Greater Scaup (Aythya marila)

SummaryFor Greater Scaup Aythya marila, classified as ‘Vulnerable’ on the European Red List of Birds, the south-western Baltic Sea is one of the most important wintering sites in Europe. In this area, a large concentration of gillnet fishery temporally overlaps periods of the most abundant occurrence of foraging diving birds. The aim of the article is to show how bycatch can impact the population of a diving duck. To assess this, we calculate the Potential Biological Removal (PBR) for the studied Greater Scaup population and we model the population change according to age-structured matrix models. Summing all the available recent figures on Greater Scaup bycatch in north-west Europe yields an estimated mean annual total of 3,991 individuals (2% of the flyway population). For a baseline stable population, an age-structured matrix model indicates that at this bycatch level the Greater Scaup population that winters in north-west Europe will decrease by 36% over the next 30 years, qualifying the status of the population as ‘Vulnerable’ according to IUCN criteria. As this population also experiences decline prior to bycatch, this decrease will be 57%, which qualifies the status as ‘Endangered’. PBR as an indicator of population vitality does not work in our case because the PBR-informed allowable bycatch values have a significantly negative impact on the population. Our results indicate unambiguously that fishery bycatch is among the most important threats responsible for the Greater Scaup’s decline. While recent data suggest that some improvement has taken place in the species’ status over the last 10 years, measures to protect Greater Scaup from bycatch are required. The solution should involve the prohibition of gillnet fishing in selected key sites and the use of mitigation techniques in other areas.

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Variation in structural size and wing stripe of Lesser and Greater scaup

Canadian Journal of Zoology ◽

10.1139/z88-300 ◽

1988 ◽

Vol 66 (9) ◽

pp. 2045-2048 ◽

Cited By ~ 2

Author(s):

Steven F. Wilson ◽

C. Davison Ankney

Keyword(s):

Principal Component Analysis ◽

Principal Component ◽

Structural Data ◽

Component Analysis ◽

Sexual Differences ◽

Aythya Affinis ◽

Structural Size ◽

Lesser Scaup ◽

Size Groups ◽

Aythya Marila

Heads, wings, and feet of Lesser Scaup (Aythya affinis) and Greater Scaup (Aythya marila) were obtained from 365 birds killed by hunters to investigate differences in structural size and in the intensity and extent of the white wing stripe. Twelve morphological measurements were taken on each bird and wing stripes were quantitatively scored using soil colour charts. Principal component analysis of the structural data separated the birds into two nonoverlapping size groups. We considered the group of large birds and the group of small birds to be Greater and Lesser scaup, respectively. Variation in the wing stripe character was extensive; 9% of the birds in our sample could not be correctly classified as Lesser or Greater scaup on the basis of wing stripe alone. However, most of the variation was due to sexual differences, i.e., female Greater Scaup with unusually dark wings and male Lesser Scaup with unusually white wings.

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