Browsing by Subject "Antarctic minke whale"

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    Application of ADAPT-VPA to Antarctic minke whales in the JARPA research area
    (2006) Mori, Mitsuyo; Kitakado, Toshihide; Butterworth, Doug S
    The ADAPT-VPA assessment methodology originally developed by Butterworth et al. (1999) has been greatly improved by taking into account various comments made during a series of IWC-SC meetings and is applied here to abundance estimates (from both IDCR/SOWER and JARPA surveys) as well as catch at age data (both commercial and scientific) for the I and P-stocks of Antarctic minke whales. The improvements to the methodology allow account to be taken of various further aspects, primarily: 1) inter-annual differences in the distribution of the population between different management Areas, 2) a stock-recruitment relationship, and 3) the effects of possible ageing-error. Furthermore sensitivities to various functional forms for selectivity and natural mortality with age are explored. The general pattern shown by the results for both stocks is of a minke whale abundance trend that increased over the middle decades of the 20th Century to peak at about 1970, and then stabilized or declined somewhat for the next three decades. The recruitment trend is similar, though with its peak slightly earlier. The annual natural mortality rate, M, is estimated to be 0.056 with a CV of 0.16 for the I-stock, and 0.069 with a CV of 0.15 for the P-stock for the “Reference case” assessments. When only the JARPA abundance estimates are used for tuning, M is estimated as 0.038 and 0.060 for the I- and P-stocks, respectively. The estimation of M is fairly robust to the various assumptions of the model. The CVs of these M estimates for the “Reference case” assessments, when compared with those of typically 0.35 for the Areaspecific assessments of Butterworth et al. (1999) which were based on fewer data, indicate an improvement in the precision of these estimates due to the accumulation of data over the long-term of the JARPA surveys. The fits of the stock-recruitment model generally require a carrying capacity for minke whales that first increased and then stabilized or declined somewhat during the last century, and suggest MSYR(1+) values in the 4-6% range. The improved precision in the estimation of M may contribute in the improvement of management and assessment of this species on a stock-specific basis, since it can reduce the uncertainty concerning the value of M and can provide an improved prior distribution for MSYR. The latter in particular, in the context of providing a measure of the productivity of which the species is capable, is essential information for effective RMP implementation through reduction of the range of plausible scenarios which need to be considered in Implementation Simulation Trials.
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    Application of ADAPT-VPA to various stock hypotheses for the Antarctic minke whales distributed through IWC management areas IIIE to VIW
    (2006) Mori, M.; Butterworth, Doug S; Kitakado, T.
    This paper focuses primarily on addressing suggestions made during the Ulsan meeting of the Scientific Committee for refinement of the ADAPT-VPA assessments of Antarctic minke whales presented in Mori and Butterworth (2005). The methodology is extended to take account of different selectivities for the Russian and Japanese fleets during the period of commercial whaling, but this has little effect on results. The slopes of catch curves for the research catches have decreased and then stabilised during the course of the JARPA programme. This is indicative of a change in recruitment trends over time, rather than of a very high natural mortality as was amongst the postulates at the time of commercial whaling. ADAPT-VPA assessments are run for the five stock structure hypotheses specified by the Scientific Committee for the minke whales distributed through Areas IIIE to VIW, and for various choices of series of abundance estimates to which to fit the model. These runs generally indicate a trend of increasing recruitment of about 4% pa until the mid-1960s, followed by a trend in total abundance that decreases or is sometimes stable, depending on the abundance estimate series selected for fitting. Results for the Istock (Areas IIIE+IV+VW) are quite sensitive to this selection, but those for the P-stock (Areas VE+VIW) less so. Estimates of natural mortality M are generally in the 0.06 to 0.09 range, with a tendency to be somewhat higher for the P- compared to the I-stock. Fits of the outputs from the ADAPT-VPA to a stock-recruitment model generally require a carrying capacity for minke whales that first increased and then declined during the last century, and suggest MSYR1+ values in the 4-7% range. Possibilities for further work are outlined, including disaggregation of the analysis by sex.
