However these methods were costly and years of data would be needed to make statistical inferences. In the 1960’s Kooyman (1965) developed the first time-depth recorder to study the physiological diving capabilities of Weddell Seals in the Antarctic. Argos receivers became operational on NOAA satellites in 1978 making it possible to determine the location of a tagged animal anywhere on the Earth’s surface. Combined photograph identification and passive acoustic monitoring, this has provided a number of tools for advancing understanding of baleen whale biology, including migration patterns (Katona et al. 1980, Clapham et al. 1992, Kooyman, …show more content…
In the late 1970’s, PDO was linked a biotic regime shift in the northeast Pacific (Francis et al. 1998, Hare and Mantua 2000). Rugh et al. (2001) found a ~7 day delay in the southbound migration of grey whales after 1980, coincident with the shift. In a longer-term study, Ramp et al. (2015) found that humpback and fin whales in the Gulf of St. Lawrence (Canada) moved their migration arrival time up roughly one month earlier over 27 years, correlating with changes in sea surface temperature (SST; a proxy for primary productivity) and sea ice. Once on foraging grounds, whales may stay longer. Hauser et al. (2016) found that Chukchi beluga whale had significantly delayed migrations (2-4 weeks) from the Beaufort and Chukchi Seas over 19 years, as regional sea ice freeze-up timing became later in the Beaufort, Chukchi, and Bering