scholarly journals Modelling the abundance of grey seals (Halichoerus grypus) along the Norwegian coast

2012 ◽  
Vol 69 (8) ◽  
pp. 1436-1447 ◽  
Author(s):  
Tor Arne Øigård ◽  
Anne Kirstine Frie ◽  
Kjell Tormod Nilssen ◽  
Mike Osborne Hammill
Keyword(s):  
Confidence Interval ◽  
Population Size ◽  
Halichoerus Grypus ◽  
Grey Seal ◽  
Norwegian Coast ◽  
Structured Population ◽  
Population Dynamics Model ◽  
Level Model ◽  
Age Structured ◽  
The Uk

Abstract Øigård, T. A., Frie, A. K., Nilssen, K. T., and Hammill, M. O. 2012. Modelling the abundance of grey seals (Halichoerus grypus) along the Norwegian coast. – ICES Journal of Marine Science, 69: . An age-structured population dynamics model of the Norwegian grey seal (Halichoerus grypus) population has been developed. The model is of a Bayesian character in the sense that priors for various parameters were used. Model runs indicated an increase in the abundance of the total Norwegian grey seal population during the last 30 years, suggesting a total of 8740 (95% confidence interval: 7320–10 170) animals in 2011. A total catch of 707 (95% confidence interval: 532–882) grey seals would maintain the population size at the 2011 level. Model runs suggest that current catch levels will likely result in a reduction in the population size in Sør-Trøndelag and Nord-Trøndelag counties, and an increase in the population size in Rogaland, Nordland, Troms, and Finnmark counties. The model runs assumed that 80% of the seals taken in Rogaland came from the UK and that 50 and 55% of the catches in Troms and Finnmark, respectively, were immigrants from Russia.

Predation by Sharks on the Grey Seal (Halichoerus grypus) in Eastern Canada

1983 ◽  
Vol 40 (3) ◽  
pp. 267-271 ◽  
Author(s):  
Paul Brodie ◽  
Brian Beck
Keyword(s):  
Key Words ◽  
Population Size ◽  
Halichoerus Grypus ◽  
Longline Fishery ◽  
Grey Seal ◽  
Eastern Canada ◽  
The Past ◽  
Harbour Seals ◽  
Commercially Important ◽  
Important Fish

The increase in population size of the grey seal (Halichoerus grypus) off eastern Canada over the past 20 yr may be attributed to a decrease in shark stocks, their supposed predators. Reduction of the shark population is presumed to have resulted from a directed longline fishery and, of greater significance, from a change in the fishery for swordfish (Xiphias gladius) from selective harpooning to pelagic longlining, which has produced a large bycatch of sharks. The resulting enhanced survival of grey seals is reflected in greater infestation of commercially important fish species by the codworm (Phocanema decipiens).Key words: grey seals, harbour seals, sharks, swordfish, codworm, predation, fisheries

Stochastic modelling of age-structured population with time and size dependence of immigration rate

2018 ◽  
Vol 33 (5) ◽  
pp. 289-299 ◽  
Author(s):  
Boris J. Pichugin ◽  
Nikolai V. Pertsev ◽  
Valentin A. Topchii ◽  
Konstantin K. Loginov
Keyword(s):  
Population Size ◽  
Branching Processes ◽  
Stochastic Modelling ◽  
Random Variable ◽  
Structured Population Model ◽  
Immigration Rate ◽  
Structured Population ◽  
Mean And Variance ◽  
Age Structured ◽  
Age Structured Population

Abstract A stochastic age-structured population model with immigration of individuals is considered. We assume that the lifespan of each individual is a random variable with a distribution function which may differ fromthe exponential one. The immigration rate of individuals depends on the time and total population size. Upper estimates for the mean and variance of the population size are established based on the theory of branching processes with constant immigration rate. A Monte Carlo simulation algorithm of population dynamics is developed. The results of numerical experiments with the model are presented.

scholarly journals British grey seal (Halichoerus grypus) abundance in 2008: an assessment based on aerial counts and satellite telemetry

