Development in the baltic grey seal (Halichoerus grypus) and ringed seal (Phoca hispida) populations during the 20th century

Ambio

Volumn 28, Issue 7, 1999, Pages 619-627

  Harding, Karin C ^a,b   Härkönen, Tero J ^a,b  

^a SWEDISH MUSEUM OF NATURAL HISTORY   (Sweden)

^b NONE   (Sweden)

Author keywords

[No Author keywords available]

Indexed keywords

HISTORICAL PERSPECTIVE; MARINE MAMMAL; POPULATION ECOLOGY;

ANIMALIA; GRYPUS; HALICHOERES; HALICHOERES GRYPUS; HALICHOERUS GRYPUS; MAMMALIA; PHOCA HISPIDA; PHOCIDAE; PINNIPEDIA;

EID: 0033384331     PISSN: 00447447     EISSN: None     Source Type: Journal    
DOI: None     Document Type: Article

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76. A recent paper by Kokko and co-workers on historical population sizes of the Baltic ringed and grey seals uses another approach. Instead of calculating the minimum realistic sizes as we do, they show the "possible ranges" of population sizes that could lead to the population sizes we see today. They find that original population sizes could have ranged between 50 000 to 450 000 ringed seals and 30 000 to 200 000 grey seals. More accurate estimates depend on assumptions of past population growth rates and the age structure of kills (Kokko et al. 1999). A contrasting concept is used in our study, where the minimum estimates are based on detailed information on the structure of catches for each single year. Kokko et al. simulate the outcome of a wide range of theoretical age structures of catches and growh rates, of which some extremes (e.g. at λ 1.15) are impossible for both studied species. Consequently, the lower limits of the study of Kokko et al. do not apply for the specific cases of the Baltic ringed seal and grey seal. On the other hand, the careful analysis they perform on the effects of different hunting strategies is of general interest for any seal population, which is useful when no detailed information is available on the composition of catches and populations. Kokko, H., Helle, E., Lindström, J., Randa, E., Sipilä, T. and Courchamp, F. 1999. Backcasting population sizes of ringed and grey seals in the Baltic and Lake Saimaa during the 20th century. Ann. Zool. Fennici 36, 65-73.
77. The study was financed by the project "Sälar och Fiske" with support from The Swedish Environmental Protection Agency, Fiskeriverket, and WWF Sweden. Special thanks to Olavi Stenman for valuable advice and initiated comments, and we are also grateful to Anders Bergman and Mats Olsson for suggestions and corrections. Peter Gustavsson, Heidi Henriksson, Bo Justusson, Ivar Jüssi, Mart Jüssi and Roustam Sagitov were all very helpful in finding local documents on seal hunting in the Baltic.
78. First submitted 26 March 1998. Accepted for publication after revision 21 October 1998.