Drift diving by hooded seals (Cystophora cristata) in the Northwest Atlantic Ocean

This work was funded through the Atlantic Seal Research Programme, International Governance Programme (GBS and MOH), the Greenland Institute of Natural Resources (ARA), and a CFI grant to YFW. The authors also acknowledge the support of the MASTS pooling initiative (The Marine Alliance for Science and Technology for Scotland) in the completion of this study. MASTS is funded by the Scottish Funding Council (grant reference HR09011) and contributing institutions (LB).Many pinniped species perform a specific dive type, referred to as a ‘drift dive’, where they drift passively through the water column. This dive type has been suggested to function as a resting/sleeping or food processing dive, and can be used as an indication of feeding success by calculating the daily change in vertical drift rates over time, which reflects the relative fluctuations in buoyancy of the animal as the proportion of lipids in the body change. Northwest Atlantic hooded seals perform drift dives at regular intervals throughout their annual migration across the Northwest Atlantic Ocean. We found that the daily change in drift rate varied with geographic location and the time of year and that this differed between sexes. Positive changes in buoyancy (reflecting increased lipid stores) were evident throughout their migration range and although overlapping somewhat, they were not statistically associated with high use areas as indicated by First Passage Time (FPT). Differences in the seasonal fluctuations of buoyancy between males and females suggest that they experience a difference in patterns of energy gain and loss during winter and spring, associated with breeding. The fluctuations in buoyancy around the moulting period were similar between sexes.Publisher PDFPeer reviewe

Habitat selection by hooded seals (Cystophora cristata) in the Northwest Atlantic Ocean

We examined annual habitat use for 65 hooded seals (32 adult females, 17 adult males, and 16 juveniles) equipped with satellite relay data loggers (SRDLs) in spring or summer during five field seasons (2004–2008). A combined approach using first passage time (FPT) analysis and a generalized additive model (GAM) was applied to test for habitat selection, with a focus on environmental parameters of depth, slope, ice, sea surface temperature (SST), and chlorophyll. The models were run on adult males, adult females, and juveniles separately, and the results identified SST, depth, and chlorophyll as the most important factors influencing habitat selection across all categories. Furthermore, males and females preferred similar habitat conditions, but were separated geographically, and by depth, at various times of the year. Males appeared to be more localized in their habitat use patterns, focusing their search effort in areas of complex seabed relief such as Baffin Bay, Davis Strait, and the Flemish cap, while females concentrated their search effort along shelf areas (e.g. the Labrador shelf). These findings support our hypothesis that hooded seals prefer areas where topography and oceanographic processes create favourable foraging conditions

Plot of fitted values (daily change in drift rate (cm/s)) from the best GAM for a) males (n = 17) and b) females (n = 30).

<p>The darker the colour, the larger the daily change in drift rate.</p

Predicted GAM results of the deviation from the mean daily change in drift rate (cm/s) over time, where the mean is at 0.

<p>Data from males and females were here run in seperate models: males: solid black line (n = 17) and females: dashed line (n = 30). Thin lines represent the standard error and red columns represent the annual fasting periods (breeding/whelping in March and moulting in July).</p

Map over the study area: Moulting area in southeast Greenland and breeding areas in Davis Strait (DS), The Front and The Gulf.

<p>Bathymetry of the study area is presented as backdrop in grey scale. Dashed white line is the 1,000</p

Percentage of drift dives as a function of month (1–12 = January–December) across females (grey; n = 30), and males (black; n = 17).

<p>Error bars represent the standard error.</p

A description of a drift dive.

<p>Time spent from point D1 to D2 represents fast descent with possibly active swimming, D2 to D3 represents a dramatic decrease in vertical speed, with no active swimming and is called the “drift phase”. D3 to D4 represents ascent with active swimming. T1 and T3 represent the duration of ascent and descent and T2 is the duration of the drift phase. T1 to T3 is the total duration of the dive.</p