Sperm Whale Seismic Study (SWSS)

Summer Breeze Daily Reports - June 19, 2005

Position at 29.17  88 24

Today was our first day of what we would describe "regular" sperm whale behavior: surfacing intervals of around 12 minutes ending with a fluke and a ~45 minute dive. However, the day started again with another group of five individuals logging at the surface and shallow-diving. It was quite remarkable that we found them at all. We had heard a few sporadic codas at first light, managed to get a direction on them and motored that way. As we heard nothing more we stopped the boat to wait and listen and had just about given up when we realized that we were looking right at a resting group of whales only 200 meters from the boat, almost invisible in the strange greasy light of daybreak. After a couple of hours the group started to make feeding dives and dispersed over a mile or so. One consistent pairing was an individual with a callus (therefore, probably a mature female) and a rather large calf. We had first classed this animal as a juvenile but then observed behavior typical of suckling during most of the day. (Sperm whale calves may continue to suckle for several years and the distinction between “calf” and “juvenile” is not as clear as in some other species.)

This large calf typically dove with its escort at the end of each surfacing, though it didn’t quite bring its flukes above the surface. Clearly though it wasn’t yet as accomplished a diver as the adults and it was often seen at the surface alone, swimming quite purposefully, as though keeping track of the diving animals below.

On one occasion when we saw the large calf by itself at the surface it was joined by a group of about eight pygmy killer whales. They were paying a lot of attention to the calf, which tried to avoid them, rolling on the surface and changing direction. There was no indication of an attack, but this species is reported to be aggressive and has been known to attack cetaceans both in captivity and in the wild. We witnessed a similar interaction between this species and a smaller calf in a group at the surface last year. Our perceptions may have been colored by the species’ name or reputation, but it felt as though they were predators testing the calf, looking for vulnerability.

Of the other members of the group of five we had seen resting in the early morning, two  individuals also consistently surfaced together, and the final animal surfaced alone. Through the day we had often seen another strong blow about a mile and a half from our assemblage, but as it surfaced at much the same time as our whales, we never managed to reach it while it was on the surface. Late in the afternoon though, we moved over to start tracking this whale. It turned out to be a sizeable male, one of the largest we have yet seen in the Gulf but still not as big as the large breeding males we have seen in other areas. The absence of putative breeding males in the Northern Gulf remains a mystery; we can only assume that breeding is confined to other times of the year.

We are now heading in to Gulfport, Mississippi a day ahead of schedule. It’s a pity to be doing this: we still have fuel and water, the weather remains good, and we feel that we are just getting into our stride. However, one of the team, Jonathan, has a bad ear infection, and there are several important things to sort out on the boat. Both areas will be better attended to sooner than later.