The largest fish we never see

When we think of the largest fish in the fraser river, we think of great chinook salmon, which may reach lengths of 3 feet, and weigh 20 pounds.  There are yet fish even larger than this - the white sturgeon.

Occasionally, they die (of either natural or manmade causes) and float downstream and may get tangled up in the lower-flow of the intertidal fraser.

Last year, a four foot specimen washed up not far from where I live. Knowing that sturgeon sometimes have tags in their heads, I notified the Fraser River Sturgeon Conservation Society to see if they'd like to check it out.  Steve, a volunteer with the organization, came out the next day. The high tide left little room for us to access the fish, with thorny bramble on one side, and water on the other, but with some amount of bouldering, we were able to access the fish.  We were not only able to get some measurements (130cm long, 53 cm girth), but his handheld sensor located a PIT tag located in the head, that told us this fish had been caught before, near Maple Ridge in 2010.

Steve said that sturgeon are among the most studied fish in the world.  The Fraser river's proximity to major population centres, its historic fishing importance, it's large enough size for tracking individuals,  and a generally charismatic creature of the Fraser has made it a popular target of study.  For example, in 2020, nearly 4000 tagged sturgeon were captured, providing valuable data for conservation purposes.

For more information of the Fraser River sturgeon, including the tagging program, see here: https://www.frasersturgeon.com/wp-content/uploads/2021/10/Lower-Fraser-Sturgeon-M-and-A-2020-Report_20211024.pdf

skate

As we are in the midst of playoff hockey, this post will probably get more accidental clicks from those looking for hockey-related terms, than from those interested in an ID for a fish carcass.

Last week, while walking on a rocky beach near UBC, I saw this near the low tide mark.

Carcass of something (I put it on a rock for a better photo)

While most of this organism was gone, what remained was its backbone, and a tail. I recognized its thorny tail as belonging to a skate.

Skates are one of many creatures in our waters whose existence is unknown by the general public. They seldom get caught by fisherman on piers, they don't appear at the surface, and they live too deeply to get caught in tide pools.

Skates are in the same class of animals as sharks. They share features like a cartilaginous skeleton, and a rough skin of denticles. However, their flattened body makes them well-suited for staying camouflaged on the bottom, eating crustaceans and other benthic (ocean-bottom dwelling) creatures.

Complete, one might look like this:

Big skate (image from wikipedia)

Oh wait, you're thinking, that looks like a sting ray!  Indeed, they are similar to rays in many ways, but with some differentiations:

- skates have teeth; rays have plates more suited for crushing

- skates have stockier tails with thorny protrusions, and rays have more whip-like tails that may or may not have a stinger

- skates produce egg cases, while rays give birth to live young

There are a few common species of skates in our waters, but I can't find any closeups of tails that would help me narrow down the species of the one I saw.