Above, DFO graphs of seal numbers in the
Scotia-Fundy region. The rest of the 300,000 grey seals live in the Gulf
of St. Lawrence. The zig-zag pattern reflects seasonal migration.
Recent signs of groundfish recovery?
Below is DFO's latest published research data (2) on
Scotian Shelf fish stocks, updated to summer 2009. "4VW" refers to the
Eastern Scotian Shelf, where grey seals are currently concentrated, and a
major seal cull demanded by the fishing industry.
"4VWX" refers to the entire Scotian Shelf and Bay of Fundy, while "4X
West" means just the Bay of Fundy. Click on graphs below to enlarge.
In July, 2009, 4VW cod biomass shot up to a
level not seen for 20 years, following a major slump. Grey seals eat cod.
A massive increase in redfish was found in 2008, and again in 2009. Grey
seals eat redfish.
Haddock increased to a level not seen since the 1970's. Grey seals do not
seem to eat haddock, but haddock will share the benefit from any
seal-induced productivity increase.
Witch flounder increased to a level not seen since the 1970's. Grey seals
eat flatfish.
It is unclear if grey seals eat turbot,
or halibut.
Grey seals eat a few lobsters.
Herring abundance is not accurately determined with a bottom trawl survey,
which is designed to sample groundfish. In fact, the success of the
commercial herring fishery has tended to vary inversely with the number of
herring in the bottom trawl. The recent relative lack of herring in the
bottom trawl as shown in this graph coincided with a tenfold increase in
the commercial catch of herring on the offshore Scotian Shelf in 2009.
Grey seals mainly eat herring and other similar, small "pelagic" schooling
fish.
The pink dots show the Eastern Scotian Shelf (4VW) total fish biomass (as
determined by DFO's bottom trawl survey), which has recently risen to a
level higher than it was in 1970, and a level unmatched at any time since
the late 1980s. An increase in overall productivity caused by a high
density of seals would be reasonably expected to raise the total biomass
index.
.
A high
density of grey seals on the Eastern Scotian Shelf now seems to be kick-starting a
cod recovery. Seals concentrate nitrogen in the surface water, raising overall
productivity and triggering faster growth of fish food.(1) Nothing else explains the recent
resurgence of cod and other groundfish in the area.*
Regardless, Canada's Department of Fisheries and Oceans and federal Fisheries
Minister Gail Shea are preparing to authorize a large, misguided grey seal cull
on Sable Island, Nova Scotia, which risks causing substantial harm to cod and
other wildlife. No public consultation on this decision is planned.
Between 1970 and 2010,
grey seal numbers in Eastern Canada grew tenfold, expanding from 30,000 to
300,000. Recently, the seal herd seems to have leveled out at "carrying
capacity". Two thirds of Canada's grey seals live on the Eastern Scotian Shelf and congregate near Sable Island.
2. How many
fish are there?
Cod on the Eastern Scotian Shelf long supported a large commercial fishery
before declining dramatically ("collapsing"), leading to a fishery closure in 1993. No sign of
cod "rebuilding" was seen until very recently, after seal numbers in the area
rebounded. See the series of graphs at right.
3. How could cod rebuild their numbers while interacting with
peak seal numbers?
Seals have never been shown to "harm" fish populations, including fish they eat
directly. A growing body of scientific information supports instead that
seals actually benefit fish populations. Compelling
relevant observations have recently been published in PLoS ONE by Joe Roman and James J.
McCarthy, (1) who conclude that "marine mammals provide an
important ecosystem service by sustaining productivity in regions where they
occur in high densities", and who warn that "An unintended effect of bounty
programs and culls could be...decreased overall productivity."
4. Will Canada cull the grey seal herd?
The fishing industry's urgent demand for a massive cull of Atlantic Canadian
grey seals to "mitigate" their "impact on fish" has led to
DFO's closed review of the (presumed only to be negative) "impact of seal
predation on fish populations" to generate "science advice" to support culling over 200,000 grey seals to "aid cod recovery".
The Canadian Broadcasting Corporation covered this story in May, 2010, (3) ten
months after DFO found (but did not publicize in the media) a dramatic increase in groundfish
(2) in the area where the
seals are living. DFO's "science advice" to support the "science based" cull is
expected before Christmas, just in time for this winter's grey seal pupping
season on Sable Island.
5. Who can prevent a misguided seal cull?
The Honourable Gail Shea
House of Commons
Minister of Fisheries and Oceans
Parliament Buildings, Wellington Street
Ottawa, Ontario
Canada K1A 0A6
