Browsing by Author "Best, Peter B"
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- ItemOpen AccessThe abundance of blue whales on the Madagascar Plateau, December 1996(International Whaling Commission, 2003) Best, Peter B; Rademeyer, Rebecca A; Burton, Chris; Ljungblad, Don; Sekiguchi, Keiko; Shimada, Hiroyuki; Thiele, Deborah; Reeb, Desray; Butterworth, Doug SAs part of the International Whaling Commission’s SOWER blue whale research programme, two sighting vessels, the Shonan Maru and the Shonan Maru No.2 , surveyed the Madagascar Plateau between 25° and 35°S, 40° and 45°E, in December 1996. A total of 95 sightings of 110 blue whales (assigned in the field as pygmy blue whales – see discussion), 14 sightings of 21 blue whales (subspecies un determined) and 12 sightings of 13 ‘like blue’ whales was made in 23 days. In the first half of the survey, the whole research area was cov ered in a mainly pre-determined zigzag search pattern, and the associated sightings and effort have been used to derive density estimates for bl ue whales for the area. Sightings in the second half of the survey, where effort was directed at blue whale concentrations, have only bee n used to provide supplementary data for calculation of the effective search half-width and mean school size. The resulting population es timate is 424 (CV = 0.42), or 472 (CV = 0.48) whales when ‘like blue’ sightings are included. Dive times and surfacing behaviour recorded in just over 21h of monitoring suggest that the assumption that all groups on the trackline were seen ( g (0) = 1) is reasonable. As the geographical extent of the survey area was substantially less than that of past catches of blue whales in the region in December, this estim ate must refer to only a portion (possibly about one third) of the total population. Some evidence of feeding on euphausiids in the region was detected, possibly as a consequence of a localised upwelling cell at the southern tip of Madagascar
- ItemOpen AccessApplication of a photo-identification based assessment model to southern right whales in South African waters(2012) Brandão, Anabela; Butterworth, Doug S; Müller, Andrea; Best, Peter BThe 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.
- ItemOpen AccessApplication of a photo-identification based assessment model to southern right whales in South African waters, now including data up to 2012(2013) Brandão, Anabela; Butterworth, Doug S; Ross-Gillespie, Andrea; Best, Peter BThis paper extends the analyses of Brandão et al. (2012) which applied the three-mature-stages (receptive, calving and resting) model of Cooke et al. (2003) to photo-identification data available from 1979 to 2010 for southern right whales in South African waters, by taking two further years of data into account. The 2012 number of parous females is estimated to be 1 321, the total population (including males and calves) 5 062, and the annual population growth rate 6.6%. This reflects a small reduction to the 6.8% increase rate estimated previously; this is a result of slightly lesser numbers in recent years than estimated previously. Information from resightings of grey blazed calves as adults with calves allows estimation of first year survival rate of 0.850, compared to a subsequent annual rate of 0.988. This information also suggests that 7% (s.e. 6%) of grey blazed calves are not recognised as such when adults; this estimate is much less than that of 27% obtained previously by Brandão et al. (2012), and is more compatible with the relative proportions of grey blazed animals amongst calves and amongst calving adults which suggest a value of 10% (s.e. 8%).
- ItemRestrictedBiopsying Southern right whales: their reactions and effects on reproduction(Wiley, 2005) Best, Peter B; Reeb, Desray; Rew, Mary Beth; Palsbøll, Per J; Schaeff, Cathy; Brandão, AnabelaCollecting skin biopsies from large whales for genetic analysis is often subject to national permit, and in the case of cow-calf pairs, it may be prohibited. We present results of 906 biopsy attempts on southern right whales (Eubalaenaustralis) in South African waters between 1995 and 1997, including 147 cow-calf pairs. Our sampling success was higher for biopsy darts with a bore of 4 mm compared to 4.6 mm. Contact periods averaged 17.7 min for cow-calf pairs and 25.4 min for whales unaccompanied by calves. There were no significant differences in the short-term reactions of males and females to biopsying, but the reaction of single animals of either sex was greater than for larger groups. Cows accompanied by calves had the strongest reactions, which were significantly greater than even single females. We found evidence of sensitization to repeat biopsying (over periods of hours to 65 days) for cows but not calves (n = 20). We compared the subsequent reproductive history of 117 biopsied cows with that of 163 unbiopsied cows from the same years, and we compared the distribution of calving intervals for biopsied animals with 829 intervals recorded from 1985 to 1995. We did not detect any adverse effects on the proportion of successful reproductive cycles, and hence calf survival, or the proportion of longer-than-normal cycles, although the power of all the statistical tests was low. We concluded that any prohibition on the biopsy sampling of cow-calf pairs should be carefully reconsidered in the light of the valuable genetic insights such sampling could achieve.
- ItemOpen AccessEstimates of demographic parameters for southern right whales off South Africa from survey data from 1979 to 2006(2010) Brandão, Anabela; Best, Peter B; Butterworth, Doug SAerial 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.
