ABSTRACT
On March 23, 1989, the oil tanker Exxon Valdez hit Bligh Reef and spilled 11 million gallons (38,800 t) of crude oil into Prince William Sound (PWS). Over the subsequent 3 years, commercial herring fishers harvested about 65,000 t of Pacific herring (Clupea pallasi). It appeared at that time that the Exxon Valdez oil spill (EVOS) had no impact on herring populations. In 1993, fishery managers forecasted an adult Pacific herring biomass of 133,852 t based on an age-structured assessment (ASA) model (Funk 1993; Quinn and Deriso 1999; Brown 2007; Hulson et al. 2008). However, commercial fishers were unable to locate fishable concentrations that year. An acoustic survey in fall 1993, the first of 20 annual acoustic surveys conducted by the senior author, estimated the adult population to be only 18,812 (95% CI ± 3140). Subsequently, the ASA model estimate was revised downward and the plunge from the 1992 estimate to the new 1993 estimate was referred to as the 1993 herring collapse (Brown 2007; Hulson et al. 2008). Because this collapse occurred 4 years after EVOS, it was not attributed to the oil spill. The 1989 year class was a recruitment failure in 1993 that was clearly associated with EVOS (Peterson et al. 2003; Brown 2003, 2007). However, this recruitment failure was too small to explain the collapse. Instead, a disease outbreak was hypothesized as the cause, even though there were no observations of surface mats of dead Pacific herring as seen in many other, much smaller, disease outbreaks and disease monitoring programs did not start until 1994 (Quinn et al. 2001).
