BUILDING UP THE BOTTOM
Oyster Harvesting Is Both A Give And Take Process
story by LESLIE DAVIS, Louisiana Sea Grant
Rolling through the fishing village of Yscloskey during the heat of June, an unexpected sight breaks up the picturesque scene of a quiet seafood town. Huge piles of crushed rock lining the road. Armed claws of multiple backhoes silhouette the sky. Deafening sounds of rock falling to the wooden decks of oyster boats on the canal.
This is not a makeshift construction zone, but rather, the local oyster harvesters beginning the annual process of cultch planting that creates new life along Louisiana’s coast.
“Depositing clean, hard substrate - or cultch - onto water bottoms in suitable oyster habitat is often the most effective means of increasing oyster abundance at large scales,” said Carolina Bourque, biologist and oyster program manager for Louisiana Department of Wildlife and Fisheries (LDWF). “The objective is to provide a hard substrate for oyster larvae to attach and grow, with the ultimate goals of creating sustaining reefs and protecting adjacent shorelines.”
According to Bourque, cultch planting, utilizing oyster shell, limestone, or concrete, has been successfully conducted in Louisiana since 1917. In 100 years, LDWF has placed over 1.5 million cubic yards of cultch material on nearly 30,000 acres. Impressive as those numbers are, individual oyster harvesters are planting the bulk of cultch along Louisiana’s coast...giving back as much they take from this renewable natural resource.
Brad Robin, a multi-generational oyster harvester and dock owner in Yscloskey, says that his business alone places more than 50,000 tons of rock, about $500,000 worth, in one year. “We start in May and go to October, five days a week, 500 to 1,000 tons a day. We use one of my big boats, and another private boat and barge, to haul it.”
Robin estimates there are about 10 harvesters on the east side of the river planting cultch, with three or four rock and crushed concrete yards in his town alone.
Further west in Terrebonne Parish, Walter ‘Buddy’ Daisy can’t estimate the amount of cultch he’s planted over his 50-plus years in the industry. But, he knows the combination of oyster shells and limestone works in his area.
Daisy’s method is to start with oyster shells as the foundation, which he has in abundance from his own shucking plant. He usually lets them sit for a year to get brittle, so they break up easier upon dredging. He will add limestone on top as oysters start taking to the reef.
“Limestone works good. An oyster takes quicker on a darker object than on a lighter or white (object). It’s funny, but they do.”
He also believes that smaller cultch material produces more single oysters than a cluster. His favorite cultch material was clamshells, when he could get them, as they would make “a pretty round oyster.”
Robin’s family also used oyster shells as cultch in the beginning, which were on hand and plentiful, before Hurricane Katrina wiped out his shucking plant. He then turned to crushed concrete; reusing the millions of tons left after the storm. Finding the right material was, and still is, a work in progress. Currently he puts out calcium rock, ‘Mexican’ rock, limestone, and the preferred crushed concrete in a larger size than LDWF is using.
“We start with something larger for the spat to catch on. As it builds we have to pull it (cultch) out, rework it, until the reefs are productive; then we switch to a little smaller rock,” explains Robin. “We learn what works from going out and trying different things.”
The tenacity of private harvesters is keeping the oyster industry, and more importantly the reef habitat that supports commercial fisheries and shoreline protection, from the brink. Around the globe, oyster populations and oyster reef habitat have decreased significantly (Beck et al. 2011), putting the coastal ecosystem at risk. But, even with the global challenges, the Gulf of Mexico is ranked as one of the best remaining regions of the world for habitat and natural-harvest production.
According to Earl Melancon, an oyster biologist with Louisiana Sea Grant and a retired Professor-Emeritus with Nicholls State University, “The oyster provides an incredible array of ecosystem services, such as structure and habitat for recreational and commercial species and shoreline erosion reduction rates, while also supplying the largest natural oyster fishery harvest in the United States in one of the best remaining oyster regions of the world. This success is due in significant part to the private-public partnerships between the industry and Louisiana’s state resource managers, and their pro-active cultch planting operations.”