2011 ◽  
Vol 68 (10) ◽  
pp. 2201-2209 ◽  
Author(s):  
Mike Lonergan ◽  
Callan D. Duck ◽  
Dave Thompson ◽  
Simon Moss ◽  
Bernie McConnell
Keyword(s):  
East Coast ◽  
Satellite Telemetry ◽  
Halichoerus Grypus ◽  
Grey Seal ◽  
Total Size ◽  
Aerial Surveys ◽  
Seal Population ◽  
Pup Survival ◽  
Age Structured ◽  
Electronic Tags

Abstract Lonergan, M., Duck, C. D., Thompson, D., Moss, S., and McConnell, B. 2011. British grey seal (Halichoerus grypus) abundance in 2008: an assessment based on aerial counts and satellite telemetry. – ICES Journal of Marine Science, 68: 2201–2209. Recent estimates of the total size of the British grey seal population have been based on fitting age-structured models to estimates of pup production. The estimates were sensitive to whether density-dependence was considered to act on fecundity or pup survival. This study provides an alternative estimate for abundance in 2008: 91 800 animals (95% confidence interval, CI, 78 400–109 900). The estimate is consistent with the results of existing models where population density influences pup survival. It suggests that reductions in fecundity are unlikely to have been the cause of the recent slowing of the rate of growth of the population. The estimate presented is based on aerial surveys of the entire Scottish coast and the east coast of England. The surveys were carried out in August of 2007–2009 and restricted to the 2 h each side of daylight low water. Data from 107 electronic tags deployed between 1995 and 2008 were used to estimate the proportion of animals hauled out during the surveys. Overall, the animals hauled out for 31% (95% CI 15–50%) of the survey windows. No significant effects on the proportion of animals hauled out were detected from year, location, age, sex, temperature, rainfall, or the timing of low tide.

scholarly journals Status of grey seals (Halichoerus grypus) in Norway

2007 ◽  
Vol 6 ◽  
pp. 23 ◽  
Author(s):  
Kjell Tormod Nilssen ◽  
Tore Haug
Keyword(s):  
Total Population ◽  
Halichoerus Grypus ◽  
Population Estimates ◽  
Grey Seal ◽  
Breeding Area ◽  
Breeding Sites ◽  
Norwegian Coast ◽  
The North ◽  
Minimum Estimate ◽  
Pup Mortality

During the period September-December in 2001-2003, ship based surveys of grey seal (Halichoerus grypus) pups, including tagging, counting and staging of pups, were conducted along the Norwegian coast. All known and other potential breeding areas were surveyed from Rogaland county in the south to Finnmark county in the north. Most of the breeding sites were surveyed only once, but some sites were surveyed 2-4 times. The investigations resulted in a total minimum estimate of 1,159 grey seal pups born in Norwegian waters. Nordland county was the most important breeding area where about 50% of the pups were born. Total population estimates were derived from the recorded number of pups born using a range of multipliers (4.0-4.7), based on observed annual growth rates of approximately 7-12% in other grey seal populations. This gave a total estimate of about 5,800-6,600 grey seals including pups in Norwegian waters. However, the total pup production was probably underestimated due to only one pup count in most of the breeding sites. Observed mean pup mortality was 1.1% during the breeding season along the Norwegian coast.

Why the Atlantic cod (Gadus morhua) stock off eastern Nova Scotia has not recovered

2001 ◽  
Vol 58 (8) ◽  
pp. 1613-1623 ◽  
Author(s):  
Caihong Fu ◽  
Robert Mohn ◽  
L Paul Fanning
Keyword(s):  
Nova Scotia ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Commercial Fishing ◽  
Sudden Increase ◽  
Annual Variations ◽  
Structured Population ◽  
Population Dynamics Model ◽  
Structured Population Dynamics ◽  
Age Structured

