The Seascapes

The Seascapes

Tuesday, December 13, 2011

The Butterfish Smackdown: “Coming Home to Roost”


Here is another blog post we got from John this afternoon...



Well not home actually but to Cape May, New Jersey for a few hours.  We are steaming in, at just above an idle, from Spencer Canyon where we fished yesterday afternoon.  Chris wants to reach the Cape May harbor entrance at first light. One engine is running too hot and we are meeting a mechanic at the dock.  Chris hopes the problem is with an engine fuel injector, a quick fix and turnaround.

Yesterday afternoon we started sampling our new plan on a cold spot on the  butterfish habitat model about 13 nautical miles west of the shelf break near the canyon.  The clouds in the satellite data didn’t give us a lot of pixels to work with, but they did give us enough. We also have the previous days’ predictions and the 2010 model hindcast movie.  All three show this area light up, the movie shows the dynamics, and the fishermen confirmed the pattern before we left the dock.  Our cold spot produced no butterfish.  I gave Chris the option of sampling his station before or after the station in the hot pixels from the model.   He decided to go next. 

We headed due east about 9 nautical miles toward the shelf break, but turned to run south along the 50 fathom line.  Chris looked back and forth from his hydroacoustics to the water, which was calm in the light breeze. The water began to get streaky, the kind of thing you see when you are sitting on the convergence between two water masses defined by temperature or salt and the current is flowing in slightly different directions causing the water to shear.  It’s the kind of thing Josh, as a physical oceanographer, understands much better than I do.  I wish he were onboard here too. 

Patches of telltale butterfish “dust” began to appear just above the bottom on the monitor of Chris’s 200 kHz acoustic machine.  “I don’t know what this will produce, but we’ll try here.”  It was show time for him in this smackdown and he looked a little nervous to me.  We spun around and set the net.  As we towed along the 50 fathom isobath we talked about his observations of the movements of fish and squid in relation to the continental shelf break, slope, and canyon walls and the movements of water masses along them over the course of the winter.  Our 20 minutes was up. It was time to haul back.  The bag was so heavy, Josh Wallace, one of three “supercrew” deckhands on the “Karen Elizabeth‚” had to wrap the “whip‚” the wire off the center crane, around the net bag before it reached deck level so it could be lifted aboard. Then Denny Stamand, supercrew number two, tripped the net into the 8 x 8 x 3 foot deck “box” which filled to the brim with a very clean catch of butterfish. They shined like silver dollars‚ 2035 pounds of silver dollars to be exact.  As Denny and Josh got the totes and baskets together to begin to sort the catch from the conveyor belt table, Mike Broniewski, supercrew three, secured the steel doors that fly like wings underwater and keep the net spread. “It’s a few,” Chris shrugged and then swung the boat around toward the south and the start of his next tow that is set by our sampling protocol to be 90 degrees to the first tow and thus “downslope.” 

As we steamed to the site he talked about really big “catastrophic” tows of butterfish down off Oregon Inlet during the fall - “how the fish settle down so tight and thick to the bottom in the late afternoon you can’t see them on the 200 kHz machines.” From his description it sounds exactly like those shape shifting flocks of tens of thousands of birds that curl like smoke in the autumn sky until one bird decides to roost and the rest follow all at once. In 10 minutes 20,000 lbs of butterfish can fill the nets so full the fishermen couldn’t get them on deck even if they wanted too.  It can take well over an hour to dump the nets and recover.  That can kill the squid fishing for the day.  Chris’s second haul produced an equally clean catch that included 2386 pounds of “silver dollars.” 

Now it was the model’s turn to define habitat, by using satellites on land and radars on the shore, bottom depth and a few other things.  We picked a random pixel in the hotzone 11 nautical miles to south and slightly to the east in 55 fathoms of water.  It was close enough to the shelf break that that our second cross isobaths haul took us down the bank.  Each haul produced 4 lbs.  This was pretty embarrassing and no contest in that “smackdown.”  But should it be embarrassing?  Both Chris’s and the model tows were pretty close together in space.  Our model is pointing us in the right direction, giving us a broad scale view of the dynamics of the environment from the fish perspective, given surface ocean features we can measure using radars on land and satellites in space, and a broad scale seasonal snapshot of butterfish abundance on the continental shelf measured from Hatteras to the Gulf of Maine by a single ship.  But within these broad scale dynamic features, there are finer scale dynamic gradients, the fish and fishermen are using as cues that are too fine for us characterize from space and a single coarse scale characterization of the continental shelf ecosystem.  Habitat is dynamic, defined by suites of particular environmental features and processes that vary at different scales of space and time and thus nest in time and space to define ocean habitats.

I felt pretty down after losing last night’s smackdown, until I realized the power of our new sampling approach.  Imagine if we had 2 or 5 other fishing boats working with us equipped with high tech sensors, focused on the area around and including each hot area defined by the model we made with the fisherman.  Let the best fisherman we can find define at least 1/3rd of the stations in each area.  We can then sample the balance of stations in a stratified random manner in both good and bad habitats, so that we can make contrasts and identify conditions fisherman and scientists might have both missed.  How exciting would that be - a high tech pirate navy for process based habitat research.

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