Harbor seal-pebble sacks-SST

In the northeast Pacific Ocean, the harbor seal exhibits its southernmost distribution in waters off the Baja California Peninsula, which includes nine islands and archipelagos and some sites on the coast. A decrease in abundance at the coastal colonies was reported for 2016, when pebble extraction at some of those beaches increased. The present study analyzed seal counts in aerial photographs taken in 2016, 2018, 2019, and 2022, evaluating them as a function of both the sea surface temperature (SST) obtained from from the US National Oceanic and Atmospheric Administration (NOAA) climate data record, as taken from its polar-orbiting satellite (ftp.oceans.ncei.noaa.gov/pub/data.nodc/pathfinder/Version5.3/L3C) for the 50 km around each colony and the occurrence of pebble extraction. We found a consistent decrease in the number of seals over time for all colonies off the Baja California Peninsula in the southern California Current Large Marine Ecosystem, coinciding with an increase in SST that could indicate lower habitat suitability. However, the decline of seal numbers on the Todos Santos, San Jeronimo, San Benito, Natividad, and San Roque islands was slower, possibly because these are more productive sites. Additionally, the disappearance of many seal colonies on the coast could result from disturbances caused by pebble extraction. We used aerial photographs to count sacks containing pebbles. The present study provides evidence of the effect of ocean warming trends and disturbance on harbor seal distribution and abundance.

在东北太平洋海域，港海豹（harbor seal）的最南端分布范围位于下加利福尼亚半岛周边海域，该区域涵盖9座岛屿、群岛及部分沿岸站点。2016年有研究报道称，沿岸聚居地的港海豹种群数量出现下降，同期部分海滩的砾石开采活动有所增加。本研究对2016、2018、2019及2022年拍摄的航空摄影照片中的海豹数量进行了统计分析，以各聚居地周边50公里范围内的海表温度（SST，数据取自美国国家海洋和大气管理局（NOAA）极轨卫星的气候数据记录，来源地址为ftp.oceans.ncei.noaa.gov/pub/data.nodc/pathfinder/Version5.3/L3C）以及砾石开采活动的发生情况作为评估变量。研究发现，南加利福尼亚洋流大型海洋生态系统（California Current Large Marine Ecosystem）范围内的下加利福尼亚半岛周边所有聚居地的港海豹数量均随时间呈持续下降趋势，这与海表温度升高的趋势相吻合，而海表温度升高或预示着栖息地适宜性下降。不过，托多斯桑托斯岛、圣赫罗尼莫岛、圣贝尼托岛、纳蒂维达岛及圣罗克岛周边的海豹种群数量下降速度较慢，这可能是因为这些区域的海洋生产力更高。此外，沿岸诸多海豹聚居地的消失可能与砾石开采活动带来的干扰有关。本研究通过航空摄影照片统计了装载砾石的货袋数量。本研究为海洋变暖趋势以及人类干扰对港海豹分布与种群数量的影响提供了实证依据。