Understanding impacts of fisheries bycatch on marine megafauna

Artisanal: fisheries that are small scale and subsistence in nature, in contrast to industrial. Artisanal fishing effort is often unmonitored by regional fishery commissions. Bycatch: the incidental take of undesirable size or age classes of the target species (e.g. juveniles or large females), or to the incidental take of other nontarget species. Individuals caught as bycatch can be unharmed, released with injuries, or killed. Demersal: a habitat or fishing range on or near the bottom of the ocean. Demersal fisheries target bottom-dwelling fish, such as halibut Hippoglos spp. and cod Gadus spp. Elasticity: the proportional contribution of each demographic parameter to total population growth. Because elasticities sum to 1, they can be compared among parameters, and can be used to identify which parameters contribute the most to changes in population growth rate. Gillnets:mesh nets of various sizes used to target many species of fish. Gillnets can range in sizes from meters to kilometers. Gillnets can be fixed (set) or free floating (Driftnets), and are a non-selective fishing method. Driftnets in international waters were banned by a 1992 UN resolution, but can still be used in sovereign waters. They are still used in international waters by illegal fishing vessels. Iteroparous: a reproductive strategy that involves producing offspring at multiple reproductive events over a long lifespan. Longline: a selective fishing gear comprised of a mainline (that can extend to 50 km) of evenly spaced branching lines, each fitted with a hook. Longline fisheries can target either pelagic or demersal habitat. Observer program: data collection plans in which observers (independent of the fishery) collect data aboard fishing vessels on catch of commercial and bycatch species. Pelagic: a habitat or fishing range in the water column, anywhere between 50 and 1500 meters. Pelagic fisheries target tuna Thunnus spp. and billfish (e.g. Xiphias gladius). Purse seines: long walls of surrounding nets that are pulled closed underneath a fish school by cinching the bottom of the nets. Purse seines are used to catch tuna and other species. Hunting by humans played a major role in extirpating terrestrial megafauna on several continents and megafaunal loss continues today in both terrestrial and marine ecosystems. Recent declines of large marine vertebrates that are of little or no commercial value, such as sea turtles, seabirds and marine mammals, have focused attention on the ecological impacts of incidental take, or bycatch, in global fisheries. In spite of the recognition of the problem of bycatch, few comprehensive assessments of its effects have been conducted. Many vulnerable species live in pelagic habitats, making surveys logistically complex and expensive. Bycatch data are sparse and our understanding of the demography of the affected populations is often rudimentary. These factors, combined with the large spatial scales that pelagic vertebrates and fishing fleets cover, make accurate and timely bycatch assessments difficult. Here, we review the current research that addresses these challengingquestions in the faceof uncertainty, analytical limitations and mounting conservation crises.