In three days is the start of a new month, and the start of a major transitional phase in our fisheries. A change that is highly anticipated for freshwater and marsh anglers alike.
Each year, as summer progresses into July and August, very warm water forces most freshwater species to go deep, feed lethargically, and mostly at night. In the marsh, larger redfish and speckled trout have mostly abandoned the shallow interior ponds for open bays where cooler water prevails. They too can be lethargic and have very limited feeding periods.
It's all about dissolved oxygen. As the chart shows, warm water holds less of the gas than cool water. In deeper freshwater lakes, such as reservoirs and oxbows, the pool of cool water found below the thermocline - known as the hypolimnion - loses it's oxygen content as summer goes on. This pool is isolated because cooler water is denser than warm water. By late August, it's practically a dead zone.
As Plank's Law states, a hot body (lake) will radiate heat to a cooler body (air). In late August, the average surface temperature of the lakes here in central Louisiana are around 89 degrees - about the maximum they reach each year. For every hour that the heat index (temperature + humidity) is greater than 89 degrees, surface water heats. And conversely, every hour less than 89 degrees, it cools.
You'd think that with early September daytime highs still in the 90s, that no cooling is taking place. Such is not the case. Since June 21st - the summer solstice - the days have been getting shorter and nights longer. And even though we won't reach the equinox until late next month, the cooling hours are already starting to exceed the heating hours because the warm mass (lake) has a greater thermal budget than the surrounding air.
As water temperatures begin to decline throughout the month, and oxygen levels rise, fish become far more active. Here in central Louisiana, we see a big increase in redear sunfish moving to the shallows, and bass feeding on schools of shad, most notably on Toledo Bend. After two consecutive nights of below 60 degrees, the crappie move into the shallows and along structure and submerged grass.
And then just as things are getting good, we hit a big pause late in September or early October. This happens when we get a major front where the lows drop below 60 degrees for a few nights - and we get strong northerly breezes to accelerate the cooling. Turnover takes place - very low (or no) oxygen in the hypolimnion mixes with now denser surface water. Across the entire water column there's a temporary drop in dissolved oxygen. The result is a period of a few days to a week of poor fishing. After recovery begins can be the best fishing outside of early Spring - until the water gets cold (and by cold, I mean below 60 degrees).
The Coast
Cooler water triggers migration of larger redfish and trout to interior waters. This begins in September, but this month we're faced with the problem of very high tides - the effect of summer-long glacial and ice cap melt in the Northern Hemisphere. I recall numerous times having to park my vehicle in flooded launches in Port Sulphur, Bayou Bienvenu, and Montegut. These high tides give plenty more spots for redfish, drum, and sheepshead to roam and hide.
September is prime time for bull reds in the passes and around the islands, and for pelagic species like jacks and mackeral. Cobia is still outstanding. Sand trout are everywhere, and on average, two or three inches bigger than they were in June. This is also the best month for a shot at inside tarpon.
Sadly, there's still a ton of catfish, ladyfish and other annoying species to deal with. They'll be around for several more weeks. And if you're older or have a lower immune system, the Vibrio bacteria still exists in high numbers and will continue as so until the water temperature dips below 75 degrees. So if you fish the salt, be sure to bring anti-bacterial spray or lotion.
