by John Page Williams
Warm weather settles in now, and the rules change for us. The surface water is downright hot, in the mid-80s. Bluefish and Spanish mackerel may be happy, but rockfish aren't. These temperatures are nearly lethal and certainly stressful for them. Even worse, the high water temperatures drive dissolved oxygen out of solution in Bay water, making cooler deep water uninhabitable. Take a close look at your depthsounder screen, and you'll see most of the fish, bait and predators alike, hanging high in the water column.
An estuary like the Chesapeake tends to stratify like this. Fresh water is less dense than salt, warm water less dense than cool. River flow rides over sea water sliding into the Bay from the Atlantic. Add the kind of nitrogen pollution from which the Chesapeake suffers and summertime deep water is going to have worse low-oxygen problems. And of course this deprives fish, crabs and other underwater life of otherwise useful habitat. If this pollution-
driven situation makes you mad, welcome to the club. Take the energy from that anger and find a way to get involved in helping our Bay recover. But don't stop fishing in the summer. Consider the following.
Last summer, the Severn River stratified as usual, though the oxygen didn't crash quite as badly as it has in the past. I got to thinking about how Captain Bill Pike, the late Perch Professor of the Severn, used to run his skiff down to the underwater remains of the old B&A Railroad bridge and catch plenty of big white perch, even on hot summer days.
One day in July, I got curious and took an oxygen meter out there. In open water at the lower end of Round Bay, the sounder showed the river stratified, with the surface temperature at 83 degrees and the fish concentrated between 8 and 15 feet. The meter said the oxygen concentration at 15 feet was 2.7 milligrams per liter (mg/l), which is approaching lethal for rockfish and white perch; at 20 feet it was 1.7 mg/l, definitely lethal. For comparison, I ran down to the railroad bridge. Sure enough, at 20 feet the dissolved oxygen was 5.3 mg/l, enough to keep both rock and perch happy. No wonder Captain Pike fished straight through the summer.
If you read "Looking Sideways" the Nautical Know-How column in the May issue of CBM, you saw high-frequency images of the remains of railroad bridge. The old roadbed stands at 20-feet deep, about five feet above the surrounding river bottom. Look closely and you'll note that timbers from the bridge stick up farther. The Severn's tidal currents accelerate slightly here because the river narrows, and they flow up and over the roadbed, through the timbers. That rough bottom creates enough turbulence to break up the stratification and aerate the water, even at summer temperatures.
One other summertime factor helps break up stratification: thunder squalls. In July and August, wind and rain are the fishes' friends. A good storm followed by a day of northwest wind can turn over a small river like the Severn. Big water like the Bay's main stem, the lower Potomac, Tangier Sound and the Rappahannock will remain at least partially stratified, but even there a good storm will drive the oxygen deeper. A week of warm, stable weather will lock the stratification back in, but for a couple of days after a storm, you may find fish on deep lumps, reefs and wrecks that they can't reach in normal summer weather. Watch your sounder. The fish will tell you what the conditions are.
The experience with the bridge bed made me recall summertime stories I had heard from Upper Bay guides who specialize in light-tackle jigging, like Captains Sean Crawford, "Walleye Pete" Dahlberg, Richie Gaines and Gary Neitzey. This time of year they all search out rough-bottom lumps in 15 to 25 feet of water and work them carefully when there is current flowing over them.
Crawford, the newest of this group, has an interesting background. Now an environmental consultant, he has a Bachelor's degree in chemical engineering and a Master's in physical oceanography. "Isn't that an odd combination?" I asked him once. "No indeed," he replied. "Chemical engineers spend a lot of time studying mixing. It's a perfect foundation for studying how an estuary works." In fact, Sean gives seminars to fishing clubs that include a very interesting PowerPoint presentation showing the effects of the Bay's tides and currents on fishing. You can view it on his website (see The Tackle Box on page 4), but it's even better in person. You'll note that he includes several slides about the way estuary currents flow over lumps and bars, creating turbulence that mixes the water and traps baitfish. It'll come as no surprise that he keys his summertime trips around NOAA's current tables.
So what other kinds of bottom features create this kind of habitat-creating turbulence? Essentially any kind of elevated, rough bottom feature. Consider what may be the finest man-made fish habitat on the Bay, the Chesapeake Bay Bridge-Tunnel between the Virginia Capes. Current flow there is strong because the two capes restrict the Bay's mouth, while the pilings and rock-covered tubes of the bridge-tunnel deflect and mix those currents. But also consider all of the bridges that cross the Bay's main tidal stem and its tidal tributaries. They all attract fish--not only because of the added turbulence, but also because of their hard surfaces. This provides habitat for small creatures like barnacles, sponges, and even oysters, which create the base of a food web. Vertical pilings create all sorts of eddies. It's no accident that some successful anglers even go to the trouble of studying engineering drawings of them, and modern side-scanning fishfinders offer more clues. Even buoys and day markers on channel edges can create fish-attracting turbulence.
Reef restoration projects also provide turbulence, especially if they are built to rise significantly off the bottom and are covered with oysters. (The huge oyster reefs that the English colonists found in the 17th-century Chesapeake may well have helped keep the Bay mixed in those summers.) Large restoration projects in Virginia waters include Bluefish Rock Reef, off the Poquoson River, the Cell above Cape Charles, Va., and the Northern Neck Reef, between Smith Point and Tangier Bar. In Maryland, off the Choptank River and just inside it, you'll find Gooses Reef, and Cooks Point Reef, respectively. The latter includes concrete reef balls built by the Dorchester Chapter of the Maryland Saltwater Sportfishermen's Association and seeded with oysters by the Chesapeake Bay Foundation. Memorial Reef off the Patapsco River, is built of crushed concrete from old Memorial Stadium and seeded by multiple partners. Reefs like these and others are all valuable in the summer, though low dissolved oxygen can still be a problem at their deepest points. If you see fish suspended well off the bottom out in open water, note the depth at their lower edges and look for places at that depth on the reefs.
Regarding the Severn River railroad bridge remnants, I don't remember Captain Pike ever pinpointing any correlations between current conditions and fish behavior, but maybe that's because in his later years he didn't need to; as a widower, he had time to burn and was content to go down there and wait the fish out. Most of us don't have that luxury, so it's well worth trying to work out the relationships between current and fish behavior. As to boat position, it was--and remains--critical on the bridge, as it is on virtually every complex bottom structure. Bill always lined up visual "marks" (ranges) and double-anchored to fish precisely onto his spots.
So the lesson to be learned from all these experts: find the churn. That is, in the oxygen-challenged water of these hot months, be on the lookout for currents and bottom structure that helps mix the all important oxygen into the water. And, to borrow the last bit of advice from Sean Crawford's presentation: Fish whenever you can!