Letters

MARINE MAMMAL SCIENCE, 17(2):427-429 (April 2001) 0 2001 by the Society for Marine Mammalogy

THE FOOD OF SPERM WHALES IN THE S~UTHEAST PACIFIC

We should like to comment on Smith and Whitehead’s interesting paper “The diet of Gal5pagos sperm whales, Physeter macrocepbalus, as indicated by fecal sample analysis” (2000). They found no beaks of the Humboldt Current squid Dosidicus gigas in their samples, whereas R. Clarke et al. 19886 have shown that sperm whales off Chile and Peru feed practically exclusively on D. gigas. We are in no way surprised by their observation.

First, D. gigas certainly occurs off the Galkpagos Islands. It was first reported by Boone (1933) and it was fished by one of us (RC) on 2 November 1959 at OO017’S, 85’28‘W (R. Clarke 1962). Now it is clear from Smith and Whitehead’s survey of sampling bias that beaks of D. gigas could not be expected in their samples. They pointed out that large beaks sink more quickly than small ones. D. gigas is a large animal, reaching 65 kg in weight (R. Clarke and Palita 2000) and its average weight from the stomachs of male sperm whales was 25.7 kg and from females 17.5 kg (R. Clarke et al. 19886, table 14).

But, apart from the sinking of large beaks, we believe that large beaks like those of D. gigas never get into the feces but are vomited, an activity which, in the Southeast Pacific, R. Clarke et al. (19886, p. 137) have estimated to take place every 7-8.4 d in female sperm whales and every 5-6.3 d in males. A glance at the contents of a sperm whale stomach from the Southeast Pacific (R. Clarke e t al. 19886, p. 136, Fig. 20) shows that, apart from the D. gigas present, there is a mass of beaks, some with buccal masses still attached, tangled with squid pens, eye-lenses, spermatophores, and nem- atode worms, and the entanglement is such that the mass is probably vomited in a single bolus. The few beaks that remain to pass through the gut of a sperm whale are small ones, as may be seen from the beaks embedded in ambergris concretions removed from the rectum. That the beaks excreted are few may be seen from Smith and White- head’s own results because their 60 fecal samples collected by a dipnet yielded only 164 lower beaks identified. Doubling the number, on the generous assumption that as many upper beaks were also collected, makes only about five beaks per fecal sample.

Because R. Clarke et al. (19886, p. 92) have shown that sperm whales in the South- east Pacific, unlike those in other oceans, have a virtually monospecific diet, Dosidicus gigas, we wish to reply to Smith and Whitehead’s observation (p. 323) “It is more likely that sperm whales in the Southeast Pacific feed opportunistically on many species of cephalopod including D. gigas when and where they are most abundant.” They also quoted a similar observation made by the International Whaling Commission’s Sci- entific Committee, Sperm Whale Subcommittee (1988), but they did not mention that Clarke et al. (19886, p. 92, footnote) had also quoted the subcommittee’s observation, pointing out that the subcommittee had received only a summary by Clarke et al. (1988a) with none of the explanation given on pp. 90-94 of Clarke et al. (19886).

M. R. Clarke et al. (1976) identified 1,000 cephalopod lower beaks from random samples of the stomach contents of four sperm whales caught off Chile and Peru between 1959 and 1961. Smith and Whitehead summarized M. R. Clarke e t al.’s results thus in their Table 3:

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% by number of beaks:

Histioteuthis A 50 Chiroteuthis 16

Other spp. 25 Octopoteuthis 9

They said (p. 319) that these results agreed “especially closely” with their results on 164 beaks from fecal samples which they presented as:

% by number of beaks:

Histioteuthids A. lesuerii Octopoteuthids Other spp.

62 16 7

15

But they did not mention that M. R. Clarke et al.’s “Other species” included 3.82% which were 36 beaks of D. gigas responsible for an estimated 3 1.61 % of the total flesh weight of their sample, and that the largest D. gigas beak must have come from a squid weighing more than 50 kg. The interpretation of the two results is now com- pletely altered. R. Clarke e t a(. (19886, p. 109 and table 16) have shown that among 6,770 D. gigas examined from sperm whale stomachs 43.32% of these squids had no heads in male sperm whales and 52.32% in female whales. They had been lost in the swallowing process, although the squid flesh lost in this way was very small, only 9.75% of the total squid flesh in males and 11.77% in females. But the squid heads contained the beaks. So the 36 D. gigas beaks in M. R. Clarke et al.’s sample (1976, table 3) can now be multiplied by two making 72 squids, half of them headless, swallowed by the four sperm whales. Because we and R. Clarke et al. (19886, pp. 90- 94) believe that nearly all the small beaks found in sperm whale stomachs from the Southeast Pacific are the remains of the food of D. gigas, then these small squids, 1,000 - 72 = 918, in M. R. Clarke et al.’s sample were eaten by 72 D. gigas, making about 12 small squids per D. gigas, a reasonable enough meal for this voracious animal. And D. gigas will have contributed not 31.61% but more than 60% of the weight of flesh in M.R. Clarke et al.’s sample, the rest being the small squids from the stomachs of the D. gigas swallowed by the sperm whale. We should add that hundreds of stomachs from specimens of D. gigas, examined from sperm whale stomachs in the Southeast Pacific, have contained no other food than squids (R. Clarke et al. 19886, p. 91).

