IMEF - Instituto de Matemática, Estatística e Física
URI permanente desta comunidadehttps://rihomolog.furg.br/handle/1/339
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18 resultados
Resultados da Pesquisa
- ItemPhoto-identification of humpback whales, Megaptera novaeangliae, off the Antarctic peninsula: 1997/98 to 1999/2000(2001) Dalla Rosa, Luciano; Secchi, Eduardo Resende; Kinas, Paul Gerhard; Santos, Marcos César de Oliveira; Martins, Marcio; Zerbini, Alexandre Novaes; Bethlem, CláudiaDuring three Summer seasons (1997/98-1999/00), photographic sampling of humpback whales was conducted by Projeto Baleia/Brazilian Antartic Programme in Waters of the Antartic Peninsula. Whales photographed totalled: 63 (1997/1998), 70 (1998/1999) and 21 (1999/2000). Of these, 74,6% (n=47), 87,1% (n=61) and 100% (n=21), respectively, were represented by photographs categorised as quality 1 (excellent) or 2 (moderate). Inter-annual comparisons showed two matches: a whale photographed on 27 January 1998 in the Gerlache Strait was resighted on 11 January 1999 in the same region; the second on 3 February 1998 in the Gerlache Strait was resighted on 25 January 1999 at almost the same coordinates. These matches indicate that humpback whales may show fidelity to feeding grounds off the Antartic Peninsula. Intra-annual comparisons showed two matches: a whale photographed on 22 January 1998 close to the King George Island and another on 27 January 1998 in the Bismarck Strait were resighted together on 7 March 1998 in the Gerlache Strait. Average índices of fluke colouration obtained for 1997/1998 and 1998/1999 were 2.39 (n=44) and 2.60 (n=53), respectively. Total average índex, including photographs from the three period, resulted in 2.54 (n=116). All values are significantly different from those obtained by Rosenbaum ET AL. (1995) for western and eastern Australia (p<0.001) and similar to that found for Colombia (p>0.05) (non-parametric test of Kolmogorov-Smirnov). These results reinforce the view that humpback whales feeding in the western side of the Antartic Peninsula probably originate from eastern South Pacific breeding grounds.
- ItemEncounter rates of whales around the Antarctic peninsula with special reference to humpback whales, Megaptera novaeangliae, in the Gerlache Strait: 1997/98 to 1999/2000(2001) Secchi, Eduardo Resende; Dalla Rosa, Luciano; Kinas, Paul Gerhard; Santos, Marcos César de Oliveira; Zerbini, Alexandre Novaes; Bassoi, Manuela; Moreno, Ignacio Benites
- ItemAspects of habitat use patterns of humpback whales in the Abrolhos bank, Brazil, breeding ground(2001) Martins, Cristiane Cavalcante Albuquerque; Morete, Maria Emilia; Coitinho, Márcia Helena Engel; Freitas, Ana Cristina; Secchi, Eduardo Resende; Kinas, Paul GerhardThe Abrolhos Bank (off the State of Bahia, northeastern Brazil) is the most important breeding and calving ground for humpback whales, Megaptera novaeangliae, in the western South Atlantic. The area is shallow with a mean depth of 30m and a group of five islands (the Abrolhos Archipelago) is located in the northern portion of the Bank. Data collected from 1992 to 1998 were analysed to identify possible different habitat use patterns by different humpback whale group types. An analysis of variance found differences in the mean water depths where different group types were recorded: single whales, 18.9m (se = 0.505); pairs, 18.6m (se = 0.386); competitive groups, 19.1m (se = 0.573); mother-calf pairs, 15.8m (se = 0.373); mother-calf-principal escort, 14.9m (se = 0.489); and competitive group with mother-calf pair, 16.4m (se = 0.889). With the exception of competitive groups, those containing calves (mother-calf alone or mother-calf-principal escort) occurred in significantly shallower water than non-calf groups (Tukey test, p<0.05). In addition, groups containing calves were found significantly more often nearer the Archipelago (within 4 nautical miles) than other groups (two-sample Kolmogorov-Smirnov test, D = 0.139; 2 = 18.516, p<0.05). Accordingly, a spatially stratified management scheme is recommended in order to protect mother-calf pairs from possible harassment by whale watching operations in the area.
