Climate regime shifts and community reorganization in the Gulf of Alaska: how do recent shifts compare with 1976/1977?

Climate regime shifts have recently occurred in the North Pacific (1998–1999) and the Arctic (2000), but the nature of biological reaction to these events is poorly understood. An index of local climate (1960–2005), and data from commercial fishery catches (1960–2004) and from small-mesh trawl surveys (1972–2005) are used to assess the impacts of these climate events in the Subarctic Gulf of Alaska. Non-linear regression showed that survey catch composition strongly responded to local climate at lags of 2 and 4 years, providing evidence of rapid ecological response to climate change in the system. A sequential regime shift detection method identified rapid change in local climate, and in survey and commercial catches following the well-documented regime shift to a positive state of the Pacific Decadal Oscillation (PDO) in 1976/1977. However, the analysis failed to detect the 1998/1999 regime shift in local climate, or in survey or commercial catches. This result is consistent with the view that the 1998/1999 climate regime shift did not represent a reversion to a negative PDO state. Local temperature increased and local sea level pressure decreased in the Gulf of Alaska during the years 2001–2005, consistent with anthropogenic warming and recent spatial reorganization in Arctic climate. There was no evidence of community reorganization following this climate event. Further observation will be required to evaluate the persistence of this new climate pattern, and the nature of community reaction to it.