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Hi there,
The following post appeared on NatureNB recently. I thought it
might interest those who have been watching the decline of terns on
Peter Island off Brier Island, across the Bay from Machias Seal.
Cheers,
Patricia L. Chalmers
Halifax
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Subject: The Machias Seal Island seabird colony
From: "Diamond, Tony" <diamond AT UNB.CA>
Date: Mon, 15 Jun 2009 14:45:13 -0300
Recently David Christie invited me indirectly to summarise the situation with
the tern colony on Machias Seal Island from the perspective of one
who has studied the
seabirds there every year since 1994. The summary below is a belated
response to that
invitation.
There seem to be many changes going on around Machias Seal Island that have
created a perfect storm for the tern colony there, which first
abandoned in 2006 and
has continued including this summer to begin nesting each year in
small numbers
but then abandon some time during June. Note that in CWS records
going back about
120 years there is only one previous record of abandonment, in 1944,
& the birds were
back the following year.
The recent changes include:
a) a bottom-up change in the foodweb, initiated by (as yet unclear)
oceanographic/climatic changes; this is suggested by the change in diet of the
seabirds, showing a steady reduction in the proportion of juvenile
herring ("brit") with
a sharp drop since 2001, in all the species monitored, and their
replacement by
lower-quality food (euphausiid shrimp, larval fish);
b) increased predation by gulls, clearly implicated in the initial abandonment
(in 2006), and increasing every year - this year and last, 20+ pairs
of Herring
gulls have nested just offshore on Gull Rock, compared with a handful
in previous years;
this is related to reduced gull-control efforts by CWS since 2000;
c) increased availability of food to those gulls (from bait discarded by
lobster- and crab-fishermen) perhaps subsidizing them to stay through
the summer; the
increase in this fishing in the Grey Zone referred to earlier by
David is part of this;
d) greening of the coastguard facility, leading to construction of solar
panels and a wind turbine; the wind turbine did NOT kill any terns, was not
operational in the year the terns first abandoned, and cannot be
fingered as a direct cause, but
is yet another construction on the island that may have had a
cumulative impact on the
birds decisions not to return;
e) Regarding fishing pressure, the last stock assessment I saw (from the Dept.
of Fisheries & Oceans) showed unprecedented fishing mortality and low stock
biomass but they maintain stoutly that herring are not being
overfished. They have however
reduced the purse-seine quota and established a quota on herring
weirs (previously
unregulated).
My research students and I continue to try to figure out this tangled web of
potential causes and their interactions, focusing now by default on
the puffins and
razorbills, whose continued presence must be put in doubt by the absence of the
protective umbrella of the tern colony and the subsequent increase in gull
predation on the island.
Tony Diamond
A.W. Diamond, Ph.D.
Research Professor, Wildlife Ecology
University of New Brunswick
P.O. Box 4400
Fredericton, NB
Canada E3B 5A3
Phone: (506)453-5006 (a.m.), -4926 (p.m.)
Fax: (506) 453-3583
http://www.unb.ca/web/acwern/index.html
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