Download or read book Decadal Variation in the Diet of Western Stock Steller Sea Lions Eumetopias Jubatus written by Elizabeth Hacker Sinclair and published by . This book was released on 2013 with total page 67 pages. Available in PDF, EPUB and Kindle. Book excerpt: Steller sea lions (Eumetopias jubatus) are listed as an endangered species in western Alaska due to a precipitous decline that occurred in the 1980s and 1990s. In 2000, cascading declines slowed or ceased and clusters of rookeries between the eastern Aleutian Islands and eastern Gulf of Alaska began to show signs of population growth. Reasons for the decline and for a range-wide failure to recover are unresolved, but reduction in the availability of prey due to commercial fishing or environmental perturbation has been hypothesized. Discerning the diet and patterns of prey use by Steller sea lions (SSL) is fundamental to isolating the mechanisms driving population health. Here we evaluate the frequency of occurrence (FO) of prey species in 3,412 scats of adult female and juvenile SSL collected during 1999-2009, across the range of the U. S. Western Stock. Thirteen primary prey are identified based on their occurrence in ≥ 5% of total scats. We reduce the dimension of the diet profile of the 13 primary prey to two categorical groups through principal component analysis (PC). A hierarchical cluster analysis of PC scores on collection site locations describes four geographic regions of SSL diet (with Amak Island as an outlier) nearly identical to those identified in a previously published 1990-1998 (n = 3,762) dataset. Geographic regions of diet continue to correspond with regional population trends of SSL. The species of primary prey consumed by SSL are analogous between 1990-1998 and 1999-2009. However, the rangewide FO of 7 of the 13 primary prey increased significantly (p ≤ 0.05) during the latter decade. Only cephalopods (Gonatidae) and walleye pollock (Theragra chalcogramma) decreased significantly in FO in any season or region between decades. Generalized linear mixed models (GLMM) of seasonal prey FO determined that trends in the FO of primary prey between decades were locally driven by significant changes within one or more of the four diet regions and fishery conservation management areas (RCA). The most significant increases (p = 0.001) in FO during 1999-2009 were for commercial fishes: arrowtooth flounder (Atheresthes sp.), Atka mackerel (Pleurogrammus monopterygius), rock sole (Lepidopsetta sp.), and Pacific cod (Gadus macrocephalus); and one non-commercial fish species (Pacific sand lance, Ammodytes hexapterus) in diet Regions 2 and 3 (RCA zones 6 and 7) between the eastern Aleutian Islands and western Gulf of Alaska. Diversity scores (H') for primary prey were also highest in these regions compared to the previous decade, and are coincident with SSL population increases that began in the same area in 2000. Atka mackerel continues to dominate SSL diet west of Samalga Pass, and walleye pollock continues to dominate SSL diet east of Samalga Pass (despite its decreased presence in diets in Regions 1-3 during 1999-2009). The results of generalized additive mixed models (GAMM) of annual trends (1990-2009) in summer prey FO on each rookery across the study area are consistent with the results of GLMM decadal comparisons. The additional 11 years of data presented here support earlier conclusions that adult female and young juvenile SSL of the Western Stock collectively eat a wide variety of prey species, but demonstrate fidelity to prey types that are predictably available in seasonal concentrations over the continental shelf or other bathymetric structures, within close range of natal rookery sites. Foraging within close proximity to birth and breeding sites keeps adult females close to pups onshore and to young juveniles learning to forage. However, it also increases their vulnerability to potential nearshore environmental and anthropogenic interference which could ultimately influence their reproductive success. It was not the objective of this study to define the relationship between SSL diet and population decline, or to identify the interactive mechanisms that drive diet change. However, coincident patterns emerged that suggest relationships between SSL diet, regional population patterns, climate and fisheries. Some of the patterns are worthy of discussion and future research: 1) the areas of greatest increases in the FO and diversity of prey (Regions 2 and 3) beginning in 1999, overlap with those of the strongest population growth since 1999; 2) the increase in primary prey FO and diversity since 1999 is coincident with increased restrictions on groundfish trawling within SSL Critical Habitat, enacted in 2000; and 3) the area of lowest prey diversity (Region 4) overlaps with those areas of continuing population declines, the most restricted foraging habitat (narrow continental shelf) and the lowest seasonal and temporal variability in sea surface temperature in all years of study.

Download or read book Seasonal and spatial differences in diet in the western stock of Steller sea lions Eumetopias jubatus written by E.H. SINCLAIR and published by . This book was released on 2002 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Decline of the Steller Sea Lion in Alaskan Waters written by National Research Council and published by National Academies Press. This book was released on 2003-05-04 with total page 217 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Steller Sea Lion Decline written by Douglas P. DeMaster and published by . This book was released on 2002 with total page 86 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Steller Sea Lion Protection Measures written by and published by . This book was released on 2001 with total page 796 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Decline of the Steller Sea Lion in Alaskan Waters written by National Research Council and published by National Academies Press. This book was released on 2003-04-04 with total page 216 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Steller Sea Lions Eumetopias Jubatus written by Andrew W. Trites and published by . This book was released on 1998 with total page 52 pages. Available in PDF, EPUB and Kindle. Book excerpt: Presents the changes in the Steller sea lion's diet over time (from a diverse diet including fatty fishes to one dominated by pollock), which has resulted in negative reproductive and survival consequences

