Sensitivity Analysis of Two Harp Seal (Pagophilus groenlandicus) Population Models

1979 ◽  
Vol 36 (4) ◽  
pp. 404-410 ◽  
Author(s):  
R. K. Mohn
Keyword(s):  
Sensitivity Analysis ◽  
Population Model ◽  
Maximum Sustainable Yield ◽  
Population Models ◽  
Harp Seal ◽  
Sustainable Yield ◽  
Relative Importance ◽  
Yield Level ◽  
Pagophilus Groenlandicus ◽  
Seal Population

Sensitivity analysis has been used to estimate the relative importance of input parameters both between and within two harp seal (Pagophilus groenlandicus) population models. The population size at maximum sustainable yield is shown to be much more poorly defined than the yield level itself. Key words: sensitivity analysis, harp seal, population model, sustainable yield, management

Production, Mortality, And Sustainable Yield Of Northwest Atlantic Harp Seals (Pagophilus groenlandicus)

1978 ◽  
Vol 35 (9) ◽  
pp. 1249-1261 ◽  
Author(s):  
G. H. Winters
Keyword(s):  
Population Size ◽  
Total Population ◽  
Historical Data ◽  
Maximum Sustainable Yield ◽  
Sustainable Yield ◽  
Natural Mortality ◽  
Northwest Atlantic ◽  
The Past ◽  
Relative Contribution ◽  
Pagophilus Groenlandicus

From recent and historical data the natural mortality rate of adult harp seals (Pagophilus groenlandicus) is estimated to be 0.10 which is within the range of previous estimates (0.08–0.11). New estimates of bedlamer and 0-group natural mortality rates were not significantly different from those of adult seals. Pup production estimates from survival indices agreed well with those from sequential population analyses and indicated a decline from about 350 000 animals in the early 1950s to about 310 000 animals in the early 1970s. Over the same period the 1+ population size declined from 2.5 to 1.1 million animals but has been increasing at the rate of 3%/yr since the introduction of quotas in 1972. The relative contribution of the "Front" production to total ("Front" plus Gulf) production during the past decade has fluctuated from 49 to 87%, the average of 64% being very similar to the 61% obtained previously. These fluctuations suggest some interchange between "Front" and Gulf adults and it is concluded that homing in the breeding areas is a facultative rather than obligatory aspect of seal behavior. Thus the heavier exploitation of the "Front" production is probably sufficiently diffused into the total population to avoid serious effects on "Front" production. The maximum sustainable yield of Northwest Atlantic seals harvested according to recent patterns is estimated to be 290 000 animals (80% pups) from a 1+ population size of 1.8 million animals producing 460 000 pups annually. The sustainable yield at present levels of pup production (335 000 animals) is calculated to be 220 000 animals which is substantially above the present TAC of 180 000 animals and coincides with present harvesting strategies designed to enable the seal hunt to increase slowly towards the MSY level. Key words: mortality, production, sustainable yield, population dynamics, marine mammal

scholarly journals Investigating the recent decline in gadoid stocks in the west of Scotland shelf ecosystem using a foodweb model

2014 ◽  
Vol 72 (2) ◽  
pp. 436-449 ◽  
Author(s):  
Karen A. Alexander ◽  
Johanna J. Heymans ◽  
Shona Magill ◽  
Maciej T. Tomczak ◽  
Steven J. Holmes ◽  
...  
Keyword(s):  
Trophic Structure ◽  
Ecosystem Model ◽  
Maximum Sustainable Yield ◽  
Sustainable Yield ◽  
Fishing Pressure ◽  
Grey Seal ◽  
The West ◽  
Considerable Part ◽  
Seal Population ◽  
Key Driver

Abstract Abundance and biomass of cod, haddock, and whiting in the waters off of the west coast of Scotland (wcoS) have undergone large changes in recent years, most notably a recent decline. These three species contribute a considerable part of Scottish demersal landings from this area and as such it is important to understand why these stocks are behaving the way they are. A number of explanations for the decline have been proposed, including: seal predation, pressure from Nephrops trawls, and fishing pressure more generally. We used an ecosystem model of the wcoS continental shelf (<200 m depth) to investigate whether these proposed explanations for declining gadoid stocks are feasible. Results suggest that the rise in the grey seal population over recent years has not led to the decline in gadoid stocks; there is insufficient bycatch by the Nephrops fleet to have a large impact on gadoid stocks; however, fishing, as a key driver of the west of Scotland shelf ecosystem, has impacted stocks and by decreasing fishing levels to maximum sustainable yield cod biomass may increase slightly though not returning to previous levels. Although this means we are little further forward in understanding the cause of recent gadoid declines in the area, the development of this model has enabled us to further our knowledge and understanding of aspects of trophic structure and the impacts of fishing on the wcoS.

scholarly journals Establishing the relative importance of sympatric definitive hosts in the transmission of the sealworm, Pseudoterranova decipiens: a host-community approach

2001 ◽  
Vol 3 ◽  
pp. 161
Author(s):  
F Javier Aznar ◽  
Juan A Balbuena ◽  
Mercedes Fernández ◽  
J Antonio Raga
Keyword(s):  
Host Community ◽  
Harp Seal ◽  
Harbour Seal ◽  
Transmission Model ◽  
Relative Importance ◽  
Geographic Scale ◽  
Hooded Seal ◽  
Pseudoterranova Decipiens ◽  
Seal Population

