|
|||||
|
|
Life history parameters and diet of Risso's dolphins,Grampus griseus,from southeastern South Africa |
|
| Authors: | Stephanie Plön Elodie R Heyns-Veale Malcolm J Smale P William Froneman |
| Institution: | 1. Earth Stewardship Science Research Institute, Nelson Mandela University, Port Elizabeth, South Africa;2. South African Environmental Observation Network (SAEON), Elwandle Node, Nelson Mandela University Ocean Sciences Campus, Port Elizabeth, South Africa
KwaZulu-Natal Museum, Private Bag 9070, Pietermartizburg, South Africa Department of Zoology and Entomology, Rhodes University, Grahamstown, South Africa;3. Port Elizabeth Museum and Department of Zoology, CMR, Nelson Mandela University, Port Elizabeth, South Africa;4. Department of Zoology and Entomology, Rhodes University, Grahamstown, South Africa |
| Abstract: | 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. |
| Keywords: | age estimation Cephalopoda Grampus griseus growth layer groups life history Risso's dolphin stomach content analysis strandings |