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Again in 2000, coordinated
counts of common seals in the entire Wadden Sea were carried
out. During simultaneous aerial surveys, the following results
were obtained. The maximum total number of counted seals amounted
to about 17,000, of which 2,140 were counted in Denmark, 6,300
in Schleswig-Holstein, 5,230 in Lower Saxony and 3,330 in the
Netherlands. The total maximum number of pups counted was 3,610.
The percentage of pups per total number is similar to the average
of 20% found in preceding years. The increase in the total number
compared to last year's is about 13%, but the increase is not
the same in all areas. Particularly in Denmark, the increase
seems to have leveled off in 1999 and 2000. It has to be mentioned
that adverse weather conditions through extended periods hampered
surveys in some areas. Particularly, the maximum figure for Schleswig-Holstein
is less complete than in other areas and therefore the total
maximum number in that area had to be extrapolated. The surveys
next year may show whether this was a good expert's estimate.
The observed increase between
1998 and 1999 was 6%. This has been lower than the average 13%
found in the years since the virus-epidemic in 1988. This low
increase prompted questions about the possibility whether this
was the start of a change in the population trend observed so
far, or just a one-off event. |
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Lower pup production and/or
higher pup mortality were discussed as possible factors explaining
the lower increase. At the time, it was not possible to conclude
about a possible change in trend.
Under the assumption that
the estimated number for Schleswig-Holstein is a roughly correct
estimate, the survey results lead to the conclusion that the
increase this year has been similar to the average annual increase
of 12-13% found from 1989 onwards. However, the numbers observed
this year are lower than predicted if the increase from 1989
onwards had continued. Although at present the question of what
could have caused the lower increase last year remains unsolved,
it is clear that the strong population growth of the last decennium
has continued, but at a slightly lower rate than before. Surveys
in the coming years will elucidate in which direction the seal
population develops.
Trilateral Seal Expert
Group
DK: Svend Tougaard, Fiskeri-og Søfartsmuseet, Esbjerg,
SH: Ursula Siebert, Kai Abt FTZ Büsum der Univ. Kiel
Nds: Ekkehard Vareschi, Universität Oldenburg,
NL: Peter H. Reijnders, Sophie Brasseur IBN-DLO Inst. for Forestry
and Nature Research |
