The worldwide smallest cetacean, the vaquita (Phocoena sinus), is on the verge of extinction with fewer than 20 individuals left as of summer 2018. The main cause of mortality is bycatch by entanglement in illegal gillnets and environmental changes. Habitat disturbances have negatively impacted prey diversity, and therefore, the vaquita’s feeding success. We investigated the trophic niche of the vaquita and its variability from 1985 to 1993 by quantifying δ¹³C and δ¹⁵N values from bone samples (n = 33). We reconstructed part of vaquita’s refuge food web and identified some prey items. Between 1985 and 1993 the vaquita’s isotopic ellipses shifted moderately, δ¹³C and δ¹⁵N without significant differences, suggesting variations in habitat baseline values and probably prey composition. We observed a high overlap in the ellipses between males and females, suggesting that both sexes were feeding in the same geographic area over several years and with similar prey composition. Together, our results indicate that the vaquita is a generalist high-TL consumer, feeding on benthic and small pelagic prey it maintained similar mean δ¹⁵N values for years. Given these results, conservation efforts should intensify to protect the biodiversity of the Upper Gulf of California and the surviving vaquita.

世界上最小的鲸类动物小头鼠海豚 ( Phocoena sin ) 濒临灭绝，截至 2018 年夏季仅剩不到 20 只。死亡的主要原因是非法刺网和环境变化造成的兼捕。栖息地的干扰对猎物的多样性产生了负面影响，因此，小头鼠海豚的摄食成功。我们通过量化骨骼样本中的δ ¹³ C 和δ ¹⁵ N 值（n = 33）研究了小头鼠海豚的营养生态位及其从 1985 年到 1993 年的变异性。我们重建了小头鼠海豚避难所食物网的一部分，并确定了一些猎物。1985 年至 1993 年间，小头鼠海豚的同位素椭圆发生了适度移动，δ ¹³ C 和δ ¹⁵N 没有显着差异，表明栖息地基线值和可能的猎物组成存在差异。我们观察到雄性和雌性之间的椭圆高度重叠，这表明两性多年来都在同一地理区域觅食，并且猎物成分相似。总之，我们的结果表明，小头鼠海豚是一种多面手的高 TL 消费者，以底栖和小型远洋猎物为食，它多年来保持相似的平均δ ¹⁵ N 值。鉴于这些结果，应加强保护工作，以保护上加利福尼亚湾和幸存的小头鼠海豚的生物多样性。