Trends in age-composition, growth and reproductive parameters of Barents Sea harp seals, Phoca groenlandica

Kjellqwist, Sten Anders; Haug, Tore; Øritsland, Torger

doi:10.1016/1054-3139(95)80035-2

Cited by 46 publications

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“…Stochastic fluctuations are generally large at K, and at this point neither population size nor age structure is a useful parameter for detecting dd. Furthermore, since adult seals have long life spans and reproduce several times during their lifetimes, dd has been shown to primarily affect pup survival and fertility (e.g., Lett et al 1979;Bengtsson and Siniff 1981;Kjellqwist et al 1995). Fig.…”

Section: Discussionmentioning

confidence: 99%

“…2a). The variability in carrying capacity is commonly assumed to affect pup survival and fecundity simultaneously and to the same extent (Lett et al 1979;Bengtsson and Siniff 1981;Kjellqwist et al 1995;Bowen et al 2007). The variability in carrying capacity in our Fig.…”

Section: The Modelmentioning

confidence: 99%

“…In real seal populations, however, environmental variability affects fecundity as well as pup survival. This does not affect the adult and subadult ratio of the population, but may lead to large fluctuations in the proportion of pups (Kjellqwist et al 1995). It is therefore difficult to use pups in age composition analysis even when estimates are accurate.…”

Section: Trend Analysismentioning

confidence: 99%

“…Juvenile survival rate often decreases rapidly with increasing density, whereas adult survival is relatively constant (Lett et al 1979;Bowen et al 2007), which can lead to changes in age composition in growing populations (Caughley 1974;Eberhardt 1977;Caswell 2001). Higher density also affects fecundity if food becomes scarce, since females show delayed age at sexual maturity and resorb fetuses if energy reserves are low (e.g., Bengtsson and Siniff 1981;Kjellqwist et al 1995;Bowen et al 2007). Moreover, it has been suggested that both males and female mature later when food is limiting (Krafft et al 2006).…”

Section: Introductionmentioning

confidence: 99%

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Detecting Density Dependence in Recovering Seal Populations

Svensson

Eriksson

Härkönen

et al. 2010

AMBIO

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Time series of abundance estimates are commonly used for analyses of population trends and possible shifts in growth rate. We investigate if trends in age composition can be used as an alternative to abundance estimates for detection of decelerated population growth. Both methods were tested under two forms of density dependence and different levels of environmental variation in simulated time series of growth in Baltic gray seals. Under logistic growth, decelerating growth could be statistically confirmed after 16 years based on population counts and 14 years based on age composition. When density dependence sets in first at larger population sizes, the age composition method performed dramatically better than population counts, and a decline could be detected after 4 years (versus 10 years). Consequently, age composition analysis provides a complementary method to detect density dependence, particularly in populations where density dependence sets in late.

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Section: Discussionmentioning

confidence: 99%

Section: The Modelmentioning

confidence: 99%

Section: Trend Analysismentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Detecting Density Dependence in Recovering Seal Populations

Svensson

Eriksson

Härkönen

et al. 2010

AMBIO

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“…However, all populations will eventually experience dramatic declines caused by variations in food supply (Kjellqwist et al 1995), fatal poisoning (Geraci et al 1989, O'Shea et al 1991, Scholin et al 2000, or epidemic diseases (Dietz et al 1989, Heide-Jørgensen et al 1992a. Such sudden declines dramatically increase the vulnerability of populations to quasiextinction (Harding et al , 2003.…”

Section: Assuming No Catastrophesmentioning

confidence: 99%

Status of Baltic grey seals: Population assessment and extinction risk

et al. 2007

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The grey seal (Halichoerus grypus) population in the Baltic Sea is recovering after a century of bounty hunting and 3 decades of low fertility rates caused by environmental pollution. A conservative estimate of the population size in 2003 was 19,400 animals, and available data suggest an annual rate of increase of 7.5% since 1990. The growing population has led to increased interactions with the fishery, and demands are being raised for the re-introduction of the hunt. We provide a demographic analysis and a risk assessment of the population, and make recommendations on how to decrease the risk of overexploitation. Although hunting increases the risk of quasi-extinction, the risk can be significantly reduced by the choice of a cautious hunting regime. The least hazardous regimes allow no hunting below a 'security level' in population size. Obviously, to implement such a hunting regime detailed knowledge of the population size and growth rate is required. It is not possible to estimate "true" risks for quasi-extinction, but we used an approach where the relative difference for different scenarios can be compared. With a security level at 5,000 females, the population quasi-extinction risk increases 50 fold at an annual hunt of 500 females compared with a scenario with no hunting. The risk of quasi-extinction is very sensitive to declines in the mean growth rate and to increased variance in growth rate. The variance in the population estimates over the last 14 years imply that it would take 9 years to detect a decline from 1.075 to 1.027 in the rate of population increase. We also show how the age composition of killed animals influences the impact of the hunt. The overall recommendation is that hunting should be kept to a minimum, carefully documented and accompanied by close population monitoring.Harding, K.C., Härkönen, T., Helander, B. and Karlsson, O. 2007. Status of Baltic grey seals: Population assessment and extinction risk. NAMMCO

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Length of intervals between epidemics: evaluating the influence of maternal transfer of immunity

Garnier

Gandon

Hårding

et al. 2014

Ecology and Evolution

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The length of intervals between epidemic outbreaks of infectious diseases is critical in epidemiology. In several species of marine mammals and birds, it is pivotal to also consider the life history of the species of concern, as the contact rate between individuals can have a seasonal flux, for example, due to aggregations during the breeding season. Recently, particular interest has been given to the role of the dynamics of immunity in determining the intervals between epidemics in wild animal populations. One potentially powerful, but often neglected, process in this context is the maternal transfer of immunity. Here, we explore theoretically how the transfer of maternal antibodies can delay the recurrence of epidemics using Phocine Distemper in harbor seals as an example of a system in which epidemic outbreaks are followed by pathogen extinction. We show that the presence of temporarily protected newborns can significantly increase the predicted interval between epidemics, and this effect is strongly dependent on the degree of synchrony in the breeding season. Furthermore, we found that stochasticity in the onset of epidemics in combination with maternally acquired immunity increases the predicted intervals between epidemics even more. These effects arise because newborns with maternal antibodies temporarily boost population level immunity above the threshold of herd immunity, particularly when breeding is synchronous. Overall, our results show that maternal antibodies can have a profound influence on the dynamics of wildlife epidemics, notably in gregarious species such as many marine mammals and seabirds.

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Trends in age-composition, growth and reproductive parameters of Barents Sea harp seals, Phoca groenlandica

Cited by 46 publications

References 0 publications

Detecting Density Dependence in Recovering Seal Populations

Detecting Density Dependence in Recovering Seal Populations

Status of Baltic grey seals: Population assessment and extinction risk

Length of intervals between epidemics: evaluating the influence of maternal transfer of immunity

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