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articles by Jason Baker
Papers by Jason Baker
During 2005 - 2007, 187 individual manta rays were photo-identified from a single cleaning statio... more During 2005 - 2007, 187 individual manta rays were photo-identified from a single cleaning station site in Maui, Hawaii. A discovery curve showed no asymptotic trend, indicating the number of individuals using the site is considerably larger than the total identified. Of these individuals, 58% were observed on more than one occasion within and across years, suggesting philopatry to this area. Males accounted for 47% of the individuals in the population, of which 69% were considered sexually mature based on the claspers extending beyond the pelvic fins. The average encounter rate per dive was 5.50 manta rays per hour. They were habitually absent at first light, with encounter rates increasing throughout the day. No matches were found when compared against 133 individuals photo-identified from a well-studied population off the Big Island (www.mantapacific.org), a distance of only 60 miles. Evidence of shark predation was seen in 12% of the population, and 6% had a missing or non-funct...
Can J Zool, 2000
... 1986; Gentry et al. ... University of California, Santa Cruz, Santa Cruz, CA 95064, USA 1Auth... more ... 1986; Gentry et al. ... University of California, Santa Cruz, Santa Cruz, CA 95064, USA 1Author to whom all correspondence should be sent at the following address: National Marine Fisheries Service, 2570 Dole Street, Honolulu, HI 96822, USA (e-mail: jason.baker@noaa.gov). ...
Conservation Biology the Journal of the Society For Conservation Biology, Feb 1, 2011
The Hawaiian monk seal ( Monachus schauinslandi) is one of the most critically endangered marine ... more The Hawaiian monk seal ( Monachus schauinslandi) is one of the most critically endangered marine mammals. Less than 1200 individuals remain, and the species is declining at a rate of approximately 4% per year as a result of juvenile starvation, shark predation, and entanglement in marine debris. Some of these problems may be alleviated by translocation; however, if island breeding aggregates are effectively isolated subpopulations, moving individuals may disrupt local adaptations. In these circumstances, managers must balance the pragmatic need of increasing survival with theoretical concerns about genetic viability. To assess range-wide population structure of the Hawaiian monk seal, we examined an unprecedented, near-complete genetic inventory of the species ( n = 1897 seals, sampled over 14 years) at 18 microsatellite loci. Genetic variation was not spatially partitioned (θ w = −0.03, p = 1.0), and a Bayesian clustering method provided evidence of one panmictic population ( K = 1). Pairwise F ST comparisons (among 7 island aggregates over 14 annual cohorts) did not reveal temporally stable, spatial reproductive isolation. Our results coupled with long-term tag-resight data confirm seal movement and gene flow throughout the Hawaiian Archipelago. Thus, human-mediated translocation of seals among locations is not likely to result in genetic incompatibilities.
Atoll Research Bulletin, 2006
... One mitigation option is to evaluate the efficacy of habitat restoration to increase availabl... more ... One mitigation option is to evaluate the efficacy of habitat restoration to increase available haul-out sites for monk seals. Such an endeavor could also increase nesting habitat for Hawaiian green sea turtle (Chylonia mydas) and numerous seabirds. ...
![Research paper thumbnail of Milk Intake and Energy Expenditure of Free-Ranging Northern Fur Seal, [ITAL]Callorhinus ursinus[/ITAL], Pups](https://attachments.academia-assets.com/47416521/thumbnails/1.jpg)
](Physiol Biochem Zool, 2002
Milk ingested by mammalian offspring, coupled with offspring's utilization of this energetic inve... more Milk ingested by mammalian offspring, coupled with offspring's utilization of this energetic investment, influences survival and growth. A number of studies have examined milk intake in otariids, but few have examined milk intake over the entire lactation period, and none has independently measured energy expendi-* Corresponding author; e-mail: Mary.Donohue@noaa.gov. percentage of total body water and positively correlated with the percentage of total body lipid (TBL). Pups increased the percentage of TBL from 16% to 37%. Northern fur seal pups increased energy intake over lactation, while concurrent changes in body composition and pelage condition resulted in massspecific metabolic savings after the molt.
