Stomach Contents of a Sperm Whale Calf Physeter macrocephalus L. Found Dead in Co Clare,IrelandAuthor(s): M. Begoña Santos, Simon D. Berrow and Graham J. PierceSource: The Irish Naturalists' Journal, Vol. 28, No. 7 (Nov. 3, 2006), pp. 272-275Published by: Irish Naturalists' Journal Ltd.Stable URL: http://www.jstor.org/stable/25536756 .

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Ir Nat J. Volume 28 No 7 2006

Stomach contents of a sperm whale calf Physeter macrocephalus L. found dead in Co Clare, Ireland

M.Begona Santos

School of Biological Sciences, University of Aberdeen, Aberdeen AB24 2TZ

Instituto Espaholde Oceanografia, Centro Oceanografico de Vigo, P.O. Box 1552,

36200, Vigo, Spain

Simon D. Berrow

Irish Whale and Dolphin Group, Merchant's Quay, Kilrush, Co Clare

Graham J.Pierce

School of Biological Sciences, University of Aberdeen, Aberdeen AB24 2TZ

Stomach contents information is presented from a male sperm whale calf thought to have

live stranded in Co Clare, Ireland, in May 2004. This is the second smallest sperm whale

recorded as stranded in the North Atlantic since stranding records began. The stomach

contents consisted of a white substance (probably milk) and the hard remains of several

hundred oceanic cephalopods, mainly squid of the family Histioteuthidae.

Sperm whales, Physeter macrocephalus (Linnaeus, 1758), achieve lengths up to 21m and are the largest species of Odontoceti (toothed whales). The social organization of sperm whales is thought to be unique and very complex with segregation by sex: males travel

seasonally to higher latitudes while females and calves stay in low latitudes all year round: in the Northern Hemisphere they do not normally travel to latitudes above 40-45? N (Berzin 1971). Females and calves have been recorded in the North Atlantic (Berrow and Rogan 1997) but these are considered exceptional cases (Smeenk 1997).

On 5 May 2004 a male sperm whale calf was reported washed up at Quilty, Co Clare

(at 52.8? N well outside the normal range of female and calves, Berrow and O'Brien 2005). It is thought to have stranded alive but died prior to discovery. At 5.8m this is the second

smallest sperm whale recorded as stranded in the North Atlantic since records began (Goold et al. 2002), the smallest being a calf of 18ft (c5.5m) long that stranded in Co Galway on 4

September 1916 (Hamer 1917). Here we present data on the stomach contents of the stranded whale calf from 2004.

Methods

During post-mortem examination of the whale, the jaws were examined to determine whether teeth had erupted, and stomach contents were examined for the presence of milk as well as remains of prey.

Cephalopod beaks in the stomach contents were identified using Clarke (1986) and a reference collection of oceanic cephalopod beaks originally provided by M. R. Clarke and now housed in the School of Biological Sciences, University of Aberdeen, UK. Standard

measurements were taken of the lower beaks: rostral length (LRL) for decapods and hood

length (LHL) for octopods (Clarke 1986), using a binocular microscope fitted with an eyepiece graticule. All undamaged lower beaks were measured. Mantle length (ML) and body weights of cephalopod prey were estimated from lower beak measurements, using regressions from Clarke (1986). The total number of individuals of each cephalopod species present in the stomach was estimated as the number of lower or upper beaks (whichever was higher).

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Ir. Nat J. Volume 28 No 7 2006

Table 1. Cephalopod species found in the stomach of a sperm whale calf stranded at Co Clare (Ireland). For all prey species, number of individuals (N) and importance (%N

=

percentage by number and %W = percentage by weight) are indicated. Numbers of beaks found are indicated (lower beaks unless otherwise stated). Some Histioteuthis beaks could not be identified to species but belonged to the "type A" group (Clarke 1986), which includes H. arcturi, H. corona, H. meleagroteuthis and H. bonnellii.

Family_Species_Beaks_N %N %W

Histioteuthidae Histioteuthis reversa 65 65 8.46 4.71

H. bonnellii 2 2 0.26 1.64

H. meleagroteuthis 3 3 0.39 0.52

H. type A 405 405 52.73 80.49

Mastigoteuthidae Mastigoteuthis schmidti 1 1 0.13 0.10

Cranchiidae Taonius pavo 1 1 0.13 0.12

Galiteuthis armata 7 7 0.91 1.87

Teuthowenia megalops 73 73 9.51 9.07

Alloposidae Haliphron atlanticus 1 1 0.13 1.48

Broken beaks 5 5 0.65

Upper beaks 768 205 26.69

TOTAL - 768 100 100

Results

Twenty round protuberances were counted in each lower jaw in the expected position of the teeth, although the fact that no teeth were exposed when those protuberances were cut

open suggests that the teeth were not close to erupting. In the fore-stomach a small volume of a white creamy substance (consistent with milk, John Underhill pers. comm.) was found

together with several hundred cephalopod beaks. The pyloric stomach was filled with a more translucent fluid.

