ABSTRACTS OF TALKS –WEDNESDAY 28 MARCH 2012 WEdnESday, 28th March 2012 09:30
cetacean movements in relation to the dynamics of the sound-scattering layer on seamounts in the azores
Irma Cascao (1), Mónica A. Silva (1,2), Marc O. Lammers (3,4), Rui Prieto (1), Ricardo S. Santos (1)
(1) Centro do IMAR & Departamento de Oceanografia e Pescas, Universidade dos Açores, Rua Professor Doutor Frederico Machado, 9901-862, Horta, Portugal (2) Biology Department, MS#33, Woods Hole Oceanographic Institution, 266 Woods Hole Road, Woods Hole, Massachusetts, 02543, USA (3) Hawaii Institute of Marine Biology, 46-007 Lilipuna Rd, Kaneohe, Hawaii, 96744, USA (4) Oceanwide Science Institute, P.O. Box 61692, Honolulu, Hawaii, 96839, USA
irmacascao@uac.pt
Several seamounts have been identified as hotspots of marine life in the Azores, possibly acting as feeding stations for top predators, including cetaceans. The pelagic predator-prey interaction is a crucial ecological factor affecting animal distribution and abundance. To understand this relationship, this study explores cetacean movements in relation to the dynamics of the sound-scattering layer (SSL) around/near different seamounts. In 2007 we deployed fixed-bottom mounted hydrophones (Ecological Acoustic Recorders) at four seamounts in the Azores to monitor the occurrence of cetaceans, their temporal patterns and changing levels of activity. We carried out several active acoustic surveys per year at those seamounts, using an echosounder, to characterize the density, spatial and temporal distribution of the SSL. Differences were observed in the spatio-temporal dynamics of the sound-scatterers between seamounts and “open-water”, with higher levels on the summit and along the slopes. The data suggested obvious diel migrations and depth variability. Migrations were evident in “open-waters”, concentrating in deeper waters (below 500 m) during the day and ascending to the top 150 m at night. Over/around the seamount, SSL was more evenly distributed across all depth layers, both during the day and at night, suggesting that micronekton organisms aggregate on the summit and along the slopes. Acoustic recordings revealed the presence of several species of cetaceans and associations between species. Seasonal patterns of cetacean occurrence were also observed, consistent with known periods of high trophic productivity which takes place during spring, especially in March. There was also a clear interaction between season and diel pattern of cetacean acoustic activity, with higher levels of activity during daytime in March and during night time periods from March onwards. Cetaceans may exploit the March trophic bloom and as it recedes in late spring they change their foraging strategy to feed on the nocturnally rising scattering layer.
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