Research Document - 2014/021

Summer abundance indices of St. Lawrence Estuary beluga (Delphinapterus leucas) from a photographic survey in 2009 and 28 line transect surveys from 2001 to 2009

By Jean-François Gosselin, Mike O. Hammill and Arnaud Mosnier

Abstract

The abundance of beluga whales (Delphinapterus leucas) in the St. Lawrence Estuary was monitored by eight photographic aerial surveys conducted between 1988 and 2009, and twenty-eight visual line transect surveys conducted between 2001 and 2009. Overall, the surveys show no clear trend in abundance since 1988, although there are some indications that the population may have increased slightly from 1988 to 2003, and thereafter declined slightly since then. The 2009 photographic survey, corrected for animals not visible at the surface, resulted in a total abundance estimate of 676 whales (CV=0.16), the lowest result in the series since 1988. Six visual line transect surveys provide an average index of abundance of 979 whales (CV=0.14) in 2009. The visual estimates are negatively biased, not having been corrected for animals at the surface that are not detected by observers (perception bias). The coefficients of variation for the surveys are high due primarily to the highly clumped distribution of belugas. Photographic surveys also provide information on the proportion of calves in relation to the total number of belugas detected. This proportion was 15-18% for the period 1990 to 1997, but has since then declined to a range of 3-8% for the period 2000 to 2009.

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