Herzing Denise L, Augliere Bethany N, Elliser Cindy R, Green Michelle L, Pack Adam A
Wild Dolphin Project, Jupiter, Florida, United States of America.
Department of Biological Sciences, Florida Atlantic University, Boca Raton, Florida, United States of America.
PLoS One. 2017 Aug 9;12(8):e0180304. doi: 10.1371/journal.pone.0180304. eCollection 2017.
Over the last 20 years, significant habitat shifts have been documented in some populations of cetaceans. On Little Bahama Bank (LBB) there are sympatric communities of resident Atlantic spotted dolphins (Stenella frontalis) and bottlenose dolphins (Tursiops truncatus), monitored since 1985. The size and social structure (three clusters: Northern, Central, Southern) have been stable among the spotted dolphin community with little immigration/emigration, even after large demographic losses (36%) following two major hurricanes in 2004. In 2013 an unprecedented exodus of over 50% (52 individuals) of the spotted dolphin community was documented. The entire Central cluster and a few Northern and Southern individuals relocated 161 km south to Great Bahama Bank (GBB), also home to two sympatric resident communities of spotted dolphins and bottlenose dolphins. During the late summer of 2013 and the summers of 2014 and 2015 both sites were regularly monitored but no former LBB dolphins returned to LBB. Uncharacteristic matriline splits were observed. Social analyses revealed random associations for those spotted dolphins and very little integration between spotted dolphins that moved to GBB (MGBB) and those dolphin resident to GBB (RGBB). Male alliances among spotted dolphins were present, with some altered patterns. On LBB, the operational sex ratio (OSR) was reduced (.40 to .25). OSR for MGBB and RGBB dolphins were similar (.45 and .43). A significant steady decrease in sea surface temperature and chlorophyll a (a proxy for plankton production) occurred on LBB leading up to this exodus. Similar trends were not present over the same period on GBB. The sudden large-scale shift of spotted dolphins from LBB to GBB in association with the gradual decline in certain environmental factors suggests that a possible "tipping point" was reached in prey availability. This study provides a unique view into social and genetic implications of large-scale displacement of stable dolphin communities.
在过去20年里，一些鲸类种群出现了显著的栖息地转移。在小巴哈马浅滩（LBB），自1985年以来一直监测着同域分布的常驻大西洋斑点海豚（Stenella frontalis）和宽吻海豚（Tursiops truncatus）群落。斑点海豚群落的规模和社会结构（分为三个集群：北部、中部、南部）一直保持稳定，很少有迁入/迁出情况，即使在2004年两场主要飓风造成大量种群损失（36%）之后也是如此。2013年，记录到斑点海豚群落出现了前所未有的超过50%（52只个体）的外流。整个中部集群以及一些北部和南部的个体向南迁移了161公里至大巴哈马浅滩（GBB），这里也是斑点海豚和宽吻海豚两个同域常驻群落的栖息地。在2013年夏末以及2014年和2015年夏天，对这两个地点都进行了定期监测，但没有一只原LBB的海豚回到LBB。观察到了不寻常的母系分裂。社会分析显示，那些斑点海豚之间的关联是随机的，并且迁移到GBB的斑点海豚（MGBB）与GBB的常驻海豚（RGBB）之间几乎没有融合。斑点海豚中存在雄性联盟，且有些模式发生了改变。在LBB，操作性别比（OSR）降低了（从0.40降至0.25）。MGBB和RGBB海豚的OSR相似（分别为0.45和0.43）。在这次外流之前，LBB的海面温度和叶绿素a（浮游生物产量的一个指标）出现了显著的稳步下降。同期GBB没有出现类似趋势。斑点海豚从LBB突然大规模转移到GBB，同时某些环境因素逐渐下降，这表明猎物可获得性可能达到了一个“临界点”。这项研究为稳定的海豚群落大规模迁移的社会和遗传影响提供了独特视角。
