Hal Whitehead

Heterogeneity in photo‐identification rates among individuals is a potentially serious problem in many studies of cetacean biology, especially the analysis of populations. However, this heterogeneity is usually difficult to identify or measure. Two instances in which closed groups of female and immature sperm whales (Physeter macrocepbalus) were tracked and identified using fluke photographs over periods of days off the Galápagos Islands allowed direct examination of heterogeneity in identification rates. A group of nine animals followed in 1999 provided almost no evidence for heterogeneity (permutation test for heterogeneity, P= 0.48), with an estimated coefficient of variation in identification rates of 0.03 (95% CI from 1,000 bootstrap replications: 0.00–0.10). In contrast, the identification rates of a group of 22 animals followed in 1995 seemed to show potentially important differences (P= 0.058, CV = 0.20, 95% CI = 0.07–0.28). These differences were not related to the internal social structure of the group or to differences in numbers of markings on the flukes, but smaller whales had lower identification rates. Thus, young sperm whales may be underrepresented in photo‐identification studies, but adults within groups seem to have similar identification rates. Situations in which animals are photo‐identified from closed populations of known size are particularly useful for examining heterogeneity. They should be vigorously exploited by those who use photo‐identification to examine population or behavioral biology.

Although the majority of commentators implicitly or explicitly accept that field data allow us to ascribe culture to whales, dolphins, and other nonhumans, there is no consensus. While we define culture as information or behaviour shared by a population or subpopulation which is acquired from conspecifics through some form of social learning, some commentators suggest restricting this by requiring imitation/teaching, human analogy, adaptiveness, stability across generations, progressive evolution (ratchetting), or specific functions. Such restrictions fall down because they either preclude the attribution of culture to nonhumans using currently available methods, or exclude parts of human culture. The evidence for cetacean culture is strong in some cases, but weak in others. The commentaries provide important information on the social learning abilities of bottlenose dolphins and some interesting speculation about the evolution of cetacean cultures and differences between the cultures of different taxa. We maintain that some attributes of cetacean culture are currently unknown outside humans. While experimental studies, both in the laboratory and in the wild, have an important role in the study of culture in whales and dolphins (for instance in determining whether dolphins have a Theory-of-Mind), the real treasures will be uncovered by long-term observational studies at sea using new approaches and technologies.

We examined patterns of affiliation within groups of sperm whales (Physeter macrocephalus), particularly concentrating on how short‐term spatio–temporal associations reflect long‐term relationships. Female and immature sperm whales live in stable, and partially matrilineal, social units. Two or more social units may move together for periods of several days, forming a cohesive group of about 20 animals. We observed that sperm whales in the eastern tropical Pacific quite consistently associated with members of their own social unit more than they did with other animals in their group with whom they did not share a long‐term relationship. There was little evidence for preferred, or avoided, affiliations within social units, except in two large and relatively unstable units. In two well‐studied groups, individuals did not show consistently favoured positions in the foraging rank relative to other members of their social unit. These results indicate the importance of long‐term relationships to female and immature sperm whales, but suggest that relationships are quite homogeneous within social units.

Fecal samples were collected while following sperm whales (Physeter macrocephalus) off the Galápagos Islands, Ecuador. They contained 133 upper beaks and 164 lower beaks of cephalopods. Analysis of the lower beaks suggests that the sperm whales fed primarily on three genera of cephalopods; Histioteutbis (62%), Ancistrocbeirus (16%), and Octopoteutbis (7%). The beak dimensions indicate that the cephalopods ranged in mantle length from 5 to 54 cm and in mass from 12 to 650 g. Fecal samples varied significantly between five study years and over different parts of the study area, but the number of beaks collected per sample did not correlate significantly with defecation rate (a measure of feeding success). Using beak material from fecal samples gives a biased estimate of sperm whale diet, reducing the frequencies of very small and very large cephalopods. However, all other available methods of assessing sperm whale diet also possess biases.

