摘要:

AbstractThe major direct effects of man on seal populations are caused by hunting. Subsistence hunting using traditional methods has a long history and generally resulted in a balance between the hunters and the seals. More recently commercial hunting, using sophisticated methods, has reduced many seal stocks to low levels. In some cases no balance was achieved and either the seals or the industry became extinct. Minor direct effects of man on seals include sport hunting and the destruction of seals for fisheries protection. These are generally of local importance only. Indirect effects may be either detrimental or beneficial to seal stocks. Detrimental effects include fishing operations which may result in the unintentional destruction of seals or compete with seals for available limited fish stocks, habitat destruction, pollution, and anthropogenic disturbance. Beneficial indirect effects include increase of available food stocks resulting from the reduction of another predator, increase of available breeding habitat as a result of human population shifts, and changes in ethical attitudes to seals.

ISSN:0305-1838    

DOI:10.1111/j.1365-2907.1978.tb00210.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

AbstractFor the past 15 years at least, government officials, scientists, observers and representatives of the news media have massed each year in the Gulf of St Lawrence, Canada, to witness the killing of Harp seals,Pagophilus groenlandicus, by the commercial sealing industry. This species has become possibly the most studied, the most reported and the most photographed species of wildlife in living memory.Much of this attention has been directed towards arousing public opinion against the annual seal hunts in the Gulf and in the ‘Front’ areas of the Northwest Atlantic off the coasts of Labrador and Newfoundland. However, considerable scientific research has been done into the behavioural habits and population dynamics of the Harp seal.Our present knowledge of this species and the co‐operation afforded by the governments of Canada and Norway, enable the Labrador herd of the Harp seal to be used as testing ground for rational herd management based on sound conservation principles. But have we achieved our obje

ISSN:0305-1838    

DOI:10.1111/j.1365-2907.1978.tb00211.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

AbstractIn 1974 and 1975 a series of trials were made to investigate the effectiveness of sound as a deterrent to marauding seals at salmon netting stations. A feasibility trial was followed by experimental work on a captive juvenile Common seal. A wide variety of sounds including pure tones, Killer whale calls and recorded loud noises were transmitted and responses were recorded on videotape. While one sound appeared to elicit an alarm reaction, habituation was rapid. Field trials were carried out at netting stations at the mouth of the River Tweed which frequently suffer damage from Grey seals. Although the frequencies used spanned the entire hearing range of seals, no sound was consistently effective in scaring seals from the nets. It is concluded that the prospect of an acoustic deterrent is remote.

ISSN:0305-1838    

DOI:10.1111/j.1365-2907.1978.tb00212.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

AbstractThe large population of Common seals in the Wash has been studied over a number of years. Aerial surveys, although useful for counting seals present at any one time, do not give a total count of the population. Various other methods including tagging, track counting and analysis of hunting returns have been used to make a population estimate. The seal population has not been significantly affected by hunting, and water storage schemes proposed for the Wash are unlikely to cause much disturbance.

ISSN:0305-1838    

DOI:10.1111/j.1365-2907.1978.tb00213.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

AbstractThe variable start and duration of the Grey seal breeding season makes the estimation of total pup production from a single census very difficult. Classifying the count into morphological age classes enables the form and timing of the birth rate curve and estimates of pup mortality rates to be elucidated. A simulation technique is described which enables the duration of each morphological stage to be determined from a series of such classified counts taken over one season. A further statistical technique uses these estimates to calculate the mean timing and duration of the breeding season from a single classified count taken from similar populations in subsequent years. This information allows total pup production to be calculated for any appropriate breeding colony. Some guidance is given as to the optimal timing of that single census which would yield the best estimate of production, although the precise date is not critical to the success of the technique. Results from single census estimates obtained in this way are compared with known production data from more detailed surveys for a number of different colonies.

ISSN:0305-1838    

DOI:10.1111/j.1365-2907.1978.tb00214.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

AbstractWhile some activity patterns in seals have been related to tidal rhythms, little work was done on diurnal rhythms until the recent development of image intensifying devices which facilitate night viewing. Individual bulls were studied over several 24‐hour periods and the frequency of behavioural items was recorded during 10‐min periods each hour. No significant differences were recorded between day and night activity levels, except in the frequency of ‘Looks’, nor was there any relationship between activity and tide state. The thesis that optimization of time spent ashore (and therefore ‘at risk’ both ecologically and energetically) is achieved by maintaining a constant level of activity through the 24‐hour period is discussed. It is concluded that night time activity of Grey seal bulls can be inferred from observations made in d

ISSN:0305-1838    

DOI:10.1111/j.1365-2907.1978.tb00215.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

AbstractElectrophoresis provides extensive information about species relationships and subspecific structure, because taxonomically separated species are unlikely to share electrophoretic characters. The technique is best for relatively immobile species and so far fish or marine mammals have proved difficult subjects; but if interbreeding occurs only at the edges of otherwise discrete populations the technique should detect this. Transferrin polymorphisms in geographically separated populations of Weddell and southern Fur seals have been found.Because the Grey seal returns to the same distinct localities to breed, for instance the Orkneys, Shetlands, Fames, North Rona, Hebrides, Wales and S.W. England, it seems sensible to seek such polymorphisms in this species.In my work serum samples from eight Orkney Grey seals and thirteen Fame seals were separated on horizontal starch gels, but no polymorphisms were found. Such a small sample is however, not likely to reveal distinct or striking polymorphism.However, a study conducted on a wider scale and with larger samples, might reveal such polymorphisms, particularly in respect of transferrins, a possibility which was suggested during the course of my work.

ISSN:0305-1838    

DOI:10.1111/j.1365-2907.1978.tb00216.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

ISSN:0305-1838    

DOI:10.1111/j.1365-2907.1978.tb00217.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

AbstractThe population of Antarctic Fur sealsArctocephalus gazellaat South Georgia is increasing rapidly and is therefore of great interest. Investigations of the population depend on two main techniques.(1) Population assessment, because the population size is now too large for direct counts to be completely reliable, and serious underestimates are appearing in areas of high density. Aerial photography was used but needs further refinement before it becomes a consistently useful technique. Marking all pups on sample beaches was largely unsuccessful because pups moved from beach to beach before they could all be marked. A mark–recapture method was finally adopted and indicated that the numbers of pups present may be up to 54% higher than the numbers actually counted.(2) The process of age determination from tooth characters, which is more difficult for Fur seals than other pinnipeds. The preparation and interpretation of the teeth of breeding cows is described, based on eleven specimens of known age. The most accurate results are obtained from whole teeth up to the age of 6, but thereafter interpretation of cement and dentine layers in thin sections must be used. It is concluded that while young animals are aged quite accurately, there is probably a tendency to underestimate the age of seals of more than 9 year

ISSN:0305-1838    

DOI:10.1111/j.1365-2907.1978.tb00218.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

ISSN:0305-1838    

DOI:10.1111/j.1365-2907.1978.tb00219.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY