Knowing the dead zones key to keep catching streak alive
By Chris D. Dollar
Jul 08, 2017 at 6:22 PM
There are few absolutes in the world, but one thing sure is: Fish and crabs don't stay in the same spot all summer. Like many of you I've enjoyed an exceptional summer striper season to date, and the crabbing ain't too shabby, either. In fact, for a while there I was downright spoiled; catching a rockfish limit was almost automatic. It's slowed for me in the open water locations I target, though the low-light, skinny water bite is surprisingly pretty good.
I don't know for certain what changed in those places I'd been jigging. Maybe the rock were chased north by those marauding pods of dolphins? Or perhaps the hot weather kicked off the annual decrease in dissolved oxygen (DO)? Researchers know these areas, which typically occur during the height of summer in the Bay's deeper, main stem, that suffer from seasonal hypoxic (low oxygen), or worse anoxic (virtually no oxygen) conditions as dead zones. In the parlance of anglers and watermen, these swaths of oxygen-depleted water are called "bad water." When they form, life gets tough for fish, crabs and shellfish.
Like many things, Bay-related dead zones are influenced by both the weather and human activities. The size of a dead zone from year-to-year, say the experts who study them, depends on the amount of rainfall. The second factor is an overabundance of nutrients from fertilizers, and sometimes sewage and other sources. Heavy spring downpours and/or snow melt in the upper watershed flush excess nutrients down big rivers like the Susquehanna, and can overload the Bay's capacity to handle them. The result can be summer algal blooms.
After these photosynthetic creatures die they begin to break down, and as they do they suck up much of the dissolved oxygen from surrounding waters. Marine animals that swim vacate these areas. Sedentary animals like oysters and other shellfish aren't so lucky. Trapped, they sometimes suffocate.
Last year's rainfall was below average, and as a result DO concentrations in the Bay's mainstem and the tidal portions of its rivers were the best in thirty years. Water quality was awesome in many rivers I frequent, so exceptionally clear it was mesmerizing. This clear water allows underwater grasses to grow, the acreage of which in Maryland's part of the Chesapeake has been on an upward trend the past few years.
Last month scientists predicted we should expect a larger-than-average dead zone due to heavier than usual spring rains. John Page Williams has been tracking the Bay's dead zone since 2003, back when we were colleagues at the Chesapeake Bay Foundation. He keeps close tabs on his home river, the Severn, monitoring the water quality with a DO meter and other equipment. So I called him the other day to ask what he's been seeing.
"Definitely we have a dead zone, in a few spots DO as low as 0.5 mg/L," he said. Compare that number to minimum levels of 3-5 mg/L needed by most fish and crabs and you quickly see that's not good. He added that most of fish are hanging around 10-15 feet, trying to stay cool in the deeper water yet high enough in water columns to benefit from DO flows. Williams said structures such as the remnants of the Route 50 drawbridge and railroad bridge helps break up these stratified waters, and therefore are good places to cast a line.
Guide Capt. Richie Gaines also has come to understand how dead zones affect his fish catching. This year, he said dead zones aren't yet an issue, in fact he's "catching quality rockfish shallow." But like many fishermen, he has experienced years when there wasn't enough DO to hold rockfish on the structure they normally love, and that made the fishing tough.
Both Gaines and Williams say one of the big keys to catching fish during the height of summer, especially if a larger dead zone is present, is being able to read your fish finder properly. For example, Williams explained that the distinct lines on your sonar screen can indicate a sharp temperature change in the water column, usually called a thermocline. Severe changes in salinity, or a combination of both, can also produce those images. When baitfish and gamefish suspend on or just above them, using pinpoint accuracy to work a jig or bait through that strike zone can mean the difference between catching fish, or just yo-yoing your fishing pole.
And science — Yeah, science! — can assist you in catching fish, too. The Virginia Institute of Marine Science and its partners have developed a cool program called the Chesapeake Bay Hypoxia Forecast that accurately forecasts where and when low-oxygen or hypoxic conditions may occur. This could help you, intrepid angler, in planning your next summer fishing trip. And while apps and technology are useful stuff, they don't come close to the real deal, what really can make fishing and crabbing better: Cleaner water and more vibrant habitats.