- ItemEstimating dyad association probability under imperfect and heterogeneous detection(2011) Klaich, Matias Javier; Kinas, Paul Gerhard; Pedraza, Susana; Coscarella, Mariano; Crespo, EnriqueIn animal behaviour studies, association indices estimate the proportion of time two individuals (i.e. a dyad) spend in association. In terms of dyads, all association indices can be interpreted as estimators of the probability that a dyad is associated. However, traditional indices rely on the assumptions that the probability to detect a particular individual (p) is either approximately one and/or homogeneous between associated and not associated individuals. Based on marked individuals we develop a likelihood based model to estimate the probability a dyad is associated ( ) accounting for p < 1 and possibly varying between associated and not associated individuals. The proposed likelihood based model allows for both individual and dyadic missing observations. In addition, the model can easily be extended to incorporate covariate information for modeling p and . A simulation study showed that the likelihood based model approach yield reasonably unbiased estimates, even for low and heterogeneous individual detection probabilities, while, in contrast, traditional indices showed moderate to strong biases. The application of the proposed approach is illustrated using a real data set collected from a population of Commerson’s dolphin (Cephalorhynchus commersonii) in Patagonia Argentina. Finally, we discuss possible extensions of the proposed model and its applicability in animal behaviour and ecological studies.
- ItemThe impact of incidental kills by gill nets on the franciscana dolphin (pontoporia blainvillei) in southern Brazil(2002) Kinas, Paul GerhardThe franciscana dolphin, Pontoporia blainvillei, is endemic to the western South Atlantic Ocean. Its distribution is restricted to waters up to 30 m depth, making it vulnerable to human influence. In southern Brazil the artisanal gillnet fisheries have increased since the early 1980s, and entanglement mortality of franciscanas has become a source for concern. Strandings have been documented for about 20 yrs, but the impact of incidental captures has remained unknown. In the 1990s numbers of franciscanas incidentally killed by the artisanal gillnet fleet, population size, and the intrinsic growth rate were estimated. I integrated all available information into a population model in order to quantify the impact of incidental kills. The statistical analysis was conducted within a Bayesian framework to maintain coherence while current biological knowledge was weighted with observational data. My analysis indicated a 99% probability that the population is decreasing. For analysis of future impact of the incidental kill the population was defined as being at ‘quasi collapse’ when it reached 10% of its current size, and the probability of quasi collapse within 30 yrs was calculated under alternative scenarios. Results indicate that current levels of entanglement mortality cannot be sustained and that protective measures are needed.
- ItemAbundance of humpback whales on the Abrolhos Bank wintering ground, Brazil(2004) Freitas, Ana Cristina; Kinas, Paul Gerhard; Martins, Cristiane Cavalcante Albuquerque; Coitinho, Márcia Helena EngelAbundance estimates are presented for the humpback whales wintering off Brazil which ‘visit’ a surveyed area off Abrolhos Bank and display fluke-exposing behaviour. The study is based on photo-identification data collected between 1996 and 2000. Chapman-corrected Petersen estimates for all pairs of data result in estimates from 1,948 individuals up to 3,001 with coefficients of variation around 0.25. A more elaborate closed population multiple-recapture maximum-likelihood estimate is 2,393 with 95% profile-likelihood confidence interval (CI=1,924, 3,060). Replacing the closed-population assumption with a population allowed to grow (or decrease) according to some constant rate over the study period, the maximum-likelihood estimate of population size for the year 2000 becomes 3,871 (CI=2,795, 5,542) associated to an estimated annual growth rate of 31% over the study period and in the surveyed area. Although the inclusion of the growth rate results in a less restrictive assumption about population size, it is unclear at this time how to interpret it since the population around the Abrolhos Bank is some (unknown) fraction of whales wintering off Brazil. Alternatively, a fit of Whitehead’s model allowing for emigration and re-immigration gives an estimate of about 3,000 whales (CI=2,500, 3,650).
