COCCONEIS DIATOM ON THE SKIN OF FRANCISCANATAKAHISA NEMOTO
Ocean Research Institute, UnivmitY of Tokyo, TokyoROBERT L. BROWNELL, JR.
Smithsonian Institution, National Museum of Natural History,Washington, D.C.

AND
TAKASHI IS HI MAR U
Ocean Research Institute, University of Tok)'O, Tokyo

ABSTRACTTwo species of diatoms are described from the skin films of Franciscanacaught in the adjacent waters to Urguay. Cocconeis ceticola is common
diatom on skin films, and one other naviculoid species is also found on thisdolphin.

INTRODUCTION

Many diatoms have been reported from skin films of larger baleen whales andsperm whales both in the North Pacific and in the Antarctic (Hart, 1935; Nemoto,1956). Species of diatoms are various, but Cocconneis ceticola is found generally on
whales examined. Those parasitic diatoms are common on all larger whales in thepolar waters and include many species which have not generally found in pelagicplankton (Nemoto, 1956). Cocconeis ceticola and its varieties and forms are common on Balaenoptera species and sperm whales, and some peculiar naviculoid diatoms, Stauroneis species are also found on sperm whales, which have not been described as a pelagic form.
Although many descriptions on parasitic diatoms have been made on larger
whales including killer ( Orcinus orca) and Baired beaked (Berardius bairdii) whales,
few observations on diatom films on the skin of small cetaceans have been reported. Only a few descriptions have been made by Harrison and Thurley (1974)and Brownell (1975) recently.
Among many Franciscana studied in Urguay, some specimens had greenbrown films of diatoms on the body surface. We studied these diatoms with reference to diatoms found on other whales.
DESCRIPTIONSThe Franciscana (Pontoporia blainvillei) has been studied from 1971 to 1973 in Punta
Sci. Rep. Whales Res. Inst.,
No. 29, 1977, 101-105.

102

NEMOTO, BROWNELL JR. AND ISHIMARU

del Diablo, Urguay by one of us Brownell. The progress report on the biology of
those Franciscana studied is already given by Brownell (1975). Diatom films weremainly observed on the dorsal and lateral surface of the most fresh dolphins examined(Brownell, 1975). This observation suggests that more Franciscana may have haddiatom films on the skin surface if they were examined in more fresh and un-rubbed
conditon. The catch of those dolphins is done by gillnets by fishermen (Brownell,1975), which possibly have removed diatom films with epidermis of the skin ofdolphins.
TABLE 1.
Field

OBSERVATIONS OF DIATOM FILMS ON SKIN FILMS OF
FRANCISCANA IN URUGUYAN WATERS

No.

Sex

Body length(cm)

Weight(kg)

Date caught

Remarks

717

M

119

19.5

9 Aug. 1971

721
753

FM

104
131

16.4

11 Aug. 1971
25 Aug. 1972

762

M
M
M

110
111
115

19.0771774

13 Sept. 1972
24 Sept. 1972
25 Sept. 1972

869
872

FM

130.5
142

27.3
31.4

5 Jan. 1973
11 Jan. 1973

889

F

136.5

29.1

23 Jan. 1973

895

F

112.5

17 .3

28 Jan. 1973

Diatom film collected from left sideof dorsal fin.
Diatom film collected.
Diatoms present on dorsal side andlateral tail stock, flippers and side ofhead. Sample collected from tail stock.
Diatom film around base of dorsal fin.
Diatom film present.
Diatom film covering all of the animalareas of heaviest concentration werearound the gape and tail stock-areasof next heaviest concentration wereflukes (dorsal and ventral), the flippers(dorsal and ventral) and the dorsal fin.
Diatom film collected.
Heavy diatom film on dorsal andlateral surfaces.
Some diatoms on dorsal surface offlippers, dorsal fin, and tail stock.
Heavy diatom film on tail stock.

