Side Scanning the Harbor

Crab Traps are shown in the red boxed area of the screen
Crab Traps are shown in the red boxed area of the screen

Charlotte County Sea Grant Extension
This article appeared in the June 2011 edition of Water LIFE magazine

Every so often cool things just happen. While I was in Hawaii in March I met a professor (Kirk) from Virginia Institute of Marine Science (VIMS). Kirk told me about work he was doing in Chesapeake Bay using side scan sonar to identify and remove blue crab traps from the water.

In Virginia, there has historically been both a trap fishery and a dredge fishery. The dredge fishery occurred during the winter months when blue crabs burrow in the mud. A few years ago the dredge fishery was closed. Because of the economic loss, Virginia applied for and received federal recovery funds to restore fisheries and habitats and also to enhance marine debris removal efforts. The marine debris project entailed the state of Virginia buying 70 side scan units and hiring 70 commercial fishermen (displaced by the dredge fishery closure) to be trained by VIMS researchers on the use of these units.

The commercial fishermen are paid by the day and are allowed to work up to 50 days during the closure. Their work entails navigating in assigned areas and marking the waypoints of every trap they see on the screen. Later they go back out and recover the traps using a weighted line with hooks (bent 12- penny nails to be exact), a method developed by the participating fishermen. They photograph each trap removed and fill out a data sheet that includes the trap waypoint, whether it was fishable or not, any by-catch and other pertinent information. At the end of each day, the fishermen save their track and waypoints to a memory card which is turned into VIMS. This data demonstrates that they did indeed do what they were assigned to do. The project now in its fourth year has turned out to be a huge success. The program has now removed over 28,000 traps from the Virginia waters of Chesapeake Bay.

The shape to the left of the thick black line is a school of fish
The shape to the left of the thick black line is a school of fish

So I told Kirk that in Florida we also have a blue crab fishery and that in the past I have worked with our commercial fishermen to conduct volunteer cleanups of trap gear. Here we have focused only on the traps we can see. I mentioned that unlike Chesapeake Bay, Charlotte Harbor (and the Peace River) is a very shallow system and asked if he thought the side scan would work here. To answer that question, Kirk said he would be happy to loan me one of his units. He also offered to send one of his researchers down to train me on its use if I thought that would be helpful.

I received the unit two weeks ago. Capt. Ralph Allen offered the use of his boat for field testing. Ralph told me he selfishly wanted to see if he could find out what one of his tour boats hit a couple weeks earlier causing considerable damage to the prop. I selfishly wanted a boat to put this cool hummingbird unit on, so this arrangement was a winwin.

Like two kids with a new toy we hooked it up and set sail. We navigated close to pilings, seawalls and sailboats to see what they looked like on the screen. We checked out the rocks outside of Fishermen’s Village then we headed out to explore. Our first encounter outside the marina was a pod of dolphins.

We circled them twice before their silhouette appeared on the screen. We went a short distance further and found what appears to be a small vessel near Gilchrest Park. This may have set some unrealistic expectations of finding sunken treasure of gold and rubies.

A sunken boat in the redboxed area of the screen
A sunken boat in the redboxed area of the screen

So far none of that though. We have however found what appear to be the remains of another small vessel in the Peace River, a bunch of crab traps, the debris piles that snag cast nets at Marker No.2, rubble piles from the old US41 Bridge, a school of bait fish, a tire and remnants of the docks at Liverpool. We found that the unit (a Hummingbird 1197c) worked in water as shallow as two feet.

Last week Kory, a VIMS researcher came down and showed us many of the unit’s features. We rewarded him with his first glimpse of a dolphin on the side scan…and of course a boat ride in sunny southwest Florida. Kory set me up with some software that will allow me to bring waypoints and tracks into Google Earth. I’m still a bit green on this, but it will be really cool when I figure it all out. Hopefully I will be able to use the waypoints collected to recover traps that may be navigation hazards during this year’s rotational closure for trap gear. Our area will be closed (to both commercial and recreational blue crab trap gear) from July 10-19th. In the interim, I’ll be out on the water looking for a gold medallion incrusted with ruby or maybe Fishin’ Frank Sr.’s lost anchor…regardless, it’s all good.

Betty Staugler is the Florida Sea Grant Agent for Charlotte County. She can be reached at 941.764.4346. Sea Grant is part of of the University of Florida IFAS Extension


Posted: June 28, 2011


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