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    Further progress on application of ADAPT-VPA to Antarctic minke whales
    (2007) Mori, Mitsuyo; Butterworth, Doug S; Kitakado, Toshihide
    The ADAPT-VPA assessment methodology originally developed by Butterworth et al. (1999) has been appreciably advanced by taking into account various comments made during a series of IWC-SC meetings and is applied here to abundance estimates (from both IDCR/SOWER and JARPA surveys) as well as catch at age data (both commercial and scientific) for the I and P-stocks of Antarctic minke whales. The improvements to the methodology allow account to be taken of various further aspects, primarily: 1) inter-annual differences in the distribution of the population between different management Areas, 2) a stock-recruitment relationship, 3) the effects of possible ageing-error, and 4) the effects of possible change in age-at-sexual maturity over time as indicated by analyses of readings of transition phases in ear plugs. Furthermore sensitivities to various functional forms for selectivity and natural mortality with age are explored. The general pattern shown by analysis for both stocks is of a minke whale abundance trend that increased over the middle decades of the 20th Century to peak at about 1970, and then stabilized or declined somewhat for the next three decades. The recruitment trend is similar, though with its peak slightly earlier. The annual natural mortality rate, M, is estimated to be 0.056 with a CV of 0.16 for the I-stock, and 0.069 with a CV of 0.15 for the P-stock for the “Reference case” assessments. When only the JARPA abundance estimates are used for tuning, M is estimated as 0.037 and 0.060 for the I- and P-stocks, respectively. The estimation of M is fairly robust to the various assumptions of the model. This analysis is considered preliminary, as conclusions relating to estimates of M and trends in abundance and recruitment obtained using this approach await further revisions of 1) abundance estimates obtained from IDCR and JARPA surveys, and 2) error-models for the catch-at-age data, particularly those obtained from the commercial harvests.
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    Observer experience and minke whale sighting ability in the IWC/IDCR-SOWER surveys
    (Journal of Cetacean Research and Management, 2003) Mori, Mitsuyo; Butterworth, Doug S; Brandão, Anabela; Rademeyer, Rebecca A; Okamura, Hiroshi; Hiroyuki, Matsuda
    The relationship between observer experience and the number of minke whale schools sighted on International Whaling Commission/International Decade of Cetacean Research-Southern Ocean Whale and Ecosystem Research (IWC/IDCR-SOWER) surveys from 1993/94 to 1998/99 is investigated for Independent Observer (IO) mode survey. Observer experience is defined as the number of past sightings surveys in which the observer participated. During the third circumpolar set of surveys (from 1991/92 onwards), about half of the observers had participated in fewer than five previous sightings surveys. Based upon the QAIC model selection criterion, the observers are classified into two groups depending on their experience: ‘Beginners’ (0-4 surveys) and ‘Experts’ ( > 4). The sighting rate for minke whale schools by Beginners is estimated to be 42% lower than that by Expert observers. Furthermore, perpendicular distances to the sightings do not show significant differences in relation to observer experience. These results jointly indicate that the probability of detection on the trackline, g(0), may be less than one when Beginners are amongst those observing. Abundance estimation for minke whales in IO mode involves the sightings made by triple observer combinations, with two observers in the barrel and one observer in the Independent Observer Platform (IOP) all searching simultaneously. Surprisingly, given the result above, no significant trend in sighting rate with the combined experience of this three-observer combination is detected. This might be an artifact of small sample size for some observer combinations, such as Experts in all platforms. When observer combinations in the barrel are pooled across, the estimated trend in the sighting rate with combined observer experience becomes steeper. Furthermore, when like-minke sightings are also taken into account, the trend becomes steeper still. In this case, when observations are pooled across observer combinations in the barrel, a model for sighting rate that includes an observer effect is selected in terms of the QAIC criteria. These analyses thus provide suggestive evidence that the introduction of Beginner observers during the third circumpolar set of surveys may have reduced g(0) and hence negatively biased abundance estimates for minke whales, both in absolute terms and compared with estimates from the second circumpolar set of surveys.
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    Some modifications to the current ADAPT-VPA model for Antarctic minke whales
    (2008) Mori, Mitsunyo; Butterworth, Doug S
    The current ADAPT-VPA model of Mori et al. (2007) for Antarctic minke whales in Areas IIIE to VW is modified in two respects. One is the revision of the stock-recruitment relationship, and the other is the simplification of the functional form of the carrying capacity. AIC indicates that the model which includes the above two modifications is better compared to the “Reference case” scenario of Mori et al. (2007). Thus, future analyses will regard this modified version as a new “Reference case” scenario, which has the incidental advantage of corresponding more closely to the assumptions made in the SCAA (Statistical Catch at Age) approach of Punt and Polacheck (2006) to analysis of these data.