What do Spring Salmon Eat?

[Stizzla]

Very cool study. Interesting that hootchies are so effective southern sog at times when squid are not in the mix

From what I’ve read in books and learned from this forum, hoochies are a closer imitation to a wounded baitfish.
I was surprised to learn that!

 

[mbowers]

I should clarify.. this graph is actually for fish prey only..... but fish are overwhelmingly dominant in these regions. Here is fish v inverts
View attachment 43279

How do you control for different digestion rates of invertebrates versus fish? Does a 1cm shrimp remain identifiable in the gut as long as a 30cm hake?

Also is anyone actually monitoring that email address? I emailed willduguid@hotmail.com as listed on the Facebook page on June 19 2018 that I had a stomach and would like a tour. I never heard back and nothing was happening on the Facebook page so I assumed the program had terminated and I stopped saving stomachs.

 

[Bugs]

How do you control for different digestion rates of invertebrates versus fish? Does a 1cm shrimp remain identifiable in the gut as long as a 30cm hake?

Also is anyone actually monitoring that email address? I emailed willduguid@hotmail.com as listed on the Facebook page on June 19 2018 that I had a stomach and would like a tour. I never heard back and nothing was happening on the Facebook page so I assumed the program had terminated and I stopped saving stomachs.

No... definitely some items digest faster than others. That said, this is a common constraint of all diet analyses. In addition, we do group digested material as far as possible as either fish or invertebrate. We follow a set series of decision rules for assigning identification to partially digested prey.

My apologies for the email. I just searched my inbox and found my reply to you in my drafts, never sent. I will send you a protocol as requested

 

[Bugs]

I’ve had a few years now where the chinook I’ve caught in March and April in area 29 just off the north arm of the Fraser ( QA). That has had sicklebacks in their stomach. Seems to also be times around the same time the brown sludge that gets stick to your lines shows up.

View attachment 43282

Very cool.. We have seen stickleback in 5 adult Chinook stomachs... 4 of these were from area 28 or 29 between January and May. My primary research focus is actually juvenile Chinook. I have been amazed that in over 1500 late summer stomachs I have examined I have not seen a single stickleback (these are 15-25 cm Chinook) even though there are tonnes of shiny little young of the year stickleback (~2-3cm) around in late summer. I guess the spines really work

 

[mbowers]

No... definitely some items digest faster than others. That said, this is a common constraint of all diet analyses. In addition, we do group digested material as far as possible as either fish or invertebrate. We follow a set series of decision rules for assigning identification to partially digested prey.

My apologies for the email. I just searched my inbox and found my reply to you in my drafts, never sent. I will send you a protocol as requested

So if 90% by mass is fish and 10% is shrimp but shrimp digests 2x faster than fish isn't the actual diet more like 80% fish and 20% shrimp? Can that effect be included or is there no number on digestion rate? I just hate to see people who don't understand the limits of the process using the results incorrectly to justify political objectives.

Thanks for checking email and glad it sounds like I am probably the only one who got missed. I will resume stomach collection.

 

[Bugs]

So if 90% by mass is fish and 10% is shrimp but shrimp digests 2x faster than fish isn't the actual diet more like 80% fish and 20% shrimp? Can that effect be included or is there no number on digestion rate? I just hate to see people who don't understand the limits of the process using the results incorrectly to justify political objectives.

Thanks for checking email and glad it sounds like I am probably the only one who got missed. I will resume stomach collection.

This is a great point... and one reason why some diet researchers advocate the use of frequency of occurrence rather than weight proportions in diet studies. You will see in the document I sent you that we calculate and report both. I am fairly confident that we would not miss crustaceans entirely if they have been consumed. Their exoskeletons are pretty robust, and in fact we find them in the intestines after they have passed through the stomach (we analyze the intestines too which is why we ask people to submit the whole digestive tract). We also find tiny crustacean larvae in the stomachs routinely. We do record digestion scores for all prey items in order to be able to retroactively address points such as the one you have raised.

There will likely not be any hard numbers out there to apply to correct for digestion rates as these also vary by temperature and likely by prey species even within a grouping (e.g. Euphausiids have thin exoskeletons while benthic shrimps are comparatively very thick).

I should emphasize that at the beginning of the report we have distributed there is a disclaimer that the document is intended as a summary for program participants, not a formal analysis. The formal analysis will be published (and peer reviewed) in time. The goal of the annual reports is to provide some feedback to those who are contributing in a timely manner... but the results should be considered very preliminary.

 

[searun]

Just wanted to say that my hat is off to you guys. This research is excellent and will prove to be very helpful going forward in terms of addressing ways to improve Chinook abundance.

Also wanted to flag for folks that other prey species are extremely important to Chinook in the early life stages. Crab larvae for example make up a significant aspect of out-migrant smolt diet. So it will be important for us to fully understand the importance of various prey sources for Chinook if we wish to protect those and help improve Chinook recovery.

This is a topic that the Technical Working Group on SRKW Prey Availability will examine as a longer term recovery strategy.