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Prymnesium parvum fish kill in Texas

Texas Red Tide Workers,

This spring several hundred thousand fish were killed in Possum Kingdom Reservoir, Lake Granbury, and Lake Whitney in north-central Texas. The culprit was a toxic alga, Prymnesium parvum. For your information, I am attaching (and pasting into the body of this message) a briefing document on P. parvum prepared by Dr. David Sager with TPWD.

Thanks,

Cindy Contreras
Water Quality Coordinator
Resource Protection Division
Texas Parks and Wildlife Department

4200 Smith School Road
Austin, TX 78744

(512) 912-7095 phone
(512) 707-1358 fax
cindy.contreras@tpwd.state.tx.us
http://www.tpwd.state.tx.us

GOLDEN ALGA FISH KILLS The Golden Alga (Prymnesium parvum)
This alga has caused extensive fish kills in Texas since the 1980s and evidence exists that it has probably caused fish kills since the 1960s. Algae are primitive plants that are usually aquatic and lack true stems, roots, and leaves. The golden alga is a microscopic, flagellated member of the yellow-green algae family that normally is suspended in the water column. The alga is a brackish-water (salt tolerant) species that has been associated with estuaries and some fish kills in several areas of the world (Israel, Denmark, Great Britain, South Africa, and Scotland). However, as far as it is known, Texas is the only place where the alga has impacted natural waters so far inland although it has caused kills in fish culture ponds in Israel.

The alga has caused major fish kills on the Pecos River, Colorado River, and tributaries to the Brazos River in years prior to the most recent events. Little in known about the environmental requirements of the alga or what allows it to gain a competitive edge over native species, bloom, and result in fish kills. It releases several toxins that effect gill-breathing organisms (mainly clams and fish). However, the toxins have no apparent lethal effect on other organisms. Cattle and other animals have been observed drinking from rivers during ongoing golden alga fish kills with no apparent effects. Texas Department of Health officials have stated that the golden alga is not known to be a human health problem, but that people should not pick up dead, or dying, fish for consumption.

There is no known cost-effective control that kills the alga, or detoxifies waters, during blooms. Control strategies in large waterbodies are not economically feasible and can result in environmental damage to non-target species. Researchers in the pond culture industry in Israel have had some success using an aggressive treatment with ammonia to reduce golden alga toxic blooms in small ponds allowing the restocking of these culture ponds. This treatment is only effective for farm ponds and hatchery settings. In addition to the cost and problems in treating large reservoirs or lakes, the amount of ammonia required would have adverse impacts on other organisms in the aquatic ecosystems. The cure could be as bad as the cause. Texas Parks and Wildlife staff members continue to search the literature and contact researchers to determine if other treatments have been found that could be used on this large-scale situation.

Present Fish Kill Assessments
On January 11, 2001, Texas Parks and Wildlife was notified of a fish kill on Possum Kingdom Reservoir. Resource Protection and Law Enforcement staff responded along with rangers from the Brazos River Authority. Nearly a dozen different fish species were identified as being affected including largemouth bass, catfish, carp, stripped bass, crappie, gar, and buffalo. Fishing guides and local boaters assisted in the investigations on the fish kills by providing information to staff about the location of dead or dying fish and unusually colored water.

The lack of an identifiable chemical spill (or other discharge), the fact that viral or bacterial diseases rarely affect so many different species of fish, and the observation of certain characteristics associated with golden alga caused fish kills (yellow tinted water, elevated salt concentrations in the water, etc.) led the Resource Protection biologist to suspect that the golden alga might be the causative agent. Water samples were collected and the golden alga was identified by Texas Parks and Wildlife staff and confirmed by university research scientists.

On January 29, a similar fish kill was confirmed on Lake Granbury and to a lesser degree in the Brazos River below Lake Granbury. The fish kills have slowly expanded in the lakes from the shallow headwater locations where they were first discovered. Investigations by the department and Brazos River Authority are continuing. The presence of the golden alga has been confirmed in Possum Kingdom Reservoir, Lake Granbury, Lake Whitney and the river from Possum Kingdom to below Lake Whitney. While the alga was present in Lake Whitney for several weeks, fish kills were not reported until April 13 in isolated areas of the reservoir.

At the present time, it is roughly estimated that over 450,000 fish valued at $486,000 have been killed. About 186,000 fish have been lost on Possum Kingdom Reservoir; 261,500 fish on Lake Granbury; and over 3,000 fish on Lake Whitney. Approximately three-fourths of these fish were bait and/or forage species (e.g., minnows, carp, and shad). The rest were game fishes (e.g., largemouth bass, smallmouth bass, stripped bass, crappie, and catfish). The fish kill continues near the dam on Possum Kingdom Reservoir although the number of fish dying has decreased. No dead fish have been reported on Lake Granbury for over a month. The areas of the reservoirs affected by the alga continue to vary with local weather and lake conditions.

