[MARMAM] two new publications on strandings of harbour porpoises

Pavel Gol'din pavelgoldin412 at gmail.com
Tue Dec 23 12:51:04 PST 2014


Dear colleagues,

We are pleased to announce two upcoming publications on the strandings of
harbour porpoises in the Sea of Azov:


Vishnyakova, K., Gol’din, Cetacean stranding rate correlates with fish
stock dynamics: Research of harbour porpoises in the Sea of Azov. Marine
Biology doi: 10.1007/s00227-014-2600-x

http://link.springer.com/article/10.1007/s00227-014-2600-x

The dynamics of the endangered population of the harbour porpoise (*Phocoena
phocoena*) in the Azov Sea is currently unknown. It can be, however,
estimated by stranding analysis. In 1999–2014, the porpoise stranding rates
were regularly monitored at the southern coast of the Azov Sea,
particularly at the uninhabited abraded coast of the Tarkhan Cape.
Specifically, the general trends and annual fluctuations in strandings were
compared to the catch reports of the Azov anchovy (*Engraulis encrasicolus*),
an important prey for porpoises. It was observed that the fluctuations in
stranding rates closely correlated with the population dynamics of the
anchovy stock. A cosine function, based on the data from 1999–2012,
correctly predicted maximum strandings in 2013 and their substantial
decline in 2014. The function worked particularly well, when possible
biases affecting carcass preservation, such as discovery rate and drift
conditions, were reduced. In certain environments and over established time
periods, the cetacean stranding rate can be an indicator of population
trends. The use of stranding rates as such indicator may be verified by
external factors, including the dynamics of prey stocks.


Vishnyakova, K., Gol’din, P., Seasonality of strandings and bycatch of
harbour porpoises in the Sea of Azov: the effects of fisheries, weather
conditions and life history. ICES Journal of Marine Science doi:
10.1093/icesjms/fsu192

http://icesjms.oxfordjournals.org/content/early/2014/11/04/icesjms.fsu192.abstract

In this study, we analyse seasonal aspects of harbour porpoise strandings
in the Sea of Azov and discuss factors affecting the stranding rate. Data
on 633 strandings were obtained from monitoring of a 35-km long area of the
south coast of the Sea of Azov in 1999–2013. A distinct peak of strandings
fell in July and August: it depended on the bycatch peak and calving
season. Stranding rates depended neither on weather conditions nor on the
seasonal fishing activities (including IUU fisheries). Moreover, stranding
peaks in the neighbouring Black Sea were also tied to the calving season
rather than to the fishing activities. We suggest that the seasonal
mortality patterns are indirectly determined by nutritional stress: in
Atlantic, winter-stranding oceanic populations and summer-stranding
inner-sea populations occur that also possibly differ in the seasonal
dynamics of body mass, weaning time or duration of mother–calf association,
and dentine structure. In a typical summer-stranding population, summer is
the season of nutritional stress, parturition, independent foraging of
yearlings and lactation of nursing females, which leads to the risky
foraging behaviour near gillnets. Another possible factor of increased
bycatch is the seasonal habitat preference, corresponding to the gillnet
preferences. Therefore, stranding and bycatch seasonality of porpoises can
largely be explained by the aspects of their life history and foraging
behaviour rather than by weather conditions and fisheries. This supports
the time–area closure strategy as an adequate conservation measure, which
would consider minimizing the conflict of interest with fisheries.

We will be grateful for your comments. You are welcome to contact me:
pago at museum-sonderjylland.dk , pavelgoldin412 at gmail.com


On behalf of the authors,
Pavel

Pavel Gol'din
Department of Natural History and Palaeontology,
The Museum of Southern Jutland,
Lergravsvej 2, 6510, Gram, Denmark
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