez
Author: Claudio Campagna
Author: National Research Council
Author: Stephen R. Meck
Author: Wendy Jane Schrader
Author: 
Author: National Research Council
Author: John L. Sease
Author: 
Author: Richard Merrick