Population Ecology Group, Institut Mediterrani d' Estudis Avançats, IMEDEA (CSIC-UIB), Miquel Marquès, 21, Esporles, 07190, Spain.
The Leatherback Trust, Goldring-Gund Marine Biology Station, Playa Grande, Costa Rica.
Ecology. 2017 Aug;98(8):2170-2179. doi: 10.1002/ecy.1909. Epub 2017 Jul 11.
The number of nesting leatherback turtles (Dermochelys coriacea) in the eastern Pacific Ocean has declined dramatically since the late 1980s. This decline has been attributed to egg poaching and interactions with fisheries. However, it is not clear how much of the decline should also be ascribed to variability in the physical characteristics of the ocean. We used data on individually marked turtles that nest at Playa Grande, Costa Rica, to address whether climatic variability affects survival and inter-breeding interval. Because some turtles might nest undetected, we used capture-recapture models to model survival probability accounting for a detection failure. In addition, as the probability of reproduction is constrained by past nesting events, we formulated a new parameterization to estimate inter-breeding intervals and contrast hypotheses on the role of climatic covariates on reproductive frequency. Average annual survival for the period 1993-2011 was low (0.78) and varied over time ranging from 0.49 to 0.99 with a negative temporal trend mainly due to the high mortality values registered after 2004. Survival probability was not associated with the Multivariate ENSO Index of the South Pacific Ocean (MEI) but this index explained 24% of the temporal variability in the reproductive frequency. The probability of a turtle to permanently leave after the first encounter was 26%. This high proportion of transients might be associated with a high mortality cost of the first reproduction or with a long-distance nesting dispersal after the first nesting season. Although current data do not allow separating these two hypotheses, low encounter rate at other locations and high investment in reproduction, supports the first hypothesis. The low and variable annual survival probability has largely contributed to the decline of this leatherback population. The lack of correlation between survival probability and the most important climatic driver of oceanic processes in the Pacific discards a climate-related decline and point to anthropogenic sources of mortality as the main causes responsible for the observed population decline.
自 20 世纪 80 年代末以来，东太平洋的筑巢棱皮龟（Dermochelys coriacea）数量急剧下降。这种下降归因于偷蛋和与渔业的相互作用。然而，目前还不清楚有多少下降应该归因于海洋物理特征的可变性。我们使用在哥斯达黎加格兰德海滩（Playa Grande）筑巢的个体标记海龟的数据，来解决气候变异性是否会影响海龟的存活率和繁殖间隔。由于一些海龟可能在没有被发现的情况下筑巢，我们使用捕获-再捕获模型来模拟存活率，同时考虑到检测失败的情况。此外，由于繁殖的概率受到过去筑巢事件的限制，我们提出了一个新的参数化方法来估计繁殖间隔，并对比气候协变量对繁殖频率的作用的假设。1993 年至 2011 年期间的平均年存活率较低（0.78），且随时间变化，范围从 0.49 到 0.99，存在负时间趋势，主要是由于 2004 年后死亡率较高。存活率与南太平洋海洋多变量厄尔尼诺指数（MEI）不相关，但该指数解释了繁殖频率的 24%的时间变异性。海龟在首次相遇后永久离开的概率为 26%。这种高比例的过客可能与第一次繁殖的高死亡率成本或第一次筑巢季节后长距离的筑巢扩散有关。尽管目前的数据不允许分离这两种假设，但在其他地点的低相遇率和高繁殖投资，支持了第一种假设。低且可变的年存活率是导致这种棱皮龟数量下降的主要原因。存活率与太平洋海洋过程最重要的气候驱动因素之间缺乏相关性，排除了与气候相关的下降，并指出人为因素导致的死亡率是造成观察到的种群下降的主要原因。
