WINDFARMS AND FISH STOCKS: WHAT WILL THE FUTURE HOLD?

 

The impact of windfarms on fish, other living marine resources, and on recreational and commercial fisheries has been the subject of an ongoing debate along the Atlantic coast.

Windfarm advocates argue that the pylons supporting the turbines, as well as the rock deposited around the bases of the pylons to prevent marine currents from scouring sand, mud and/or gravel away from such structures, will provide needed hard bottom habitat on an otherwise featureless bottom, providing new places for sessile marine organisms to inhabit, which will in turn attract structure oriented marine fish.  Comparisons to the supposed habitat created by oil rigs in the Gulf of Mexico have often been made.

Such advocates point to seemingly improved fishing taking place around small wind projects built off Virginia and Rhode Island to support their positions.

Not everyone agrees.  Windfarms have their detractors, as well as advocates.  

Fishermen’s experiences off Rhode Island suggest that the noise created during the construction of the structures can temporarily chase fish out of the area, although the fish return once construction activities cease.  Commercial fishermen have sued, so far unsuccessfully, to prevent the federal government from leasing areas of the ocean bottom for windfarm development, claiming that such development will cause them to lose access to traditional fishing areas.  And there have been many claims, unsupported by scientific data of any kind, that wind development has resulted in the deaths of a number of marine mammals.

So what are the potential positive and/or negative impacts of windfarm development on the ecosystems of the Atlantic coast?  While we will only know for certain after the development occurs and observations can be made, a recently published paper provides some structure for the inquiry.  Titled “Anticipating the winds of change:  A baseline assessment of the Northeastern US continental shelf surficial substrates,” it appeared in the July 24, 2024 edition of Fisheries Oceanography.

The purpose of the paper was to describe the current bottom habitats off the upper Atlantic coast (roughly, from the southern Gulf of Maine and Georges Bank south to the continental shelf off the Delmarva Peninsula), a necessary first step toward predicting how windfarm development, and the resulting hard, high-profile structure, might change the status quo.

Early in the paper, its authors address the seemingly analogous changes that offshore oil development brought to the Gulf of Mexico, noting that about 7,000 oil rigs have been constructed in the Gulf since 1942, about half of which are currently still standing.  With respect to those rigs, the paper notes,

“Within weeks of constructions, plants and invertebrates begin to attach to these platforms, and in the following months and years, a highly complex food chain was created with each platform seasonally serving as habitat for fish densities 20 to 50 times high [sic] than the surrounding open water.”

However, such platforms were not an unalloyed benefit, as

“Invasive species also colonize these platforms very successfully, providing a steppingstone for their spread.”

The authors, rather than accepting the common wisdom that the rigs were entirely beneficial for marine life in the Gulf, raise important questions, noting

“Rigs-to-Reef program encourages the reuse of obsolete offshore oil rigs as artificial reefs, benefitting recreational fishers in the Gulf of Mexico.  This suggests a significant change in the Gulf of Mexico ecosystem, but was it?  What were the components of the original Gulf of Mexico ecosystem and did their makeup change?  Was there a significant increase in hard substrate?  Did these platforms create new complex food chains, enhance existing food chains, or only serve to concentrate and spatially reallocate existing food chains?  Finally, and perhaps most importantly, did the installation of platforms cause a regime shift?  Did they abruptly and persistently change the structure and function of the original ecosystem creating new essential fish habitat resulting in ecosystem reorganization, as the implementation of the Rigs-to-Reef program strongly suggests?  [references omitted]”

We may never know, for

“With no baseline data collected in a scientifically rigorous design prior to 1942, these questions will remain unanswered.”

The paper's authors created a baseline survey of bottom habitats on the upper Atlantic coast, so that the impact of windfarm development might be better gauged.  The authors use over a quarter-million observations of the bottom composition throughout that region, with the intention

“to (1) provide insights regarding how the areas selected for wind energy development compare with other locations, (2) motivate the development of a priori expectations for ecosystem changes to inform monitoring and research efforts, and finally (3) to provide a base-line characterization of the Northeastern US continental shelf surficial substrates to support robust examination of the changes observed in areas impacted by these installations.”

As was already recognized, soft bottom dominates the continental shelf off the upper East Coast.  Sand (defined as particle sizes between 0.07 and 2 millimeters) is the most common substrate, covering 59 percent of the region’s bottom.  The smaller particles of mud/silt, most common in deeper waters, account for 34 percent of the bottom, while gravel, found primarily off river mouths, in the area of canyons and sea mounts, and along the northern edge of Georges Bank, makes up another 6 percent, while cobble and rock outcroppings are the least common bottom types, making up about 0.1 percent each.

Soft bottom is particularly prevalent in the mid-Atlantic region, where cobble and rock are less abundant than they are off New England.

In addition, the various bottom types are generally overlain with pieces of broken clam and scallop shells, which are present on well over 90 percent of the region’s continental shelf.

However, it should be noted that regions of bottom are not homogeneous; patches of different bottom types can appear adjacent to one another.  Thus, when the bottom is broken down into a grid of 250-meter squares sand, which makes up 59 percent of the bottom, appears in 94 percent of such squares, while mud appears in 72 percent of them; among harder substrates, gravel appears in 27 percent of the grid squares, while cobble and rock appear in 4 and 3 percent, respectively.

The historical prevalence of soft bottom, particularly in the mid-Atlantic region, raise the question of whether the added hard structure provided by the windfarms will be as beneficial as people believe.  As the authors of the paper note,

“Large tracks of open uniform sand with shell debris accumulated over centuries and the fish and invertebrate communities of the Mid-Atlantic continental shelf have evolved in this homogeneous habitat.  This area supports many fisheries including Atlantic sea scallop, summer flounder, scup, Atlantic mackerel, long and short finned squid, butterfish, blue fish [sic], surfclam and ocean quahog, Golden and Blueline tilefish, and monkfish with a combined biomass of about 800,000 metric tons (excluding sea scallops)…The richness of this resource contradicts the generally held assumption that soft sediment habitat has a low value from a biological standpoint and that increasing the biodiversity by introducing hard substrate is ecologically beneficial.  What the creation of a windfarm will do is change the ecosystem by adding hard substrate as well as intertidal and subtidal zones that support new and possibly invasive species, instead of the original continental shelf ecosystem.”

It is still too soon to know with any certainty whether the windfarms will cause beneficial or detrimental change to the ecosystem of the upper Atlantic coast continental shelf.  Arguments can be, and are being, made on both sides of the debate.  

By presenting a baseline description of the region’s bottom today, before extensive energy development has begun, the paper’s authors have provided a way to measure any changes, and perhaps to determine whether such changes are causing significant harm while there is still time to amend development plans and moderate the extent of any likely damage.