30
At the same time, many other changes have occurred:
dogfish are more widely distributed, young of year herring
are larger and pollock are more abundant. The larger size
of young herring may have a negative impact, due to
limits of the mouth size of juvenile Chinook and Coho
since many may be unable to switch to feeding on these
important prey.
CONDITIONS SINCE 2017
During 2017, physical oceanographic processes associated
with the marine heat wave reverted to more normal
conditions. The 2017 Strait of Georgia spring bloom
had close to average start timing, and phytoplankton
community composition in the Strait also showed a
return to a more normal distribution. However, although
surface temperatures in the Strait of Georgia from May
to September 2017 were below the observations for
2015-16, they were still above average for the previous
30 years. These continued higher temperatures may
have contributed to some ongoing impacts in the Strait.
For example, biomass of most zooplankton groups,
including jellies, remained above average; spring
spawning biomass of Pacific Herring showed near
historic high levels; and Northern Anchovy continued
to be abundant in the Strait of Georgia.
Since 2017, new heat waves have been observed again
in the North Pacific. Warming of both offshore and
coastal waters has led to changes in the food web and
coast wide decreases in Chinook Salmon as well as low
returns of Fraser River Sockeye Salmon.
SUMMARY
In summary, the story is complex. Warming waters in the
Strait of Georgia over the course of SSMSP are conditions
that are outside of our experience, and that likely have
created a mixture of positive and negative outcomes for
salmon. We did see some negative impacts on stocks that
entered the Pacific Ocean during the presence of the Blob,
with results such as a coast-wide decline of Sockeye Salmon
returns in 2017, and generally negative outcomes for BC's
central and south coast salmon. However, increasing Coho
residency led to many anglers in the Strait being able
to take advantage of the first Coho fishing opportunity
around the Strait of Georgia in some years.
Our challenge now is to try and understand the relative
consequences of these complex conditions. Having the
SSMSP studies occur during years when the early marine
period appeared to provide particularly good feeding and
rearing conditions for Coho and Chinook within the Strait,
but likely negative impacts outside of the Strait, is a key
consideration for our analyses and understanding.
Figure 7. Northern Anchovy displaying an unusual increase in the Strait of Georgia since 2015. Image provided by Ryan Miller.
Figure 8. Herring are a primary fish prey for Coho and Chinook:
but YOY herring are at or above the pretty length threshold for
most Chinook. Photo by Will Duguid, UVic.
