Large-scale range expansion and variability in ommastrephid squid populations: a review of environmental links
Over the last four decades, several ommastrephid squid stocks have shown rapid expansion and contraction, driving highly variable and sometimes boom and bust fisheries. These include Illex illecebrosus in the northwest Atlantic Ocean, I. argentinus in the southwest Atlantic Ocean, Todarodes pacificus in the northwest Pacific Ocean, T. sagittatus in the Norwegian fjords, and Dosidicus gigas in the Peru and California Current systems. Explanations for the highly variable behavior of squid populations include: (1) direct effects of environmental variability; (2) changes in prey availability, especially for the early life stages; (3) changes in predation, disease and parasitism; and (4) exploitation of predatory fish which might reduce predation pressure and thus create vacant niches into which the short-lived, ecologically opportunistic squid call expand. This review focuses oil the effects of environmental variability oil Populations and possible interactions with fisheries. Apart from Dosidicus gigas, which is associated with the coastal upwelling systems of the pacific Ocean's eastern boundary currents, the ommastrephid fisheries are mostly pursued in the high energy, western boundary current systems. The environmental variability that will drive changes in population size will differ between these environments. The recent range expansion of Dosidicus gigas ill the Eastern Pacific Ocean seems to have increased predation pressure on hake stocks off North and South America, which may affect fisheries. The El Nino/Southern Oscillation event in the Pacific Ocean is a well-documented, highly variable oceanographic event and the fisheries along the western seaboard of North and South America are also among the best documented. The Dosidicus gigas range expansion over the last decade may provide an opportunity to explore the interacting effects oil a squid population of environmental variability and ecological change caused by fishing.