Figure 3. Preliminary map of ribbon (green) and spotted (purple) seal movements from ARGOS satellite tags from April to July 2014. Tagging locations are shown as yellow stars.
Adult spotted and ribbon seals undergo an annual molt in May and June, so the SPLASH tags are expected to provide data for only a few weeks or months before being shed. Data from the deployed tags are already providing information (Fig. 3). As observed from tags deployed in previous years, both ribbon and spotted seals have a strong association with the sea ice. As the sea ice retreated in early summer, the spotted seals tended to head towards more coastal habitats along Alaska or Russia while ribbon seals remained in the ice-free waters near the shelf break and over the Aleutian Basin.
In addition to location estimates, the SPLASH tags deployed on this cruise provide important behavioral data. Diving is an indicator of foraging activity and long periods at the surface indicate haul-out and resting behaviors. Figure 4 provides a graphic representation of dives for one adult and four young-of-the-year spotted seals. The adult seal exhibits reduced dive activity and more surface behavior leading up to the annual molt. The young animals show increased dive activity as they learn to dive and survive on their own. These spotted seals are likely focused on demersal fish species and, thus, variation in the maximum dive depth values over time is largely an indicator of the Bering Sea shelf bathymetry.
Figure 4. Plot of diving behavior for one adult and four young-of-the-year spotted seals from late April to early July 2014. The length of each bar indicates the maximum depth of each dive and the color indicates the dive’s duration, with warmer colors indicating dives up to 15 minutes long.
The sampling for each seal typically included morphometrics (i.e., length, girth, and mass measurements) and the collection of numerous tissue and fecal samples for studies of pathology, genetic population structure, blood chemistry, diet, contaminants, health, and condition. Data from two ribbon seals were submitted for consideration as cases in the Northern Pinniped Unusual Mortality Event. Many of the seals we sampled were mother‐pup pairs, dependent pups, or recently weaned pups—a primary focus of this cruise, which was timed to coincide with the whelping, nursing, and maturation of pups. These samples will begin to form a reference database that can be used to assess the future impacts of climate disruption and loss of sea ice.
This project’s success was made possible by outstanding support from the command and crew of the Oscar Dyson, the Alaska Fisheries Science Center, Pacific Islands Fisheries Science Center, Marine Mammal Health and Stranding Response Program, and The Marine Mammal Center.
