Kesselring Tina, Viquerat Sacha, Brehm Ralph, Siebert Ursula
Institute for Terrestrial and Aquatic Wildlife Research (ITAW), University of Veterinary Medicine Hannover Foundation, Büsum, Germany.
Institute for Anatomy, University of Veterinary Medicine Hannover Foundation, Hannover, Germany.
PLoS One. 2017 Oct 20;12(10):e0186951. doi: 10.1371/journal.pone.0186951. eCollection 2017.
The harbour porpoise is the only cetacean species native to German waters. Since human pressures are suggested to shorten their reproductive lifespan, basic knowledge on reproduction is strongly required. One parameter is the onset of sexual maturity in female harbour porpoises. Therefore, we investigated the first signs of sexual maturity for a period of almost two decades (1990-2016). Ovaries from 111 female harbour porpoises from the German North Sea and Baltic Sea were examined for the presence and morphological structure of follicles, corpora lutea and corpora albicantia. Based on the ovarian characteristics we performed the first model-based estimation of age at sexual maturity for harbour porpoises from German waters. Additionally, we produced a demographical age structure based on all female strandings and bycatches from German coasts. Our results showed that corpora lutea and corpora albicantia as signs of former ovulation could be found in individuals at an age of 4.95 (± 0.6) years. No significant differences between specimens from the North Sea and Baltic Sea were detected. However, the average age at death differed significantly with 5.70 (± 0.27) years for North Sea animals and 3.67 (± 0.30) years for those in the Baltic Sea. Growing evidence exists that the shortened lifespan of Baltic Sea harbour porpoises is linked to an anthropogenically influenced environment with rising bycatch mortalities due to local gillnet fisheries. Thus, our findings support the idea of local management plans based on a model-based detection of age at sexual maturity and considering the anthropogenic impacts on the population for effective protection of harbour porpoises and the North Sea and Baltic Sea.
港湾鼠海豚是德国海域特有的唯一鲸类物种。由于人类活动的压力可能会缩短它们的繁殖寿命，因此迫切需要有关繁殖的基础知识。其中一个参数是雌性港湾鼠海豚的性成熟起始年龄。因此，我们对近二十年（1990 - 2016年）间性成熟的最初迹象进行了调查。对来自德国北海和波罗的海的111头雌性港湾鼠海豚的卵巢进行了检查，以确定卵泡、黄体和白体的存在及形态结构。基于卵巢特征，我们首次对德国海域港湾鼠海豚的性成熟年龄进行了基于模型的估计。此外，我们根据德国海岸所有雌性搁浅和兼捕记录生成了一个人口年龄结构。我们的结果表明，在4.95（±0.6）岁的个体中可以发现黄体和白体作为先前排卵的迹象。北海和波罗的海的样本之间未检测到显著差异。然而，平均死亡年龄存在显著差异，北海动物为5.70（±0.27）岁，波罗的海动物为3.67（±0.30）岁。越来越多的证据表明，波罗的海港湾鼠海豚寿命缩短与人为影响的环境有关，当地刺网渔业导致的兼捕死亡率上升。因此，我们的研究结果支持基于性成熟年龄的模型检测并考虑人为对种群的影响来制定地方管理计划的想法，以有效保护港湾鼠海豚以及北海和波罗的海。
