Award: OCE-1338973

This project addresses the impact of climate variation on Humboldt squid (Dosidicus gigas), a large squid of the eastern Pacific Ocean. Humboldt squid are an important part of the oceanic food-web, preying on midwater fishes and invertebrates and providing food for top predators like sperm whales. This squid is also the target of the worldÆs largest fishery for an invertebrate species, with worldwide landings approaching 1 million tons. Between 1995 and 2009 Humboldt squid landings in the Gulf of California averaged 50,000 tons per year and were consistently one of the top 5 by volume in Mexico. Over half of these landings were made by artisanal fishers on the Baja California peninsula, primarily in Santa Rosalia, BCS, a town of ~10,000 with several hundred vessels and many residents participating in the fishery. El Nino impacted the Gulf of California in 2009-2010 and led to a crash in the squid fishery (Fig. 1). Our previous work revealed that El Nino also led to greatly decreased size (from ~20 kg weight to 0.1 kg) and age (1.5 years to 6 months) at which Humboldt squid mature in this region. These changes were accompanied by a fewer eggs produced (from 20 million to 1million per female) and alterations in diet (more krill and less fish). In addition, smaller squid moved away from the coastal shelf area that was previously inhabited (and commercially fished) to blue-water habitat offshore. These responses lead to accelerated population turnover, less reliance on feeding grounds that can be negatively impacted by El Nino (through reduced nutrient delivery by upwelling) and colonization of alternative areas that may not depend on upwelling. Acoustic surveys carried out before and after El Nino 2009-10 suggest that Humboldt squid biomass in the study area was not greatly changed, suggesting that changes in squid size and distribution may be largely be responsible for the failed commercial fishery. These changes in life history effectively transform the giant form of Humboldt squid, which occurs only in highly productive temperate systems into the small form that is associated with tropical waters of lower productivity. El Nino transforms the upper 100 m of the water column in temperate upwelling systems to resemble the oceanographic situation in equatorial waters. Thus, in an adaptive response to El Nino, Humboldt squid take on a phenotype that is appropriate for tropical areas of limited productivity. A major focus of this award was to study recovery from El Nino. Squid size at maturity in the Gulf of California incrementally increased between 2012 and 2014, and in July-August of 2014 "large" squid (> 50 cm mantle length) reappeared (Fig. 2). But "recovery" was short-lived, and squid throughout 2015 were smaller than at any time since 2010. During this same period the Santa Rosalia (and Sonora) fishery continued to decline, and in 2015 there were zero landings. This lack of recovery contrasts to the full recovery of squid landings (Fig. 1) and size (not illustrated) within 3-4 years after El Nino 1997-98, a much stronger event than that in 2009-10. Our work has identified two relevant factors. First, winter winds off Sonora decreased greatly during El Nino and have been only slowly recovering (Fig. 3). Productivity as estimated from Chl-a concentration fell to a low level in 2010 and has remained low, presumably due to impaired upwelling (Fig. 4). Chronic failure of seasonal productivity has left the Sonora coastal shelf unsuitable to support large numbers of squid as it did prior to El Nino when half of the commercial landings were made here during winter. This change has also disrupted the previously established seasonal migration of squid across the Gulf, greatly decreasing recruitment to the Santa Rosalia fishery from Sonora and vice versa. Rapid recovery after El Nino 1997-98 appears to have been facilitated by unusually strong winds and upwelling. A second factor is that temperature at depths to 75 m in Sa...