Research Document - 2013/130

St. Lawrence Estuary beluga (Delphinapterus leucas) population parameters based on photo-identification surveys, 1989-2012

By Robert Michaud

Abstract

Between June and October of 1989-2012, small-boat photo-identification surveys (PID) were conducted throughout the St. Lawrence Estuary beluga’s summer range. A total of 1 476 PID surveys were completed for a total of 2 754 encounters, an average of 62 (± 17 SD) surveys and 115 (± 32 SD) encounters per year. Of these encounters, 1 702 and 1 285 where retained to estimate the proportion of grey individuals (in %), so called “greys” (as an index of younger individuals), and calves. Calf production indices varied between 1.2% and 4.2% (coefficients of variation: 16.6% - 35.0%) with marked year-to-year variations following 2 to 3-year cycles, with a pause of 5 years, between 1999 and 2004, when calf production remained low. The proportion of greys varied between 22.6% and 39.6% (coefficients of variation: 10.3% - 18.1%) with a slight but significant increase over the study period (R2 = 0.20, p < .05) and a recent transition to a negative trend in the mid- to late 2000s. This transition followed the 1999-2004 period of low calf production, suggesting the low calf production in the early 2000’s resulted in low juvenile recruitment in the following years.  Both time series presented here provide useful independent data set to test predictions from an aged-structured Bayesian population model and explore both short-term and long-term population level reactions to environmental changes.

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