Special Issue Survey of Cetaceans in Captive Care

330 Couquiaudon soil conditions. After the membrane is put inplace, another layer of sand is placed over themembrane. It needs to be at least 50 cm thick.If the sand bed is less than 50 cm, the dolphinsmay expose the membrane by their foraging andtail movements. Anaerobic bacterial activity willdevelop in the sand and stabilise; this shouldnot create problems providing the turnover ofthe water is appropriate. Metal ions in the watermight give the sandy substrate a brownish colour.Metal ion composition of the groundwater at thesite location will be investigated to ensure thatit is safe for the animals. There is a potentialdanger of impurities leaking into the system, butif the turnover rate of the water is good, it can beavoided. A second membrane layer above a thicklayer of several meters of sand can be added tocreate a buffer zone and guarantee watertightnesswhen impermeable membrane is preferred.• The perimeter of the recreated lagoon can beeither left sandy with the membrane sealedunderneath on a concrete beam or lined with athick layer of stones, preferably hand-placed onthe upper surface of the inclined batter and downto approximately two-thirds of the lagoon’sdepth. Some portions can slope gently to form asandy beach. Boulders also can be added. Sumpgrates should be placed at a higher level thanthe bottom, and their perimeter should be linedwith stones or concrete to maintain the membranein place around them.• Bank stability may also be a problem accordingto the nature of the substrate. The geotechnicalqualities of each site must be assessed beforethis type of environment can be designed orconstructed.• On a rocky substrate, a membrane might berequired if the rock is not solid and uniform,or if it is mixed with soil. Lava rock makes anexcellent lagoon substrate and acts as an efficientnatural filter. Granite also makes a goodnatural substrate that can provide a dramaticunderwater landscape.The primary advantage of this type of environmentis that it offers a more natural habitat withgreater possibilities for the animals to interactwith their environment because marine organismssuch as fish, crustaceans and shrimps can thrive,provided the life support system (LSS) allows it. Itcan be much larger than concrete pools and offersa wide variety of shapes and topography. It also iseasier to maintain and clean because algae are partof the environment and do not need to be removedfrequently. It is cost-effective compared to concretepools for construction and maintenance.Artificial Environment – Concrete pools havebeen used to house dolphins since the beginningof modern oceanaria. Facilities have reportedFigure 5.9. Semi-natural show lagoonFigure 5.10. Semi-natural lagoonFigure 5.11. Semi-natural lagoonseveral problems related to concrete foundationsand have proposed recommendations for adequateconstruction and maintenance:• The structure of the pool will be designed toresist changes in pressure when the pool isempty. This can be achieved by means of athick slab or multiple anchored ground piles.For budget constraints, this aspect often isneglected, resulting in concrete failure at thefirst attempt to empty the pool.• Concrete pools with geometrical shapesand regular surfaces are built traditionallyusing formwork. To create free shapes and