BALANCING ACT

The Unique Oyster Fishery in Calcasieu Lake Requires Careful Management

story by Steve Beck, LDWF Oyster Program Manager 

and George Melancon, LDWF Marine Fisheries Manager

 When it comes to commercial oyster production, Louisiana is unrivaled. The Bayou State produces about a third of the nation’s annual take of the delicious bivalve with about 1.7 million sacks, more than any other state.

The reason is simple. The large size of the Mississippi River drainage basin delivers a tremendous amount of freshwater to the Gulf of Mexico, creating a vast delta where fresh and salt water mix throughout a network of coastal marshes and bays. These estuaries create excellent oyster habitat.

Louisiana oyster reefs also provide important services to the coastal ecosystem such as filtering water, creating habitat for other aquatic species and stabilizing shorelines.

While Louisiana’s deltaic coast is a rare oyster paradise, the southwest region of Louisiana contains an oyster fishery unique within the state that is located entirely within a single body of water, Calcasieu Lake.

It’s an area that produces quality oysters and accounts for 3 percent of Louisiana’s total annual oyster landings on average. But it also requires the Louisiana Department of Wildlife and Fisheries (LDWF) to manage the resource carefully because of various factors that can adversely affect the population.

Although concerns about declining oyster stocks in Calcasieu Lake have been expressed by LDWF biologists, the local oyster industry relies heavily on this natural resource for its economic stability. Recognizing the importance of oyster harvest to the local communities, the Louisiana Wildlife and Fisheries Commission determined that the oyster season should be opened on Nov. 1, 2016, with a seven-sack daily limit.

The commission did, however, instruct the department to monitor the harvest closely and gave the LDWF Secretary authority to close the season if biological and/or enforcement concerns occurred.

So what makes Calcasieu Lake and its oyster population so special and what are the challenges faced? It’s best to go back to the beginning.

A HISTORY OF CALCASIEU LAKE OYSTERS

The primary habitat type in southwestern Louisiana is referred to as the Chenier Plain, which formed from fine sediments transported westward from the Mississippi River and were deposited in flats with small parallel ridges, or cheniers, over thousands of years. The Calcasieu River is located in this area and is hydrologically separate from the Mississippi River. This separation occasionally results in local drought or flood conditions that can be quite different from what the rest of the state experiences, creating a unique prairie-like landscape interspersed with wetlands.

As the Calcasieu River flows south past Lake Charles, it widens into Calcasieu Lake, an isolated coastal lake with an oyster history defined by changes in hydrologic patterns. Calcasieu Lake is 52,700 acres with an average depth of six feet. Cheniers on the southern side of this area contributed to the creation of the lake and historically forced water to flow through a narrow sinuous connection into the Gulf of Mexico known as Calcasieu Pass.

There is evidence that prior to 1900, Calcasieu Lake was likely too fresh for oysters to survive in abundant numbers. The first published reference of oysters in Calcasieu Lake was in 1898 when H.F. Moore discussed sparse and “insignificant” oyster beds found at Calcasieu Pass.

In 1904 while working at the Gulf Biologic Station in Cameron, O.C. Glaser of the Louisiana Department of Conservation, the precursor to the Louisiana Wildlife and Fisheries Commission, surveyed oyster reefs in the pass and found oysters on the stone jetties that extended a mile into the Gulf of Mexico. In the 1920s, several private oyster leases were issued by the Department of Conservation and were located at the “mouth of the Calcasieu River.”  Oyster reefs in Calcasieu Pass were also depicted as hazards on nautical charts published in 1935.

The U.S. Army Corps of Engineers first dredged Calcasieu Pass in 1871 to improve navigation to the Port of Lake Charles.  These dredging efforts continued and created a shipping channel through Calcasieu Pass and northward along the western side of the lake to accommodate increased shipping activity.

The Calcasieu Ship Channel was enlarged during the 1950s, again in the 1960s, and since 1968 has been maintained to be 400 feet wide and 40 feet deep. Periodic dredging is required to maintain the channel at this size and dredge spoil is deposited on either side, forming continuous islands by the early 1970s.

These modifications to Calcasieu Pass and formation of the channel substantially altered the hydrology of the area. Calcasieu Lake now has a larger connection to the Gulf of Mexico that has resulted in increased salinity throughout the lake and surrounding wetlands. The continuous dredge spoil islands have affected flow patterns as well. The southwestern lobe of the lake, West Cove, became more separated from the rest of the lake, Big Lake, or the East Side.

The elevated salinities in Calcasieu Lake shifted the oyster habitat zone northward into the lake and likely increased oyster reef acreage. Landings of oysters increased from 4,780 sacks in 1946 to 37,734 sacks in 1963, with no oyster landings reported from 1948-1960.