The extant population of Hawaiian monk seal (Monachus schauinslandi) numbers around 1,00 distribu... more The extant population of Hawaiian monk seal (Monachus schauinslandi) numbers around 1,00 distributed among six island atolls in the remote Northwestern Hawaiian Islands (NWHI) and at several small, emerging colonies on the Main Hawaiian Islands. Demographic studies have identified poor juvenile survival as the ultimate primary cause of substantial declines at all colonies and of slow recent recovery at some. Variable foraging success may be a key proximate effect, but the knowledge of habitat needs of foraging monk seals has not been adequate to test that hypothesis nor to provide management with the necessary information to address resource conservation issues. We documented the geographic and vertical foraging patterns of 1 Hawaiian monk seals from all six NWHI breeding colonies from 1 through 00 to describe the marine habitats that may be key to the species' viability. We found that seals foraged extensively within barrier reefs of the atolls and on the leeward slopes of reefs and islands at all colony sites. They also ranged away from these sites along the Hawaiian Islands Archipelago submarine ridge to most nearby seamounts and submerged reefs and banks. Most dives were less than 10 m deep, though dives of some seals exceeded 0 m. Suitable foraging habitat may be a resource limiting the population of monk seals in the NWHI. Moreover, the foraging biogeography of Hawaiian monk seals may vary spatially and temporally with variation in the extent of physical substrate, prey community composition and species' abundance, and demographic composition of seal colonies. _________________________________________________
Journal of Experimental Biology, Mar 15, 2000
Coral Reefs of the USA, 2008
Biological Conservation, 2004
Most of the extant circa 1400 Hawaiian monk seals Monachus schauinslandi live in the Northwestern... more Most of the extant circa 1400 Hawaiian monk seals Monachus schauinslandi live in the Northwestern Hawaiian Islands (NWHI). However, an increasing number of sightings and births have recently occurred in the main Hawaiian Islands (MHI), where no systematic surveys of monk seals were conducted prior to 2000. We estimate that there were at least 45 seals in the MHI in
Proceedings of the Royal Society B: Biological Sciences, 2007
Estimates of variability in pinniped survival rates are generally based on observations at single... more Estimates of variability in pinniped survival rates are generally based on observations at single sites, so it is not certain whether observed rates represent the whole population. Here, we provide a comprehensive analysis of spatio-temporal variation in age-specific survival rates for endangered Hawaiian monk seals (Monachus schauinslandi ) based on capture-recapture analyses of more than 85% of the pups weaned in this population over the last two decades. Uniquely, these data have been collected from six subpopulations, encompassing all major breeding sites across its 1800 km long core range. Analyses of individual subpopulations revealed similar patterns in age-specific survival, characterized by the relatively low survival rates from weaning to 2 years of age, intermediate rates to 4 years of age, and then by relatively high 'mature' survival rates until 17 years of age, after which a senescent decline was observed. Juvenile, subadult and adult survival rates all varied significantly over time. Trends in survival among subpopulations were coherent with their relative geographical positions, suggesting regional structuring and connectedness within the archipelago. Survival rates for different age classes tended to be positively correlated, suggesting that similar factors may influence the survival for seals of all ages.
Marine Mammal Science, 2002
We examined the effects of research handling on free-ranging endangered Hawaiian monk seals, Mona... more We examined the effects of research handling on free-ranging endangered Hawaiian monk seals, Monachzls scbauinslandi, by analyzing differences in subsequent year survival, migration, and condition between handled seals and controls during 1983-1998. Each of 549 handled seals was matched to a control seal of the same age, sex, location, and year. Handling included instrumentation with telemetry devices ( n = 93), blood sampling (n = 19), and tagging ( n = 437). No significant differences were found between handled seals and their controls in one-year resighting rates, observed migration rates, or condition. Resighting rates of handled and control seals were high (SO%-l00%). Available sample sizes were sufficient to detect reasonably small (9%-20%) differences in resighting rates had they existed among instrumented or tagged seals and controls (a = 0.05, power = 0.90). Too few seals were captured for blood sampling to detect even large differences in their resighting rates. However, blood samples were drawn from most instrumented seals, and there was no indication that this larger group suffered harmful effects. Duration of restraint during flipper tagging had no effect on subsequent probability of resighting. Our analysis suggests that conservative selection procedures and careful handling techniques have no deleterious effects on Hawaiian monk seals.
