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Designing a shipboard line transect survey to estimate cetacean abundance off the Azores archipelago

Publication . Faustino, Cláudia E. S.; Silva, Mónica A.; Marques, Tiago A.; Thomas, Len

Management schemes dedicated to the conservation of wildlife populations rely on the effective monitoring of population size, and this may require the accurate and precise estimation of this parameter. Line transect distance sampling can be an effective approach for estimating abundance. Little information is available regarding cetacean abundance in the Azores. This paper had two aims: 1) to design a line transect shipboard survey to estimate the absolute abundance of the most common cetaceans off the Azores; and 2) to provide a set of potential survey effort scenarios to policy makers and environmental managers. Three survey scenarios are assessed, and one detailed survey design is presented. A total of 8,800 km of survey effort is recommended; at this level the expected coefficient of variation of estimates is less than 0.3 for most species. However, if logistic constraints prevent this, at least 5,000 km of survey effort should be used to achieve minimum sample size requirements; this is estimated to take 36 days of effort. It is also recommended to conduct a pilot survey. This would provide more detailed information that could be used to improve the survey design of what would be the first survey of this magnitude ever to be implemented in the Azores.

2010Journal article

Open access

Diet of mid-Atlantic Sowerby’s beaked whales Mesoplodon bidens

Publication . Pereira, José N.; Neves, Verónica C.; Clarke, D. C.; Prieto, Rui; Silva, Mónica A.; Cascão, Irma; Oliveira, Cláudia I.; Cruz, Maria J.; Barreiros, João P.; Medeiros, J. V.

The first mid-Atlantic diet of Mesoplodon beaked whales is presented, from ten Sowerby's Mesoplodon bidens stranded in the Azores region between 2002 and 2009. This doubles the worldwide number of stomachs sampled, and reveals new feeding habits for this species. The mean number of prey items per stomach was 85±89 (range: 12–238), with fish accounting for 99.3% and cephalopods contributing less than 1% of total prey. Fish otoliths from 15 families and cephalopod lower mandibles from three families were identified, representing 22 taxa. The diet consisted mainly of small mid-water fish, the most numerous being Diaphus sp., Lampanyctus sp. and Melamphaidae species. Myctophids were present in all stranded individuals, followed by Diretmidae, Melamphaidae and Opisthoproctus soleatus, while the remaining fish species were scarce or single occurrences. Consistency of diet in four different years reveals a divergence from all previous records in continental areas, where mainly neritic and shelf-break benthopelagic fish species have been reported. Mid-Atlantic Sowerby's beaked whales' showed dietary plasticity, feeding on the most abundant mid-water groups occurring between 0 and750 m. Trophic level from prey numerical frequency was estimated at 4.4±0.46.

2011-11Journal article

Open access