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Temporal variability of cetaceans in the Azores and its relation with oceanographic features as derived by satellite imagery
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Abstract(s)
O Arquipélago dos Açores (Portugal) é composto por nove ilhas vulcânicas no Nordeste Oceano Atlântico e detém uma elevada diversidade de cetáceos, com 28 espécies documentadas. Este é o primeiro estudo nos Açores, que avalia a utilidade de dados do turismo de observação de baleias para estudos científicos sobre a distribuição dos cetáceos, e que relaciona a sua ocorrência e variabilidade com imagens MODIS/AQUA de clorofila a (Chla) e temperatura à superfície (SST) com 1 km de resolução obtidas através do site da NASA Ocean Color. Neste estudo, cinco anos de dados de campo (2010-2014) foram utilizados para avaliar a presença das baleias azul, comum, sardinheira e bossas. Foram consideradas três escalas temporais (quatro anos em conjunto, anuais e mensais). Dado que o esforço não foi consistente ao longo dos anos, as taxas de avistamento (Encounter rate, ER=avistamentos.esforço-1) foram utilizadas como medidas padronizadas para comparações temporais de presença. Imagens diárias de Chla e SST foram processadas estatisticamente, obtendo-se médias mensais, sazonais, anuais, tendências e anomalias para o período de 2010 a 2014 para a região dos Açores e relacionados com a variabilidade local de quatro espécies de baleias de barbas para tentar explicar as diferenças registadas ao longo dos anos. Os principais resultados mostraram que a presença das quatro espécies de baleias de barbas nos Açores variou entre os anos. Diferenças intra-sazonais foram encontradas para as taxas de presença e estas variaram de acordo com a espécie. A presença de Bm foi observada durante a primavera sugerindo que estas baleias usam os Açores como área de alimentação durante estes meses enquanto estão na sua rota de migração para norte e que, a variação de Chla e o início do crescimento do fitoplâncton são bons indicadores do tempo efectivo destas na região. Resultados semelhantes foram encontrados para a BP, mas a sua associação com Chla e o momento do crescimento do fitoplâncton é posterior à Bm Sendo a Bp mais oportunista e tendo uma dieta mais variada, as suas presas podem estar a níveis diferentes cadeia alimentar. O pico de Bb variou nos meses de primavera e verão e estas diferenças podem ser explicadas pela suposição, já referida por outros autores, de que os Açores provavelmente são visitados por duas populações diferentes de Bb, uma durante a fase de migração na primavera e a segunda durante o final do verão e no outono. Assim sendo, a concentração de Chla seria um parâmetro biológico associado com o pico de Bb apenas para uma das populações. Por último, os picos de presença de Mn foram observados principalmente durante a primavera e o número de meses dos avistamentos duplicou em 2014 e 2015, sugerindo que Mn poderia utilizar os Açores como área de alimentação durante estes meses, durante o seu caminho de migração para norte. A temperatura da superfície do mar, a concentração de Chla e o início do crescimento do fitoplâncton, aqui ilustrados como médias gerais, médias ajustadas (tendências) e anomalias, suportam a hipótese de que o ciclo sazonal e a variabilidade inter-anual são bem demarcados nesta região podendo explicar as diferenças observadas na presença das baleias ao longo os anos. Ao remover o ciclo sazonal, SST é muito conservador ao longo dos anos, com uma ligeira tendência de aumento com o tempo. Com relação à Chla, nem todos os anos apresentam floração de primavera, mas 2010 e 2014 revelam os picos maiores de Chla, coincidindo também com um aumento global de observação das baleias, particularmente para 2014. O uso de plataformas de oportunidade pode dar aos cientistas um meio de recolha de dados sobre uma ampla gama de fauna marinha quando o financiamento da investigação é limitado. No entanto, face às limitações encontradas nos dados de cetáceos, este estudo apresenta novas sugestões de introdução nos protocolos de amostragem por forma a que os dados MONICET possam produzir dados detalhados para fins científicos.
