American white pelicans reveal their presence by their large webbed tracks and guano-stained (whitewashed) landscapes. Other than fish losses and the presence of Bolbophorous damnificus (a flatworm that can infect channel catfish, for which the American white pelican is a host), direct observation is the only way to determine if pelicans have been in an area.
Fish losses at harvest, the presence of B. damnificus, and direct observation are the only ways to determine if pelicans have foraged on aquaculture ponds. Direct observation of pelican predation may not always be possible because pelicans will forage at night, especially on aquaculture facilities with active daytime harassment programs.
Trampling of vegetation is characteristic of pelican damage agricultural crops, such as rice.
Damage to Livestock and Pets
American white pelicans threaten aquaculture producers by direct predation and disease transfer. The impact of direct predation can be substantial. For example, assuming that pelicans foraging in a catfish pond consumed exclusively catfish averaging 10.2 inches, each bird would require 11 of these catfish to meet its energetic requirement of 2 pounds per day. This consumption rate would translate into 2,750 catfish consumed per day by an average-sized flock of 250 pelicans. If these fish reached harvestable size of 1.5 pounds and were valued at $0.70 per pound, catfish farmers could potentially lose approximately $2,900 from a single day of pelican foraging. Actual depredation losses would depend on pelican abundance at ponds, the size and number of catfish consumed, and the duration of pelican foraging at catfish ponds. American white pelicans also kill vegetation on pond levees by trampling and deposition of guano.
Pelicans are one of the hosts of commercial catfish parasites, especially the digenetic trematode Bolbophorus damnificus. This trematode has caused substantial economic losses to several aquaculture producers in Louisiana, northwest Mississippi, and southeast Arkansas.
Although the economic impact of pelican foraging can be significant, the potential for pelicans to transmit trematode infections to catfish ponds can be more devastating. Whole ponds of catfish have died from trematode infections, and little can be done to treat these infections. Even mild infections of B. damnificus can result in a more than 60% reduction of net returns. A 2004 analysis of the economic impact of trematode infections to commercially raised catfish in Mississippi estimated economic losses of $27.1 million per year.
Damage to Landscapes
American white pelicans can damage recently planted crops such as rice by trampling and depositing guano, although the extent of these losses is not known.
Pelicans can be perceived as nuisance wildlife by aquaculturists and sportsfishermen by either predating farmed fish or consuming sportsfish prized by anglers.
Health and Safety Concerns
Pelicans are not known to transmit any significant diseases to humans. Aircraft collisions have been documented.