Marine Mammal Science, 2011
Total estimated abundance of Hawaiian monk seals was just 1,161 individuals in 2008 and this numb... more Total estimated abundance of Hawaiian monk seals was just 1,161 individuals in 2008 and this number is decreasing. Most monk seals reside in the remote Northwestern Hawaiian Islands (NWHI) where the decline is approximately 4%/yr, whereas relatively fewer seals currently occupy the main Hawaiian Islands (MHI). It is widely accepted that the MHI population is increasing, although there are no formal estimates of total abundance, population growth rate or vital rates. This lack of information has hampered efforts to anticipate future scenarios and plan conservation measures. We present the first estimates of MHI monk seal survival and age-specific reproductive rates. Using these rates, a conservative estimate of current MHI abundance and a previously published stochastic simulation model, we estimate the MHI population growth rate and projected abundance trend. Analogous estimates for the NWHI are derived from a much richer data set. Estimated survival from weaning to age 1 yr is 77% in the MHI, much higher than recent NWHI estimates ranging from 42% to 57%. Moreover, MHI females begin reproducing at a younger age and attain higher birth rates than observed in the NWHI. The estimated MHI intrinsic rate of population growth is 1.07 compared to a 0.89-0.96 range in the NWHI. Assuming an initial abundance of 152 animals 78 BAKER ET AL.: HAWAIIAN MONK SEAL DISTRIBUTION 79 in the MHI, projections indicate that if current demographic trends continue, abundance in the NWHI and MHI will equalize in approximately 15 yr. These results underscore the imperative to mitigate the NWHI decline while devoting conservation efforts to foster population growth in the MHI, where documented threats including fishery interactions, direct killing, and disease could rapidly undo the current fragile positive trend.
Marine Mammal Science, 2006
We investigated the pattern of first sighting of individual seals over the course of a field seas... more We investigated the pattern of first sighting of individual seals over the course of a field season, or the "discovery curve," as a means for estimating abundance of the endangered Hawaiian monk seal, Monachus schauinslandi. We empirically derived a criterion to determine whether or not total enumeration had been accomplished at a given site and year. When greater than 100-h field effort was expended without a new individual being identified, we concluded that total enumeration was likely achieved. To evaluate the potential for estimating abundance through extrapolation of nonlinear asymptotic functions fitted to discovery curves, we conducted simulations under a range of capture probability scenarios, including some based on observed individual variability in monk seal sighting frequencies. We demonstrated that if capture heterogeneity existed among individuals, the fitted asymptotes tended to yield biased estimates of abundance. Moreover, the levels of bias and uncertainty tended to increase inversely with the proportion of the population identified. While extrapolation shows little promise for generating unbiased abundance estimates, discovery curves have practical appeal for determining whether total enumeration has been achieved, and for optimizing field effort allocation. This is especially true for relatively small, closed populations of marked individuals.
Marine Mammal Science, 2007
We evaluated reproductive patterns of the Hawaiian monk seal (Monachus schauinslandi) using a com... more We evaluated reproductive patterns of the Hawaiian monk seal (Monachus schauinslandi) using a combination of fitted age-specific reproductive curves and analysis of reproductive patterns of individual females. We review the difficulties inherent in the acquisition and modeling of reproductive data with emphasis on the significance of reproductive senescence to populations with dissimilar age/sex compositions. Validation of the fitted reproductive parameters was accomplished by Monte Carlo sampling of parameter distributions to compare the expected number of pups with the observed production. Although the fitted reproductive functions appear to provide an acceptable fit to the raw reproductive data, we found that the fitted curves did a poor job of predicting the actual pup production in individual years because of high variability among years. To further verify, and elaborate on, the patterns in the pooled (multi-seal, and multi-year) rates, we examined attributes of the reproductive performance of individual seals. The attributes included age of primiparity, reproductive rates computed over several age ranges, and the relationship between reproductive performance and seal longevity. Analysis of individual seal patterns reinforced the conclusion that reproductive senescence is operative in monk seal populations.