- ItemIncidental catches of franciscana in coastal gillnet fisheries in the franciscana management area III: period 1999-2000(2004) Secchi, Eduardo Resende; Kinas, Paul Gerhard; Muelbert, Monica Mathias CostaBycatch of franciscanas in fishing operations along the western South Atlantic Ocean has been observed for approximately 60 years. Reports on bycatch in shark gillnet fisheries off Uruguay date back to the early 1940s. A decade later, gillnet fisheries for bottom-dwelling fish became the major conservation concern for franciscanas in both Brazil and Argentina. A small portion (c. 10%), of the coastal gillnet fleet which operate from the port of Rio Grande (southern Rio Grande do Sul, Brazil) was monitored in 1999-2000. The total annual bycatch was estimated to be 946 franciscanas (non-parametric CI = 467 – 1525) for the year 1999 and 719 (non-parametric CI = CI: 248 – 1413) dolphins for 2000. The total bycatch for the whole FMA III was 1106 (CI: 578 – 1915) for 1999 and 992 (CI: 475 – 1832) for 2000. Since data were not normally distributed confidence intervals were estimated by non-parametric bootstrap. Despite strong evidence of decline for the stock from FMA III, no mitigation strategy has been established or designed. Instead, fishing effort is still very high, it is increasing and bycatch is uncontrolled. Thus, prompt management action is required. Regulation of gillnet fishing effort might be the only suitable immediate action to mitigate the bycatch.
- ItemA first estimate of franciscana (Pontoporia blainvillei) abundance off southern Brazil(2001) Secchi, Eduardo Resende; Ott, Paulo Henrique; Crespo, Enrique; Kinas, Paul Gerhard; Pedraza, Susana; Bordino, PabloThe franciscana, Pontoporia blainvillei, is endemic to the western South Atlantic Ocean and is perhaps one of the most threatened small cetacean species in this region. This paper presents a first abundance estimate for the coastal waters of Rio Grande do Sul State (southern Brazil) and Uruguay. In March 1996, an aerial survey was conducted along the Rio Grande do Sul State coast. Thirty-four franciscanas (29 groups) were recorded leading to a mean density estimate of 0.657 individuals/km2 (95% CI: 0.516 to 0.836) for the study area (435km2) after applying a correction factor for submerged dolphins. This corresponds to an estimated abundance of 286 franciscanas (95% CI: 225 to 364). The study area represents only 0.7% of the suggested distribution of the stock. The paper discusses possible management implications of this study in the light of reported incidental mortality estimates for this region. Further surveys covering a larger area are recommended in order to obtain more reliable abundance estimates for the stock.
- ItemEstimation of birthdates and catch-at-age using length frequency analysis (LFA), with application for skipjack tuna (Katsuwonus pelamis) caught in the Southwest Atlantic(2004) Andrade, Humber Agrelli; Kinas, Paul GerhardConverting length frequencies into age frequencies is an important component of a fisheries assessment. In this paper we use a length frequency analysis (LFA) to estimate birthdates after converting length data into catch-at-age, and use simulation studies to compare modelselection criteria and to examine the reliability of the resulting estimates. Deviance and an adaptation of the Akaike Information Criterion performed best. LFA results in useful estimates of birthdates and of catch-at-age if reliable length frequency data and estimates of growth parameters are available. The analysis is applied to skipjack tuna (Katsuwonus pelamis) caught in the Southwest Atlantic Ocean. Although spawning is reported to be seasonal in subtropical waters, the birthdates of the fish caught there were spread uniformly across the year. Young skipjack become vulnerable to fishing mainly in the first quarter of each year. Recruitment of strong year classes did not affect fishery yields equally in the Southwest Atlantic and the Caribbean Sea, so the assumption of a unit western stock for management purposes and the stock structure of skipjack in the Atlantic need further evaluation.
- ItemVolume de madeira em área reflorestada: um estudo simulado de inferência estatística(2003) Kinas, Paul Gerhard; Neves, Juarenze CardosoO entendimento de conceitos de inferência estatística clássica como distribuição amostral e intervalos de confiança pode ser facilitado e ampliado recorrendo-se a estudos simulados. Apresenta-se um exemplo fictício em que o volume médio de madeira por hectare precisa ser estimado a partir de informações amostrais sobre a quantidade, perímetros e alturas de árvores. A simulação é implementada no Statistica. Análise descritiva de 2000 réplicas permite conhecer as características do estimador não-convencional utilizado. Verifica-se que sua distribuição amostral é aproximadamente lognormal e que o estimador tem viés. A cobertura do intervalo de confiança e a probabilidade do erro II em um teste de hipótese são avaliadas, e os efeitos resultantes de suposições não atendidas, verificadas. Conclui-se que o processo de simulação é simples, e que sua utilização em cursos introdutórios de inferência é viável. Além da oportunidade de vivenciar concretamente os conceitos, abre-se ao estudante a possibilidade para explorar situações não-convencionais.