Download or read book Steller Sea Lion and Northern Fur Seal Research written by and published by . This book was released on 2007 with total page 518 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Aquatic Food Webs written by Andrea Belgrano and published by Oxford University Press. This book was released on 2005-04-07 with total page 262 pages. Available in PDF, EPUB and Kindle. Book excerpt: This volume provides a current synthesis of theoretical and empirical food web research. Whether they are binary systems or weighted networks, food webs are of particular interest to ecologists in providing a macroscopic view of ecosystems. They describe interactions between species and their environment, and subsequent advances in the understanding of their structure, function, and dynamics are of vital importance to ecosystem management and conservation. Aquatic Food Webs provides a synthesis of the current issues in food web theory and its applications, covering issues of structure, function, scaling, complexity, and stability in the contexts of conservation, fisheries, and climate. Although the focus of this volume is upon aquatic food webs (where many of the recent advances have been made), any ecologist with an interest in food web theory and its applications will find the issues addressed in this book of value and use. This advanced textbook is suitable for graduate level students as well as professional researchers in community, ecosystem, and theoretical ecology, in aquatic ecology, and in conservation biology.

Download or read book Diet Comparisons of Steller Sea Lions Eumetopias Jubatus and California Sea Lions Zalophus Californianus written by Sara Young and published by . This book was released on 2011 with total page 50 pages. Available in PDF, EPUB and Kindle. Book excerpt: California sea lions (Zalophus californianus) and Steller sea lions (Eumetopias jubatus) bred in overlapping habitat areas in southern California until Steller sea lions began to vacate the area in the 1960s. This study analyzed the diets of Steller sea lions and California sea lions over a period of 50 years, from 1949 to 2003. Prey items from individual sea lion diets were collected from the literature for both species and Shannon-Weaver Index values and Simpson Index values were calculated for each study. The Shannon and Simpson indices quantify the same data in different ways. Although the Shannon Index values were affected by sample size, the Simson index was not. Trophic levels of prey were also considered, with California sea lions eating a significantly wider range of trophic levels than Stellers. While the Shannon Index was significantly affected by sample size and thus inconclusive, the Simpson Index, which was not affected by sample size, found that California sea lions have a more diverse diet than Steller sea lions.

Download or read book Recovery Plan for the Steller Sea Lion Eumetopias Jubatus written by Steller Sea Lion Recovery Team and published by . This book was released on 1994 with total page 108 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Seasonal Oscillations in the Mass and Food Intake of Steller Sea Lions written by and published by . This book was released on 2004 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Morphometric measurements and daily feeding records of 62 captive Steller sea lions (Eumetopias jubatus) were analyzed to provide information about seasonal growth and food consumption that has been impossible to collect from wild animals. Data from nursing pups, intact and castrated males, and pregnant, lactating and non-reproductive females were also used to determine differences in rates of sexual maturity, and the effects that climate, sexual maturity, castration and reproduction have on growth and food intake. Data were fit with seasonal and annual growth models, and showed that males achieved larger body sizes than females by undergoing a growth spurt during puberty and by extending their growth throughout adulthood. Annual increases in the length and mass of females slowed significantly following sexual maturity. Males and females both experienced seasonal oscillations in body mass, but the seasonal fluctuation in male mass peaked later (April) and was far more dramatic than that of females. The mass of lactating and non-reproductive females peaked in early spring (March), while increases in the mass of pregnant females paralleled fetal growth, reaching a maximum before parturition. Changes in mass did not parallel changes in consumption. Fish intake by males and females peaked during winter and bottomed during spring, while seasonal changes in body mass reached their high and low 3 to 4 months later than food intake. Pregnant and non-reproductive females differed little in the amount of prey they consumed, unlike lactating females that significantly increased their consumption during summer and winter. The differences between females highlight the relatively low additional energetic requirements of pregnancy and the high costs of lactation. Differences between neutered and intact males further suggest that testosterone affected overall male growth, but had smaller effects on seasonal oscillations in mass and did not affect food intake. The reproductive cycle.

Download or read book Steller Sea Lion Research written by I. L. Boyd and published by . This book was released on 1995 with total page 186 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book A bioenergetic model for estimating the food requirements of Steller sea lions Eumetopias jubatus in Alaska USA written by A.J. WINSHIP and published by . This book was released on 2002 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Systematics of Steller Sea Lions Eumetopias Jubatus written by Caleb D. Phillips and published by . This book was released on 2009 with total page 15 pages. Available in PDF, EPUB and Kindle. Book excerpt: Previous studies have revealed discontinuities in the distribution of genetic markers that led to the recognition of eastern, western, and Asian stocks of Steller sea lions (Eumetopias jubatus). The most profound break separates the eastern and western stocks and is based upon both nuclear and mitochondrial genetic markers. Here, a morphometric analysis of skulls was used to re-evaluate geographic variation in light of the genetics data and to possibly identify characters to distinguish between the eastern and western stocks. For males, three variables were used in stock assignment to correctly identify 88.13% and 86.59% of individuals from the eastern and western stocks, respectively. Through the same method the correct identification in stock assignment using five selected variables for female eastern and western stock individuals was 86.27% and 88.1%, respectively. Furthermore, plots from canonical discriminant analyses clearly separate individuals into stocks with very minimal overlap. Based on the observed morphological differences between these genetically differentiated stocks, we recognize two subspecies of E. jubatus; one includes the Asian and western stocks, and the other the eastern stock. The vernacular name Loughlin's northern sea lion is used to signalize the eastern subspecies.