Marine Mammal Science, 2004
Marine Mammal Science, 1994
A mark-recapture study conducted in 1987-1992 provided weight measurements of juvenile male north... more A mark-recapture study conducted in 1987-1992 provided weight measurements of juvenile male northern fur seals (Callorhinus ursinus) on St. Paul Island, Alaska, at ages ranging from approximately 1.5 mo to 5 yr. Males born in 1987 tended to weigh less at ages 3 and 4 yr than those born in other years. Weights of individuals at ages 2, 3, and 4 yr were significantly correlated with their weights as pups (P < 0.05). Weights at ages 2 and 3, 7 and 4, and 4 and 5 yr were significantly correlated (P < 0.00 I), although weight changes with age were highly variable. Data indicate that larger than average male p~qx born during [1987][1988][1989][1990] were more likely to survive, but this effect was less evident than among pups born during [1960][1961][1962][1963][1964][1965] when average pup weights were lower.
Marine Mammal Science, 1990
Tooth weight and body length of juvenile male northern fur seals, Callorhinus ursinus, collected ... more Tooth weight and body length of juvenile male northern fur seals, Callorhinus ursinus, collected on St. Paul Island, Alaska, from 1948 to 1984 were compared. The relationship between these variables was investigated for individual and combined age classes. A density-dependent increase in mean tooth weight occurred during a decline in fur seal abundance. Consistent, though poorly understood, differences in tooth weight were found among males associated with different rookeries (breeding grounds). Storing the teeth for long periods may affect the weights, but such effects, if any, are too small to account for the changes observed.
Marine Mammal Science, 2014
ABSTRACT
Marine Mammal Science, 2013
During 2005 - 2007, 187 individual manta rays were photo-identified from a single cleaning statio... more During 2005 - 2007, 187 individual manta rays were photo-identified from a single cleaning station site in Maui, Hawaii. A discovery curve showed no asymptotic trend, indicating the number of individuals using the site is considerably larger than the total identified. Of these individuals, 58% were observed on more than one occasion within and across years, suggesting philopatry to this area. Males accounted for 47% of the individuals in the population, of which 69% were considered sexually mature based on the claspers extending beyond the pelvic fins. The average encounter rate per dive was 5.50 manta rays per hour. They were habitually absent at first light, with encounter rates increasing throughout the day. No matches were found when compared against 133 individuals photo-identified from a well-studied population off the Big Island (www.mantapacific.org), a distance of only 60 miles. Evidence of shark predation was seen in 12% of the population, and 6% had a missing or non-funct...
Can J Zool, 2000
... 1986; Gentry et al. ... University of California, Santa Cruz, Santa Cruz, CA 95064, USA 1Auth... more ... 1986; Gentry et al. ... University of California, Santa Cruz, Santa Cruz, CA 95064, USA 1Author to whom all correspondence should be sent at the following address: National Marine Fisheries Service, 2570 Dole Street, Honolulu, HI 96822, USA (e-mail: jason.baker@noaa.gov). ...
