Experimental investigations on the respiration and diving of the florida manatee

Abstract

Besides the seals and cetaceans, the sea cows (Sirenia) may be said to represent the most marked adaptation to aquatic life of all mammals.A distinguishing feature of the sea cows is that they are the only forms of herbivorous mammals which are adapted exclusively to aquatic life. Compared with the great number and variety of seals and cetaceans the sca cows form a strikingly small order, comprising only the marine dugongs with three closely interrelated geographical races (Halicore dugong, Halicore hemprichi and Halicore australe) inhabiting the coastal waters from East Africa and India to Australia, and the three species of manatee living in fresh or brackish water, Trichechus latirostris from Florida to northern Brazil, Trichechus inunguis in Brazil and Trichechus senegalensis in West Africa (Weber, '28). It was considered to be of interest to try to outline experimentally the respiratory characteristics of a sea cow, especially with a view to its adaptation to prolonged diving, and to relate the analytical data from the sea cow especially to those obtained from seals Previous w7ork on the respiration of sea cows is confined to observations of their breathing rate and diving times in captivity. Particularly valuable are the systematic observations by Parker ('22) on three Florida manatees (Trichechua latirostris), the same species as our animals. The size of his animals were: I, less than 2 m, 11, 24 m, and 111, 3 m. The average diving times were respectively 43 minutes, 8+ minutes, and 12 minutes. The average number of breaths taken per 10 minutes was 3.1, 2.4 and 2.2. The loiigest diving time was observed in the biggest animal with a maximum of 16 minutes and 20 seconds. Parker's observations, redrawn after his

Cardiovascular responses to diving in the turtle, Pseudemys scripta

“…In fact, some whales have weight-specific lung volumes much smaller than non-divers, such as man (Irving et al, 1941a;Scholander and Irving, 1941). This small lung volume may be an adapta tion to diving in animals which descend to great depths (Andersen, 1955), such as Sperm whales which have been found entangled in submarine cables A f npnfhc ov/on AyrooHi nn T 00.0 mof ore 1 Q!>7 ^ Mr 5/aa n anri Pav»!+nn (1977) have shown that beavers have a smaller lung volume/body weight ratio than man.…”

“…T n Haon H 4 fko 1 « mnc rnlTançû X i iv~i nn H ccr on f a nri a i on f may become contained wholly within the respiratory dead space (Scholander» 1940). Of course, whether total lung collapse is possible or not depends on the size of the lungs relative to the size of the dead space.…”

“…This reduces the distribution of gases from the lungs to the tissues and thus reduces the chances for decompression sickness. In ad- The blood volume of diving animals is usually greater than for nondivers (Scholander, 1940). Expressed relative to body weighty it has I w# 11\.…”

“…The muscles of diving mammals and birds (but not reptiles (Berkson, 1966)) are known to have a higher myoglobin (Mb) concentration than in most non-divers (Scholander, 1940). It has been suggested that this is a valuable store of O2 in permitting divers to remain submerged for long periods of time, and Robinson (1939) stores of non-civers (Lenfani ex al., 197Ob;McrCaan and Ccrlton, 1977).…”

“…consumption have been made for a few divers (Scholander, 1940;Andersen, 1959a). From this data can be calculated an estimated dive duration, as suming the dive is dependent upon aerobic metabolism at the predive level.…”