122 



The brown pelican has already disappeared from the gulf coast of 

 AlaJbama, Mississippi, Louisiana, and Texas, where it was a common 

 sight prior to 1960. This disappearance coincided with the heavy fish 

 kills of 1960-64 in the lower Mississippi River, which were caused by 

 excessive residues of pesticides. One theory proposed that the dead and 

 dying pelicans observed during that period had accumulated lethal 

 dosages (fig. IV.2.9) . This assumption, however, was not verified and 

 another theory used to explain the lack of any recovery was the de- 

 struction of nesting grounds in black mangroves by the severe cold. 



The 80 species of waders, which include the egrets, storks, herons, 

 ibis, and spoonbills, are predominantly residents of the southern 

 United States, particularly in Florida. The recent drought and man- 

 made changes in the Everglades have drastically reduced the number 

 of these species in Florida. For some species, this represents a serious 

 setback in their gradual recovery from near extinction at the hands of 

 the plume hunters. Waders elsewhere on the southern coast have also 

 diminished in numbers, apparently because of irresponsible shooting 

 and manmade environmental changes. 



AQUACULTURE 



The great fish and shellfish resources of United States coastal waters 

 have adequately supplied the seafood demands of the increasing pop- 

 ulation for over 300 years. Now, however, the demand for some prod- 

 ucts is so large that the normal fishing grounds and fisheries are in 

 great danger of being exhausted, both from overfishing and from 

 the indirect effects of man's encroachment into the esuarine environ- 

 ment. To supply future needs of some fish products new approaches 

 toward commercial fishing are needed, both in harvesting the natural 

 growth and in controlling the entire fishery. 



Aquaculture is defined as the rearing of aquatic organisms, both 

 plants and animals, under controlled conditions using the techniques 

 of plant and animal husbandry. It involves a variety of operations: 

 some are highly sophisticated where man exercises control over the 

 principal environmental factors affecting the cultured species, and 

 others are very simple with only minimal control or manipulation of 

 the habitat and the cultural animal. 



The following examples illustrate the variety of aquacultural activi- 

 ties that are now practiced : 



(1) Rearing aquatic species from selectively bred strains to com- 

 mercial size under controlled conditions where the optimum require- 

 ments for food, temperature, salinity, and other physiological and 

 environmental needs are provided; predators and competitors are 

 eliminated and diseases controlled, and highly mechanized methods 

 are used to reduce labor costs. This is the ultimate in aquacultural 

 operations and has been achieved only for a few species (e.g., carp). 



(2) Rearing aquatic species in natural or artificial enclosures to 

 commercial size, with or without supplemental feeding, predator con- 

 trol, environmental adjustment, and selective breeding. Enclosures 

 may be man-made tanks, natural or artificial ponds, or enclosed areas 

 of the sea. Such techniques are now used for the production of oysters, 

 clams, shrimp, catfish, carp, and baitfish. (fig. IV.2.10) . 



(3) Rearing aquatic species in hatcheries through the juvenile 

 stages, the period of greatest natural mortality, to stock natural areas. 



