Browsing by Subject "Humpback whales"

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    A Bayesian assessment of breeding stocks B, C and G of Southern Hemisphere humpback whales using a prior for growth rate from analyses for stocks D and E
    (2005) Johnston, Susan J; Butterworth, Doug S
    Bayesian assessment of breeding stocks B, C and G of the Southern Hemisphere humpback whales are presented. These assessments incorporate a prior for the maximum growth rate r derived from similar assessments for breeding stocks D and E. This is the first time an assessment for breeding stock B has been attempted. Results show current abundance estimates for breeding stocks B and G are low (less than 0.15K), whilst the current abundance estimate for breeding stock C much further recovered at 0.79K. Projections under a zero continued harvesting strategy estimate breeding stock C to be fully recovered by 2020, whilst breeding stocks B and G will be fully recovered only by about around 2030.
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    Corrected assessment results for Southern Hemisphere humpback whales from breeding stocks D and G
    (2007) Johnston, Susan J; Butterworth, Doug S
    Corrected Bayesian stock assessment results for breeding stocks D and G which take into account trend information from the IDCR/SOWER survey results are presented. At the 2006 IWC scientific meeting, the authors presented various stock assessments for breeding stocks D and G (Johnston and Butterworth 2006, IWC 2006). Some of the assessment scenarios presented involved fitting to trend information from the IDCR/SOWER circumpolar surveys which was reported in Branch (2006). The authors inadvertently used the raw abundance estimates provided which had not been adjusted for comparability with respect to areal coverage. Corrected assessment results are thus presented here, for which the appropriate IDCR/SOWER survey trend infomration for comparable areas are used.
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    Population 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 H
    Although 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.
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    Satellite Tagging and Biopsy Sampling of Killer Whales at Subantarctic Marion Island: Effectiveness, Immediate Reactions and Long-Term Responses
    (Public Library of Science, 2014) Reisinger, Ryan R; Oosthuizen, W Chris; Péron, Guillaume; Toussaint, Dawn Cory; Andrews, Russel D; de Bruyn, P J Nico
    Remote tissue biopsy sampling and satellite tagging are becoming widely used in large marine vertebrate studies because they allow the collection of a diverse suite of otherwise difficult-to-obtain data which are critical in understanding the ecology of these species and to their conservation and management. Researchers must carefully consider their methods not only from an animal welfare perspective, but also to ensure the scientific rigour and validity of their results. We report methods for shore-based, remote biopsy sampling and satellite tagging of killer whales Orcinus orca at Subantarctic Marion Island. The performance of these methods is critically assessed using 1) the attachment duration of low-impact minimally percutaneous satellite tags; 2) the immediate behavioural reactions of animals to biopsy sampling and satellite tagging; 3) the effect of researcher experience on biopsy sampling and satellite tagging; and 4) the mid- (1 month) and long- (24 month) term behavioural consequences. To study mid- and long-term behavioural changes we used multievent capture-recapture models that accommodate imperfect detection and individual heterogeneity. We made 72 biopsy sampling attempts (resulting in 32 tissue samples) and 37 satellite tagging attempts (deploying 19 tags). Biopsy sampling success rates were low (43%), but tagging rates were high with improved tag designs (86%). The improved tags remained attached for 26±14 days (mean ± SD). Individuals most often showed no reaction when attempts missed (66%) and a slight reaction-defined as a slight flinch, slight shake, short acceleration, or immediate dive-when hit (54%). Severe immediate reactions were never observed. Hit or miss and age-sex class were important predictors of the reaction, but the method (tag or biopsy) was unimportant. Multievent trap-dependence modelling revealed considerable variation in individual sighting patterns; however, there were no significant mid- or long-term changes following biopsy sampling or tagging.
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    Simulation testing of the sabbatical model estimator for the assessment of Southern Hemisphere humpback whale breeding Stock C and its component Sub-stocks
    (2009) Johnston, Susan J; Butterworth, Doug S; Muller, A
    Johnston and Butterworth (2009) implement four models (Resident, Sabbatical, Tourist and Migrant) to estimate parameters for the C1 and C3 substocks, including the probability of interchange between them, using a Bayesian approach which takes account of capture-recapture information from photo-id data. This estimator generally captures the underlying parameter values reasonably, though with a tendency to estimate r too low and K too high. Interchange rates are also reasonably estimated, both when the true rates are low and high. In the latter case, abundance estimates in terms are lower. Here a range of Operating Models (OMs) are defined and used to test the Sabbatical estimator
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    Simulation testing of two estimators for the assessment of Southern Hemisphere humpback whale breeding Stock C and its component Sub-stocks
    (2009) Johnston, Susan J; Butterworth, Doug S; Muller A
    This paper develops operating models of the C1 and C3 substocks of humpback whales in the western Indian Ocean which allow interchange between the two on the basis of the Sabbatical model for this mixing process. These operating models are used to compare the performance of the Sabbatical and Resident estimators, in what is intended as a preliminary exercise whose primary aim is to illustrate this simulation testing approach in the context of the substocks of breeding stock C of Southern Hemisphere humpback whales., .
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    Summary of the data and information available for the assessment of breeding stock C of the Southern Hemisphere humpback whales
    (2008) Johnston, Susan J
    • Fair amount of evidence to suggest three possible substocks C1 (Mozambique, and South African East Coast migration corridor), C2 (Mayote, Comores and other Islands of the Mozambique Channel) and C3 (Madagascan waters including Antongil Bay) • SC/A06/HW38 – suggests separation of C1 from the other, and lumping C2 and C3 • C2 considered small
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    Updated assessments of Southern Hemisphere humpback whale breeding stock C and its component sub-stocks
    (2008) Johnston, Susan J; Butterworth, Doug S
    Bayesian stock assessment results for a mixed model breeding sub-stocks C1 and C2+3 are presented. The modelling approach allows mixing on the feeding grounds and fits to various data sources, including capturerecapture data from both sub-stocks. A baseline case which inputs all capture-recapture data directly suggests posterior median 2006 abundances for each sub-stock of a little more than 7000, with C1 at about 85% and C2+3 at about 55% of their pristine levels. These results are intended to be illustrative only, and the variety of choices available for the various model inputs require further discussion by the IWC Scientific Committee.
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    Updated assessments of Southern Hemisphere humpback whale breeding sub-stock B1
    (International Whaling Commission, 2008) Johnston, Susan J; Butterworth, Doug S
    Updated Bayesian stock assessment results for humpback breeding sub-stock B1, which take into account recently advised capture-recapture data, are presented. These suggest this population presently to be within the range of 65-90% of its pre-exploitation size in terms of posterior median estimates. However, alternative options for inputs to this assessment are possible, and need to be discussed by the Scientific Committee.
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    Updated assessments of Southern Hemisphere humpback whales from breeding stocks D and G
    (2006) Johnston, Susan J; Butterworth, Doug S
    Bayesian stock assessment methodology is used to update the stock assessments of breeding stocks D and G of the Southern Hemisphere humpback whales. These assessments take into account the recently updated historic catch series, as well as the most recent estimates of current abundance and population trend information as presented at the Southern Hemisphere humpback whale workshop held in Hobart in April 2006. These stock assessments provide estimates of current as well as past abundances. Projections under a zero harvesting strategy are also presented.