[MARMAM] New paper: Net loss of humpback dolphins

Shanan Atkins shananatkins at gmail.com
Fri Aug 19 09:57:32 PDT 2016

Dear Marmam community

We’re pleased to tell you about our recently published study on how bycatch
can potentially influence populations.

Atkins S, Cantor M, Pillay N, Cliff G, Keith M, Parra G (2016) Net loss of
endangered humpback dolphins: integrating residency, site fidelity, and
bycatch in shark nets. Mar Ecol Prog Ser 555:249–260

ABSTRACT: Fisheries bycatch—the incidental catch of non-target species
during fishing—is problematic for large marine vertebrates. Bather
protection programmes that use gillnets to kill sharks cause the incidental
mortality of humpback dolphins *Sousa *spp., potentially impacting the
long-term survival of these threatened species. Understanding dolphins’
spatial and temporal use of gillnetted areas is critical for designing
effective mitigation strategies. We photo-identified dolphins over 8 yr in
a high-bycatch area (Richards Bay, South Africa) to assess the residency,
site fidelity, and movement patterns of Indian Ocean humpback dolphins *S.
plumbea *and evaluate how emigration, immigration, and mortality rates
influence the use of Richards Bay at various temporal scales. Overall,
residency was low but site fidelity was high, leading to high population
turnover in the short term but low turnover over 6 mo and longer. There was
clear individual variation in visitation but no evidence of seasonality. By
considering such movements, the net loss of dolphins from the area became
evident. While dolphins naturally emigrate from the area, the recognition
of several catalogued individuals among the bycaught dolphins indicated
that mortality in the shark nets contributes to the permanent loss of both
residents and transients. Richards Bay may represent an ecological trap:
high site fidelity indicates dolphins perceived the area as ecologically
attractive, but high mortality due to shark nets makes it risky. We
examined these results relative to gillnet bycatch mitigation methods and
recommend that stakeholders collaborate as a mitigation team to prioritise
management actions to reduce bycatch without compromising bather safety.

The paper can be found http://www.int-res.com/abstracts/meps/v555/p249-260/
 or send a request to me: shananatkins at gmail.com <shananatkins at vgmail.co.za>

Kind regards


Shanan Atkins

shananatkins at gmail.com <shananatkins at vgmail.co.za>

Source-toSea Programme, Endangered Wildlife Trust

School of Animal, Plant and Environmental Sciences, University of

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