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Juvenile Chinook derby sees anglers become researchers

By Pacific Salmon Foundation, 🕔Mon, Apr 20th, 2015


  


A juvenile salmon is scanned for a PIT tag. Photocredit: Will Deguid

By: Brian Riddell, CEO/President, Pacific Salmon Foundation

Many anglers talk about the epic search for MONSTER Chinook. This summer the Pacific Salmon Foundation is flipping the script with a derby focused on baby Chinook, and we're inviting BC anglers to participate. "Why would I do that?," you may ask. For salmon conservation and science of course!

Many readers may be aware of the Pacific Salmon Foundation's major research program the Salish Sea Marine Survival Project developed in partnership with Long Live the Kings in Seattle, Washington. The goal of this project is to understand what is limiting production of salmon in local marine waters with Canadian efforts focused on the Strait of Georgia. One of the key questions is 'where and when does most of the mortality occur?' The prevailing idea is that mortality is highest early in the first year of life within marine waters such as the Strait of Georgia and Puget Sound. But to be honest, this remains a critical hypothesis that still needs to be tested and validated. That's why we're reaching out to BC anglers to help us definitively answer this question. If it's true, then it will help pinpoint what is causing the losses and help focus mitigation efforts so we can restore production and sustainable fisheries to the Strait. Thanks to University of Victoria PhD student Will Deguid, a new technique coined as 'micro-trolling' could provide an important new tool in understanding the production of Chinook salmon in the Strait of Georgia.

Tiny gear for tiny salmon

Why on earth would we need small boats to troll for salmon? We don't, but we do have an idea for using a much smaller version of the gear used by commercial and recreational fishers when trolling. Duguid wanted to capture juvenile Chinook salmon just months after entering the sea, to study their feeding along tidal fronts or mixing areas. Large net gears typically wouldn't capture the precise data needed for location and depth that Duguid required. But he was able to capture that information he using hook-and-line gear with light gear and small hooks (i.e., micro-trolling).

A simple idea to build on with your help!

Illustration of Juvenile Salmon with PIT tag

Now, add to Will's innovation, the use of PIT tags that can be injected into small salmon in the marine waters. These tags are uniquely coded for identification and are the smallest tags available

because they do not have a battery. These tags are read by passing over an antenna that charges the tag and instantly allows the code to be read by the antenna's receivers. Work by Duguid and the British Columbia Conservation Foundation during 2014 has proven that the handling, tagging, and release of small Chinook is possible. If the vast majority of juvenile Chinook are lost within the first couple of months after they enter coastal waters, then applying tags to different groups.

Graphs of Microtrolling salmon data
 

 

Figure 1 represents our belief that the mortality of juvenile salmon is very high immediately after entry into sea water and the rate of mortality decreases as the juveniles adjust to the marine environment. But in most tagging programs, we release a known number of tagged fish (day 0) and we recover the tagged fish that survived much later (usually mature adults, for simplicity, I have just used a 90 day period). In Figure 1, the only information we actually have is the number of fish at day 0 and the number estimated at day 90. We cannot really assess our belief because a straight line from Day 1 to Day 90 is the simplest explanation based on the observed information, and implies an equal rate of mortality per day. But, using micro-trolling and applying PIT tags, allows us to create new tagged groups of fish (say at 25 days and 50 days at sea, Figure2). Now we can use the estimated mortality rates for the different time periods (Day 0 to Day 90, Day 25 to Day 90, and Day 50 to Day 90) to better test our belief. If our belief is correct, then we can design statistical models to differentiate the rates between the different Chinook groups created. Such studies are critical to determine where critical periods of mortality occur in the early life of juvenile salmon at sea and to direct our mitigation efforts.

But this is where the Salish Sea Marine Survival Program and the Pacific Salmon Foundation need your help. To apply sufficient PIT tags to small Chinook requires capturing a large number of fish over a short period of time. Who better to collaborate with than BC's recreational fishers ... through a juvenile Chinook derby funded by the Pacific Salmon Foundation? So, watch for our ads and save the dates (mid-June to mid-July 2015), as we are going to try this!

I want especially to recognize and thank Will Duguid (UVic) and Kevin Pellet (BC Conservation Foundation) for their efforts and insights during 2014 to bring this opportunity forward. The Pacific Salmon Foundation will fund these derbies as part of the Salish Sea Marine Survival Project. (www.marinesurvivalproject.com).


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