Cormorants roosting  in a cypress break in the Mississippi Delta One of the most successful harassment techniques being used against cormorants by catfish producers is roost dispersalmdashPhoto by Jim Steeby

Cormorants roosting in a cypress break in the Mississippi Delta. One of the most successful harassment techniques being used against cormorants by catfish producers is roost dispersal.—Photo by Jim Steeby

Surveys will determine impact of cormorants on Delta catfish ponds

Aerial and ground surveys will be conducted this winter to determine where, when, and on what types of catfish ponds cormorants forage in the Mississippi Delta.

The impact of double-crested cormorants on aquaculture has long been a concern of catfish producers in Mississippi.

Research and management biologists from the USDA Wildlife Services, National Wildlife Research Center, and Mississippi State University are teaming up to conduct research on double-crested cormorants foraging in the Mississippi Delta region, according to Paul Burr, Ph.D. research assistant at Mississippi State University, and Dr. Brian Dorr, research wildlife biologist, USDA Wildlife Services, National Wildlife Research Center.

Burr will be performing a study to determine where and how many cormorants are on both catfish aquaculture and natural water bodies throughout the central Delta region.

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Daytime aerial surveys will be flown twice a month from October 2015 to April 2016 to try and answer questions about cormorant foraging in the Delta region. In addition, ground surveys of aquaculture facilities will be done to evaluate where, when, and on what types of catfish ponds cormorants forage. These surveys will be an extension of past surveys conducted about 15 years ago.

The Wildlife Services and National Wildlife Research Center conducted surveys during the winters of 2000 and 2003 to determine these impacts, Burr notes. “That research determined that cormorants consuming catfish resulted in an estimated economic loss between $5.6 and $12 million annually.

“At the time of these surveys, the aquaculture industry was at its peak in Mississippi. Since then it has experienced a 60 percent decrease. Cormorant numbers, however, may have changed little since the early 2000s.

Changes in foraging patterns?

Comparisons of previous surveys will examine how cormorants have adjusted their foraging to today’s smaller Mississippi Delta aquaculture industry.

“With less acreage devoted to aquaculture, it is important to determine how cormorants will adjust their foraging behavior. These birds may concentrate on the remaining aquaculture ponds and have a larger impact on the industry, or they may be foraging more on natural habitat found in the area, such as oxbow lakes.”

Ideally, Burr says, cormorants will seek out other foraging options and use aquaculture to a lesser extent. But if the birds are selecting for aquaculture ponds rather than available natural habitat, producers may be experiencing greater losses.

Surveys planned for this winter will document the current extent of cormorant distribution and use of catfish aquaculture and natural habitat in the Delta. These surveys will also help to develop and evaluate current economic losses experienced by catfish producers due to cormorant depredation.

Comparisons of these surveys with previous work will gauge how cormorants have adjusted their foraging to today’s smaller aquaculture industry. While cormorants will be the main focus of this study, all other fish-eating bird species, such as pelicans, herons, etc., will also be recorded during the surveys.

Similar questions will be addressed to determine how these other species are distributed in the Delta, how they impact the aquaculture industry, and how their impacts compare with cormorants.

Over the next eight months, staff from the agencies will be flying surveys and contacting catfish producers to obtain information concerning bird depredations on their facilities. “The success of these surveys depends on the continued cooperation with producers in the industry,” Burr says. “We look forward to working with producers during the 2015-2016 winter surveys, and will appreciate their support.”

Comments or questions regarding this research may be sent to Paul Burr via email at [email protected]

 

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