TY - JOUR

T1 - The stranding anomaly as population indicator

T2 - the case of harbour porpoise Phocoena phocoena in North-Western Europe

AU - Peltier, Helene

AU - Baagøe, Hans J.

AU - Camphuysen, Kees C. J.

AU - Czeck, Richard

AU - Dabin, Willy

AU - Daniel, Pierre

AU - Deaville, Rob

AU - Haelters, Jan

AU - Jauniaux, Thierry

AU - Jensen, Lasse F.

AU - Jepson, Paul D.

AU - Keijl, Guido O.

AU - Siebert, Ursula

AU - van Canneyt, Olivier

AU - Ridoux, Vincent

PY - 2013/4/22

Y1 - 2013/4/22

N2 - Ecological indicators for monitoring strategies are expected to combine three major characteristics: ecological significance,statistical credibility, and cost-effectiveness. Strategies based on stranding networks rank highly in cost-effectiveness, buttheir ecological significance and statistical credibility are disputed. Our present goal is to improve the value of strandingdata as population indicator as part of monitoring strategies by constructing the spatial and temporal null hypothesis forstrandings. The null hypothesis is defined as: small cetacean distribution and mortality are uniform in space and constant intime. We used a drift model to map stranding probabilities and predict stranding patterns of cetacean carcasses under H0across the North Sea, the Channel and the Bay of Biscay, for the period 1990–2009. As the most common cetacean occurringin this area, we chose the harbour porpoise Phocoena phocoena for our modelling. The difference between these strandingsexpected under H0 and observed strandings is defined as the stranding anomaly. It constituted the stranding data seriescorrected for drift conditions. Seasonal decomposition of stranding anomaly suggested that drift conditions did not explainobserved seasonal variations of porpoise strandings. Long-term stranding anomalies increased first in the southern NorthSea, the Channel and Bay of Biscay coasts, and finally the eastern North Sea. The hypothesis of changes in porpoisedistribution was consistent with local visual surveys, mostly SCANS surveys (1994 and 2005). This new indicator could beapplied to cetacean populations across the world and more widely to marine megafauna.

AB - Ecological indicators for monitoring strategies are expected to combine three major characteristics: ecological significance,statistical credibility, and cost-effectiveness. Strategies based on stranding networks rank highly in cost-effectiveness, buttheir ecological significance and statistical credibility are disputed. Our present goal is to improve the value of strandingdata as population indicator as part of monitoring strategies by constructing the spatial and temporal null hypothesis forstrandings. The null hypothesis is defined as: small cetacean distribution and mortality are uniform in space and constant intime. We used a drift model to map stranding probabilities and predict stranding patterns of cetacean carcasses under H0across the North Sea, the Channel and the Bay of Biscay, for the period 1990–2009. As the most common cetacean occurringin this area, we chose the harbour porpoise Phocoena phocoena for our modelling. The difference between these strandingsexpected under H0 and observed strandings is defined as the stranding anomaly. It constituted the stranding data seriescorrected for drift conditions. Seasonal decomposition of stranding anomaly suggested that drift conditions did not explainobserved seasonal variations of porpoise strandings. Long-term stranding anomalies increased first in the southern NorthSea, the Channel and Bay of Biscay coasts, and finally the eastern North Sea. The hypothesis of changes in porpoisedistribution was consistent with local visual surveys, mostly SCANS surveys (1994 and 2005). This new indicator could beapplied to cetacean populations across the world and more widely to marine megafauna.

U2 - 10.1371/journal.pone.0062180

DO - 10.1371/journal.pone.0062180

M3 - Journal article

C2 - 23614031

VL - 8

JO - PLoS ONE

JF - PLoS ONE

SN - 1932-6203

IS - 4

M1 - e62180

ER -