Conservation Biology the Journal of the Society For Conservation Biology, Feb 1, 2011
The Hawaiian monk seal ( Monachus schauinslandi) is one of the most critically endangered marine ... more The Hawaiian monk seal ( Monachus schauinslandi) is one of the most critically endangered marine mammals. Less than 1200 individuals remain, and the species is declining at a rate of approximately 4% per year as a result of juvenile starvation, shark predation, and entanglement in marine debris. Some of these problems may be alleviated by translocation; however, if island breeding aggregates are effectively isolated subpopulations, moving individuals may disrupt local adaptations. In these circumstances, managers must balance the pragmatic need of increasing survival with theoretical concerns about genetic viability. To assess range-wide population structure of the Hawaiian monk seal, we examined an unprecedented, near-complete genetic inventory of the species ( n = 1897 seals, sampled over 14 years) at 18 microsatellite loci. Genetic variation was not spatially partitioned (θ w = −0.03, p = 1.0), and a Bayesian clustering method provided evidence of one panmictic population ( K = 1). Pairwise F ST comparisons (among 7 island aggregates over 14 annual cohorts) did not reveal temporally stable, spatial reproductive isolation. Our results coupled with long-term tag-resight data confirm seal movement and gene flow throughout the Hawaiian Archipelago. Thus, human-mediated translocation of seals among locations is not likely to result in genetic incompatibilities.
Atoll Research Bulletin, 2006
... One mitigation option is to evaluate the efficacy of habitat restoration to increase availabl... more ... One mitigation option is to evaluate the efficacy of habitat restoration to increase available haul-out sites for monk seals. Such an endeavor could also increase nesting habitat for Hawaiian green sea turtle (Chylonia mydas) and numerous seabirds. ...
Physiol Biochem Zool, 2002
Milk ingested by mammalian offspring, coupled with offspring's utilization of this energetic inve... more Milk ingested by mammalian offspring, coupled with offspring's utilization of this energetic investment, influences survival and growth. A number of studies have examined milk intake in otariids, but few have examined milk intake over the entire lactation period, and none has independently measured energy expendi-* Corresponding author; e-mail: Mary.Donohue@noaa.gov. percentage of total body water and positively correlated with the percentage of total body lipid (TBL). Pups increased the percentage of TBL from 16% to 37%. Northern fur seal pups increased energy intake over lactation, while concurrent changes in body composition and pelage condition resulted in massspecific metabolic savings after the molt.
The extant population of Hawaiian monk seal (Monachus schauinslandi) numbers around 1,00 distribu... more The extant population of Hawaiian monk seal (Monachus schauinslandi) numbers around 1,00 distributed among six island atolls in the remote Northwestern Hawaiian Islands (NWHI) and at several small, emerging colonies on the Main Hawaiian Islands. Demographic studies have identified poor juvenile survival as the ultimate primary cause of substantial declines at all colonies and of slow recent recovery at some. Variable foraging success may be a key proximate effect, but the knowledge of habitat needs of foraging monk seals has not been adequate to test that hypothesis nor to provide management with the necessary information to address resource conservation issues. We documented the geographic and vertical foraging patterns of 1 Hawaiian monk seals from all six NWHI breeding colonies from 1 through 00 to describe the marine habitats that may be key to the species' viability. We found that seals foraged extensively within barrier reefs of the atolls and on the leeward slopes of reefs and islands at all colony sites. They also ranged away from these sites along the Hawaiian Islands Archipelago submarine ridge to most nearby seamounts and submerged reefs and banks. Most dives were less than 10 m deep, though dives of some seals exceeded 0 m. Suitable foraging habitat may be a resource limiting the population of monk seals in the NWHI. Moreover, the foraging biogeography of Hawaiian monk seals may vary spatially and temporally with variation in the extent of physical substrate, prey community composition and species' abundance, and demographic composition of seal colonies. _________________________________________________
Journal of Experimental Biology, Mar 15, 2000
Coral Reefs of the USA, 2008
Biological Conservation, 2004
Most of the extant circa 1400 Hawaiian monk seals Monachus schauinslandi live in the Northwestern... more Most of the extant circa 1400 Hawaiian monk seals Monachus schauinslandi live in the Northwestern Hawaiian Islands (NWHI). However, an increasing number of sightings and births have recently occurred in the main Hawaiian Islands (MHI), where no systematic surveys of monk seals were conducted prior to 2000. We estimate that there were at least 45 seals in the MHI in
Proceedings of the Royal Society B: Biological Sciences, 2007
Estimates of variability in pinniped survival rates are generally based on observations at single... more Estimates of variability in pinniped survival rates are generally based on observations at single sites, so it is not certain whether observed rates represent the whole population. Here, we provide a comprehensive analysis of spatio-temporal variation in age-specific survival rates for endangered Hawaiian monk seals (Monachus schauinslandi ) based on capture-recapture analyses of more than 85% of the pups weaned in this population over the last two decades. Uniquely, these data have been collected from six subpopulations, encompassing all major breeding sites across its 1800 km long core range. Analyses of individual subpopulations revealed similar patterns in age-specific survival, characterized by the relatively low survival rates from weaning to 2 years of age, intermediate rates to 4 years of age, and then by relatively high 'mature' survival rates until 17 years of age, after which a senescent decline was observed. Juvenile, subadult and adult survival rates all varied significantly over time. Trends in survival among subpopulations were coherent with their relative geographical positions, suggesting regional structuring and connectedness within the archipelago. Survival rates for different age classes tended to be positively correlated, suggesting that similar factors may influence the survival for seals of all ages.
