The life history of Risso's dolphins (Grampus griseus) remains poorly known and data from strandings can help provide important information. Data from 126 Risso's dolphins stranded or bycaught along the southeastern coastline of South Africa between 1958 and 2017 were analyzed in relation to their sex, age structure, and diet. Mean estimated length at birth was 146.9 cm, while maximum length was 325 cm for males and 313 cm for females; small sample sizes precluded detailed examination of sexual dimorphism. Age estimates for 33 individuals (14 males, 17 females, 2 unknown sex) indicated a maximum age of 13 years (males) and 17 years (females), respectively; the oldest animal was 19 years (unknown sex). Mean length and age at attainment of sexual maturity were estimated at 280 cm and 7.1 years in males and at 282 cm and 7.7 years in females. Stomach contents from 27 individuals showed that diets of immature and mature males and females overlapped and consisted predominantly of cephalopods. Reported strandings decreased between 2000 and 2017, possibly due to a lack of reporting associated with a ban on driving on beaches or related to the collapse of the local “chokka” squid (Loligo reynaudii) fishery in 2014–2015.

中文翻译：

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南非东南部里索海豚（Grampus griseus）的生活史参数和饮食

里索海豚的生活史（Grampus griseus）的信息仍然鲜为人知，而来自搁浅的数据可以帮助提供重要的信息。分析了1958年至2017年之间在南非东南海岸线上搁浅或被捕获的126里索的海豚的性别，年龄结构和饮食状况。出生时的平均估计长度为146.9 cm，而男性的最大长度为325 cm，女性的最大长度为313 cm；由于样本量小，无法详细检查性二态性。对33个人的年龄估计（14名男性，17名女性，2名性别未知）分别表明最大年龄为13岁（男性）和17岁（女性）；最老的动物是19岁（未知性）。男性达到性成熟的平均长度和年龄估计为280 cm和7.1岁，女性为282 cm和7.7岁。。报告的搁浅现象在2000年至2017年之间有所减少，这可能是由于缺乏有关禁止在海滩上开车或与2014-2015年当地“ chokka”乌贼（Loligo reynaudii）渔业崩溃相关的报道。