Johnston David W, Frungillo Jaime, Smith Ainsley, Moore Katie, Sharp Brian, Schuh Janelle, Read Andrew J
Division of Marine Science and Conservation, Nicholas School of the Environment, Duke University of Marine Laboratory, 135 Duke Marine Lab Rd., Beaufort, NC, 28516, United States of America.
Division of Marine Science and Conservation, Nicholas School of the Environment, Duke University of Marine Laboratory, 135 Duke Marine Lab Rd., Beaufort, NC, 28516, United States of America; Integrated Statistics, 16 Sumner Street, Woods Hole, MA, 02543, United States of America.
PLoS One. 2015 Jul 22;10(7):e0131660. doi: 10.1371/journal.pone.0131660. eCollection 2015.
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.
港海豹和灰海豹是分布于温带和亚北极北大西洋沿海水域的同域鳍脚类海豹。在西北大西洋，这两个物种因生存捕猎和政府支持的赏金而数量减少，现在正重新占据其原始分布范围的很大一部分。虽然这两个物种在过去20年里似乎都已恢复，但我们对它们在美国水域的种群动态的了解并不完整。在此，我们通过探索性曲线拟合练习和结构断点分析，描述了过去16年美国东北部（NEUS）港海豹和灰海豹的搁浅和兼捕率趋势。通过拟合正指数模型和线性模型，能最好地描述新英格兰南部灰海豹搁浅和东北沉底刺网渔业兼捕的变化情况，其增长率高达22%。相比之下，线性模型和指数模型都无法拟合研究期间港海豹搁浅和兼捕的波动情况。然而，断点邹检验显示，马萨诸塞州科德角地区的港海豹搁浅情况以及东北沉底刺网渔业的港海豹兼捕情况在20世纪90年代有所增加，然后在21世纪初至中期开始下降。我们的分析表明，NEUS港海豹和灰海豹的自然死亡率和人为死亡率的持续变化并不同步，这可能代表了这些物种在该地区海洋生态系统中扮演新角色时数量的不同变化趋势。
