Saturday, July 26, 2008

Pond of Dreams re-revisited: the riffling water.

Review: the pond at the Garden City Park was scraped out from the overgrown backyards of old residential properties that had been rezoned for park land. The pond covers perhaps 3 acres and is only about 3m deep at its deepest. Its source of water is groundwater (the water table there is very high) and inflow from the city storm drainage system. The pond is only a few years old, yet already is ringed by emergent vegetation, including significant stands of cat-tail. Wildlife that use this mid-city instant wetland include Muskrat, Great Blue Heron, Pied-billed Grebe, Red-winged Blackbird (nesting), various ducks (year-round residents, winter residents and migrants), and notably this spring, Osprey. What the heck would an osprey, a piscivorous raptor famous for its foot-first dives into rivers, lakes and seas to snare gamefish with its talons, find to eat, even to hunt in this ersatz, muddy body of water? Someone told me that someone told him that the second someone had seen the bird catch a bullhead. What, a catfish? The brown bullhead, Ameiurus nebulosus, which is native to eastern North America?


The water riffles.

Today I visited the pond, intending to photograph whatever insect life might be found among the flowering fireweed at pond’s edge. That’s when I saw the riffling water. Not the entire pond, just a doormat-sized, kidney-shaped patch that was moving along slowly, paralleling the shore. I stepped closer, almost slipping off the grassy bank into the water, and could see faintly the tell-tale tentacles of the leading edge. It was a shoal of baby bullheads, a sight I hadn’t seen since I was a kid in Ontario. It was very difficult to make out (or photograph) because the overcast sky was layering a grey sheen atop the water's brown murk. It’s likely an adult catfish accompanied them, but was invisible. The babies are black, but the adults are, as the name says, brown, undetectable in a brown world beneath a grey sky, unless you are an osprey.

As with all the other zoological prizes that have shown up at or in this pond, the presence of bullheads doesn’t represent an outlier on a map of that species' distribution, but nonetheless is surprising, given the age and origin of this pond, this pond surrounded by roads and high-rises and schools and densified housing and everything else that’s part of a growing city. Although not a native species, the brown bullhead is well established in the Lower Fraser valley:

The brown catfish (Ameiurus nebulosus) is abundant in the lower Fraser Valley. This introduced species is common in sloughs and creeks that are closely associated with the main river; however, it is also found in the Serpentine and Little Campbell rivers and in several small lakes and ponds throughout the lower Fraser Valley (McPhail and Carveth, 1993).

It’s a tough fish, known for tolerating polluted waters with low levels of dissolved oxygen. It can survive exposure to air for prolonged periods if kept damp. Some fish! And now, in suburban Richmond. Welcome to the food chain.

Click to see the silhouettes of the youngsters at the leading edge.

Here, just to the left of the orange blur, if you click you can see the face of a baby bullhead about to break the surface. Hello!

And there they go back the other way.


McPhail J.D. and R. Carveth. 1993. Field Key to the Freshwater Fishes of British Columbia. Province of British Columbia.


Aunt Debbi/kurts mom said...

Great post.

kompoStella said...

hey there -
keep returning to your blog, i'm really enjoying your writing and your writing. wanted to ask whether you're ok with me linking to your blog?

Hugh said...

Thanks, Aunt Debbi.

Yes, certainly. Thank you!

Mother Nature said...

I like the pond concept. Glad you have it to enjoy.

Tim said...

You write so much about this park that I had to visit it tonight. I first saw the large brown bullheads emerge to suck down some crumbs intended for the ducks thrown into the pond. Later on, we saw the patch of ripples thinking they were tadpoles that have evolved schooling behaviour, but re-examination of my photos saw the telltale whiskers of the fishlings (they seemed to be smaller than the ones in your pic as it still is earlier in the year).