Identifying the "demon whale-biter": Patterns of scarring on large whales attributed to a cookie-cutter shark Isistius sp

The presence of crater-like wounds on cetaceans and other large marine vertebrates and invertebrates has been attributed to various organisms. We review the evidence for the identity of the biting agent responsible for crater wounds on large whales, using data collected from sei ( Balaenoptera borealis ), fin ( B . physalus ), inshore and offshore Bryde's ( B . brydeii sp) and sperm whales ( Physeter macrocephalus ) examined at the Donkergat whaling station, Saldanha Bay, South Africa between March and October 1963. We then analyse the intensity and trends in its predation on large whales. Despite the scarcity of local records, we conclude that a cookie-cutter shark Isistius sp is the most likely candidate. We make inferences about the trends in (1) total counts of unhealed bitemarks, and (2) the proportion of unhealed bitemarks that were recent. We use day of the year; reproductive class, social grouping or sex; depth interval and body length as candidate covariates. The models with highest support for total counts of unhealed bitemarks involve the day of the year in all species. Depth was an important predictor in all species except offshore Bryde's whales. Models for the proportion of recent bites were only informative for sei and fin whales. We conclude that temporal scarring patterns support what is currently hypothesized about the distribution and movements of these whale species, given that Isistius does not occur in the Antarctic and has an oceanic habitat. The incidence of fresh bites confirms the presence of Isistius in the region. The lower numbers of unhealed bites on medium-sized sperm whales suggests that this group spends more time outside the area in which bites are incurred, providing a clue to one of the biggest gaps in our understanding of the movements of mature and maturing sperm males

Estimates of demographic parameters for southern right whales off South Africa from survey data from 1979 to 2006

Aerial counts of right whale cow-calf pairs on the south coast of South Africa between 1971 and 2006 indicate an annual instantaneous population increase rate of 0.069 a year (95% CI 0.064, 0.074). Annual photographic surveys since 1979 have resulted in 1 968 resightings of 954 individual cows with calves. Observed calving intervals ranged from 2 to 23 years, with a principal mode at 3 years and secondary modes at 6 and 9 years, but these made no allowance for missed calvings. Using the model of Payne et al. (1990), a maximum calving interval of 5 years produces the most appropriate fit to the data, giving a mean calving interval of 3.16 years with a 95 % confidence interval of (3.13, 3.19). The same model produces an estimate for adult female survival rate of 0.990 with a 95% confidence interval of (0.985, 0.996). The Payne et al. (1990) model is extended to incorporate information on the observed ages of first reproduction of grey-blazed calves, which are known to be female. This allows the estimation of first parturition (median 7.74 years with 95% confidence interval (7.15, 8.33)). First year survival rate was estimated as 0.713 (0.529, 0.896) and the instantaneous population increase rate as 0.070 (0.065, 0.075). The current (2006) population is estimated as some 4 100 animals, or about 20% of initial population size: the latter parameter needs re-consideration

Estimates of demographic parameters for southern right whales off South Africa from survey data from 1979 to 2006

Aerial counts of right whale cow-calf pairs on the south coast of South Africa between 1971 and 2006 indicate an annual instantaneous population increase rate of 0.069 a year (95% CI 0.064, 0.074). Annual photographic surveys since 1979 have resulted in 1 968 resightings of 954 individual cows with calves. Observed calving intervals ranged from 2 to 23 years, with a principal mode at 3 years and secondary modes at 6 and 9 years, but these made no allowance for missed calvings. Using the model of Payne et al. (1990), a maximum calving interval of 5 years produces the most appropriate fit to the data, giving a mean calving interval of 3.16 years with a 95 % confidence interval of (3.13, 3.19). The same model produces an estimate for adult female survival rate of 0.990 with a 95% confidence interval of (0.985, 0.996). The Payne et al. (1990) model is extended to incorporate information on the observed ages of first reproduction of grey-blazed calves, which are known to be female. This allows the estimation of first parturition (median 7.74 years with 95% confidence interval (7.15, 8.33)). First year survival rate was estimated as 0.713 (0.529, 0.896) and the instantaneous population increase rate as 0.070 (0.065, 0.075). The current (2006) population is estimated as some 4 100 animals, or about 20% of initial population size: the latter parameter needs re-consideration

A note on possible changes in some demographic parameters for southern right whales off South Africa