ABSTRACT: The Archipelago of the Azores (Portugal) is composed of nine volcanic islands in the northeast Atlantic Ocean and it holds a high diversity of cetaceans, with 28 species documented. This is the first study in the Azores that assesses the utility of whale watching data for scientific studies on cetacean distribution, and that relates their occurrence and variability with 1 km resolution MODIS/AQUA near-surface chlorophyll a (Chla) and Sea Surface Temperature (SST) data obtained from NASA Ocean Color website. In this study, five years of field data (2010-2014) were used to evaluate blue, fin, sei and humpback whales presence. Three temporal scales (four years, yearly, and monthly) were considered. Given that effort was not consistent throughout, then encounter rates (ER=sightings.effort-1) were used as standardized measures for presence temporal comparisons. Daily satellite Chla concentrations and SST values were statistically processed such as to obtain monthly, seasonal, annual averages, trends and anomalies for the period 2010 to 2014 for the Azores region. Baleen whales presence was related with the oceanographic data to infer possible causes for whales inter-annual variability Main results showed that the presence of the four baleen whale species in the Azores varied among the years. Intra-seasonal differences were found for presence rates and these varied with the species. The Bm presence was observed during the springtime suggesting that they use the Azores for foraging activity during these months while they are in their migration journey to north and that the variation of Chla and the initiation of the bloom could determine their time in the area. Similar results were found for Bp but their association with Chla and the timing of the bloom is later than the Bm. Since Bp is more opportunistic and has a varied diet, this happened since their prey could be in another level of the food chain. The peak for Bb varied in the spring and summer months and these differences could be explained by the assumption previously made by other authors, that maybe the Azores is visited by two different stocks of Bb, one during the migration in spring time and the second during late summer and autumn. Furthermore, the Chla concentration could be a biological parameter associated with the peak of Bb only for one stock. Lastly, the presence peaks of Mn were observed mostly during the spring and the number of sightings per month doubled in 2014 and 2015, suggesting that Mn could have foraged during these months while they were in their migration journey to north. Sea surface temperature and Chla concentration overall averages, adjusted averages (trends) and anomalies, as well as, calculations of the timing of the blooms show that the seasonal cycle is strong at these latitudes and inter-annual variability may explain differences in whales presence over the years. By removing the seasonal cycle, SST is very conservative over the years, and its trend reveals slight increase with time. Regarding Chla concentrations, spring blooms are not always observed in the region, but 2010 and 2014 reveal the strongest ones, coincident also with an overall increase in baleen whales observation, particularly for 2014. The use of platforms of opportunity may provide scientists a means of collecting data on a wide range of marine fauna when research funding is limited. Nevertheless, and in face with all the limitations found in the cetacean data, this study presents new suggestions for sampling protocols improvement such data from whale watching in MONICET might yield better possibilities for scientific purposes in the Azores.
ABSTRACT: The Archipelago of the Azores (Portugal) is composed of nine volcanic islands in the northeast Atlantic Ocean and it holds a high diversity of cetaceans, with 28 species documented. This is the first study in the Azores that assesses the utility of whale watching data for scientific studies on cetacean distribution, and that relates their occurrence and variability with 1 km resolution MODIS/AQUA near-surface chlorophyll a (Chla) and Sea Surface Temperature (SST) data obtained from NASA Ocean Color website. In this study, five years of field data (2010-2014) were used to evaluate blue, fin, sei and humpback whales presence. Three temporal scales (four years, yearly, and monthly) were considered. Given that effort was not consistent throughout, then encounter rates (ER=sightings.effort-1) were used as standardized measures for presence temporal comparisons. Daily satellite Chla concentrations and SST values were statistically processed such as to obtain monthly, seasonal, annual averages, trends and anomalies for the period 2010 to 2014 for the Azores region. Baleen whales presence was related with the oceanographic data to infer possible causes for whales inter-annual variability Main results showed that the presence of the four baleen whale species in the Azores varied among the years. Intra-seasonal differences were found for presence rates and these varied with the species. The Bm presence was observed during the springtime suggesting that they use the Azores for foraging activity during these months while they are in their migration journey to north and that the variation of Chla and the initiation of the bloom could determine their time in the area. Similar results were found for Bp but their association with Chla and the timing of the bloom is later than the Bm. Since Bp is more opportunistic and has a varied diet, this happened since their prey could be in another level of the food chain. The peak for Bb varied in the spring and summer months and these differences could be explained by the assumption previously made by other authors, that maybe the Azores is visited by two different stocks of Bb, one during the migration in spring time and the second during late summer and autumn. Furthermore, the Chla concentration could be a biological parameter associated with the peak of Bb only for one stock. Lastly, the presence peaks of Mn were observed mostly during the spring and the number of sightings per month doubled in 2014 and 2015, suggesting that Mn could have foraged during these months while they were in their migration journey to north. Sea surface temperature and Chla concentration overall averages, adjusted averages (trends) and anomalies, as well as, calculations of the timing of the blooms show that the seasonal cycle is strong at these latitudes and inter-annual variability may explain differences in whales presence over the years. By removing the seasonal cycle, SST is very conservative over the years, and its trend reveals slight increase with time. Regarding Chla concentrations, spring blooms are not always observed in the region, but 2010 and 2014 reveal the strongest ones, coincident also with an overall increase in baleen whales observation, particularly for 2014. The use of platforms of opportunity may provide scientists a means of collecting data on a wide range of marine fauna when research funding is limited. Nevertheless, and in face with all the limitations found in the cetacean data, this study presents new suggestions for sampling protocols improvement such data from whale watching in MONICET might yield better possibilities for scientific purposes in the Azores.
Description
Dissertação de Mestrado, Estudos Integrados dos Oceanos, 28 de abril de 2017, Universidade dos Açores.
Keywords
Baleia de Barbas Cetáceos Temperatura Superficial Atlântico Norte Açores Baleen Whales Azores
Citation
Olio, Marília Pereira. "Temporal variability of cetaceans in the Azores and its relation with oceanographic features as derived by satellite imagery". 2017. 115 p.. (Dissertação de Mestrado em Estudos Integrados dos Oceanos). Horta: Universidade dos Açores, 2016. [Consult. Dia Mês Ano]. Disponível em www:<http://hdl.handle.net/10400.3/4637>.