The first water quality investigation regarding bacterial contamination of oysters was conducted in 1955 by the LWFC, precursor to the Louisiana Department of Wildlife and Fisheries, and the state health department.  A large oyster transplant, 25,500 sacks, was conducted in 1964 to avoid ship channel dredging operations. Oysters were still negatively impacted as the population substantially declined after 1964.

While no biological investigations were conducted, LWFC biologists Charles White and William “Corky” Perrett hypothesized the continuous dredge spoil islands, or levees, created by ship channel dredge material disrupted water circulation, preventing oysters from receiving adequate amounts of food and dissolved oxygen.

In the spring of 1969, the LWFC planted cultch in several areas in an attempt to increase oyster production, which is one of the most effective methods of oyster restoration. Cultch planting occurs when clean, hard material, including oyster shell, clam shell, gravel or crushed concrete, is placed onto water bottoms in oyster habitat zones to mimic natural reef habitat.

Oyster larvae drift with water currents and cultch material to provide a place for larvae to settle and grow. Freshly settled oyster larvae are referred to as spat and oyster larvae typically settle in large numbers. This event is called a spat-set or spat-fall. The 1969 cultch plants in the southern part of the lake were not successful, likely due to poor circulation.

No commercial oyster landings were reported from Calcasieu Lake from 1966-1974. In the early 1970s, erosion created several breaks in the ship channel levees, or washouts. These washouts improved circulation in the lake and oysters recovered. Former LDWF biologist Ron Dugas estimated that 85 percent of the population in the lake was located in these washout areas. The LWFC formed an agreement with the Army Corps to discontinue placement of dredge spoil in these areas, thus maintaining circulation and water quality.

While water quality and the salinity regime throughout Calcasieu Lake was now more suitable for oyster growth after construction of the ship channel, oysters still need hard substrate to settle and grow. The extensive reefs in the southern portion of the lake likely formed through the expansion of historic reefs that existed in the pass before the ship channel was constructed.

Most of the lake bottom is soft mud or clay, but small reef areas formed throughout the lake such as those north of Rabbit Island, near Lambert’s Bayou and Commissary Point, with the aid of a cultch plant, and as far north as Turner’s Bay.  There are also several areas where the oyster resource is more scattered shell as opposed to solid reef.

While higher salinity throughout Calcasieu Lake increased oyster production throughout the latter half of the 20th century, there is evidence that salinities are continuing to rise. In particular, salinities in late summer are much higher on average today than 15 years ago.

While oysters can thrive in the higher salinity portions of estuaries, so do more oyster predators and diseases. The historically productive reefs surrounding the ship channel on the southern end of the lake now contain few oysters. It is believed that a predatory snail known as the oyster drill is playing a role in reducing oyster abundance on reefs surrounding the ship channel.

In 1989, a levee system was built around Calcasieu Lake to maintain freshwater habitats and prevent marsh loss beyond the lake rim, which could also be influencing conditions within the lake. In another effort to decrease salinities throughout Calcasieu Lake, a ship channel isolation project is being designed by the Louisiana Coastal Protection and Restoration Authority.

Management Activities Conducted by LDWF

The primary role of the oyster program at LDWF is to assess and monitor oyster stocks in the public oyster areas of Louisiana and make biological recommendations for management actions that will maintain or improve oyster production.

In Calcasieu Lake, oyster stock assessment sampling has been completed each year in July since 1992, utilizing divers to determine the average oyster density, measured in number of oysters per square meter, on reef areas.

Through the years, sample stations are occasionally added or moved as conditions change or more information becomes available in an effort to best characterize oyster populations. LDWF field biologists observe where the fleet of oyster luggers and skiffs harvest during the season to help confirm that sample stations represent all reef conditions.

Average oyster density is then expanded by reef acreage to estimate the total size of the oyster stock. Reef acreage was originally determined by extensive poling surveys where the lake was repeatedly crossed and bottom types, mud and reef, were determined by tapping with a pole.

LDWF now uses reef maps created using side-scan sonar which provides complete surveys of the water bottom. In addition, dredge samples have been collected monthly since 1992 and this information is used to monitor oyster reproduction and mortality.

LDWF monitors oyster reproduction by the number of spat found in dredges and when spat-sets occur. Mortality events occur naturally and contribute to reef formation since oyster shells provide excellent settlement surfaces for larval oysters. Recent spat-sets and large mortality events are often reasons the oyster season is delayed or closed. After reviewing all available data, the appropriate management action is determined.

In Calcasieu Lake, management actions include regulating oyster harvest by setting oyster seasons and daily harvest limits. West Cove and the East Side can be managed independently and season length is often heavily influenced by the Louisiana Department of Health and Hospitals closures based on the height of the Calcasieu River. High river levels can increase oyster reef exposure to contaminants.

In other areas of the state, harvest of small seed oysters for transport to private leases is allowed, as are larger dredges, which results in larger vessel sizes and requires additional consideration with regards to seasons.

