Thoughts on the Treasure Sands Dredging

I have been asked by a number of people to comment on the Treasure Sands dredging project near Treasure Cay. The following thoughts are based on my observations and experience in similar systems.

Please note that my knowledge/expertise pertains to the ecology and biology of the existing dredged channel and the future dredging plans.  I understand that much of the controversy at the site revolves around the permitting process.  All development projects that will impact the environment should be properly permitted/approved and there should be a transparent, accessible, system for developers to obtain the necessary permits/approval.  I have no additional comment on the permitting process here. Likewise, I will not provide commentary on cultural/historical issues, flood risks, hazardous waste disposal, etc.  This post contains my opinions on the ecological implications of the dredging component of the project.

An important point to make up front is that dredging per se isn’t always a “bad” thing.  Dredging changes the environment – that is a fact.  But whether those changes are “good” or “bad” depends on many factors.  In some circumstances, a case can be made that the changes associated with dredging are quite damaging to the environment (think of the current Bimini disaster).  In other instances, dredging may lead to changes that would be regarded as either neutral or beneficial to the health of a system.  For example, when water flow has been reduced due to human activities (e.g., road construction across a wetland) or natural changes (e.g., shifting currents that lead to increased sedimentation), dredging may lead to improved tidal flushing, water quality and greater access for fishes and other animals.  In fact, creek restoration projects often include some mini-“dredging”, that is, a channel is re-created to increase tidal ebb and flow.

So, that being stated, let’s take a closer look at the Treasure Sands project, starting with the channel that has already been dredged. (The water level view is the first picture in the gallery; an aerial map is the 5th image.)  This channel is in a “dead-end” portion of the creek in relatively shallow water–less than 2 foot depth at low tide.  The substrate in this area is sandy/silted, with sparse amounts of macro-algae, turtle grass (Thalassia testudinum), and shoal grass (Halodule wrightii). (The 2nd photo in the gallery is representative of the substrate in this area.)  I would argue that this dredged channel is actually a slight improvement for some ecological aspects of the creek system.  I suggest this for two reasons.  First, the deeper channel helps to increase water flow, providing better flushing for this branch of the creek.  Second, it improves habitat quality for fishes and invertebrates, simply because of the greater depth and vertical relief provided by the sides of the channel.  In just a quick survey of the channel, I observed ~15 different fish species, including juveniles of reef fishes (e.g., parrotfish, snapper, butterfly fish).  In short, the dredging that has been conducted already has not damaged any critically important benthic habitat. The fill was disposed of properly. The channel provides additional habitat.

I am not clear on the extent of the additional dredging.  Delineating the specific boundaries may be critical for accurate assessment. If it is (roughly) along the yellow line in the map (not sure how far south) the proposed path goes through two distinct areas, each requiring a separate discussion.  The most ecologically important area of the creek is the roughly 75,000ft² area indicated with the green circle on the map.  This is a deeper area (>3ft at low tide) with a series of turtle grass banks and ledges (see 3rd photo in sequence).  The seagrass is so well-developed here that it can easily be seen in aerial imagery (see Bing Maps for instance).  Thousands of fish inhabit the mangrove fringe along the north shore.  In just a few minutes, a graduate student counted 11 turtles in this area.  If the intention is to create a channel for flats boats, dredging should not be required in this area.  If this area were dredged, there would be an ecological cost – primarily the loss of quality habitat provided by productive sea grass banks, as well as the ledges beneath these banks.  Such habitat loss would result in fewer fish, turtles and other animals utilizing the area.

(As a side note, there is evidence of illegal net and trap fishing occurring here.  Nets were strewn throughout the mangroves (see 4th photo) and I saw a 3ft nurse shark in an old trap.)

Once the creek broadens as it turns back to the south (see area just to the left of the green circle on the map), it becomes much shallower (<1ft at low tide in some places) and the substrate shifts back to sand with scattered seagrass and macro-algae.  This is lower quality habitat.  I have similar thoughts regarding this area as I do the channel that is already dredged.  A channel here may increase water flow and therefore slightly increase available habitat for fishes and invertebrates.  It would also likely increase movement of transient fishes (e.g., lemon sharks, barracuda) that feed in creeks on incoming tides.  Again, my concern is that I haven’t seen a specific plan for how far this dredging will extend to the south.

As with any dredging project, proper measures should be taken to control siltation. However, due to the relatively small scale of the project, the existence of shallow flats adjacent to the dredged channel, and the lack of any sensitive habitat (especially coral) nearby, siltation should not be a major problem here (unlike the Bimini project, for instance, a massive project immediately adjacent to sensitive habitat).

Finally, I have been asked about potential mitigation projects that could be conducted in conjunction with the Treasure Sands project.  There is an obvious possibility here – installing a small span bridge at the site indicated on the map.  Currently, a 0.65m² culvert allows water to flow under the road. This is much too small for the amount of water that could be flowing through this area.  Installing a span bridge would greatly increase water flow to a large mangrove wetland, improving habitat quality and providing access for fishes, turtles and other animals.  It would be a rather inexpensive project that would have significant ecological benefits.

I am happy to follow up on any points if you have further questions.

By | 2017-12-01T14:02:31-04:00 August 18th, 2014|Categories: development, economy, EIAs, Mangroves and Creeks, Uncategorized|0 Comments

About the Author:

Craig Layman
My lab’s interdisciplinary pursuits provide for a multi-faceted understanding of environmental change in the coastal realm. We are ecologists, asking questions that span population, community, ecosystem and evolutionary sub-disciplines. We often use a food web based perspective, exploring top-down (e.g., predation) and bottom-up (e.g., nutrient excretion) mechanisms by which animals affect ecosystem processes. All of our efforts are framed within a broader outreach framework, directly integrating science and education, using approaches such as this website.

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