- ItemOpen AccessEstimating the abundance of common dolphins on the southern coast of South Africa(2009) Best, Peter B; Meyer, Michael A; de Decker, Michelle; Müller, Andrea; Sekiguchi, KeikoSightings made on an aerial survey in December 1982 and on a ship-based survey in January/February 1983 have been used to assess the size of the population of common dolphins (Delphinus capensis) occurring over the continental shelf south of South Africa. Thirteen sightings (12 primary) were made in 2,445.7 n. miles flown on the aerial survey and 10 sightings (6 primary) in 1,772.2 n. miles steamed on the ship-based survey. Sightings and effort in both surveys have been stratified by water depth (0-100 m, 100- 200 m) and geographical region (west coast, south coast). Because of difficulties in accurately estimating the size of schools in this highly gregarious species, numbers of individuals were counted in composite aerial photographs taken of the school. Radial distance and angle estimates to sightings from the ship were smeared to allow for estimation errors. Assuming g(0) = 1.0, both data sets resulted in roughly similar estimates of the number of schools (52-58 for aerial, 40-59 for ship-based across a range of sensitivity tests), but mean school size estimates differed significantly (454 SE 90 for aerial, 159 SE 27 for ship-based). As the aerial estimates were based on counts of animals in composite vertical photographs, they are considered more reliable than the ship-based estimates that were made from a lower vantage point and at a greater angle. Given the small number of primary sightings on each survey, it was considered preferable to produce a combined estimate using school density estimates from both surveys weighted by their inverse variances but applying the mean school size from the aircraft. The resultant population estimate of 49 schools (CV = 0.29) and 22200 individuals (CV = 0.35) is discussed in relation to known or estimated incidental mortalities in South African waters.
- ItemOpen AccessGeographical variation in the body size of adult female sperm whales (Physeter macrocephalus) – an example of McNab’s resource rule?(De Gruyter, 2016) Best, Peter B; Tormosov, Dmitri; Brandão, Anabela; Mikhalev, YuriThis 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.
- ItemOpen AccessIdentifying the "demon whale-biter": Patterns of scarring on large whales attributed to a cookie-cutter shark Isistius sp(Public Library of Science, 2016) Best, Peter B; Photopoulou, TheoniThe 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.
- ItemOpen AccessA note on possible change in the mean calving interval for southern right whales off South Africa(International Whaling Commission, 2010) Brandão, Anabela; Best, Peter B; Butterworth, Doug SA simple approach has been applied to investigate whether resightings of female right whales with calves on annual aerial surveys off South Africa provide any evidence for a change in calving interval over the period from 1979 to 2006 for which data are now available. Updated data, including some corrections to the data from 1979 to 2003 that were considered in previous reports (Best et al., 2001, 2005), are shown in Table 1. The methodology applied is that of Cooke et al. (1993), and is set out in the Appendix. Two possible parameterisations of a change in calving interval probabilities are considered, as reflected in Equations (7) and (8) of that Appendix.
- ItemOpen AccessA note on possible changes in some demographic parameters for southern right whales off South Africa(2010) Brandão, Anabela; Best, Peter B; Butterworth, Doug SThe 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.
- ItemOpen AccessPopulation structure of humpback whales from their breeding grounds in the South Atlantic and Indian Oceans(Public Library of Science, 2009) Rosenbaum, Howard C; Pomilla, Cristina; Mendez, Martin; Leslie, Matthew S; Best, Peter B; Findlay, Ken P; Minton, Gianna; Ersts, Peter J; Collins, Timothy; Engel, Marcia HAlthough humpback whales are among the best-studied of the large whales, population boundaries in the Southern Hemisphere (SH) have remained largely untested. We assess population structure of SH humpback whales using 1,527 samples collected from whales at fourteen sampling sites within the Southwestern and Southeastern Atlantic, the Southwestern Indian Ocean, and Northern Indian Ocean (Breeding Stocks A, B, C and X, respectively). Evaluation of mtDNA population structure and migration rates was carried out under different statistical frameworks. Using all genetic evidence, the results suggest significant degrees of population structure between all ocean basins, with the Southwestern and Northern Indian Ocean most differentiated from each other. Effective migration rates were highest between the Southeastern Atlantic and the Southwestern Indian Ocean, followed by rates within the Southeastern Atlantic, and the lowest between the Southwestern and Northern Indian Ocean. At finer scales, very low gene flow was detected between the two neighbouring sub-regions in the Southeastern Atlantic, compared to high gene flow for whales within the Southwestern Indian Ocean. Our genetic results support the current management designations proposed by the International Whaling Commission of Breeding Stocks A, B, C, and X as four strongly structured populations. The population structure patterns found in this study are likely to have been influenced by a combination of long-term maternally directed fidelity of migratory destinations, along with other ecological and oceanographic features in the region.
- ItemOpen AccessPreliminary results for a photo-identification-based assessment of southern right whales in South African waters(2011) Butterworth, Doug S; Brandão, Anabela; Müller, Andrea; Best, Peter BThis working paper presents preliminary results of a photo-id based assessment of southern right whales in South African waters using the three-mature-stages (receptive, calving, resting) model of Cooke et al. (2003). The application of the approach is near-identical to that of Cooke et al. (2003), except that here the starting population is not assumed to reflect a steady age-structure corresponding to the Leslie matrix model describing the population dynamics. The photo-id data for grey-blazed female calves, which are identifiable when giving birth themselves, are used to link the dynamics of the mature females with the output of their reproduction by allowing for estimation of parameters for first-year mortality and the maturity ogive.
- ItemRestrictedPreliminary results for a photo-identification-based assessment of southern right whales in South African waters(University of Cape Town, 2011) Butterworth, Doug S; Brandão, Anabela; Müller, Andrea; Best, Peter BThis working paper presents preliminary results of a photo-id based assessment of southern right whales in South African waters using the three-mature-stages (receptive, calving, resting) model of Cooke et al. (2003). The application of the approach is near-identical to that of Cooke et al. (2003), except that here the starting population is not assumed to reflect a steady age-structure corresponding to the Leslie matrix model describing the population dynamics. The photo-id data for grey-blazed female calves, which are identifiable when giving birth themselves, are used to link the dynamics of the mature females with the output of their reproduction by allowing for estimation of parameters for first-year mortality and the maturity ogive.
- ItemOpen AccessUpdated estimates of demographic parameters for Southern right whales off South Africa(International Whaling Commission, 2005) Best, Peter B; Brandão, Anabela; Butterworth, Doug SAerial 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.