Abstract

In October 1993, the New England Aquarium Marine Mammal Stranding Department accessed a single neonate male pilot whale (Globicephala melaena) that had washed ashore on Nantucket, Massachusetts. The animal presented with rake marks on most of its body, some of which penetrated the blubber layer. Some lacerations were well healed while others were fresh.

The animal's small size of inured us the opportunity to augment our standard necropsy methods with Computer Aided Tomography and Magnetic Resonance Imaging techniques' These scans revealed a fracture of the base of the skull and an infection of the left middle ear. The lesions were confirmed on postmortem along with the additional finding of chronic pneumonia. In our experience, the stranding of a lone neonate pilot whale is an uncommon occurrence. Along with a chronic illness, this animal appears to have been the subject of nonspecific aggression.

Introduction

At 3:00 PM on October 10, 1993, the New England Aquarium received a call about a small live whale, stranded on the island of Nantucket, Massachusetts. The whale was reported as small, thin and has numerous "propeller wounds". Efforts to push the whale off the beach several times and resulted with the animal returning to shore and dying within 2 hours. It was transported to the New England Aquarium for post mortem examination.

The whale showed signs of severe physical trauma upon initial examination, with deep gash marks covering most of its body, some were bleeding; others scarred over. Because of its small size and the extent of external damage Computer Aided Tomography (CAT) and Magnetic Resonance Imaging (MRI) was used to enhance routine post mortem examination and possibly pinpoint specific pathologies. These enhancements would help quantify external and internal damage, and match hard tissue trauma to external signs.

Materials and Methods

CAT and MRI scans were performed at the Massachusetts Eye and Ear Infirmary on a Seimens Somatom Plus CAT and a Seimens Magnetic Resonance Imager, The animal was scanned from the tip of the rostrum to the 1 st cervical vertebrae at 1-8 mm intervals. The rest of the body was scanned at 10-12 mm intervals. Data was first viewed in cross sectional images then later reconstructed and examined in 3 dimensional images. (See Figure 1)

A gross necropsy, following the standard protocol of the New England Aquarium Marine Mammal Stranding Program was performed on October 13, 1993. Tissues were collected for histology and preserved in 10% buffered formalin for sectioning at a later time. Samples for influenza virus isolation, pesticide analysis and DNA separation were double bagged and archived in a -20°C freezer.

Results

The whale was a 204 cm, 115 kg, juvenile, male Globicephala melaena, long finned pilot whale (Table 1). The fresh gash marks located around the head and genital areas were characteristic of extensive conspecific tooth "rake marks." Some of the lacerations penetrated through the blubber and fascia into the underlying muscle layers. A number of similar lacerations were in various stages of healing. The whale was also thin and in poor body condition.

MRI

The MRI produced soft tissue images of lesions that were later confirmed at postmortem. The lacerations penetrated the blubber and fascia layers into the underlying muscle. (See Figure 2) Bruising could be seen underlying fresh wounds while scar tissue was imaged at healed wound sites. There was a differential density between the left and right lungs. Gas was evident in the intestines suggestive of starvation or post mortem changes. Reproductive organs were easily imaged.

Cat

The CAT scan produced hard tissue images of lesions that were confirmed at necropsy: fracture of the right cochlea and an infection of the left ear. Expansion of the left lamUdoid suture was suggestive of episodic trauma. (See Figure 3) Areas of focalized mineralization were observed in both lungs.

Gross Necropsy

The animal had a mid-ventral blubber thickness of less than 0.5 cm thick. There was approximately 250 ml of serosanguinous fluid in the thorax. Many small, round, irregular, firm foci containing mineralized material were found in the parenchyma of both lungs. (See Figure 4) The left lung appeared congested. The heart appeared slightly enlarged. The left accessory lymph nodes appeared very edematous and active and were estimated to be 2-3 times normal size. The liver was very dark brown and firm. No parasites were found in the ear sinus, but the left middle ear was filled with a purulent material that drained into the eustachian tubes and bony nares. Microscopic examination on the material showed a large number of polymorphonuclear cells and cellular debris. The left lambdoid suture lesion was open but showed recent growth at the margins. The right lambdoid suture appeared closed.

Discussion

Mass strandings of pilot whales have been regularly reported within the Cape Cod Bay and the Islands (W. McFee). However it is rare to find singly stranded adult pilot whales; and rarer still to find neonates. Of 467 pilot whale strandings documented by NEA since 1980, only 20 have been single stranded. Of the 20 single stranded animals, 4 have been under 239 cm, the mean size of weaned whales.

