Long-term hydrographic changes in the Gulf of California and ecological impacts: A crack in the World's Aquarium?

Although the Gulf of California is widely recognized as a region of high productivity and biodiversity, recent oceanographic and ecological changes have had a significant impact on its overall health. We review the relevant history of the economically important fishery based on large Humboldt (jumbo flying) squid (Dosidicus gigas) (>50 cm mantle-length and 10 kg body weight) that existed in the Guaymas Basin from the 1990′s until 2009, when a strong El Niño was accompanied by precocious spawning of squid at extremely small size (<30 cm mantle length and 0.1 kg). This short-lived phenotype is characteristic of the equatorial part of the species range and cannot be profitably fished. This phenomenon also occurred in conjunction with the strong 1997–1998 El Niño. Although rapid recovery of squid size and landings occurred after the 1997–1998 event, recovery after 2009–2010 El Niño was still incomplete when another strong El Niño occurred in 2015–2016. This last event has led to fixation of the small size-at-maturity phenotype in the Gulf of California — an effective poleward migration of the tropical phenotype. We also document years between El Niño 2009–2010 and 2015–2016 as being characterized by significant subsurface warming, leading to decreased productivity and restricted nighttime foraging opportunities for squid in the upper water column. These climatic trends have likely altered trophic webs throughout the Gulf of California, impacting many other taxa, including small pelagic fishes that are ecologically vital and commercially harvested in large quantities, as well as a suite of larger teleost fishes that are targeted by sport fishers. From these disparate data sources, collected and collated in coordination with regional resource users and environmental monitoring programs, an overall pattern emerges of long-term decline across multiple taxa. We also present evidence of a significant abatement of subsurface warming after 2015 and consider when – or if – the Gulf of California will return to a ‘normal’ state like that prior to 2010. Despite the potential for shifting to a cooler oceanic regime, the small phenotype for jumbo squid has persisted until present (2022), and the overall trajectory of ecological recovery is unclear. Integrated analyses of additional oceanographic and biological time-series, fisheries records, and other data will be necessary to identify critical processes and trajectories occurring in the Gulf of California.