Planned Fish Releases and Management Actions
The department regularly stocks fish into reservoirs in this area as part of the recreational fisheries management plans for the reservoirs. The amount and place of the fish releases vary from year to year depending on the need and fish available for stocking. Preparations for fish stockings on Possum Kingdom Reservoir are moving forward, despite lingering threats of the toxic algal bloom. A regularly scheduled gill net survey by Inland Fisheries management staff was conducted from February 13-20, 2001, about one month after the fish kill started. The survey included 15 randomly selected stations throughout the reservoir and is designed to sample primarily catfish and striped bass. Ninety-nine striped bass were sampled for an average catch rate of 6.6 per net. This is about 2/3 the catch rate of the previous survey conducted in 1999.

On April 5, Resource Protection staff found that the golden alga was no longer present in the upper end of the reservoir and beneficial green algae was beginning to bloom. As a result, plans were finalized to restock threadfin shad in that portion of the lake. On April 9, 800 adult threadfin shad were stocked in three locations from near Costello Island to Rock Creek Camp. These fish will spawn this spring and, because of early maturation of this species, their offspring will spawn this summer and should result in reestablishment of an abundant forage population.

Texas Parks and Wildlife plans to stock game fish in Possum Kingdom in early June. The department is scheduled to stock 123,900 striped bass fingerlings and 442,500 Florida bass fingerlings. Possum Kingdom is at the top of the statewide fish stocking priority list.

It is too early to draw any conclusions about the health of the fishery at Possum Kingdom, but a complete assessment is planned. A number of fish found refuge from the toxic alga in the upstream river and unaffected feeder creek areas in the reservoir, particularly the striped bass, and those fish are moving back into the lake and people are catching them. The fish still have not redistributed over the lake and it's difficult to say what the damage has been to the resources.

Texas Parks and Wildlife is planning to conduct gill net surveys in May to assess the status of striper and catfish populations in Possum Kingdom and will evaluate crappie and largemouth bass during fall electro-fishing and trap net surveys. It is expected that a decrease in numbers will be found for all species, but how much of a decrease is unsure.

Public Inquiries
Texas Parks and Wildlife staff members have continued to monitor and investigate the fish kills associated with the alga bloom on Possum Kingdom, Lake Granbury, Lake Whitney, and the Brazos River. Citizens, government officials, and the news media have contacted many department staff members with requests for information, concerns, and complaints about the fish kills. Inquiries have been made about what can be done to control (or end) the algal bloom, how will the department¹s fish stocking schedules for these reservoirs be impacted, and what is being done to provide information about the events. Hopefully, this document will help address most of those questions.

Department media staff issued news releases to provide the public with information about the fish kills and the organism causing them. In this effort, staff members had to balance numerous concerns between getting the facts to the public, causing the public (or media) to overreact to the situation, or making promises or statements that the department could not guarantee (such as when the kills would end and how far they might spread). Quotes were provided from the Texas Department of Health in the news releases in an effort to provide the public with information that the alga toxin was not a threat to human health. Questions received concerning human health issues were referred to the Department of Health since this is not our area of expertise and we do not want to give out any erroneous information. Unfortunately, staff members have received complaints that many people scheduled for recreational activities in the areas are canceling reservations. Similar situations have been seen with oil spills, red tides, and bad weather along coastal beaches. People do not want to risk their vacations when they might have a bad experience due to the on-going event. This also impacts our state parks. The department has promised to release information when these fish kills end. Staff members try not to provide inflammatory statements, but cannot control how others use the information released. While the department does not want to have a negative impact on peoples¹ livelihoods, department staff members feel obligated, and are required, to answer the public¹s questions and requests for information honestly.

Contact List Fish Kill Assessment (Resource Protection Division)

Joan Glass	Regional Biologist	254-867-7956	joan.glass@tpwd.state.tx.us
Jack Ralph	KAST Coordinator	512-912-7153	jack.Ralph@tpwd.state.tx.us
David Sager	Freshwater Conservation	512-912-7150	david.sager@tpwd.state.tx.us

Fisheries Management (Inland Fisheries Division)

Mark Howell	Management Biologist	940-766-2383	mark.howell@tpwe.state.tx.us
Roger McCabe	Regional Director	254-867-7974	roger.mccabe@tpwd.state.tx.us