Diatom films are observed at least 10 dolphins in the studies carried out since1971, in which three diatom specimens have been collected from three dolphins.
The data of observations are given in Table 1. Generally diatom films are foundon the side of dorsal fin and the dorsal surface of flippers and tail stocks. It is considered also that diatom films are common on the surface of dorsal fins and flukes.
The seasons of catch of dolphins are both in winter (January) and summer (August) of the southern ocean, and dolphins which have been caught in both seasons
were infected with diatoms.
The collected samples are examined by scanning electron and ordinary microscopes. Among all samples, Cocconeis ceticola specimens are found. On one porpoise (RLB-717), naviculoid diatoms are also found.
Cocconeis diatoms found on the skin films of Franciscana are considered allceticola type and the variety form such as constricta form has not been found in samples. Although the shape of ceticola is somewhat oval but it is similar to thosefound on sperm whales. Sizes of diatoms are all within the general distributionof size which are reported up to date (Nemoto, 1958). Another naviculoid diatom
Sci. Rep. Whales Res. Inst.,
No. 29, 1977.

103

DIATOM FROM FRANCISCANA

is also found in specimens collected from No. 721 dolphin. This naviculoid diatom
is considered to be one of the definite records from the skin films of whales like thereport by Harrison and Thurley (1974), although there was some description ofNavicula sp. from fin whales (Amemiya, 1916), which is considered as Stauroneisspecies.

CD(I)iIIceticola)

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f. constricta

BALEEN WHALES

v. arctica
Fig. 1.

Variety and deformation of Cocconeis diatoms on whales.

DISCUSSION

Many descriptions and discussions have been reported on diatom infection on theskin films of larger cetaceans. On the other hand, rather small numbers of observation have been reported on smaller cetaceans including dolphins. In theAntarctic and both in the Atlantic and the Pacific, many diatom films have been
observed from blue, fin, humpback and sei whales even from sperm whales (Hart,1935; Nemoto, 1956). Diatom films have also been observed in moderate sizedwhales of bottle-nose (Hyperoodon ampullatus) and the killer whales ( Orcinus orca) (Bennett, 1920) in the Antarctic. Although diatom films have been observed on dolphins in other occasions, few precise descriptions have been reported after 1920.
The notice of diatom films on dolphins, Lagenorhynchus cruciger and Cephalorhynchus commersonii was reported at South Georgia by Hart (1935), however no taxonomical observation was made on those diatoms. Harrison and Thurley (1974)
Sci. Rep. Whales Res. Inst.,

No. 29, 1977.

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DIATOM FROM FRANCISCANA

105migration. The most of records of parasitic diatoms have been recorded from thewaters colder than 20°C. Especially Cocconeis ceticola has only been reported in thepolar waters.
The water temperature around the fishing ground of Franciscana are ranging
between 13° and 23°. The seasonal difference of water temperature is not sogreat as to show clear decline or decrease of infection of diatoms on the skin.
Perhaps more extensive research on dolphins and whales reveals the infection ofCocconeis diatoms on whales are common in Urguay waters throughout the year.
REFERENCESAMEMIYA, I., 1916. [The propagation of diatoms on the skin of whales] (In Japanese). Rep. Jap. Soc.
Sci. Fish., l : 378-379.
BENNETT, A. G., 1920. On the occurrences of diatoms of the skin of whales (With an appendix by Nelson,E.W.) Proc. Roy. Soc. London., 91 : 352-357.
BROWNELL, Jr. R. L. 1974. Progress report on the biology of the Franciscana dolphin, Pontoporia blainvillei,in Uruguayan waters. J. Fish. Res. Bd. Can., 32: 1073-1078.
DAILEY, M. D., and R. L. BROWNELL, Jr., 1972. A checklist of marine mammal parasites.
In: Sam H. Ridgway [ed.], Mammals of the sea. Biology and medicine. 528-589. Charles C. Thomas,
Springfield Ill.
HARRISON, R.J. and K. W. THURLEY, 1974. Structure of the epidermis in Tursiops, Delphinus, Orcinus
and Phocoena. In: R.J. Harrison (ed.), Functional anatomy of marine mammals, 45-71. Academic Press.
HART, T. ]., 1935. On the diatoms of the skin film of whales and their possible bearing on problemsof whale movements. Discovery Rep. 10: 249-282.
KLIASHTORIN, L.B., 1962. The diatoms of the skin film of whales in the Far Eastern seas. Truqy Inst Okeanology A.N. U.S.S.R. 58: 314-321.
NEMOTO, T., 1956. On the diatoms of the skin film of whales in the Northern Pacific. Sci. Rep. Whales
Res. Inst., No. 11 :97-132.
NEMOTO, T., 1958. Cocconeis diatoms infected on whales in the Antarctic., Sci. Rep. Whales Res. Inst., 13:
185-191. 3 pls.

Sci. Rep. Whales Res. Inst.,
No. 29, 1977.