Estimation of Harp Seal (Phoca groenlandica) Pup Production from Age Samples

1985 ◽  
Vol 42 (3) ◽  
pp. 468-473 ◽  
Author(s):  
Justin G. Cooke
Keyword(s):  
Maximum Likelihood ◽  
Mathematical Formulation ◽  
Harp Seal ◽  
Index Method ◽  
Northwest Atlantic ◽  
Numerical Example ◽  
Phoca Groenlandica ◽  
Survival Index ◽  
Maximum Likelihood Criterion

A simple numerical example shows that previously used procedures such as the "survival index" method for estimating the pup production in populations of harp seals (Phoca groenlandica) from samples of aged adults are unreliable because of their poor mathematical formulation. A corrected formulation, based on a maximum likelihood criterion, performed well in simulations tests. This was applied to age data from the Northwest Atlantic harp seal stock to obtain revised pup production estimates. A method to correct for the effects of errors in ageing also performed favourably in simulation trials.

Pup Production of Harp Seals, Phoca groenlandica, in the Northwest Atlantic

1993 ◽  
Vol 50 (11) ◽  
pp. 2429-2439 ◽  
Author(s):  
G. B. Stenson ◽  
R. A. Myers ◽  
M. O. Hammill ◽  
I- H. Ni ◽  
W. G. Warren ◽  
...  
Keyword(s):  
Developmental Stages ◽  
Harp Seal ◽  
Northwest Atlantic ◽  
Black And White ◽  
Aerial Surveys ◽  
Phoca Groenlandica ◽  
Best Estimate ◽  
Age Related

Northwest Atlantic harp seal, Phoca groenlandica, pup production was estimated from aerial surveys flown off eastern Newfoundland ("Front") and in the Gulf of St. Lawrence ("Gulf") during March 1990. One visual and two independent photographic estimates were obtained at the Front; a single photographic estimate was obtained in the Gulf. Photographic estimates were corrected for misidentified pups by comparing black-and-white photographs with ultraviolet imagery. Estimates were also corrected for pups absent from the ice at the time of the survey using distinct age-related developmental stages. Stage durations in the Gulf appeared consistent with previous studies but were increased by 30% to improve the fit to staging data collected at the Front. The best estimate of pup production at the Front was obtained from the visual surveys. A total of 467 000 (SE = 31 000) pups were born in three whelping concentrations. The photographic estimates were comparable. Pup production estimates for the southern (Magdalen Island) and northern (Mecatina) Gulf whelping patches were 106 000 (SE = 23 000) and 4 400 (SE = 1300), respectively. Thus, total pup production was estimated to be 578 000 (SE = 39 000).

Mark–Recapture Estimates of Harp Seal Pup (Phoca groenlandica) Production in the Northwest Atlantic

1983 ◽  
Vol 40 (6) ◽  
pp. 728-742 ◽  
Author(s):  
W. D. Bowen ◽  
D. E. Sergeant
Keyword(s):  
Reporting Rate ◽  
Harp Seal ◽  
Short Term ◽  
Northwest Atlantic ◽  
Tag Loss ◽  
Phoca Groenlandica ◽  
Seal Population ◽  
Sources Of Variation ◽  
Variance Estimates

Pup production of the northwest Atlantic harp seal population (Phoca groenlandica) was estimated using a modified Petersen model corrected for tag loss and nonreporting of recovered tags. Variance estimates were corrected for the additional sources of variation due to tag loss, reporting rate, and the estimation of the number of seals examined for tags. Experiments were conducted in March of 1978, 1979, and 1980 with 9154, 4939, and 6246 pups being tagged in each year, respectively. Estimates from short-term recoveries (within the same year) were unreliable because of failure to satisfy the assumption of uniform mixing of marked and unmarked seals. Pooled estimates from long-term recoveries (1–3 yr) were considered more reliable, with the 1978 estimate of 506 000 ± 77 000 (1 SE) and the 1979 estimate of 489 000 ± 71 000 being most reliable. Based on the results of this study and on the trend in catches of pups and immatures in West Greenland, we conclude that harp seal pup production and hence population size has probably increased since the imposition of catch quotas in 1971.

Mandibular dental anomalies of Northwest Atlantic harp seals, Phoca groenlandica

1987 ◽  
Vol 65 (3) ◽  
pp. 769-771 ◽  
Author(s):  
R. E. A. Stewart ◽  
B. E. Stewart
Keyword(s):  
Genetic Variation ◽  
Harp Seal ◽  
Dental Anomalies ◽  
Supernumerary Teeth ◽  
Missing Teeth ◽  
Northwest Atlantic ◽  
Frequency Distributions ◽  
Phoca Groenlandica

We examined 2267 harp seal mandibles to determine the frequency of extra, missing, and malformed teeth; to examine the effect of these anomalies on longevity; and to assess the usefulness of anomalies in identifying stocks of seals. Supernumerary teeth occurred in 1.7% of the seals, 0.5% of the seals were missing teeth (none because of trauma), and 0.6% had morphologically deviant teeth. Only 0.2% of the seals had more than one type of anomaly and none had all three. Average age and age–frequency distributions for anomalous and normal seals were not different. Anomalies were probably too rare and combined too much genetic variation to be useful in stock delineation.