The behavior of groups of female and immature sperm whales (Physeter macrocephalus) was measured on 117 d within an 11‐yr period off the Galápagos Islands, Ecuador. On each day, up to 18 measures of visually observable behavior were calculated. These concerned speeds, headings, movement patterns, diving synchrony, foraging formations, time spent socializing, and aerial behavior. The measured behavior of the sperm whales was considerably more variable when they were socializing than when foraging. None of the measures showed much correlation with sea‐surface temperature, and only measures of consistency of movement were significantly correlated with defecation rate, an indicator of feeding success. However, month‐long time periods accounted for over 50% of the variance in eight of eighteen measures, and, in the cases of surface speed and dive synchrony, the effects were statistically significant. In contrast, there was no autocorrelation with lag of one day in the residuals of any of the measures. Thus, behavior may be tracking substantial temporal variation in the whales' environment over scales of about several months. Groups of whales had significantly different travel patterns, but there was little other evidence for group‐specific behavior, perhaps because tests of group‐specific effects were not of adequate statistical power. Variation in sperm whale behavior, especially over time scales of a few months or longer and spatial scales of a few hundred kilometers or larger, should be considered when estimating densities from sighting surveys.

Low diversities of mitochondrial DNA (mtDNA) have recently been found in four species of matrilineal whale. No satisfactory explanation for this apparent anomaly has been previously suggested. Culture seems to be an important part of the lives of matrilineal whales. The selection of matrilineally transmitted cultural traits, upon which neutral mtDNA alleles “hitchhike,” has the potential to strongly reduce genetic variation. Thus, in contrast to other nonhuman mammals, culture may be an important evolutionary force for the matrilineal whales.

It is generally expected that exploited whale populations should rebuild following the end of whaling. Using photographic identification of individuals during a series of field projects, we studied female and immature sperm whales ( Physeter macrocephalus) that visit the waters off the Galápagos Islands, Ecuador. Analysis of mark‐recapture data, using a likelihood model, indicates the population decreased at a rate of about 20% per year (95% c.i. 7–32%) between 1985‐1995. During the study period the animals were not hunted and were not obviously the subject of other immediate anthropogenic threats. Rates at which research vessels encountered whales also fell over this interval. The decline seems to be due principally to migration into waters off the Central and South American mainland. The population also has a very low recruitment rate, about 0.05 calves/female/year, as indicated by rates of observation of calves. Although other causes cannot be ruled out, both the high emigration rate and low recruitment rate are probably related to heavy whaling in Peruvian waters which ended in 1981. Whales from the Galápagos are moving east to fill productive but depopulated waters near the coast, and the virtual elimination of large breeding males (in their late twenties and older) from the region has lowered pregnancy rates. The case of the Galápagos sperm whales strongly suggests that exploitation can continue to have substantial negative impacts on the size and recruitment rate of an animal population well outside the range of the hunt and for at least a decade after it has ended. Explotación en el Pasado y la Rápida Declinación de los Cachalotes de las Islas Galápagos Generalmente se espera que las poblaciones de ballenas que han sido explotadas se recuperen al término del período de explotación. Por medio de identificación fotográfica de individuos estudaimos hembras e inmaduros de cachalotes ( Physeter macrocephalus) que visitan las aguas cercanas a las Islas Galápagos, Ecuador. El análisis de datos de captura‐recaptura, utilizando un modelo de probabilidad, indica que la población declinó a una tasa aproximada de 20% por año (95% c.i. 7‐32%) entre 1985 y 1995. Durante el estudio los animales no fueron cazados ni estuvieron sujetos a otras amenazas antropogénicas inmediatas y obvias. Durante este intervalo también decrecieron las tasas de avistamiento de ballenas desde barcos de investigación. La declinación parece deberse principalmente a la migración hacia aguas cercanas a la costa de Centro y Sudamérica. La observación de crías indica que la población también tiene una tasa de reclutamiento muy baja, approximadamente 0.5 crías/hembra/año. Aunque no se pueden descartar otras causas, tanto la elevada tasa de emigración como la baja tasa de reclutamiento probablemente se deben a la cacería intensiva en aguas peruanas que terminó en 1981. Ballenas de las Galápagos se están moviendo hacia el este para ocupar aguas productivas pero despobladas cercanas a la costa y la eliminación virtual de machos reproductores (de 20 años o más) ha reducido la tasa de reproducción. El caso de los cachalotes de las Galápagos sugiere que la cacería puede causar impactos negativos significativos sobre el tamaño y la tasa de reclutamiento de una población animal fuera del área de caza y por lo menos una década después de terminada la cacería.