Massastranding van Alken Alca torda op de Nederlandse kust, Jan-Mrt 1990: Aantal, Leeftijd en oliebesmeuring
Sula , Volume 4 - Issue 4 p. 135- 138
In Jan-Mar 1990, an estimated 1345 Razorbills washed ashore on the Netherlands’ coast (table 1). Most casualties were reported on the mainland coast of Noord- and Zuid-Holland, while relatively few Razorbills were found on the Wadden Sea islands. Some 221 Razorbills were aged using bill-characteristics (0+0 juvenile, W+0 immature, W+ grooves ’adult’), and it was found that 32.6% were juveniles, 10.9% were immatures and 56.6% were adults. Compared to standings in 1983, another year with mass mortality on the Netherlands’ coast, the number of juveniles in 1990 was significantly larger (Gadj= 13.92, d.f. 1, p< 0.001), but immatures/adults still predominated. Of all Razorbills, 69.7% were oil contaminated. The proportion of oiled birds declined during Jan-Mar (89.4, 72.8, 49.3%; n= respectively 47, 636, 142) and of the juveniles a significantly smaller proportion was oiled (juveniles 50% oiled, n= 58; immatures/adults 74.6%, n= 130; Gadj= 10.69, d.f. 1, p< 0.01). The overall proportion of birds being oiled is below that in years with smaller numbers. Also in 1983, the proportion of oiled birds was comparatively low, indicating that these standings are wrecks rather than pure oil incidents. Mass mortality of Razorbills was also found in Scotland, on Orkney and Shetland in 1990. It is concluded that the mechanisms behind these wrecks should be studied in far more detail, now that the Scottisch populations are actually declining. The interactions with (industrial) fisheries deserve more attention, and not only during the breeding season.
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