[MARMAM] New publication: External indicators of fisheries interactions in known bycaught dolphins from bather protection nets along the KwaZulu-Natal coastline, South Africa

Stephanie Plön, PhD stephanie.ploen at gmail.com
Thu Sep 29 09:28:45 PDT 2022


Dear MARMAM Subscribers,



On behalf my co-authors, I am pleased to share our new publication on ‘
External indicators of fisheries interactions in known bycaught dolphins
from bather protection nets along the KwaZulu-Natal coastline, South
Africa’.



Roussouw, N., Wintner, S., Hofmeyr, G. J. G., Wohlsein, P., Siebert, U.
and S. Plön. 2022. External indicators of fisheries interactions in known
bycaught dolphins from bather protection nets along the KwaZulu-Natal
coastline, South Africa. Journal of Cetacean Research and Management 23(1):
127-140. https://doi.org/10.47536/jcrm.v23i1.338



Abstract

Detailed examinations of dolphins incidentally caught in bather protection
nets along the KwaZulu‐Natal coastline, South Africa, over the past 10
years have yielded a dataset that can assist in the examination of external
signs of bycatch. Investigating these external signs of fisheries
interactions could aid in determining whether they could be used as
unequivocal indicators of entanglement in stranded dolphins for which cause
of death is unknown. The aim of this study was to investigate the
occurrence of netmarks and other external injuries on individuals of two
dolphin species (*Tursiops aduncus* and *Sousa plumbea*), both bycaught and
stranded, along the south‐east coast of South Africa. Necropsy reports and
photographs of 107 bycaught and 15 stranded dolphins between 2010 and 2017
were investigated to determine prevalence of netmarks and other external
injuries in relation to species, sex, age class, and water temperature. Our
results indicated that 36% of the bycaught dolphins and 13% of stranded
dolphins showed netmarks on the skin. In bycaught animals, females were
more likely to show netmarks (58%) and the majority of dolphins with
netmarks were immatures (66%; immatures included calves, neonates and
subadults). There was little evidence for water temperature affecting the
appearance of netmarks. Furthermore, species, sex or age class did not play
a significant role in the probability of netmark occurrence. Other external
injuries were also observed in the bycaught (3–50%) and stranded animals
(7–100%), with subcutaneous bruising being the most prominent sign in
bycaught animals. Our study showed that only a small percentage of known
bycaught animals actually present external signs of entanglement. Thus,
additional evidence, such as histopathological examinations, is required to
reliably identify entanglement cases in stranded animals.



You can access the full-text at the following link:

https://journal.iwc.int/index.php/jcrm/article/view/338



Alternatively, please feel free to e-mail me for a pdf copy or any queries.



 Kind regards,

 Stephanie
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