The age of this whale was estimated to be six months based on physical characteristics and by comparing its length with age/length tables published by Sergeant and Sergeant and Kasuya. Basing an age estimate on age/length regression tables alone may be somewhat misleading in this case, however, due to the possibility that this whale was chronically malnourished and stunted. Newly erupted teeth was the best indicator of this whale's age and it's status as a still nursing, maternally dependent neonate. According to Sergeant, tooth eruption generally occurs at a mean body length of 213 cm or at an age of approximately 6 months. Weaning is described by Sergeant as the length at which squid and milk can be found in examined animals. This length range is 221 cm to 244 cm with a mean length of 239 cm corresponding to an approximate age of 6-9 months. With newly erupted teeth, at a length of 204 cm, this whale would almost certainly be entirely maternally dependent.

Body condition and nutritional status for this whale can be quantified by comparing it's weight with weight/length regressions, and comparing blubber thicknesses with published measurements. Using Sergeant's weight length chart a whale of 204 cm should weigh roughly 200 kg. This whale was 57.5% of the published value. Blubber thickness should be a minimum of 2.0 cm for this age category, instead of the <.5 cm measured on this whale. A critically thin blubber layer would indicate acute malnutrition.

The possibility of chronic malnutrition and stunting may be indicated by the mismatch between tooth eruption signs and length. According to Sergeant tooth eruption generally occurs at an age of 6-9 months and a mean length of 239 cm. The length of this whale (204 cm) is well outside this range and therefore shows signs of both acute and chronic malnutrition.

The trauma to this neonate Globicephala melaena appears to have been episodic with at least one previous set of injuries. The partially healed fracture of the right cochlea indicates a traumatic head injury in the past. The seemingly chronic infection of the left ear draining into the eustachian tubes and bony nares could have seeded a secondary infection of the lungs.

All the data obtained during the scans was confirmed during the gross necropsy. CAT and MRI imaging helped pinpoint subtle lesions that may have been overlooked in the gross postmortem. With the data obtained two reasonable hypothesis may possible be drawn. In the first hypothesis this whale developed the chronic ear infection, becoming disorientated and behaviorally erratic, resulting in rejection from the pod. In the second hypothesis the whales' mother died or would not nurse him. He, in turn, much like the weaner elephant seals (King, 1983), attempted to nurse off of other lactating females and in the process became the target of aggression.

The appearance of "rake marks" in Globicephala melaena has been documented in two contexts. During a drive of pilot whales in Newfoundland Sergeant observed the following: "Rows of parallel tooth marks occurred in practically all animals after a drive. Since these were fresh, and very few old scars were found, it was assumed that they were made during the course of the drive as the result of the disorganization of normal behavior". "The absence of fresh naturally occurring wounds of either type in our sample suggests that fighting in Globicephala melaena is confined to the breeding season." (Sergeant, 1962). Because this whale was probably too young to be directly involved in breeding activity it is likely that the aggression may have been the result of a disruption of normal behavior. This aggression appears to have been severe enough to cause death.

Figure 1. 3D reconstruction of neonate pilot whale	Figure 2: Deep laceration.
Figure 3: Left lambdoid suture.	Figure 4: Lung foci.

References

1.  Kasuya, T., D.E. Sergeant,and K. Tanaka. 1988. Re-examination of life history parameters of long-finned pilot whales in the Newfoundland waters. Sci. Rep. Ehales Res. Inst 39.

2.  Kasuya, Toshio, and Marsh, Helene., Life History and Reproduction Biology of the Short Finned Pilot Whale, Globicephala macrorhynchus, off the pacific Coast of Japan. Rep. International Whaling Commission (Special Issue 6)55pp.

3.  Kato, Hidehiro., Observation of Tooth Scars on the Head of Male Sperm Whale, as an Indication of Intra-Sexual Fightings. Sci. Rep. Whales Res. Inst., No 35, 1984, pp.39-46.

4.  King Judith E. 1983. Seals of the World. British Museum (Natural History) and Cornell University Press. McFee, W.E.1990. An analysis of mass strandings of the longfinned pilot whale, Globicephala melaena on Cape Cod. Master thesis, Northeastern University, Boston, MA, 85pp.

5.  Sergeant, D. E., 1962 The Biology of the pilot of pothead whale Globicephala melaena (Trail!) in Newfoundland Waters. Fisheries Research Board of Canada, 1962.