Further Analysis of Population Trends in the Northwest Atlantic Harp Seal (Phoca groenlandica) from 1967 to 1985

1986 ◽  
Vol 43 (3) ◽  
pp. 553-564 ◽  
Author(s):  
Derek Roff ◽  
W. Don Bowen
Keyword(s):  
Simulation Model ◽  
Age Structure ◽  
Population Trends ◽  
Harp Seal ◽  
Population Increase ◽  
Northwest Atlantic ◽  
Phoca Groenlandica ◽  
Precise Estimation ◽  
Rate Of Increase ◽  
Minimum Estimate

We examined changes in the age structure of the northwest Atlantic harp seal (Phoca groenlandica) population from 1967 to 1983. Through this period there has been a statistically significant population increase in the proportion of seals aged 2–6 yr. Precise estimation of the rate of increase is hindered by a tendency for immature seals to be overrepresented in samples of molting males. Two methods were developed to correct for this bias; these provide a minimum estimate of the proportion of seals aged 2–6 yr present in 1967. Utilizing a simulation model, we showed that the unadjusted and adjusted age distributions are both extremes and that the correct distribution probably lies between them. In both cases the data are more consistent with an increasing than a decreasing population, given the level of catch experienced by this population up to 1982. Recent total catches of 75 000 or less in 1983 and 1984 are substantially below the most conservative estimates of replacement yield in 1985 and will result in a further, more rapid population increase.

Box-Cox Transformations

2017 ◽  
Author(s):  
Russell Cheng
Keyword(s):  
Maximum Likelihood ◽  
Normal Form ◽  
Maximum Likelihood Estimate ◽  
Likelihood Estimate ◽  
Grouped Data ◽  
Numerical Example ◽  
Alternative Method ◽  
Modified Likelihood

This chapter examines the well-known Box-Cox method, which transforms a sample of non-normal observations into approximately normal form. Two non-standard aspects are highlighted. First, the likelihood of the transformed sample has an unbounded maximum, so that the maximum likelihood estimate is not consistent. The usually suggested remedy is to assume grouped data so that the sample becomes multinomial. An alternative method is described that uses a modified likelihood similar to the spacings function. This eliminates the infinite likelihood problem. The second problem is that the power transform used in the Box-Cox method is left-bounded so that the transformed observations cannot be exactly normal. This biases estimates of observational probabilities in an uncertain way. Moreover, the distributions fitted to the observations are not necessarily unimodal. A simple remedy is to assume the transformed observations have a left-bounded distribution, like the exponential; this is discussed in detail, and a numerical example given.

Cytochrome P450-mediated enzyme activities and polychlorinated biphenyl accumulation in harp seal (Phoca groenlandica)

1999 ◽  
Vol 48 (1) ◽  
pp. 59-72 ◽  
Author(s):  
J Wolkers ◽  
I.C Burkow ◽  
M Monshouwer ◽  
C Lydersen ◽  
S Dahle ◽  
...  
Keyword(s):  
Cytochrome P450 ◽  
Enzyme Activities ◽  
Polychlorinated Biphenyl ◽  
Harp Seal ◽  
Phoca Groenlandica

Gastroliths in the harp seal Phoca Groenlandica

1995 ◽  
Vol 14 (3) ◽  
pp. 335-338
Author(s):  
Erling Sverre Nordøy
Keyword(s):  
Harp Seal ◽  
Phoca Groenlandica

scholarly journals First independent feeding of harp seal (Phoca groenlandica) and hooded seal (Cystophora cristata) pups in the Greenland Sea

2000 ◽  
Vol 2 ◽  
pp. 29 ◽  
Author(s):  
Tore Haug ◽  
Kjell T Nilssen ◽  
Lotta Lindblom
Keyword(s):  
Interspecific Competition ◽  
Niche Overlap ◽  
Harp Seal ◽  
Minor Importance ◽  
Greenland Sea ◽  
The West ◽  
Hooded Seal ◽  
Cystophora Cristata ◽  
Phoca Groenlandica

Data were collected from harp seal (Phoca groenlandica) and hooded seal (Cystophora cristata) pups belonging to the Greenland Sea (or "West Ice") stocks in 1995-1997. Pups of both species were observed to feed independently shortly after weaning, and their first food was almost exclusively crustaceans. Parathemisto sp., particularly P. libellula, dominated the diet of both the harp and the hooded seal pups, but the diet also contained sympagic amphipods of the genus Gammarus. Krill (Thysanoessa sp.) was of minor importance as food for seal pups in 1995, but occurred more frequentlyin the diet of both species in 1996 and 1997. Considerable niche overlap may suggest some interspecific competition between harp and hooded seal pups in the West Ice.

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