Daly Ryan, Smale Malcolm J, Cowley Paul D, Froneman Pierre W
Department of Zoology & Entomology, Rhodes University, Grahamstown, South Africa; Port Elizabeth Museum at Bayworld, Humewood, Port Elizabeth, South Africa.
Port Elizabeth Museum at Bayworld, Humewood, Port Elizabeth, South Africa; Department of Zoology, Nelson Mandela Metropolitan University, Port Elizabeth, South Africa.
PLoS One. 2014 Oct 8;9(10):e109357. doi: 10.1371/journal.pone.0109357. eCollection 2014.
Bull sharks (Carcharhinus leucas) are globally distributed top predators that play an important ecological role within coastal marine communities. However, little is known about the spatial and temporal scales of their habitat use and associated ecological role. In this study, we employed passive acoustic telemetry to investigate the residency patterns and migration dynamics of 18 adult bull sharks (195-283 cm total length) tagged in southern Mozambique for a period of between 10 and 22 months. The majority of sharks (n = 16) exhibited temporally and spatially variable residency patterns interspersed with migration events. Ten individuals undertook coastal migrations that ranged between 433 and 709 km (mean = 533 km) with eight of these sharks returning to the study site. During migration, individuals exhibited rates of movement between 2 and 59 km x d(-1) (mean = 17.58 km x d(-1)) and were recorded travelling annual distances of between 450 and 3760 km (mean = 1163 km). Migration towards lower latitudes primarily took place in austral spring and winter and there was a significant negative correlation between residency and mean monthly sea temperature at the study site. This suggested that seasonal change is the primary driver behind migration events but further investigation is required to assess how foraging and reproductive activity may influence residency patterns and migration. Results from this study highlight the need for further understanding of bull shark migration dynamics and suggest that effective conservation strategies for this vulnerable species necessitate the incorporation of congruent trans-boundary policies over large spatial scales.
牛鲨（Carcharhinus leucas）是全球分布的顶级掠食者，在沿海海洋群落中发挥着重要的生态作用。然而，对于它们栖息地利用的时空尺度以及相关生态作用，我们知之甚少。在本研究中，我们利用被动声学遥测技术，调查了在莫桑比克南部标记的18条成年牛鲨（全长195 - 283厘米）的居留模式和洄游动态，标记时间为10至22个月。大多数鲨鱼（n = 16）表现出时空可变的居留模式，并穿插着洄游事件。10条个体进行了沿海洄游，洄游距离在433至709公里之间（平均 = 533公里），其中8条鲨鱼返回了研究地点。在洄游过程中，个体的移动速度在2至59公里×天⁻¹之间（平均 = 17.58公里×天⁻¹），记录到的年洄游距离在450至3760公里之间（平均 = 1163公里）。向低纬度的洄游主要发生在南半球的春季和冬季，并且研究地点的居留时间与月平均海温之间存在显著的负相关。这表明季节变化是洄游事件背后的主要驱动因素，但需要进一步调查以评估觅食和繁殖活动如何可能影响居留模式和洄游。本研究结果强调了进一步了解牛鲨洄游动态的必要性，并表明针对这种脆弱物种的有效保护策略需要在大空间尺度上纳入一致的跨界政策。
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