6. SPECIAL ASPECTS OF SPERM WHALES AND THEIR RELEVANCE TO WHALE WATCHING

Sperm whales have two predominant modes of behaviour: foraging and resting/socialising (Box 1). Female groups are engaged in foraging and resting/socialising activities for approximately 75% and 25% of their time respectively (Leaper et al. 1992). The proportion of time mature males spend resting is less well known.

Box 1. Sperm Whale Behavioural Modes

Sperm whales have two predominant modes of behaviour: Foraging (~75% of time for female groups): a dive of about 35-55min is followed by a surface period of about 7-12min. During the surface period the whale generally moves steadily, does not turn or suddenly accelerate, blows regularly, and continually breaks the surface. The surface period ends with a deliberate fluke-up which may be accompanied by defecation and is usually preceded by a slight increase in blow rate and some dorsal-ventral flexing. While underwater sperm whales typically click regularly at 1-2 clicks/sec for much of the time. They are mostly silent during breathing periods at the surface. Socialising/Resting (~25% of time for female group): Socialising behaviour is characterised by whales staying at or near the surface for periods of 20min-12hr. When socialising, female groups form close clusters of 4-40 whales. Behaviour is varied, ranging from all whales lying still and very close to one another at the surface, to active socialising characterised by rolling, touching, spy-hopping, breaching and the production of codas (stereotyped patterns of 2-20 clicks). Occasionally, large males associate with socialising female groups for short periods. Large males may lie still and silent at or near the surface alone or, occasionally, in pairs, for an hour or more when resting.

Relevance of behavioural modes to whale-watch activity

6.1 Differences Between The Sexes In Body Size, Geographic Distribution, And Association Patterns

Relevance of sex differences to whale-watch activity

Recognition of group type is important because the nature of a whale watch focusing on mature males is likely to be quite different from that targeting female groups. For example, sex differences in responses to whale-watch operations have been described for sperm whales. The two most highly developed whale-watch operations both focus on mature male sperm whales. In each case, operators have reported a small number of males, often those living near shore, that are tolerant of or habituated to close approaches by boats. Because these whales are highly visible and easily accessible, they are approached disproportionately often by whale-watch operators. In contrast, tolerant or habituated whales have not been reported by whale watch operators who focus on female groups.

Box 3: Sex Differences In Body Size, Geographic Distribution, And Association Patterns

Social Group	Definition	Body Size	Geographic distribution
Female Group	Stable matrilineal group comprised of adult females and young (including male offspring aged < 6yrs) Move together as a unit but may spread out over > 1km May include visiting adult male(s) on temporary basis	Adult: <12m Calf: <9m	Temperate or tropical waters, i.e., typically at latitude <35
Mature Males	Single or in small all-male groups	<18m	Colder waters, i.e., typically at latitude >45 (or 55 in N. Pacific)

Box 4. Guide To Recognising Sperm Whale Social Groupings

Female sperm whales and males less than about 6yr old live in groups of about 20 animals (usually 6-40). The members of a group may be spread over 1km of more of ocean, and only 1-2 (or sometimes none) may be visible at the surface at any time. Male sperm whales older than about 6yr may be found alone, accompanying female groups, or in "bachelor" schools. If you are with sperm whales, a female group is probably present if: latitude <35, or small whales (<9m) are present or more than 2 whales are clustered together at the surface, or more than 5 clicks/s can be heard consistently through a hydrophone. A female group is probably not present it, latitude>45 (55 in N. Pacific), or only whales > 12m long are visible. If in doubt, assume a female group is present.

Recognition of female groups is also important because these groups may be especially vulnerable to disturbance by whale-watch activities. For example, features of female groups -- large group size and presence of calves -- both enhance the whales' appeal and visibility to whale-watch operations but decrease the whales' mobility and ability to avoid whale-watch vessels.

The vulnerability of calves in female groups is of particular concern. The rearing of calves in large groups of related females is likely to be an adaptation that promotes calf survival, social development, and learning. Calves are dependent upon their mothers tor extended periods. Though they take their first solid food in their first year, they may continue to suckle for up to 13 years (Best et al. 1984). Other members of the matrilineal group may also play important roles in the care and protection of calves during the lengthy maturation period. Neonates , which are unable to dive with other group members and thus remain visible at the surface, are particularly accessible to whale-watch operations. These young calves are also particularly curious and may approach and investigate vessels. A report that calves may be inadvertently injured while investigating vessels (Watkins, pers comm) indicates how inappropriate this behaviour can be.

There is also concern that mating activity, which takes place when mature males visit female groups, may be disrupted by whale-watch activity. Mating opportunities may be a limiting factor for population growth in some areas, such as the Galapagos, where mature males are particularly rare, perhaps as a consequence of past whaling (Clarke et al. 1980; Whitehead and Waters 1990; Whitehead 1993). Whale-watch activities in these areas may be directly disruptive to mating or may indirectly reduce the rate at which mature males encounter receptive females.

Potential disturbance to sperm whale reproduction - either mating or calf survival -- is of especial concern because sperm whales have the lowest reproductive rate of any mammal. Females do not begin to breed until approximately 9 years of age; gestation is approximately 15 months long and singleton births are the rule; calves are dependent upon their mothers for approximately 4 years; and inter-calving intervals are 5-6 years. In addition, calf mortality may be high. Maximum growth rate for sperm whale populations has been estimated at 0.86% (Calculation by Whitehead based on IWC (1982)).

Social Organisation
Deep Diving and Acoustically Meditated Species
Widely Distributed In Oceanic Waters

Spiritual/Cultural Significance

To Be Continued

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