'The fish that stop': drivers of historical decline for Pacific cod and implications for modern management in an era of rapidly changing climate

Abstract

In the Gulf of Alaska, a series of marine heat waves depleted Pacific cod (Gadus macrocephalus) biomass to the lowest abundance ever recorded and led to the fishery's closure in 2020. Although the fishery has been productive for decades, this collapse may have historical precedents. Traditional knowledge holders refer to cod as 'the fish that stop', and there is a suggested period of decline in the 1930s. Here we conduct a catch reconstruction of the early commercial fishery (1864-1950), confirming a rapid catch decline in the 1920s and 1930s. Next, we evaluate evidence for possible drivers. We document changes to demand and technology that contributed to declining catch. However, we also find both qualitative and quantitative evidence of depletion, suggesting catch declines were not driven entirely by social factors. Overfishing may have contributed to localized catch declines as evidenced by declining catch rates in heavily fished localities. We also find evidence for climate as a driver of regional decline, with the period of catch decline characterized by up to 2°C higher temperatures as compared to the earlier period of high fisheries production. Our analysis underscores the importance of understanding long-term drivers of fisheries productivity and the value of linking fisheries and climate histories.This article is part of the theme issue 'Shifting seas: understanding deep-time human impacts on marine ecosystems'.

Keywords: Pacific cod; climate change; climate history; historical ecology; marine heatwaves; overfishing.

Figure 1.

Images from the American salt cod fishery. (A) Map of the region with place names mentioned in the text. (B) Alaska Codfish Company’s schooner ‘Alasco’ on her trial trip [25]. (C) A dory fisherman returning with a load of fish, in a news article titled ‘Some Codfish!’ [26]. (D) An American fisherman in Alaska, ca 1910−1930, University of Washington Archives, John Cobb Collection. (E) Advertisement for salt cod sold by the Robinson Fisheries Company, Anacortes, Washington [27]. Photograph used with permission from the University of Washington Archives; map created using R Statistical Software and Adobe Illustrator.

Figure 2.

Pacific cod catch reconstruction for the BS, AI and GOA, 1864−1950. Periods of catch increase (1895−1915) and catch decline (1925−1945) correspond to the periods used for analysis in figure 5, with a 5-year time lag to account for the time it would take for affected year classes to mature into the fishery.

Figure 3.

Social factors that contributed to decline of the Pacific cod fishery, 1915−1940.

Figure 4.

Catch per vessel tonne. Annual averages for (A) the Shumagin Islands and (B) all other fishing grounds, 1870−1925. After 1915, Shumagin Island data are combined with all other data in the original dataset.

Figure 5.

Differences in SST between periods of catch decrease (1925−1945) and catch increase (1895−1915) in the cod fishery show warming in the later period, particularly in summer months. Average temperature differences are shown for (A) spring (February–April), (B) summer (May–July) and (C) autumn (August–October). The white triangle is the reference region represented in figure 6. Differences in water column temperature across the same years and seasons are shown in the electronic supplementary material, figure S4.

Figure 6.

Temporal trends in temperature in the GOA (reference region indicated by the white triangle in figure 5). Sea surface temperature (SST) anomaly for the years of our catch reconstruction (1864−1950). The blue box corresponds to the period of catch increase (1895−1915), and the red box corresponds to the period of catch decrease (1925−1945) used in spatial analysis (figure 5), with a 5-year time lag to account for the time it would take for affected year classes to mature into the fishery. Full temperature time series are shown in the electronic supplementary material, figure S5, and SST in °C are shown in the electronic supplementary material, figure S6.