In their table 3 Smith and Whitehead give a fair summary of R. Clarke et al.’s results (19886) on the identification of flesh remains of squid in the carefully examined stomachs of no less than 2,403 sperm whale carcases, examined in the southeast Pacific between 1959 and 1962, thus,

Dosidicus gigas 99% A. lesuerii 0.4% Histioteuthids 0.1% Other spp. 0.05%

Smith and Whitehead say that this list is not representative of the sperm whale’s food off Chile and Peru because many small species like histioteuthids will have been digested before the stomachs could be examined. Against this R. Clarke et al. (1988b, p. 91) have pointed out that “M. R. Clarke (1980, p. 51, fig. 27) was unable to show that the numbers of flesh remains (’buccal masses +’) in sperm whale stomachs de- creased with post-mortem time, and was led to conclude that digestion appears to be much less rapid after death than would be expected in the living animal.”

R. Clarke et al. (19886, p. 139 ff.) were able to estimate the annual consumption

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of the squid D. gigas by the estimated population of sperm whales in the Southeast Pacific between 1959 and 1962. The estimates (with appropriate confidence limits) came to 8.69 million tons of D. gigas per year based on the normal full meal, and 13.67 million tons based on the full meal at satiety. With these results R. Clarke et a!. (p. 141) recommended a modern fishery for D. gigas off Chile and Peru. Within a few months of the publication of their report a Japanese squid-jigging vessel arrived in 1989 for exploratory fishing and was overwhelmingly successful. The present enor- mous squid fishery in the Southeast Pacific had begun. Only D. gigas is taken on the jigs. We have not at hand the FA0 reports on the annual catches of this fishery since 1989, but it may be sufficient to mention that the Peruvian Government alone during 1994 received 51.45 million dollars for authorizing Japanese and Korean vessels to take 240,000 tons of D. gigas from Peruvian waters (R. Clarke and Paliza 2000). This should give an idea of the abundance of D. gigas in the Southeast Pacific. We may now quote R. Clarke et a!.’s observation (19883, p. 93) that sperm whales are in the Southeast Pacific “because of the immense squid population in the Humboldt Current, and now we are in no doubt that this population is Dosidicus gigas.” And moreover we repeat with absolute conviction R. Clarke et a!.’s further observation (p. 94) that “col- lections from faeces cannot give reliable indications of the diet of sperm whales, either around the Galhpagos Is. or elsewhere.”

We are concerned with the need for regulation of the fishery for D. gigas because of its possible effect on the recovery of the sperm whale stock and, indeed, on the con- dition of other predators of D. gzgas in the Southeast Pacific. These matters are dealt with in our monograph on the Humboldt Current squid (R. Clarke and Palita 2000).

LITERATURE CITED

BOONE, L. 1933. Scientific results of cruises of the yatchs ‘Eagle’ and ‘Ara’, 1921- 1928. Mollusca. Bulletin of the Vanderbilt Marine Museum 4165-210.

CLARKE, M. R. 1980. Cephalopods in the diet of sperm whales of the southern hemi- sphere and their bearing on sperm whale biology. Discovery Report 37:l-324.

CLARKE, M. R., N. MACLEOD AND 0. PALIZA. 1976. Cephalopod remains from the stomachs of sperm whales caught off Peru and Chile. Journal of Zoology, London 180:477-493.

CLARKE, R. 1962. Whale observation and whale marking off the coast of Chile in 1958 and from Ecuador towards and beyond the Galhpagos Islands in 1959. Norsk Hvalfangst Tidende 51:265-287.

CLARKE, R., AND 0. PALIZA. 2000. The Humboldt Current squid Dosidicus gigas (Or- bigny, 1835). Revista de Biologia Marina y Oceanografia, Chile 35:l-39.

CLARKE, R., 0. PALIZA AND A. AGUAYO L. 1988a. Summary of the report “Sperm whales of the Southeast Pacific. Part IV. Fatness, food and feeding.” Paper SC/39/Sp. 2. Report of the International Whaling Commission 38:503. RCsumC Section.

CLARKE, R., 0. PALIZA AND A. AGUAYO L. 19886. Sperm whales of the Southeast Pacific. Part IV. Fatness, food and feeding. Investigations on Cetacea, Berne. 21:53-195.

INTERNATIONAL WHALING COMMISSION. 1988. Report of the Scientific Committee. An- nex D. Report of the Sub-committee on Sperm Whales. Report of the Interna- tional Whaling Commission 38:67-7 5.

SMITH, S. C., AND H. WHITEHEAD. 2000. The diet of Galhpagos sperm whales Physeter macrocephalus as indicated by fecal sample analysis. Marine Mammal Science 16:

ROBERT CLARKE AND OBLA PALIZA, Apartado 30, Pisco-Playa, Pisco, Peru; e-mail: oblapal@latinmail.com. Received 26 July 2000. Accepted 7 September 2000.

315-325.