A Bayesian assessment of the conservation status of humpback whales (Megaptera novaeangliae) in the western South Atlantic Ocean

Abstract

The population of humpback whales (Megaptera novaeangliae) wintering off the eastern coast of South America is referred to by the International Whaling Commission as ‘Breeding Stock A’ (BSA). This population was heavily exploited in 20th century modern commercial whaling operations. After more than 30 years of protection, its present status remains unknown. A deterministic sex and age-aggregated population dynamics model was used to estimate the pre-exploitation population size (K), the maximum net recruitment rate (rmax), the maximum depletion level (Nmin/K), and other quantities of interest of BSA. Input data included modern whaling catch series, absolute estimates of abundance, observed growth rates and indices of relative abundance. A Bayesian statistical method was used to calculate probability distributions for the model parameters. Prior distributions were set on rmax – an uninformative (Uniform [0, 0.106]) and an informative (Normal [0.067, 0.042]) – and on the population size in 2005 – N2005 (Uniform [500, 22,000]). A total of 10,000 samples were used to compute the joint posterior distribution of the model parameters using the Sampling-Importance-Resampling algorithm. Sensitivity of model outputs to the priors on rmax, a genetic constraint, data inclusion and catch allocation scenarios was investigated. Medians of the posterior probability distributions of quantities of interest for the base case scenario were: rmax = 0.069 (95% probability intervals [PI] = 0.013–0.104), K = 24,558 (95% PI = 22,791–31,118), Nmin/K = 2% (PI = 0.31%–12.5%), N2006/ K = 27.4% (PI = 18.3%–39.5%), N2020/K = 61.8% (PI = 23.8%–88.6%), and N2040/K = 97.3% (PI = 31.6%–99.9%). Despite apparent recovery in the past three decades, the western South Atlantic humpback whale population is still low relative to its pre-exploitation size and requires continued conservation efforts.

Assessing the recovery of an Antarctic predator from historical exploitation

“…Population trajectories of WSA humpback whales were reconstructed using a density-dependent population dynamics model [31,36]. The model was implemented in a Bayesian statistical framework to explicitly account for uncertainty in the data [37].…”

“…-Modern whaling catches compiled by the Scientific Committee of the IWC for the Comprehensive Assessment of Southern Hemisphere humpback whales performed between the mid-2006 and 2015 [45]. The catch series used in a previous assessment of WSA humpback whales [31] was developed based on whaling statistics obtained from coastal-based operations off the coast of Brazil, the Magellan Strait, the Falkland Islands, South Georgia, the South Sandwich Islands, the South Shetland Islands and the South Orkney Islands, as well as pelagic whaling conducted in the low and middle latitudes of the WSA and the Southern Ocean sector of the Atlantic and Pacific Oceans; they also included illegal Soviet catches [8,28,[46][47][48][49]. Uncertainty in the distribution of catches in the feeding grounds due to the potential of mixing with whales from adjacent breeding populations were addressed by developing three catch allocation scenarios [17,46], named 'Core', 'Fringe' and 'Overlap' (figure 1 and table 2) [31,46].…”

“…Between 2006 and 2015, the IWC conducted an assessment of the status of all stocks of Southern Hemisphere humpback whales, which revealed that the WSA population had recovered to only about 30% of its pre-exploitation abundance by the mid-2000s [30,31]. Since this assessment was completed, new information on catches, abundance and trends for this population has become available.…”

Interação antropogênica e sanidade de baleias-jubarte (Megaptera novaeangliae) na costa brasileira

“…Estimativas apontam que a população de baleias-jubarte que se reproduz na costa do Brasil era de aproximadamente 25 mil animais antes da modernização da caça, e chegou a cerca de 500 animais na década de 1950, ou seja, 2% da população original (ZERBINI et al, 2011a). No Brasil, a caça comercial de baleias foi proibida em 18 de dezembro de 1987, pela Lei Federal nº 7.643.…”

“…No Brasil, a caça comercial de baleias foi proibida em 18 de dezembro de 1987, pela Lei Federal nº 7.643. Em anos recentes, a população tem mostrado evidências de recuperação (ANDRIOLO et al, 2010), e em 2006 chegou a 27% do tamanho pré-caça (ZERBINI et al, 2011a). Atualmente a baleia-jubarte consta na lista do IBAMA de espécies da fauna brasileira ameaçadas de extinção, no apêndice I da CITES -Convenção sobre o Comércio Internacional de Espécies Ameaçadas da Flora e Fauna Selvagens, e na categoria de menor preocupação ("least concern") da IUCN (União Internacional para a Conservação da Natureza e dos Recursos Naturais).…”