Pelagic predators

Abstract

Pelagic predators (larger elasmobranchs, teleost fishes, squid, sea turtles, seabirds, and marine mammals) congregate in the photic zone, often in regions of increased primary production such as ocean current divergences or convergences, regions of localized upwelling, fronts, or eddies. They are generally large in body size compared to other marine predators with relatively high metabolic rates. The combination of these factors leads to relatively high average daily prey requirements. Because primary production is relatively low in pelagic ecosystems, these predators must adapt to a nutritionally dilute three-dimensional system where prey resources are patchy and ephemeral. Thus, most species range long distances in search of patchy and ephemeral concentrations of prey. Compared to other pelagic predators, squid tend to be short-lived with rapid growth and population turnover rates and thus they are capable of responding rapidly to ecosystem change, and some have speculated that squid populations may rapidly exploit prey resources made available by the removal of other predators. Many species are directly targeted or incidentally taken in fisheries, and several species have declined precipitously or have been driven to extinction. Some researchers have speculated that they play an important top-down role in pelagic ecosystems, leading to concerns regarding their recent declines. Given their dependence upon ocean processes that serve to enhance productivity and concentrate prey, climate change may have important direct and indirect impacts on these predators including changes in movement patterns, species ranges, food web interactions, trophic status, and life-history traits.