Living Shorelines: Does breakwater design matter to fish?

Objectives

The project will develop and test a metric of the relative value of different breakwater structures and the shoreward habitats they protect for several economically and culturally important fisheries species, including red drum Sciaenops ocellatus, speckled trout Cynoscion nebulosus, southern flounder Paralichthys lethostigma, and sheepshead Archosargus probatocephalus. To achieve this, it will address the following objectives:

1. To quantify sportfish preference or avoidance of microhabitats associated with restored shorelines and the various wave attenuation structures that protect them.
2. To quantify sportfish residency around living shorelines protected by a variety of wave attenuation structures.
3. To develop a metric, using the above calculations, to evaluate the success of living shorelines in enhancing habitat for fisheries species, that can be applied to future shoreline restoration initiatives.

Methodology

The project will use a combination of fine- and broad-scale acoustic tracking of fish to quantify the proportion of time each species spends on 4 different living shoreline breakwater structures (established pyramids on Little Bay Peninsula; new pyramids at Point aux Pins, established oyster reefs at Point aux Pins, and rip rap at Lightning Point), the habitats they protect, and the broader seascape. It will capitalize on existing acoustic infrastructure at the site to provide in-depth assessment of the relative values of the different structures, to guide future project design. The team currently has a broad-scale array in Little Bay near Bayou la Batre (supported in part by Mississippi-Alabama Sea Grant Consortium (MASGC) funds), and is about to deploy a fine-scale array on the new Point aux Pins Pyramid Breakwater and Oyster Reef structures (from RESTORE Living Shorelines funds). Funds from this MASGC proposal will allow us to add two additional fine-scale acoustic arrays, one at the Little Bay Peninsula, and one at Lightning Point. The addition of these arrays will allow the team to directly compare use of four living shoreline breakwater structures by four of the most economically and culturally important fish species, red drum, speckled trout, flounder and sheepshead. These finds will allow us to tag and monitor a total of 40 fish during the study.

Rationale

Shoreline erosion is a significant problem for both coastal properties and the rich natural coastal ecosystems that occur in these areas. Traditional armored shorelines (bulkheads, seawalls) have a range of negative effects on fish habitat values and other natural processes. Over the last couple of decades, shoreline protection has shifted towards using “living shorelines” that attempt to mimic or promote natural structures and processes that protect shorelines as well as provide additional ecosystem services such as nutrient sequestration, water quality improvements, and the enhancement of habitats used by a diversity of species. Many living shoreline projects aim to protect or restore coastal habitats such as seagrasses and salt marshes, in part, because of their values for fisheries species. The breakwater structures that are part of most living shorelines can themselves be valuable fish habitat, offering shelter or foraging habitats for some species. However, there is a perceived trade-off between structures that maximize fishery benefits and those that maximize shoreline protection, and different structures will have different values as habitat for fishery species. Despite around $30 million being spent in Alabama over the past 15 years to restore coastal habitats, and with plans to spend another $30 million on shoreline restoration in the near future (TNC 2021), we still have limited understanding of how important fisheries species may benefit from these restoration projects. This proposed project addresses this critical knowledge gap by assessing the relative values of different breakwater structures for a suite of highly important coastal fisheries species. Findings from this research will help guide the design of future living shoreline projects that wish to maximize fish habitat enhancement as one of their outcomes.