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HOW?
The DFO has a monitoring program in the Strait of Georgia
for juvenile Pacific Herring and the nearshore pelagic fish
community. It also samples the zooplankton community,
as well as the physical water column properties
(e.g., temperature, salinity, oxygen). This yearly survey
(in September-October) uses a purse seine to sample
10 transects after dusk and at night when herring
are near the surface. The program has been carried
out during 1992-2019 (except 1995) (Figure 1).
SUMMARY OF RESULTS TO DATE
1. The age-0 herring index may be a leading indicator of
numbers of recruits joining the SOG herring population
2.5 years later and the amount of prey available
to predators in the Strait.
2. An index of the relative biomass of age-0 herring in the
SOG was lower and stable during 2013-2019 compared
to the peaks within the time series (1992-2017) (Figure 2).
This index peaked every 2-3 years with the peaks
occurring in even years during 2004-2012; however, this
pattern stopped after 2013. The reason for the alternat-
ing peaks is unknown.
3. Age-0 herring were heavier for a given length (i.e., in
better condition) in 2007-2019 compared to previous
years (Figure 3).
4. Abundance and condition of age-0 herring in the fall is
related to many factors including their prey, timing of
availability of prey, and other factors including herring
spawn biomass and water temperatures.
5. When ocean conditions are good for age-0 herring (i.e.,
higher abundance of herring), they also appear
to be good for juvenile salmon (all species).
6. Anchovy have been abundant, observed in stomach
contents of juvenile Chinook and successfully spawning
in the Strait since 2014. In addition to acting as competi-
tors or prey, abundant anchovy could potentially reduce
predation pressure by harbour seals on juvenile Chinook
and Coho. Abundance of anchovy appears related to
periods of elevated ocean temperature. Little is known
of the biomass of Sand Lance or Surf Smelts in the Strait,
though much information exists on habitat require-
ments and preferred spawning habitats.
Figure 2. Mean catch weight per-unit-effort (CPUE) of age-0 Pacific
Herring caught in DFO's Strait of Georgia juvenile herring survey
1992-2019 (no survey in 1995).
Figure 3. Mean age-0 Pacific Herring condition (length-weight
(LW) residuals) from DFO's Strait of Georgia juvenile herring survey,
1992-2019 (no survey in 1995).
Figure 1. DFO's Strait of Georgia juvenile herring core survey transects
(#1-11, there is no #7). Figure provided by Jennifer Boldt, DFO.
