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WHAT WE HAVE LEARNED ABOUT HARBOUR SEALS
AND IMPACTS ON JUVENILE SALMON?
QUESTIONS ADDRESSED DATA CONCLUSIONS
How many Chinook and Coho smolts
are consumed in the Strait of Georgia
by harbour seals?
What is the impact of seals on
salmon production?
How can we mitigate the impact
of seals?
Seal scat collections from the
Strait of Georgia for 2012-2018.
PIT tagging of Big Qualicum
hatchery Coho for a seal feeding
study using head-mounted PIT tag
scanner "beanies".
GPS backpacks to look at seal
feeding strategies.
Seals may be taking more than 40%
of juvenile Coho and Chinook in the
Strait, but these estimates need to be
reassessed and updated given recent
studies showing significant year to
year variability in seal diet.
Harbour seals appear to target Coho,
Chinook and sockeye smolts in the
spring, while largely ignoring juvenile
chum and pink smolts—but primarily
take adult pink and chum in the fall.
Seal predation on smolts in estuaries
occurs primarily at dusk.
Only a small portion of the seal popu-
lation specialises in feeding on smolts
exiting rivers and entering salt water.
Figure 1. Harbour seal census counts (dark blue triangles) and
modelled data (dark blue line) by UBC, together with sport fishery
catches and effort.
Graph provided by Carl Walters.
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1970 1975 1980 1985 1990 1995 2000 2005 2010 2015 2020
HARBOUR
SEAL
ABUNDANCE
CATCH
AND
EFFORT
Year
GEORGIA STRAIT SPORT FISHERY TRENDS
E ort Chinook catch Coho catch Seal model Seal census
OBJECTIVES OF STUDY
The long-term goals of this research are to:
1. Estimate the numbers of Chinook and Coho smolts
consumed in the Strait of Georgia by harbour seals;
2. Evaluate their impact on salmon production; and
3. Propose ways to mitigate the impact of seals.
BACKGROUND
Since the 1970s, native stocks of Chinook and Coho Salmon
have declined throughout the Strait of Georgia (SOG),
despite sizable reductions in harvest from commercial
and recreational sources. Coinciding with the decline of
these species were rapid increases in populations of pinni-
peds native to the SOG, primarily harbour seals (Figure 1).
Adult salmon are a significant dietary component of seals
and sea lions in the SOG, particularly in estuaries where
adult salmon return to their natal steams. There is also
direct scientific evidence of seals preying on out-migrating
juvenile salmon during the spring. Such predation in
combination with habitat loss, fishery removals, declining
prey abundance and climate regime shifts may explain
declines in salmon abundance in the SOG. Some scientists
suggest that predation on salmon by marine mammals
may also be impeding recovery.
Photo
by
Ryan
Miller
