Abundance, survival and population trend of fin whales ( Balaenoptera physalus ) in the Gulf of St. Lawrence, Canada

• Main Authors: Ramp, Christian, Delarue, Julien, Bérubé, Martine, Hammond, Phil, Sears, Richard
• Format: Conference Object
• Language: English
• Published: 2011
• Subjects: Canada; Petersen; Rorqual; Balaenoptera physalus
• Online Access: https://hdl.handle.net/11370/4c717fc8-63fa-40f8-9c5c-a5307d7bbe61; https://research.rug.nl/en/publications/4c717fc8-63fa-40f8-9c5c-a5307d7bbe61

The Gulf of St. Lawrence (GSL) is a major summer feeding ground for several rorqual whale species. The stock structure of fin whales within eastern Canadian waters is unknown. The high reencounter rate of fin whales suggests a high site fidelity to the GSL. Thus we treat the animals as sub stock of a larger population. We applied mark-recapture models to 439 photo-identified fin whales from the Jacques-Cartier Passage in GSL, Canada (1982-2009). Annual sample size varied over the years, and with the implementation of digital SLR cameras and image processing software in 2004, the recapture rate increased, varying around 0.6 in recent years. We applied Cormack-Jolly-Seber models and AIC model selection criteria to estimate apparent survival for non-calves. The estimates for females were slightly, but not significantly, higher than for males and the most supported estimate was 0.977 (95% CI 0.968-0.984) for both sexes for 1982-2009. We applied closed population models to the 2004-2009 data to estimate abundance. The Chapman modification of the Lincoln Petersen estimator between single years resulted in estimates from 171 to 289 animals. We further divided each sampling season in 4 sampling occasion and applied a variety of closed models. Models with two mixtures and time varying capture and recapture M(thb) had most support. The estimates for the single years ranged between 120 and 250 animals, but were decreasing in the most recent years. The negative population trend was confirmed by the Pradel models, and was caused by a negative trend of survival. Comparing the results with ship (1974) and aerial (1997) surveys in the GSL, which yielded 340 and 180-340 animals respectively; there is no indication of a recovery of this population. Increasing (reports of) anthropogenic caused mortalities, like ship strikes and entanglements, might be one cause for the lack of recovery.