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[swimmingwiththefishes]

Taken from https://www.psf.ca/sites/default/files/FINAL%20-%20Email%20version%20PSF_Salish_Sea_Project_2016_Report_.pdf

40% is a huge number...

Key Findings 2016

• An outbreak of Heart and Skeletal Muscle
Inflammation (or HSMI) was found in fish from one
Atlantic salmon fish farm. This was the first time
HSMI was diagnosed in British Columbia.
• Results from juvenile salmon predation studies
included:
• initial estimates that Harbour seals in the Strait
of Georgia are consuming up to 40 per cent of
juvenile Chinook and 47 per cent of juvenile
Coho;
• in Cowichan Bay and the Big Qualicum River
estuary, Harbour seals are:
• showing different feeding strategies in the
estuary compared to further afield; and;
• consuming different kinds of salmon during
the year, with more juvenile Chum eaten in
the fall and more juvenile Chinook and Coho
in the spring.
• Tracking of “tagged” Cowichan hatchery
Chinook showed that their survival in-river may
be significantly impacted by predators such
as other fish, mergansers, otters, and even
raccoons.
• The survival of Cowichan hatchery fry increased
when they were released at locations further
downstream from the hatchery, which could inform
future hatchery release strategies.
• Our Citizen Science oceanography project allowed
nine vessels to be out on the Salish Sea for 22
days, with all of the Strait of Georgia sampled each
day. They undertook 1,369 sampling events, which
resulted in more than 8,000 samples for analysis.

[Dave]

I wonder what the percentage breakdown between hatchery and wild chinook juveniles are in that 40% estimate ...

[Jk47]

The seals don't care if they're wild or hatchery fish, just sayin...

[swimmingwiththefishes]

Found some more info here.

http://marinesurvivalproject.com/resources/

Lot's to see here too. I think there might be a study on steelhead to look into on the hatchery/wild question.  The abstract of Thomas's(2016) work (in the link above) is telling...

Knowing the species and life stages of prey that predators consume is important for understanding the impacts that predation may have on prey populations, but traditional methods for determining diets often cannot provide sufficient detail. We combined data from two methods of scat analysis (DNA metabarcoding and morphological prey ID) to quantify the species and life stages of salmon (Oncorhynchus spp.) consumed by harbour seals (Phoca vitulina) in the Strait of Georgia, Canada, where juvenile Chinook (Oncorhynchus tshawytscha) and coho (Oncorhynchus kisutch) salmon survival is poor. Harbour seals primarily consumed adult salmon of lesser conservation concern in the fall (August–November): chum (Oncorhynchus keta: 18.4%), pink (Oncorhynchus gorbuscha: 12.6%), sockeye (Oncorhynchus nerka: 7.4%), Chinook (7.1%), and coho (1.8%). However, the opposite species trend occurred during the spring when seals preferred juvenile salmon of greater conservation concern (April–July): coho (2.9%), Chinook (2.9%), sockeye (2.5%), pink (1.4%), and chum (0.8%) — percentages that can equate to many individuals consumed. Our data suggest that harbour seals select juveniles of salmon species that out-migrate at ages >1 year and provide evidence of a potential causal relationship between harbour seal predation and juvenile salmon survival trends.

[Dave]

The seals don't care if they're wild or hatchery fish, just sayin...

True enough but there is plenty of data to suggest seals key in on the huge dumps of coho and chinook hatchery smolts every spring.  They, like gulls, mergansers and herons, have learned, almost to the day, when and where these fish will be in abundance.

[wildmanyeah]

I wonder what the percentage breakdown between hatchery and wild chinook juveniles are in that 40% estimate ...

I suspect pretty high percentage of hatchery. I went to two different release events for Chinook and mergansers were feasting at both. Extrapolate that all the way down the creeks and rivers as I am sure they just follow the schools down, Then add in seals...

The data may also be skewed as it looks like they tracked "tagged" fish? so wouldn't that mean hatchery only?

[Dave]

The fish are indeed tagged but not necessarily of hatchery origin.  There is some controversy using these fish as a model because the trauma involved in the tagging process most likely has a degree of swimming and behavioral issues attached.  But this science is the best we have right now. These tags are getting smaller all the time so many more opportunities for this kind of research will be coming down the pipe.

[RalphH]

Harbour seals appear to focus on juvenile Chinook
and Coho, and even a low level of predation can
be significant when the seal population is large.
Our project provides evidence of a relationship
between seal predation and the survival of Coho
and Chinook salmon. Modeling studies have
suggested that an average of 55 per cent of Coho
smolts and 44 per cent of Chinook smolts were
eaten by seals during their first year at sea each
year between 1999 and 2007. However, low levels
of predation by seals in the estuaries suggest
that targeted seal removals would be unlikely to
significantly improve salmon survival

Best I know most of this work was focused on hatchery rivers such as the Big Q and the Puntledge. The seals know where the feed is. itis also bad news for any wild stocks because as noted the seals don't care. They also note that loss of cover such as eel grass and bull kelp may contribute to high predation levels

[Tylsie]

It strikes me as odd. Chinook spend almost their entire first year either in fresh water or in the estuary, and this study claims that almost 50% of them are eaten as smolts in their first year, but the seals do not target them in the estuary. I am curious then, where do they target them? Up the river? right at the edge of the estuary? I seldom see large colonies of seals away from river mouths, do others? I am somewhat familiar with the local rivers, and can say with certainty that there are 4 distinct seal colonies with in the estuaries of the 3 rivers south of the Fraser (one of the colonies splits 2 of them), the Capilano has a couple within a few km of the estuary (would probably be closer if it wasn't for human activity) and I won't even do into the Fraser as their is too many to count. 

