Trends in Stranding and By-Catch Rates of Gray and Harbor Seals along the Northeastern Coast of the United States: Evidence of Divergence in the Abundance of Two Sympatric Phocid Species?

Journal Article (Journal Article)

Harbor seals and gray seals are sympatric phocid pinnipeds found in coastal waters of the temperate and sub-Arctic North Atlantic. In the Northwest Atlantic, both species were depleted through a combination of subsistence hunts and government supported bounties, and are now re-occupying substantial portions of their original ranges. While both species appear to have recovered during the past 2 decades, our understanding of their population dynamics in US waters is incomplete. Here we describe trends in stranding and bycatch rates of harbor and gray seals in the North East United States (NEUS) over the past 16 years through an exploratory curve-fitting exercise and structural break-point analysis. Variability in gray seal strandings in Southern New England and bycatch in the Northeast Sink Gillnet Fishery were best described by fitting positive exponential and linear models, and exhibited rates of increase as high as 22%. In contrast, neither linear nor exponential models fit the oscillation of harbor seal strandings and bycatch over the study period. However, a breakpoint Chow test revealed that harbor seal strandings in the Cape Cod, Massachusetts region and harbor seal bycatch in the Northeast Sink Gillnet Fishery increased in the 1990s and then started declining in the early to mid-2000s. Our analysis indicates that ongoing variation in natural and anthropogenic mortality rates of harbor and gray seals in the NEUS is not synchronous, and likely represents diverging trends in abundance of these species as they assume new roles in the marine ecosystems of the region.

Full Text

Duke Authors

Cited Authors

  • Johnston, DW; Frungillo, J; Smith, A; Moore, K; Sharp, B; Schuh, J; Read, AJ

Published Date

  • January 2015

Published In

Volume / Issue

  • 10 / 7

Start / End Page

  • e0131660 -

PubMed ID

  • 26200461

Pubmed Central ID

  • PMC4511798

Electronic International Standard Serial Number (EISSN)

  • 1932-6203

International Standard Serial Number (ISSN)

  • 1932-6203

Digital Object Identifier (DOI)

  • 10.1371/journal.pone.0131660


  • eng