• Ben Neely

This seal hits the spot

The spotted seal gets its name from its coat pattern: dark spots on a silvery-gray to light gray background. They can weigh between 140 and 250 pounds (63 to 113 kilograms) and reach 4.5 to 5.5 feet (1.4 to 1.7 meters) in length. They prefer arctic to sub-arctic waters, often on the outer margins of ice floes. Specifically in U.S. waters, they migrate through the Bering Strait from the Chukchi Sea in the fall, spending the winter in the annual pack ice over the continental shelf there. In the spring, following the retreat of sea ice, they migrate to coastal habitats from Siberia and Alaska to coastal Japan and the northern Yellow Sea. During summer months they can be found in the open ocean or hauled out on shore.

Photo Credit: Dave Withrow (NOAA); Marine Mammal Permit: 15126

In contrast to notorious deep divers like the Weddell or elephant seal, spotted seals feed almost exclusively over the continental shelf in waters less than 650 feet (200 meters) deep. Though their global population is estimated at more than 500,000 individuals, they are sensitive to changes in the environment that affect the annual timing and extent of sea ice formation and breakup since they rely on sea ice during reproduction and to some extent during molting.


Spotted seals are also big on family time. Though unusual among true seals, spotted seals form annual family groups consisting of an annually monogamous male, a female and a pup during the breeding season. Gestation lasts just over 10 months and pups are born with a white coat. Pups are then nursed for 3 to 6 weeks as they triple in weight, and usually shed their white coat for a spotted coat when they are weaned.


Today we release the genome assembly for the spotted seal! This is a $1K genome assembly with a contig n50 = 56 KB and scaffold n50 = 142 MB, strategy described in (Dudchenko et al., 2018). See our Methods page for more details.


This is the 5th Phocidae species that the DNA Zoo has released! Check out these posts on the Hawaiian monk seal, Northern elephant seal, the bearded seal and the harbor seal. In places that harbor seals and spotted seals co-habit such as Bristol Bay, they can be confused with each other due to their similar appearance.


This work was performed under Marine Mammal Health and Stranding Response Program (MMHSRP) Permit No. 18786-03 issued by the National Marine Fisheries Service (NMFS) under the authority of the Marine Mammal Protection Act (MMPA) and Endangered Species Act (ESA). The spotted seal (Phoca largha) specimen used in this study was collected from Kotzebue Sound, AK by James Jones and Sherman Anderson. The specimen was provided by the National Marine Mammal Tissue Bank, which is maintained by the National Institute of Standards and Technology (NIST) in the NIST Biorepository, which is operated under the direction of NMFS with the collaboration of USGS, USFWS, MMS, and NIST through the Marine Mammal Health and Stranding Response Program and the Alaska Marine Mammal Tissue Archival Project.


Check out the interactive Juicebox.js map with the 16 chromosomes of the new assembly below!



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