BARNDOOR SKATE...
Sketch done by Jim
Bourdon, Copyright Jim Bourdon © 1996 & 97
Taken from Science, July 31 1998 (Jill M. Casey and Ransom A. Myers) :
Are extinctions of marine vertebrates as rare and unlikely as current data
indicate? Longterm research surveys on the continental shelf between the Grand
Banks of Newfoundland and Southern New England reveal that one of the largest
skates in the northwest Atlantic, the barndoor skate (Raja laevis), is
close to extinction. Forty-five years ago, research surveys on St. Pierre Bank
(off southern Newfoundland) recorded barndoor skates in 10% of their tows; in
the last 20 years none has been caught and this pattern of decline is similar
throughout the range of the species.
Above is a map of the Northwest Atlantic Fisheries Organization
Subdivisions in which populations were assessed in this analysis. The 300
meter isobath (dotted line) is given for reference. 3NO = southern Grand Bank,
3Ps = St. Pierre Bank, 4Vn = Sydney Bight, 4Vs = Banquereau Bank, 4W = Sable
Island Bank, 4X = Browns Bank, 5Y = Gulf of Maine, 5Ze = Georges Bank,
5Zw = Southern New England.
Above are estimates of absolute biomass for barndoor skate (Raja
laevis) from the southern Grand Bank (the northern limit of the range) to
southern New England (close to the southern limit of the range). Open circles
are zero catches. An exponential decay curve was fit to
the data using non-linear least squares. The
estimated rate of population decline was lowest in the
northern and highest in southern regions. If only data since 1960 are
considered, the population decline on St. Pierre Bank, Sydney Bight and
Banquereau Bank is similar to that in southernmost regions (that is, Gulf of
Maine, Georges Bank, and southern New England).