The possibility of changes in demographic parameters for right whales off South Africa is examined through analysis of resightings data for females with calves over the 1979–2006 period. No statistically significant change in either adult survival rate or population growth rate is detected. However the mean calving interval shows a decrease from 3.2 to 3.1 years somewhere between 1985 and 1990

Updated estimates of demographic parameters for Southern right whales off South Africa

Aerial counts of right whale cow-calf pairs on the south coast of South Africa between 1971 and 2003 indicate an annual instantaneous population increase rate of 0.069 a year (SE 0.003) over this period. Annual photographic surveys since 1979 have resulted in 1,504 resightings of 793 individual cows with calves. Observed calving intervals ranged from 2 to 23 years, with a principal mode at 3 years and secondary modes at 6 and 9 years, but these made no allowance for missed calvings. Using the model of Payne et al. (1990), a maximum calving interval of 5 years produces the most appropriate fit to the data, giving a mean calving interval of 3.15 years with a 95 % confidence interval of (3.11, 3.18). The same model produces an estimate for adult female survival rate of 0.990 with a 95% confidence interval of (0.983, 0.997). The Payne et al. (1990) model is extended to incorporate information on the observed ages of first reproduction of greyblazed calves, which are known to be female. This allows the estimation of first parturition (median 7.69 years with 95% confidence interval (7.06, 8.32)). First year survival rate was estimated as 0.734 (0.518, 0.95) and the instantaneous population increase rate 0.073 (0.066, 0.079). The current population is estimated as some 3,400 animals, or about 17% of initial population size: the latter parameter needs re-consideration

Geographical variation in the body size of adult female sperm whales (Physeter macrocephalus) – an example of McNab’s resource rule?

This study investigates possible regional variations in size composition of adult female sperm whales (Physeter macrocephalus) using data from 3302 pregnant individuals taken on Soviet whaling expeditions to the Southern Hemisphere 1961/62–1974/75. A general linear model (GLM) was used to take the covariates of expedition, latitude and ocean basin into account. The average body size decreased from south to north in each ocean basin, with the biggest decrease (about 200 cm) in the Indian Ocean; followed by the Pacific Ocean (about 110 cm), and the Atlantic Ocean (about 80 cm). Independent data confirm the small size of female/immature sperm whales in some tropical areas of the Indian and Pacific Oceans. The mechanism responsible for this geographic variation in sperm whale growth could reflect culturally transmitted differences in foraging behaviour between clans of female/immature sperm whales in response to differing availabilities of prey resources by geographical region – McNab’s resource rule. However there is little available information for such a mechanism to be readily identifiable. Although data for oceanic squids (sperm whale’s main source of food) are lacking, there is evidence that the individual sizes of neritic species are positively correlated with latitude. Hence feeding in equatorial regions may be energetically more demanding due to smaller individual prey size, with consequent effects on growth rate

Application of a photo-identification based assessment model to southern right whales in South African waters

The three-mature-stages (receptive, calving and resting) model of Cooke et al. (2003) is applied to photo-identification data available from 1979 to 2010 for southern right whales in South African waters. The 2010 number of females having reached the age at first parturition is estimated to be 1 205, the total population (including males and calves) 4 725, and the annual population growth rate 6.8%. The probability (average 11%) that a resting mature whale rests for a further year appears to vary annually, whereas the probability (7%) that a receptive whale rest (or aborts) rather than calves the next year appears to be constant. Information from resightings of grey blazed calves as adults with calves allows estimation of first year survival rate of 0.914 (compared to a subsequent annual rate of 0.987, and an age at 50% maturity of 6.4 years. However this suggests also that 27% (s.e. 6%) of grey blazed calves lose their marking before becoming adults. In contrast, the relative proportions of grey blazed animals amongst calves and amongst calving adults suggest rather a value of 10% (s.e. 8%). If the proportion losing markings is in fact 10%, first year survival rates estimate drops to 0.837 and the population growth rate to 6.4% pa

Identifying the "demon whale-biter" : patterns of scarring on large whales attributed to a cookie-cutter shark Isistius sp