A total of 788 upper and 563 lower beaks was recovered from the stomach (Table 1). The oceanic cephalopod family Histioteuthidae comprised more than 85 per cent of the estimated weight of prey items eaten by the whale and it was also numerically the most

important family. Other cephalopod species found in the stomach included Mastigoteuthis schmidti, Taonius pavo, Galiteuthis armata, Teuthowenia megalops, Histioteuthis bonnellii and Haliphron atlanticus.

The estimated size of the two most abundant species identified (Histioteuthis reversa and Teuthowenia megalops) ranged from 25 to 55mm ML with a mode at 45mm (H. reversa) and 95 to 265mm ML with a mode at 195mm (Teuthowenia).

Discussion

Sperm whale body length at birth is believed to average 4m (Rice 1989). Birth is

thought to be followed by rapid growth although there are very few data on young specimens. The whale stranded at Co Clare was clearly a very young animal. The apparent presence of milk in the fore-stomach suggests that it was still suckling, even though it was already taking solid food. Suckling in sperm whales can last up to three years (although mean suckling period has been estimated as 2 years in most regions, Rice 1989). There is evidence that calves start taking solid food, while still suckling, within the first year (Rice 1989).

Santos et al. (1999, 2002) analyzed stomach contents of a number of subadult and adult sperm whales stranded in the north-east Atlantic. Of the 24 whales examined, only one

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Ir. Nat J. Volume 28 No 7 2006

had come from the west coast of \re\and (stranded on the 28 March 1996 on Tory Island, Co

Donegal), in this whale, the octopus Haliphron atlanticus was the main prey by reconstructed

weight but Histioteuthis bonnellii was the most abundant prey species (Santos et al. 2002). Teuthowenia megatops was also found in the stomach, ranging in estimated length from 215 to 295mm, although sample size was small (n=13 lower beaks).

The cephalopod species found in the stomach of the calf (present study) were mainly oceanic squids, although mainly of smaller sizes than those taken by the adult whale documented by Santos et al. (2002). Only one squid species, T. megatops, was common to both individuals. The specimens eaten by the calf (juveniles, 70-180mm and subadults

<260mm) were mainly smaller than those taken by the adult. The diet of calves is expected to differ from that of adult sperm whales since the calves are unable to dive as deep as the adults while searching for prey.

There is little information available on the distribution and biology of many of the oceanic cephalopods eaten by sperm whales. Indeed, records from whale stomachs may provide the only data available (see Clarke 1983). Among the best known is Gonatus fabricii, the main prey of adult sperm whales stranded in the north-east Atlantic {e.g. Santos et al.

2002). Juveniles of this species are caught in the surface layers, while bigger squid are

caught at depths of 200-550m with deep pelagic and bottom trawls (Wiborg et al. 1982). Concerning species recorded in the stomach of the calf in the present study, information on the two most common prey, Teuthowenia megalops and Histioteuthis reversa, is also scarce. T. megalops reaches 380mm mantle length and has been found from the surface to 1500m

depth. Its northern limit in the Atlantic is 65?-66? N, between Greenland and Iceland (Voss 1985). Teuthowenia larvae migrate to the surface after hatching in deep waters, while in later

stages of development the squid spreads vertically in the water column (Lu and Clarke 1975). Histioteuthis reversa is an oceanic squid with a recorded maximum size of 186mm DML. It has been found from the surface to more than 1000m depth, moving closer to the surface at

night and remaining in deeper waters during the day (Voss et al. 1998).

Rice (1989) notes that young sperm whales begin feeding independently years before the teeth erupt. The presence of squid in the stomach of the calf in the present study confirms this, as well as supporting the suggestion by Clarke (1980; see also Rice 1989) that sperm

whales use their teeth only for grasping their prey. Fresh cephalopod and fish found in the

sperm whale stomachs are generally intact and food has been found in the stomachs of whales with deformed jaws (Rice 1989).

Acknowledgements

We wish to thank Joanne O'Brien for help with the post-mortem examination and an

anonymous referee provided very helpful comments on the manuscript.

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