Marine Mammal Science, 2002
We examined the effects of research handling on free-ranging endangered Hawaiian monk seals, Mona... more We examined the effects of research handling on free-ranging endangered Hawaiian monk seals, Monachzls scbauinslandi, by analyzing differences in subsequent year survival, migration, and condition between handled seals and controls during 1983-1998. Each of 549 handled seals was matched to a control seal of the same age, sex, location, and year. Handling included instrumentation with telemetry devices ( n = 93), blood sampling (n = 19), and tagging ( n = 437). No significant differences were found between handled seals and their controls in one-year resighting rates, observed migration rates, or condition. Resighting rates of handled and control seals were high (SO%-l00%). Available sample sizes were sufficient to detect reasonably small (9%-20%) differences in resighting rates had they existed among instrumented or tagged seals and controls (a = 0.05, power = 0.90). Too few seals were captured for blood sampling to detect even large differences in their resighting rates. However, blood samples were drawn from most instrumented seals, and there was no indication that this larger group suffered harmful effects. Duration of restraint during flipper tagging had no effect on subsequent probability of resighting. Our analysis suggests that conservative selection procedures and careful handling techniques have no deleterious effects on Hawaiian monk seals.
Marine Mammal Science, 2011
Total estimated abundance of Hawaiian monk seals was just 1,161 individuals in 2008 and this numb... more Total estimated abundance of Hawaiian monk seals was just 1,161 individuals in 2008 and this number is decreasing. Most monk seals reside in the remote Northwestern Hawaiian Islands (NWHI) where the decline is approximately 4%/yr, whereas relatively fewer seals currently occupy the main Hawaiian Islands (MHI). It is widely accepted that the MHI population is increasing, although there are no formal estimates of total abundance, population growth rate or vital rates. This lack of information has hampered efforts to anticipate future scenarios and plan conservation measures. We present the first estimates of MHI monk seal survival and age-specific reproductive rates. Using these rates, a conservative estimate of current MHI abundance and a previously published stochastic simulation model, we estimate the MHI population growth rate and projected abundance trend. Analogous estimates for the NWHI are derived from a much richer data set. Estimated survival from weaning to age 1 yr is 77% in the MHI, much higher than recent NWHI estimates ranging from 42% to 57%. Moreover, MHI females begin reproducing at a younger age and attain higher birth rates than observed in the NWHI. The estimated MHI intrinsic rate of population growth is 1.07 compared to a 0.89-0.96 range in the NWHI. Assuming an initial abundance of 152 animals 78 BAKER ET AL.: HAWAIIAN MONK SEAL DISTRIBUTION 79 in the MHI, projections indicate that if current demographic trends continue, abundance in the NWHI and MHI will equalize in approximately 15 yr. These results underscore the imperative to mitigate the NWHI decline while devoting conservation efforts to foster population growth in the MHI, where documented threats including fishery interactions, direct killing, and disease could rapidly undo the current fragile positive trend.