An age-structured population dynamics model, incorporating interactions between Atlantic cod (Gadus morhua), the fishery, and the grey seal (Halichoerus grypus) population, was applied to the cod stock off eastern Nova Scotia (Northwest Atlantic Fisheries Organization Divisions 4Vs and 4W, commonly abbreviated to 4VsW), a stock that has dramatically declined since the late 1980s. Mortality was modeled as having three components: fishing mortality (F), seal predation (Mp), and all other sources of natural mortality (M). Specifically, M was assumed to be distinct for immature cod (ages 1–4; Mi) and mature cod (age 5 and older; Mm), and respective annual variations were estimated. Parameters estimated also included recruitment (cod abundance at age 1; R), F, and Mp. Based on our estimates of F, Mp, and M, it is unlikely that the collapse of the 4VsW cod stock can be attributed to a sudden increase in M; fishing appears to have been the primary cause for the stock's decline. However, after the moratorium on commercial fishing in 1993, increasing Mp and Mm and low R may have contributed to the failure of the 4VsW cod stock to recover.

First Record of a Grey Seal (Halichoerus grypus) Predating a Tope Shark (Galeorhinus galeus) in the UK

2021 ◽  
Vol 47 (5) ◽  
pp. 465-469
Author(s):  
Georgia Catherine Anne Jones ◽  
Andrew John Roberts ◽  
David George Edwards
Keyword(s):  
First Record ◽  
Halichoerus Grypus ◽  
Grey Seal ◽  
Galeorhinus Galeus ◽  
The Uk

scholarly journals First isolation of Arcanobacterium pinnipediorum from a grey seal pup (Halichoerus grypus) in the UK

2021 ◽  
Author(s):  
Mazen Alssahen ◽  
Geoffrey Foster ◽  
Abdulwahed Ahmed Hassan ◽  
Jörg Rau ◽  
Christoph Lämmler ◽  
...  
Keyword(s):  
Elongation Factor ◽  
Bacterial Pathogen ◽  
Halichoerus Grypus ◽  
Rrna Gene ◽  
Grey Seal ◽  
Flight Mass Spectrometry ◽  
Bacterial Rna ◽  
Ft Ir ◽  
The Uk

AbstractIn the present study, a single Arcanobacterium (A.) pinnipediorum strain isolated from discharge of a jaw swelling of a grey seal pup (Halichoerus grypus) in England, UK, was identified. This strain was further characterized by phenotypical investigations, by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), by Fourier transform infrared spectroscopy (FT-IR), and genotypically by sequencing the 16S rRNA gene and the genes gap encoding glyceraldehyde 3-phosphate dehydrogenase, tuf encoding elongation factor tu, and rpoB encoding the β subunit of bacterial RNA polymerase. The present study gives a first detailed characterization of the species A. pinnipediorum from a grey seal in the UK. However, the route of infection of the grey seal with the bacterial pathogen remains unclear.

A Stochastic Age-Structured Population Model of Striped Bass (Morone saxatilis) in the Potomac River

1983 ◽  
Vol 40 (12) ◽  
pp. 2170-2183 ◽  
Author(s):  
Joel E. Cohen ◽  
Sigurd W. Christensen ◽  
C. Phillip Goodyear
Keyword(s):  
Growth Rate ◽  
Stochastic Model ◽  
Population Size ◽  
Striped Bass ◽  
Morone Saxatilis ◽  
Potomac River ◽  
Structured Population ◽  
Age Structured ◽  
Average Population Size ◽  
Age Structured Population

Deterministic age-structured models of fish populations neglect apparently stochastic fluctuations in the catch per unit effort of yearlings and of adult fish. We describe a model of an age-structured population in which the survival of eggs to yearlings fluctuates randomly, but all other age-specific rates of survival and of egg-laying are constant. For such a stochastic model, two measures of the long-term population growth rate are the average growth rate of the population size and the growth rate of the average population size. We compute both measures analytically for a simplified model representing only eggs and reproductive adults. For a model of the striped bass (Morone saxatilis) population spawning in the Potomac River, we compute both point and interval estimates of the growth rate of the average population size. We illustrate some statistical tests of the correctness of our stochastic model.

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