The presence of crater-like wounds on cetaceans and other large marine vertebrates and invertebrates has been attributed to various organisms. We review the evidence for the identity of the biting agent responsible for crater wounds on large whales, using data collected from sei (Balaenoptera borealis), fin (B. physalus), inshore and offshore Bryde’s (B. brydeii sp) and sperm whales (Physeter macrocephalus) examined at the Donkergat whaling station, Saldanha Bay, South Africa between March and October 1963. We then analyse the intensity and trends in its predation on large whales. Despite the scarcity of local records, we conclude that a cookie-cutter shark Isistius sp is the most likely candidate. We make inferences about the trends in (1) total counts of unhealed bitemarks, and (2) the proportion of unhealed bitemarks that were recent. We use day of the year; reproductive class, social grouping or sex; depth interval and body length as candidate covariates. The models with highest support for total counts of unhealed bitemarks involve the day of the year in all species. Depth was an important predictor in all species except offshore Bryde’s whales. Models for the proportion of recent bites were only informative for sei and fin whales. We conclude that temporal scarring patterns support what is currently hypothesized about the distribution and movements of these whale species, given that Isistius does not occur in the Antarctic and has an oceanic habitat. The incidence of fresh bites confirms the presence of Isistius in the region. The lower numbers of unhealed bites on medium-sized sperm whales suggests that this group spends more time outside the area in which bites are incurred, providing a clue to one of the biggest gaps in our understanding of the movements of mature and maturing sperm males.S1 Code. Code for fitting GAMs to total number of unhealed bitemarks.S1 Dataset. Minimal dataset.S1 Fig. Scoop of blubber found in the stomach of a sperm whale at Donkergat whaling station, 2 September 1963 (platform # 1066), showing: A—dorsal, B—lateral, and C—ventral views (scale in cm).S1 Table. Average numbers of unhealed bites on 226 mature sei whales of different reproductive classes examined at the Donkergat whaling station, South Africa, September/October 1963, with results of Tukey HSD Test.S1 Text. A review of the identity of the biting agent: evidence for and against Isistius as the biting agent. Including a comparison of wounds made by I. brasiliensis and I. plutodus, the biting technique of Isistius and a case study of a “reverse scoop” found in a sperm whale stomach and a review of other potential biting agents.S2 Code. Code for fitting GAMs to the proportion of unhealed bitemarks that were recent.S2 Table. Location of unhealed bitemarks on 169 sperm whales examined at the Donkergat whaling station, South Africa, 1963.S2 Text. Interpretation of missing records.S3 Table. Location of unhealed incomplete bites on whales examined at the Donkergat whaling station, South Africa, 1963.S3 Text. Account of an outlying observation of a sperm whale with a large number of unhealed bitemarks.S4 Table. Incidence of recent bites on large whales landed at the Donkergat whaling station, South Africa, 1963, and mean number of bites per whale bitten, by depth interval.http://www.plosone.orgam2016Mammal Research InstituteZoology and Entomolog

Identifying the "demon whale-biter" : patterns of scarring on large whales attributed to a cookie-cutter shark Isistius sp

The presence of crater-like wounds on cetaceans and other large marine vertebrates and invertebrates has been attributed to various organisms. We review the evidence for the identity of the biting agent responsible for crater wounds on large whales, using data collected from sei (Balaenoptera borealis), fin (B. physalus), inshore and offshore Bryde's (B. brydeii sp) and sperm whales (Physeter macrocephalus) examined at the Donkergat whaling station, Saldanha Bay, South Africa between March and October 1963. We then analyse the intensity and trends in its predation on large whales. Despite the scarcity of local records, we conclude that a cookie-cutter shark Isistius sp is the most likely candidate. We make inferences about the trends in (1) total counts of unhealed bitemarks, and (2) the proportion of unhealed bitemarks that were recent. We use day of the year; reproductive class, social grouping or sex; depth interval and body length as candidate covariates. The models with highest support for total counts of unhealed bitemarks involve the day of the year in all species. Depth was an important predictor in all species except offshore Bryde's whales. Models for the proportion of recent bites were only informative for sei and fin whales. We conclude that temporal scarring patterns support what is currently hypothesized about the distribution and movements of these whale species, given that Isistius does not occur in the Antarctic and has an oceanic habitat. The incidence of fresh bites confirms the presence of Isistius in the region. The lower numbers of unhealed bites on medium-sized sperm whales suggests that this group spends more time outside the area in which bites are incurred, providing a clue to one of the biggest gaps in our understanding of the movements of mature and maturing sperm males.Publisher PDFPeer reviewe