Data from: Genetic structure of populations of whale sharks among ocean basins and evidence for their historic rise and recent decline

This study presents genetic evidence that whale sharks, Rhincodon typus,
are comprised of at least two populations that rarely mix and is the first
to document a population expansion. Relatively high genetic structure is
found when comparing sharks from the Gulf of Mexico with sharks from the
Indo-Pacific. If mixing occurs between the Indian and Atlantic Oceans, it
is not sufficient to counter genetic drift. This suggests whale sharks are
not all part of a single global meta-population. The significant
population expansion we found was indicated by both microsatellite and
mitochondrial DNA. The expansion likely happened during the Holocene, when
tropical species could expand their range due to sea level rise
eliminating dispersal barriers. However, the historic trend of population
increase may have reversed recently. Declines in genetic diversity are
found for 6 consecutive years at Ningaloo Reef in Australia. The declines
in genetic diversity being seen now are likely due to commercial-scale
harvesting of whale sharks and collision with boats in past decades in
other countries in the Indo-Pacific. Whale shark hunting is banned in
Australia but continues in other countries despite bans in places like
China. The study findings have implications for models of population
connectivity for whale sharks and advocate for continued focus on
effective protection of the world’s largest fish at multiple spatial
scales.

本研究通过遗传证据证实，鲸鲨（Rhincodon typus）至少存在两个极少发生基因交流的种群，且本研究首次记录了鲸鲨的种群扩张事件。对比墨西哥湾（Gulf of Mexico）与印度-太平洋（Indo-Pacific）海域的鲸鲨样本，可观测到较高程度的遗传结构分化。即便印度洋与大西洋海域的鲸鲨存在基因交流，其交流程度也不足以抵消遗传漂变（genetic drift）的影响。这表明鲸鲨并非单一的全球集合种群（meta-population）。我们通过微卫星（microsatellite）标记与线粒体DNA（mitochondrial DNA）两种分子标记，均检测到了显著的种群扩张信号，该扩张大概率发生在全新世（Holocene）时期：彼时海平面上升消除了物种扩散的地理障碍，使得热带物种得以拓展自身分布范围。不过，鲸鲨种群此前的增长趋势近期或已发生逆转。澳大利亚宁格鲁礁（Ningaloo Reef）海域的鲸鲨遗传多样性已连续6年出现下降。当前观测到的遗传多样性衰退，大概率与近数十年来印度-太平洋海域多国对鲸鲨的商业性捕捞，以及船只碰撞事故有关。尽管澳大利亚已明令禁止鲸鲨捕捞，但包括中国在内的部分国家虽已颁布相关禁令，鲸鲨捕捞活动仍未停止。本研究结果可为鲸鲨种群连通性模型的构建提供参考，同时呼吁在多个空间尺度上持续加强对这一全球最大鱼类的有效保护。