Robin points to the number of recreational anglers that fish over his reefs as one example of the importance of this habitat. “It’s (oysters) one of the biggest filtration systems that go unrecognized,” says Robin. “The recreational fishing industry depends on water quality; it makes for great sport fishing. If we don’t have that filter system, what kind of water quality will we have?”
Daisy says that the reefs are particularly effective against wave action - they combat erosion and keep the marsh from disappearing. “It helps when you get storm surge coming in; it helps break that down.”
Planting cultch is a never-ending process, as over time, the material degrades, gets buried, or is removed during oyster harvest. Success depends on finding the best location to deploy the material, and whether an adequate source of oyster larvae is present.
Location is key, says Melancon, because oysters are sensitive to fluctuations in water temperature, and salinity in particular, with salinity between 25-50 percent of ocean-strength for best survival. “The oyster is a sessile estuarine animal that only has a free-swimming larval stage for a couple of weeks, and after never moves again. Therefore, it becomes vulnerable to environmental changes within our estuaries, but also becomes a great environmental sentinel to let us know when those changes occur.”
To that point, Daisy recounts a story about fresh water in Lake Pelto (Terrebonne Parish) some years back. “The Corps of Engineers put some weirs in the Atchafalaya, which pushed more fresh water down the Intracoastal and canals. Within three years, it was blooming like crazy with beautiful, round, single oysters. Lake Pelto never had oysters for years, but put that (weirs) in and we had good salinity and oysters growing. The Corps took it out, and oysters started dying again.”
On the east side of the Mississippi River, Robin believes that the inundation of fresh water in 2010 to keep oil at bay continues to keep his reefs from full production. He agrees with his fellow fisherman that typically, after an influx of fresh water, you would see oyster abundance in the third year. However, many of his lease areas still have little to no production; the only thing that does work is new cultch.
“This town, since BP, put between 80 million and 100 million (dollars) of cultch down...that’s just the private sector. We want to get production back and fix the problem.
“Is it a science? I don’t know, but right when we think we have it in hand, Mother Nature changes course. But in order to survive, we’ve got to do it.”
As the oyster program manager, Bourque believes that the new cultch material, especially if oyster shell is used, can be an excellent substrate for larval oyster spat recruitment, settlement and harbors fewer oyster predators if placed in a suitable oyster environment. The availability of oyster shell is limited and costly, therefore alternative cultch materials are used, such as clamshell, concrete, limestone, among others. There is still a lot to learn about oyster reef restoration, and the need for coastal and oyster reef restoration is high. Lots of studies are being conducted and revisions being made to standard management practices; it is a constant learning process.
“Under ideal conditions, oyster spat that settle on cultch can survive and grow into seed oysters within one year. In Louisiana, oysters can grow to sack size by approximately two years of age. LDWF conducts biological monitoring in the public oyster grounds in each cultch area for at least two years post planting.”
There are 1.68 million acres of public oyster grounds in Louisiana, primarily in large areas east of the Mississippi River, but also scattered across the rest of the coast. Much of that acreage is in areas that have never been conducive to oyster production, and some of the areas have become less productive in recent years. Another 400,000 acres of Louisiana estuaries are in private oyster leases.
There has been a significant decline in the public oyster grounds production but the annual commercial harvest is variable with a recent annual harvest of 11 million pounds, which also reflects the historical long term average harvest in Louisiana. More of the harvest is from private lease grounds. Unfortunately, LDWF has no quantitative picture of what’s happening in terms of numbers of oysters present on private grounds, only the landings from those areas. From 2000 to 2005, harvest from private grounds averaged 7.8 million pounds, while from 2010 to 2016 it increased to 11.5 million pounds. Perhaps all the cultch and cultivation done on private leases might have contributed to the increase. Also, leaseholders may be increasing their use of seed sourced from areas other than public seed grounds to improve the production on their grounds. There has also been an increase in aquaculture (off-bottom oyster culture) since 2008.
Melancon states, “Each oysterman is not only an independent businessman, but also an independent manager of his resources. Oyster habitat, and estuaries in general, have their own way of organizing nature to meet the needs of that particular area of the coast. Therefore, what is considered best management practices for one oysterman may be different from another’s best practices. That, to me, is the beauty of the industry and the challenge for resource managers.”
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