The importance of a given host to a particular parasite can be determined according to three different criteria: host preference, host physiological suitability and host contribution to transmission. Most studies on the sealworm Pseudoterranova decipiens have focussed on the latter factor, but few attempts have been made to develop a quantitative transmission model evaluating the relative importance of each host. The purpose of this study was to propose a flow-chart model to study sealworm transmission within a seal community. The model was applied to hypothetical data of four seal species acting as definitive hosts of P. decipiens sensu stricto in eastern Canada: harp seal Phoca groenlandica, harbour seal P. vitulina, grey seal Halichoerus grypus and hooded seal Cystophora cristata. The dynamics of the model was studied using population estimates from 1990 to 1996. To illustrate the interrelationship of the seal populations in the flow dynamics, the model’s behaviour was explored by manipulation of the harp seal population size. The results showed that grey seals accounted by far for most transmission from and to the seals. The harbour seal population also sustained a biologically significant proportion of the flow, whereas the role of hooded and harp seals seemed negligible despite their large population sizes. The hypothetical removal of the harp seal population resulted in small increases in the relative flows to the other seals. These results conform to previous qualitative assessments on the relative importance of these seal species in sealworm transmission. The model provided some heuristic rules useful to understand transmission patterns. The data suggested that the harbour seal population should be about twice that of the grey seals to account for a larger share of transmission than grey seals. Although this is unlikely to occur at a large geographic scale, harbour seals outnumber grey seals in some areas and, therefore, the role of each host may change locally. To make this approach more realistic, further work should seek accurate estimates of parasite population parameters, better definition of the host community boundaries (at a local scale) and improved control of confounding variables.

The relative effectiveness of two expanding bullet designs in young harp seals (Pagophilus groenlandicus): A randomised controlled field study in the Norwegian harp seal hunt

2021 ◽  
Vol 30 (2) ◽  
pp. 155-167
Author(s):  
KA Ryeng ◽  
SE Larsen
Keyword(s):  
Relative Effectiveness ◽  
Weather Condition ◽  
Condition Index ◽  
Harp Seal ◽  
Time To Death ◽  
Pagophilus Groenlandicus ◽  
Parallel Group ◽  
Seal Population ◽  
The Difference ◽  
Randomised Controlled

The aim of this study was to investigate the relative effectiveness of a rapidly expanding Bonded hunting bullet and an explosively expanding Varmint bullet in young harp seals (P). The study was conducted as an open, controlled and randomised parallel-group designed field trial. The animals were pre-randomised (1:1) into one explosively expanding (Varmint) and one expanding (Bonded) bullet type group, with 75 animals in each. The study sample consisted of young, weaned harp seals, 2–7 weeks of age, of both sexes, from the Greenland Sea harp seal population. The study was conducted during the regular hunt. Instantaneous death rate (IDR) and time to death (TTD) were the main variables. The observed IDR was 84 in both bullet groups. Correcting for Weather Condition Index, the IDR for the Varmint bullet was significantly higher compared to the Bonded. The mean TTD was shortest in the Varmint group, but the difference did not reach significance. Compared to the Bonded, a significantly higher total cranial damage score and bleeding intensity, and significantly lower frequencies of bullet exit wounds were detected in the Varmint group. The post mortem reflex movements caused by the Varmint bullet were significantly more powerful with longer duration and higher frequencies of clonic contractions. In conclusion, the results indicate a higher effectiveness of the Varmint bullet relative to the Bonded. The Varmint bullet may thus improve animal welfare in the hunt of young harp seals.

scholarly journals OPTIMISASI EKONOMI PENGELOLAAN SUMBERDANA PERIKANAN UDANG

Agro Ekonomi ◽  
2016 ◽  
pp. 67
Author(s):  
Purwanto Purwanto ◽  
Kamiso H Nitimulyo ◽  
Tumari Jatileksono
Keyword(s):  
Yield Function ◽  
Fishing Effort ◽  
Maximum Sustainable Yield ◽  
Sustainable Yield ◽  
Allocation Of Resources ◽  
Economic Optimization ◽  
Yield Level ◽  
Central Java ◽  
The Government ◽  
The Relationship

This paper presents the economic optimization of the shrimps fishing industry in the south coast of Central Java and adjacent waters. The physical yield function of the shrimps fishery is incorporated in an economic model to analyze the relationship between the level of fishing effort and the economic efficiency of the fishery. The open access fishery and the controlled fishery at maximum sustainable yield level causes inefficient allocation of resources. Only through control the effort at the level where marginal oost of production equal price resources can be allocated efficiently. The government intervention is necessary to restrict fishing effort to a level that would be economically optimum

scholarly journals OPTIMISASI EKONOMI PENGELOLAAN SUMBERDANA PERIKANAN UDANG

Agro Ekonomi ◽  
2016 ◽  
pp. 67
Author(s):  
Purwanto Purwanto ◽  
Kamiso H Nitimulyo ◽  
Tumari Jatileksono
Keyword(s):  
Yield Function ◽  
Fishing Effort ◽  
Maximum Sustainable Yield ◽  
Sustainable Yield ◽  
Allocation Of Resources ◽  
Economic Optimization ◽  
Yield Level ◽  
Central Java ◽  
The Government ◽  
The Relationship

This paper presents the economic optimization of the shrimps fishing industry in the south coast of Central Java and adjacent waters. The physical yield function of the shrimps fishery is incorporated in an economic model to analyze the relationship between the level of fishing effort and the economic efficiency of the fishery. The open access fishery and the controlled fishery at maximum sustainable yield level causes inefficient allocation of resources. Only through control the effort at the level where marginal oost of production equal price resources can be allocated efficiently. The government intervention is necessary to restrict fishing effort to a level that would be economically optimum

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