Marine Mammal Science, 2006
We investigated the pattern of first sighting of individual seals over the course of a field seas... more We investigated the pattern of first sighting of individual seals over the course of a field season, or the "discovery curve," as a means for estimating abundance of the endangered Hawaiian monk seal, Monachus schauinslandi. We empirically derived a criterion to determine whether or not total enumeration had been accomplished at a given site and year. When greater than 100-h field effort was expended without a new individual being identified, we concluded that total enumeration was likely achieved. To evaluate the potential for estimating abundance through extrapolation of nonlinear asymptotic functions fitted to discovery curves, we conducted simulations under a range of capture probability scenarios, including some based on observed individual variability in monk seal sighting frequencies. We demonstrated that if capture heterogeneity existed among individuals, the fitted asymptotes tended to yield biased estimates of abundance. Moreover, the levels of bias and uncertainty tended to increase inversely with the proportion of the population identified. While extrapolation shows little promise for generating unbiased abundance estimates, discovery curves have practical appeal for determining whether total enumeration has been achieved, and for optimizing field effort allocation. This is especially true for relatively small, closed populations of marked individuals.
Marine Mammal Science, 2007
We evaluated reproductive patterns of the Hawaiian monk seal (Monachus schauinslandi) using a com... more We evaluated reproductive patterns of the Hawaiian monk seal (Monachus schauinslandi) using a combination of fitted age-specific reproductive curves and analysis of reproductive patterns of individual females. We review the difficulties inherent in the acquisition and modeling of reproductive data with emphasis on the significance of reproductive senescence to populations with dissimilar age/sex compositions. Validation of the fitted reproductive parameters was accomplished by Monte Carlo sampling of parameter distributions to compare the expected number of pups with the observed production. Although the fitted reproductive functions appear to provide an acceptable fit to the raw reproductive data, we found that the fitted curves did a poor job of predicting the actual pup production in individual years because of high variability among years. To further verify, and elaborate on, the patterns in the pooled (multi-seal, and multi-year) rates, we examined attributes of the reproductive performance of individual seals. The attributes included age of primiparity, reproductive rates computed over several age ranges, and the relationship between reproductive performance and seal longevity. Analysis of individual seal patterns reinforced the conclusion that reproductive senescence is operative in monk seal populations.
Marine Mammal Science, 2004
Marine Mammal Science, 1994
A mark-recapture study conducted in 1987-1992 provided weight measurements of juvenile male north... more A mark-recapture study conducted in 1987-1992 provided weight measurements of juvenile male northern fur seals (Callorhinus ursinus) on St. Paul Island, Alaska, at ages ranging from approximately 1.5 mo to 5 yr. Males born in 1987 tended to weigh less at ages 3 and 4 yr than those born in other years. Weights of individuals at ages 2, 3, and 4 yr were significantly correlated with their weights as pups (P < 0.05). Weights at ages 2 and 3, 7 and 4, and 4 and 5 yr were significantly correlated (P < 0.00 I), although weight changes with age were highly variable. Data indicate that larger than average male p~qx born during [1987][1988][1989][1990] were more likely to survive, but this effect was less evident than among pups born during [1960][1961][1962][1963][1964][1965] when average pup weights were lower.
Marine Mammal Science, 1990
Tooth weight and body length of juvenile male northern fur seals, Callorhinus ursinus, collected ... more Tooth weight and body length of juvenile male northern fur seals, Callorhinus ursinus, collected on St. Paul Island, Alaska, from 1948 to 1984 were compared. The relationship between these variables was investigated for individual and combined age classes. A density-dependent increase in mean tooth weight occurred during a decline in fur seal abundance. Consistent, though poorly understood, differences in tooth weight were found among males associated with different rookeries (breeding grounds). Storing the teeth for long periods may affect the weights, but such effects, if any, are too small to account for the changes observed.
Marine Mammal Science, 2014
ABSTRACT
Marine Mammal Science, 2013
Marine Mammal Science, 2004