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Author: John Michael Maniscalco Publisher: ISBN: Category : Steller's sea lion Languages : en Pages : 268
Book Description
Steller sea lions (Eumetopias jubatus) were listed as endangered following a collapse of the western population beginning in the late 1970s. Low juvenile survival and reduced reproductive rates (natality) have been implicated as important factors in the decline. I conducted separate mark-recapture analyses to estimate juvenile survival and natality in an area of the western population where Steller sea lions have begun to show signs of recovery since the early 2000s. I then used these vital-rate estimates in a population matrix to estimate the strength of the recovery and assess which rates pose the greatest threats to recovery. First year survival was estimated at 80% for both males and females, but second-year survival dropped to a low of 40.6% for males and 64.2 % for females that were weaned at age 1. In contrast, survival was greatly improved (88.2%) for males and females that continued to suckle between ages 1 and 2. Cumulative survival to age 4 was double (35.7%) that estimated during the population decline. Natality was also higher in recent years (70%) than during the height of the decline in the 1980s (55%). The mean rate of population growth, based on matrix modeling of vital rates estimated in this study, was 4.1% per year between 2003 and 2013. By projecting these trends into the future, I estimated that the population in the study area may be fully recovered within 14 years, if density independent growth is to be expected in the near future. If density dependent factors come into play, the population will need another 37 years to fully recover. As would be expected from a long-lived, K-selected species, population growth rate was most sensitive to variation in adult survival, less sensitive to juvenile survival, and least sensitivity to natality. The findings of this study have important implications for Steller sea lion population management and suggest research priorities should be shifted from an emphasis on natality to an emphasis on survival rates and causes of mortality.
Author: John Michael Maniscalco Publisher: ISBN: Category : Steller's sea lion Languages : en Pages : 268
Book Description
Steller sea lions (Eumetopias jubatus) were listed as endangered following a collapse of the western population beginning in the late 1970s. Low juvenile survival and reduced reproductive rates (natality) have been implicated as important factors in the decline. I conducted separate mark-recapture analyses to estimate juvenile survival and natality in an area of the western population where Steller sea lions have begun to show signs of recovery since the early 2000s. I then used these vital-rate estimates in a population matrix to estimate the strength of the recovery and assess which rates pose the greatest threats to recovery. First year survival was estimated at 80% for both males and females, but second-year survival dropped to a low of 40.6% for males and 64.2 % for females that were weaned at age 1. In contrast, survival was greatly improved (88.2%) for males and females that continued to suckle between ages 1 and 2. Cumulative survival to age 4 was double (35.7%) that estimated during the population decline. Natality was also higher in recent years (70%) than during the height of the decline in the 1980s (55%). The mean rate of population growth, based on matrix modeling of vital rates estimated in this study, was 4.1% per year between 2003 and 2013. By projecting these trends into the future, I estimated that the population in the study area may be fully recovered within 14 years, if density independent growth is to be expected in the near future. If density dependent factors come into play, the population will need another 37 years to fully recover. As would be expected from a long-lived, K-selected species, population growth rate was most sensitive to variation in adult survival, less sensitive to juvenile survival, and least sensitivity to natality. The findings of this study have important implications for Steller sea lion population management and suggest research priorities should be shifted from an emphasis on natality to an emphasis on survival rates and causes of mortality.
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: Kathryn Lynne Sweeney Publisher: ISBN: Category : Mammal surveys Languages : en Pages : 91
Book Description
There is strong evidence that both the western and eastern distinct population segments (DPSs) of Steller sea lion (Eumetopias jubatus) increased in overall abundance in Alaska between 2000 and 2012. Counts of both non-pups (adults and juveniles) and pups during the breeding season in the western DPS were lowest in 2000, and increased at average rates of 1.67% per year (95% credible interval of 1.01-2.38% per year) and 1.45% per year (0.69-2.22% per year), respectively through 2012. However, there was considerable regional variability in non-pup and pup trends in 2000-2012 across the western DPS, with strong evidence of increases in three of the four regions east of Samalga Pass (eastern and western Gulf of Alaska, and eastern Aleutian Islands; ranges of 2.39% per year to 4.51% per year for non-pups and 3.03% per year to 3.97% per year for pups) being offset somewhat by both weak and strong declines in the two regions west of Samalga Pass (central and western Aleutian Islands; slow, uncertain declines in the central [-0.56% per year and -0.46% per year for non-pups and pups, respectively] and steep, certain declines in the western Aleutians [-7.23% per year and -9.36% per year for non-pups and pups, respectively]). Within the central Aleutian Islands, non-pup and pup trends varied east and west of 177°W (roughly Tanaga Pass): in the two rookery cluster areas to the east, trends were generally positive (0.51% per year and 2.25% per year for non-pups, and 2.56% per year and 0.45% per year for pups), while to the west, there was strong evidence of decline (-4.48% per year and -3.24% per year for non-pups, and -4.83% per year and -1.74% per year for pups). In southeast Alaska (eastern DPS of Steller sea lion), both non-pup and pup counts increased between 2000 and 2010, continuing the upward trend begun in the mid-1970s. Movement of young Steller sea lions into and out of the eastern Gulf of Alaska was observed during surveys conducted 'early' and 'late' in 2008, 2009 and 2010. Analysis of the movement of sea lions branded as pups in 2000-2011 on rookeries extending from southeast Alaska through the Kodiak archipelago (including work by Jemison et al. in review) suggests a net movement from the central to the eastern Gulf of Alaska of ~1,600 sea lions during the breeding season, as well as a smaller net movement (of ~180 sea lions) from southeast Alaska to the western DPS. Inter-regional movement of this magnitude within the western DPS could affect regional trend estimation, and therefore it may be inappropriate to treat the eastern and central Gulf of Alaska as 'closed' populations; non-pup counts in the combined eastern-central Gulf of Alaska increased at 2.40% per year between 2000 and 2012. Average annual inter-DPS movement represents
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: John Michael Maniscalco
Author: John Michael Maniscalco
Author: National Research Council
Author: Richard Merrick
Author: John L. Sease
Author: 
Author: Morgen Crow
Author: Jindřich Matiegka
Author: Kathryn Lynne Sweeney
Author: National Research Council
Author: Richard L. Merrick