Inshore and open-ocean (pelagic) squid are the most athletic of all invertebrates. They are highly active, jet-propelled swimmers, have high metabolic rates and grow at a prodigious rate throughout their short life spans of one to two years. Such squid are abundant in all the world's oceans where they play important ecological roles as major predators. Adult squid serve as essential prey for many top predators, including sharks, tuna, billfish and marine mammals. In addition, squid are becoming increasingly important in commercial fisheries worldwide as they replace slow-growing fish, particularly where these stocks are being depleted. Dosidicus gigas, also known as the jumbo or Humboldt squid, is a true giant, reaching 2-3 m in overall length and over 50 kg in mass. It is widely distributed over the eastern Pacific, ranging from Chile to Canada and nearly to Hawaii at the equator. It forms the basis of a major commercial fishery, presently the third largest in Mexico. Despite the ecological and economic importance of D. gigas, little is known about its life history, behavior or physiology. Its large size and open-ocean habitat complicate traditional field and laboratory studies. This project focuses on integrative field and laboratory studies of D. gigas in the Gulf of California using recently developed techniques that facilitate such studies. Pilot tagging studies have revealed that D. gigas spends the daytime in cold, deep, oxygen-depleted water (~10 deg C at 300 meters) and migrates at night to shallow, aerated surface waters that can reach 30 deg C. Frequent rapid dives at night to daytime depths cover several hundred meters in minutes. It is a mystery how these large, metabolically active squid can tolerate the stress of chronic daytime hypoxia at depth. Conversely, warm surface waters also may present a stress that limits the time squid can spend in this zone. This proposal will employ electronic tagging to track vertical migrations of this pelagic predator and to monitor natural jetting and respiration at different depths. Oxygen consumption determined from these data, with calibrations provided by laboratory swim-tunnel experiments and biochemical indices of anaerobic metabolism, will provide a measure of the true energetic costs to the squid itself. Extreme low-light video methods will reveal natural behaviors over the range of a typical vertical migration, both day and night. Thus, this project will reveal what this remarkable squid is doing in its oceanic habitat, why it is doing it, and what physiological and biochemical adaptations permit these behaviors at some depths and preclude them at others.
This study will greatly advance our understanding of the biology of D. gigas and provide a model for an integrated approach to studying the ecological physiology of other pelagic predators. It will also establish a life-history framework that will ultimately be necessary to manage this fishery at the ecosystem level in Mexico and elsewhere. It includes training of a postdoctoral fellow and two graduate students, and collaboration with two Mexican scientists and their students. Cephalopods, particularly large squid, are charismatic and appealing to the public, and this project has significant potential for mass public outreach through a variety of media.