I am not saying that the wholesale slaughter of seals is what is needed, but nature is clearly out of balance.

 

[RalphH]

I certainly have seen large groups of seals away from river estuaries. Seals are also mobile as are sea lions. They will go to where feed is plentiful.

My other comment is that this report doesn't mention, that the biggest predator on salmon and steelhead is us. We a also have damaged and continue to damage the habitats they depend on. Seals may eat them but they don't damage the habitat. In fact humans have, unintentionally modified those habitats in ways that make it easier for seals to feed on those salmon smolts.

[swimmingwiththefishes]

When I come across the odd area from Richmond to Maple Ridge on the Fraser that looks more like the estuary looked back in the day (sand, shallow flood land, all the different water/shore grass for cover, etc etc, It seems obvious that habitat destruction is one of the main if not the main problem for the Salmon. Now 99% of the lower Fraser is big steep grade dyke rocks dumped along the entire length of the river. No more hiding spots from all these predators! It's open game on those tasty baby salmon.

I often think about how most of the population wouldn't even notice anything odd about the rocky dyke shore line but it's supposed to all be flooded grass as far as the eyes can see down the shores!

50% is pretty big number.  It is so high that one could make a logical prediction that the massive increase in seal population, which has lead to the present predation rate, is a significant reason for the decline in especially coho and chinook. 
I think it is fair to speculate that if the seal population decreased to levels in the 70s (whether we should/can do this is another question) salmon predation rates would likely decrease and salmon survival would in turn increase.

Let's not ignore this science and instead recognize the profound impact of exponential increases of seal populations on the coast and how these have effected salmon and get on with it. There should be a serious debate about the longstanding ban on seal harvesting enacted when the populations where very depressed many years ago.

Again 50% is a huge number and of course habitat and climate change are huge factors as well, but this is too, and we shouldn't shy away from the discussion about it because it's uncomfortable. This science is giving us pretty big clues as to what is happening and we should honor this and do something with it.

[RalphH]

What this report doesn't mention and what we don't have it was the historic consumption pattern? Perhaps seals have been taking such a large bite out of the smolt population since the salmon have been here.

Also when the seals were hunted and culled down to about 1/4 of their current # was there a corresponding jump in salmon returns? I don't think so.

It's important to consider the % was based on a few localities and not the entire straight or all the river esturaries. The 40-50% are based on extrapolating the estimated (and it was based on collected seal scat samples) consumption across the entire inside waters.

There is good reason to be cautious with these estimates.

[IronNoggin]

With about 40,000 of the seals in the Straits of Georgia, the impact on juveniles is huge. Harbor seals consume about 2 kilograms of fish per day (4.4 pounds) and if those are all juvenile salmon, the total impact for coho salmon alone amounts to 5.7 million in one month (assumes the average hatchery coho smolt weighs 20 grams (0.044 pounds) and a seal diet is 4.8 percent coho smolts). This may be “driving regional survival patterns of Chinook and coho salmon,” the study concludes.

https://www.cbbulletin.com/439218.aspx

When Congress passed the Marine Mammal Protection Act in 1972, making it illegal to kill or harass marine mammals, the California sea lion population hovered around 10,000... Today they number an estimated 300,000, stretching from Mexico to Southeast Alaska.

If they are not removed, salmon won't recover. "This is not just a loss for my tribe," he said, "but everyone in the Northwest."

Oregon, Washington and tribes again take aim at sea lions in dispute over salmon:

http://www.oregonlive.com/environment/index.ssf/2017/07/oregon_washington_and_tribes_a.html

Cheers,
Nog

[wildmanyeah]

If there numbers are in abundance why are we not allow to harvest? seems to me they must still be below the historic avg.

If only our first nations still wanted to harvest them... I knew one old FN man in campbell river that harvest them about 20 years ago and that's it.

[RalphH]

if...assume...may...

doesn't sound like strong conclusions.

also from https://www.cbbulletin.com/439218.aspx

Our fish management strategies often involve intensive supplementation of salmon resources that result in abundant, energy-rich juvenile salmon that strongly resemble the ideal harbor seal prey (forage fishes like herring and sardine). So, we should not find it surprising when seals and other marine mammals take advantage of those resources.”


Although the study doesn’t address potential management actions, Thomas said that predator removal is likely just “a temporary solution, if a solution at all.”


“While it is tempting to conclude that a simple removal of the predators will result in increased survival of these salmon populations, that neglects the possibility that the ultimate cause of mortality could be something other than the predator, i.e. the ‘dead fish swimming hypothesis,’” Thomas said. “The thought is, even if you removed one predator from the equation, those fish would either be gobbled up by another predator or die of other causes because they simply weren’t fit to survive.”

here is a link to Dr Austen Thomas current research: http://mmru.ubc.ca/personnel/austen-thomas/

he authored one of the papers on seal predation on juvenile chinook and coho