I'm probably considered an "old timer" at this shrimping game. I've researched shrimp behavior by published marine researchers at the university levels, and, yes, even shrimp farm ponds. Coupled the behavior with weather phenomena in the ML and IRL systems and the overall topology (water depths ) of the system. Looked at past Haulover canal data to see how rainfall affects the canal water conductivity (an indicator of how salty the water is)
Taking all this data and forming a cohesive explanation of when to shrimp is difficult, but here goes:
The main driver for the lagoon system is weather.
A cold front is preceded by lower atmospheric pressure.
This pressure change is driven by a cold weather front heading more or less South.
The low pressure and cold front causes higher and colder than normal winds, mostly from Northerly directions.
The Northerly colder winds cool the shallow waters quickly. It’s not only the colder weather, but also the winds cause rapid evaporation of the water, which takes water heat energy out of the water and cause an even more rapid lowering of water temperature.
Carefully crafted University research on small shrimp and water temperature shows the smaller shrimp will migrate up or down depended on water temperature. Optimum favored temp is about 70 deg F. Salinity held constant. At near 30 parts per thousand. This is average Ocean salinity.
The rapid change in weather induced temperature causes shrimp to rise off the bottom to the top in deeper waters of the IRL and ML water system.
The higher and cooler winds and water evaporation leaves the dissolved salts behind. This raises the lagoon salinity in the system, particularly in the shallow areas. The Saltier conditions and rapid temperature swings couple with the age of the shrimp triggers the migration.
Shrimp, like bait fish school up for protection. At least. This is the observed behavior seen in farm ponds by a research diver with re breathing apparatus at night. The shrimp eventually covered him once the water settled after entry. An amazing bit of observation.
Haulover canal conductivity measurements, measurement of salinity, showed a rapid change of lowering salinity following a day to several days later.
All of the results above affect shrimp behavior.
University researchers have found that small shrimp can detect salinity changes in the vicinity of a 1% change, and they will migrate from higher to lower salinity in the winter months when salinity is highest.
Incoming tides bring lower salinity water into the ICW initially, mixing with the saltier lagoon water.
This triggers migration.
Shrimp swim with moving water. The big ones swim faster and are the larger shrimp early at the start of migration. The smaller shrimp are laggards and will reach the ocean later in the season.
Winter shrimp are nocturnal shrimp and swim at night. They avoid any bright lights if possible, for protection.
The old adage of 3 days before, and 3 days after the full moon, but not THE full moon are best times to go. This comes from better shrimp catches not because of moonlight per se, but from the stronger tide flow, sweeping more shrimp by your fixed position in the water. Moonshine is reflected sunlight with the moon/sun coverage between about 90 % to 100 % and back to 90% of the moon lighted by the sun. The 10% brighter reflected full moon sunlight is small and easily absorbed by the cloudy, typical water seen by us. The shrimp may run deeper and out of your sight, but they are there non the less. At least IMHO.
The rest is up to you. Don’t use bright lights close to the surface. You’ll drive the shrimp down deeper into the water or around the light, just out of reach.
That’s all there is to it, good luck. You have just learned what has taken me years to learn, and hours of research. But it’s a good starting point.
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