Download or read book Comparing the Nutritional Quality of Steller Sea Lion Eumetopias Jubatus Diets written by Monica Kaho Herkules Bando and published by . This book was released on 2002 with total page 94 pages. Available in PDF, EPUB and Kindle. Book excerpt: "Though the primary cause(s) of the Steller sea lion decline remains unknown, one hypothesis is nutritional stress, possibly the result of climatic regime shifts reducing prey availability and/or quality. Researchers at the Alaska SeaLife Center formulated three feeding regimes representative of Steller sea lion diets: prior to and during their population decline and from a stable population. The purpose of this project was to compare the nutritional quality of these diets using proximate composition and bomb calorimetry. The pre-decline and stable diets are composed of more high-fat prey, like herring, with resulting energy densities being significantly higher than the decline diet, comprising more low-fat prey, like octopus. Assumining the feeding regimes analyzed represent Steller sea lion diets prior to and during their population decline and in stable populations, results from this study are consistent with the possibility that nutritional stress is a cause of the Steller sea lion decline"--Leaf iii.

Download or read book Steller Sea Lions Eumetopias Jubatus of Oregon and Northern California written by Jonathan Scordino and published by . This book was released on 2006 with total page 186 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Steller Sea Lion Research Initiative was passed in 2001 to provide funding to help scientists determine causes and solutions for the population crash of Steller sea lions (Eumetopias jubatus). In response to need to understand population dynamics of Steller sea lions, NOAA Fisheries has spearheaded a large-scale, range-wide research program. The study involved capturing and hot-iron branding sea lions at rookeries from northern California around the Pacific Rim to Russia to provide individually recognizable animals for studies of behavior and vital rates. I report the results of monitoring pups branded and tagged at Rogue Reef, Oregon and St. George Reef, California to determine movement patterns and the affects of branding on apparent survival of Steller sea lion pups immediately after branding. Counts of Steller sea lion adult female, adult male, juveniles, and pups were collected at haulouts and rookeries of Oregon and northern California from 2002 through 2005. Movement patterns of Steller sea lions were inferred from count data. Adult males were seasonal inhabitants of Oregon and California during the breeding season from May through September before dispersing to northern feeding grounds. Females, juveniles, and pups were dispersed throughout haulouts in Oregon and northern California during all seasons but have seasonally high concentrations at Sea Lion Caves, Oregon in the winter and at the breeding rookeries during the summer breeding season. The high wintertime abundance of females and pups at Sea Lion Caves suggests that it should be considered as critical habitat for Steller sea lions of the eastern stock. Resights of marked sea lions collected between northern California and Alaska between 2001 and 2005 were analyzed to determine juvenile and pup dispersal patterns. Most pups stay close to their natal rookery, although 9 - 22% of individuals each year were observed to disperse further than 500 km. As 1-year olds, the mean maximum dispersal range expanded, which may have been a sign of weaning. Sexually dimorphic patterns in sea lion movements were apparent at 3 years of age as males were observed to disperse farther north than females. The percentage of females observed at their natal rookery increased each year to a maximum of 87% as 4-year-olds. This suggested that sexual maturity occurs at, or close to, 4 years of age for females. Branding provided a useful tool for analyzing movements of Steller sea lions, yet it may have impacts on survival of individuals. Concerns raised by NOAA Fisheries over branding impacts on pup survival were addressed with a study at Rogue Reef in 2005. One-hundred-and-sixty pups captured on 18 July, 2005 were randomly assigned to a treatment of flipper tag only (unbranded pups) or flipper tag and hot-iron branding (branded pups). Aside from the treatment of branding, all pups were handled and treated identically. Over the 73-day course of this study, I found lower apparent survival for branded pups than unbranded pups, with a final apparent survivorships of 0.23 (95% CI 0.01? 0.48) for branded pups and 0.46 (95% CI 0.15? 0.77) for unbranded pups. Apparent survivorship includes both mortality and emigration, so differences may be due to differences in emigration rates of the two groups, mortality rates, or both. The scope of inference for this study is only to Rogue Reef in 2005. However, it should provide a good model for future brand evaluation studies at other rookeries and for other pinniped species. Branding is currently the best and only available tool for long-term studies of survival, reproduction rates, and age at sexual maturity which are all critical for demographic models. Nonetheless, researchers should assess the impacts of branding at each rookery, and will need to consider whether knowledge from branding Steller sea lions is worth the potential reduction in pup survival or change in pup emigration behavior observed in this study.