There are no private leases in southwestern Louisiana and only market-size oysters are typically harvested from Calcasieu Lake. The oyster season is typically opened in the lake on Nov. 1 and since 1990, average total oyster harvest per season is just more than 41,000 sacks.

In an attempt to self-regulate, oyster harvesters were able to pass legislation in 2011 restricting the number of vessels allowed to harvest in the lake. However that restriction was removed in 2012.

Oyster harvest in Calcasieu Lake was historically limited to using oyster tongs or collecting oysters by hand, typically from small skiffs less than 25 feet in length.  It is not clear when this regulation was first implemented, and all harvest between the 1960s and 2004 was limited to tonging or hand collection.

In the 1990s there was much debate on whether small dredges or scrapers should be allowed. Advocates stated dredges would spread reefs, promote growth of oysters into more marketable shape and improve oyster production by exposing shell covered in sediment.

Oysters found on natural reefs compete for space and as a result tend to grow long and narrow, where oysters found on harvested reefs tend to be more round, the preferred shape for serving raw on the half-shell.  However, harvest using dredges needs to be carefully regulated. Dredging effectively removes large numbers of oysters and may spread reefs too thin, possibly making reefs more susceptible to sinking or burial in soft sediment.

Dredging may increase oyster production by exposing buried shell but could possibly degrade reefs if harvest disturbance exceeds rates of oyster reproduction and growth.

In 2004, legislation was passed to allow small hand dredges to harvest oysters in Calcasieu Lake, and in 2006, this legislation was expanded to allow mechanical dredge retrieval. LDWF cannot regulate gear-types as that is reserved for legislative authority.

Since at least the 1980s, the northern portion of Calcasieu Lake has been closed to oyster harvest by LDHH due to water quality concerns.  The size of this closed area has shifted over time and was most recently reduced in 2009.

Aside from regulating harvest, other oyster management actions include restoration activities such as cultch planting and transplanting oysters and releasing hatchery raised oyster larvae and spat. Since 1963, nine cultch plants have been established in an attempt to increase oyster abundance. Three of these plants were constructed in 2015 at a total cost of almost $900,000.

Each cultch plant in Calcasieu Lake is typically 20 acres in size, ranging from four to 59 acres and several have been funded to offset oyster impacts from dredging operations or oil and gas activities.

LDWF is currently planning on constructing a large cultch plant at least 100 acres in size within the next two years if adequate funding can be obtained. Two artificial reefs have also been constructed by the Coastal Conservation Association to enhance recreational angling opportunities. It is likely these reefs have been colonized by oysters.

Oyster transplants have occurred in 1964, ‘72, ‘80, ‘81 and ‘86 often to move oyster resources from the closed areas in the north to the southern harvestable areas, where after six months oysters can be harvested for consumption. Additional transplants are currently being considered by LDWF. As for hatchery raised oysters, more than 780 million oyster larvae and 34 million spat have been released since 2012.

The relatively unique conditions in Calcasieu Lake support an oyster population that is heavily influenced by the Gulf of Mexico and the Calcasieu River. The northern portion of the lake that is closed by LDHH has had the benefit of creating a spawning stock area that likely provides larvae to the southern portion of the lake. However, the Calcasieu Lake population is isolated compared to other oyster production areas of the state.

In other areas of Louisiana, interconnected estuaries allow the exchange of larvae between reefs over large areas which helps maintain oyster populations.  The oyster resource in Calcasieu Lake, however, can be considered in ecological terms, a true population of animals. The isolated nature of the Calcasieu Lake oyster population is why this area has been managed with conservative seasons and gear types.

Despite the restoration actions described above, the oyster stock in Calcasieu Lake has been declining since 2009. The East Side was closed from 2011-2015 and recovery of the stock has not been observed. Stock size is presently less than 17 percent of the long-term average. Since 2009, the West Cove stock size has declined and is presently less than 15 percent of the long-term average.

There was a reduction in harvest during 2015-16 season, but a much larger percentage of the available resource was harvested, 37 percent, compared to average harvest from before the stock decline, less than 10 percent. This trend has been increasing over the past several years.

The optimal salinity regime for oyster production appears to have shifted away from the historic reefs surrounding the ship channel and into areas where reef material is more scattered and sparse. There does not seem to be issues with oyster reproduction, as there are several small cultch plants and reef areas that are productive and spat-fall is regularly observed. The oyster stock decline appears to be caused by a combination of hydrologic shifts, harvest pressure and a lack of reef habitat in areas with optimal salinities.

As the harvest season continues, both the department and the local oyster industry look for positive responses by the oyster resource that will continue to prove its resiliency for years to come. To further support this resiliency, LDWF will continue its efforts to improve oyster production in Calcasieu Lake and throughout Louisiana.

--- Much of the historical information contained in this article was compiled by Ron Dugas, LDWF biologist and oyster program manager, who retired from the department in 2000.

 

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