Photo credit: Will Dickey,

This post is by Dr. Clay L. Montague.  Clay is an Associate Professor Emeritus at the University of Florida in the Department of Environmental Engineering Sciences.

How Harbor Deepening Impacts Migratory Fishes

Decisions about JAXPORT harbor deepening are being based on incomplete data that may affect you and your food supply. Harbor deepening could eliminate key habitat for seafood production near the freshwater ends of tidal creeks.

Duval County alone includes more than sixty tributaries of the St Johns River estuary, from tiny Mud Flats Creek at Spanish Point to large ones like Clapboard Creek, Trout River, Arlington River, Ortega River and Julington Creek. You may live near a creek that connects to the St Johns River estuary. Many if not all of these tributaries include sensitive habitat for coastal fishes.
Harbor deepening lets in more saltwater from the ocean. The salt travels upstream with the incoming tides, eventually squeezing the brackish and fresh habitat into a smaller space between salt marsh and upland, or overwhelming it altogether. 

Over the past 50 years, shad, herrings, striped bass, and eels have been in steep decline all along the Atlantic seaboard owing to a variety of assaults on their habitat. Most other commercially and recreationally important fish, shrimp, and crabs also depend on fresh or brackish habitat during some part of their lives. Fishery managers are now trying to restore habitat for all those special coastal species we use as food. Unmitigated impacts of harbor deepening will set back this effort. 

The modeling studies to assess the impact of JAXPORT deepening have not adequately evaluated loss of habitat in the vital upstream portions of the many tributaries. In particular, data available to compare with model predictions at the upper reach of Clapboard Creek apparently went unused. 

Also, model calibration was done only for a period of drought, incorrectly assuming a worst case scenario. In fact, salinity intrusion during a wet period would be the time when these fresher habitats are well used by fishes, and are therefore most sensitive to a salinity increase caused by harbor deepening. 

Furthermore, in a wetlands assessment for the project, upstream impacts of downstream activities seemed to be discounted, perhaps unwittingly, if the assessors hired were not familiar with tidal creeks. In estuaries, effects of downstream actions can easily reach upstream habitats on every incoming tide. 

Predictions about upstream impacts in tributaries are crucial to get right if we are to manage seafood production effectively, and compensate appropriately for any damage. Since both validation and calibration of the models seem wholly inadequate, conclusions that impacts are insignificant are unsupportable and probably wrong.

Some have quipped that since sea level is rising, more salt is entering anyway, so why bother? We would not apply that reasoning to our own passing, lest it become an excuse for murder. In the coming century, rising sea level may indeed drive a general retreat from the coast. Even if the only value of fish is for food, our imperative would naturally be to care dearly for the remaining habitat we have for as long as we can. With care, the next century of fish production will support many seafood dinners in spite of rising sea level. 

We need not retreat from the coast before necessary, but we can plan better. We can insist on impact predictions based on the best possible modeling efforts and data. With accurate predictions, we can decide together if the project is worth the damage.

Click here for more information about the proposed dredging of the St. Johns River.