Cross Harbour is a tidal creek and wetland system located on the southwestern tip of Abaco Island, Bahamas, near the Abaco National Park. Wetland area associated with the system covers ~500 hectares, much of which is littered by sparse dwarf red mangroves. The entire wetland is flooded by one main tidal creek channel that is located toward the southern end of system. In the creek mouth area, the channel is deep (up to ~15ft) with fast flowing water on incoming and outgoing tides. There is a diverse suite flora and fauna that can be found throughout the mouth area. Seagrasses, sponges, macroalgaes, and some corals are all common. More than 50 fish species have been observed, ranging from juveniles of reef fishes (angelfish, parrotfishes) to large marine transient species such as lemon sharks and spotted eagle rays. It is a perfect location for a snorkeling or kayak trip.

Historically, there was a major channel that extended ~2 miles north of the mouth flooding the majority of the wetland area. In the early part of the 20th century, a road was built across this creek (~1 mile from the mouth of system) to allow access to the beach and Cross Harbour. Through time, the road eroded away and water began to filter through to the upstream wetland. However, in the 1970's, the road was re-built thus blocking almost all the natural tidal flow.

This fragmentation has drastically altered the physico-chemical environment and thus the suite of organisms that inhabit the wetland (see Layman et al. article).

A unique aspect of the Adopt a Fish, Adopt a School project is that it is set within the context of a large-scale restoration project of the tidal creek that was completed in April 2006. In this project, spear-headed by Friends of the Environment and supported by various other Bahamian organizations (Bahamas National Trust, Bahamas Reef Environmental Education Foundation, Wetland Care Bahamas, Bahamas Ministry of Works), tidal flow was restored to the ~140 hectares of wetland area that were blocked by the road. The restoration project was conducted in two phases.

First, culverts were installed under the road to allow tidal waters to again flood and ebb upstream of the road.

Second, in conjunction with many local schools and community members, mangroves that had encroached into the historic tidal channel were removed. Mangroves are critical components of coastal tropical and sub-tropical ecosystems, and their removal is an unwanted activity in almost all situations. However, this project was a focused effort to re-create a channel for water to flow freely, and only removed <0.1% of all the mangroves in the system.

This project was developed as a "hand-on" educational experience that was highlighted in many local schools, and almost 200 students had a hand in the creek restoration itself. It was a true "win-win" situation: an extremely valuable project was completed for the environment of Abaco (at relatively low cost), and it served as an excellent partnership-building and educational tool for Bahamians. This project has been featured in many regional publications, including an article in Continental Airlines Air Currents magazine.

Use of ultrasonic transmitters implanted in fish, in conjunction with arrays of automated, submerged acoustic receivers, has increased the capacity to continuously monitor activity patterns and movement dynamics of marine organisms, particularly fish. This technology permits remote monitoring of fish in the natural environment, and alleviates the need to continuously track each tagged individual. In this project, we are using a series of acoustic telemetry receivers and transmitters produced by Vemco.

Transmitters, or "tags", use a series of pings to form unique "ID codes" followed by a period of silence. The period of silence can be multiple minutes long, thus providing time for other transmitters to be detected with minimum overlap or "code collision". This type of coding scheme is designed for automated monitoring experiments where low cost single channel receivers can be distributed throughout a study area to detect the time and date of passage of each tagged animal. The transmitters are potted in cylindrical shapes of six standard diameters, with electronics and battery sealed in epoxy to survive underwater at high pressure. Each transmitter is implanted in individual fish via a live fish surgery (see below). Three sizes of tags are used, small (diameter = 7mm), medium (9mm), and large (13mm). The larger tags have longer battery lives and detection ranges, but can only be used in larger fishes. Small tags will last for ~240 days, medium for ~580 days, and large ~800 days). The "ping" rate, or the rate at which the transmitter sends out its signal, is set at ~2 minute intervals.

The Vemco VR2 receivers are utilized in this study to detect the transmitter signals. These receivers are submersible, single channel devices, capable of identifying the Vemco coded transmitters. Receivers are mounted to cinder blocks or re-bar for stability, and placed directly into the water. At the study site, there is currently an array of 16 receivers deployed (see map). The array is designed so that both small-scale movements (e.g., above the road depending on tidal phase), and movements from the creek to the marine environment can be detected. Two receivers are located on patch reefs in the ocean to detect those fishes which ultimately move to coral reef habitats. The battery life of receivers is approximately 15 months, and batteries can be replaced relatively easily at the study sites each year. Every time a fish with an implanted transmitter passes a receiver, the unique code of that transmitter (i.e. the fish) is recorded by the receiver. The detection range of the receivers depends on the depth and water conditions. In shallow water (e.g. upstream of road at Cross Harbour), the detection range may reach 75ft. In deeper water (Cross Harbour mouth) detection ranges may reach hundreds of feet.

The data are downloaded from each receiver at the study sites. The receiver is removed from the water and brought to the shoreline. A special interface is used to attach to the receiver to a field computer, and data is loaded directly onto the computer. In this project, data will be downloaded from receivers every 2-3 months and immediately uploaded to this site.

Fish are collected by either hook-and-line or fish traps. The are immediately placed in coolers filled with clean, cool water. All surgical tools and the radio transmitter are first soaked in an iodine solution, then rinsed in deionized water, before the surgery begins. The surgery takes place in a water cooler with the fish turned upside down and just below the water surface. This calms the fish and prevents the need to use anesthetics.

With a curved scalpel a small lengthwise incision is made just to the ventral side of the dorsal region of the fish (its stomach). The incision is roughly the same length as the diameter of the radio transmitter and is located halfway between the pectoral and dorsal fins. The transmitter is inserted into the incised area, with much care taken to keep the transmitter aligned parallel to the body of the fish and pushing it toward the pectoral fins. Using a C-curved needle with attached suture, one stitch is made across the incision. The suture passed through the incision and simple surgeons knot is tied to close the incision. The fish is released in the cooler, and allowed to recover for ~15 minutes. If the fish seems to be swimming normally, it is then carefully released at its capture location. (The Surgery page has more detailed photos of implanting a transmitter.)

Data will be uploaded to this website every 2-3 months, and can accessed for individual fishes (see fish maps). There is also a map that shows the most recent place all fishes were observed, and identifies which fishes have moved out of the creek and/or to coral reef habitats. These data are then used to examine a series of critical questions regarding fish movements and their utilization of various back reef habitat types. Two particular questions form the core of this study:

1. Do fishes move into the newly restored areas upstream of the road?
2. Do fishes that utilize this upstream area eventually move from the mangrove creek system to coral reefs in the nearshore marine environment?

Through the Adopt a Fish, Adopt a School program, anyone can become involved with generating or analyzing the data collected. As for the former, you can adopt your fish today. In doing so, you will have your own fish that you can track through time on this website, e.g. to see if the fish eventually moves out of the creek to the reefs. Second, you can become involved in with analyzing the data. Careful study of the fish movement maps may reveal particular aspects of movements, and please contact Craig Layman with any patterns you see that develop. If you are interested in more extensive collaborations and/or analyzing the data in more detail, the complete database can be obtained by contacting Craig Layman.