Effects of Fisheries on Seabird Community Ecology

Significant depletions of marine fish populations due to overfishing are becoming more and more common. Such depletions have serious consequences not only for the fished species, but also for those organisms that depend on them for food. For seabirds, in particular, the effects of fisheries can be felt via a number of pathways. However, few studies have considered those effects in terms of seabird community ecology. In this review, seabirds were separated into three functional groups based on their primary foraging strategy when they are likely to interact with fishing vessels: kleptoparasites, scavengers, and pursuit-divers. Theoretical effects webs were built for three different gear types: gillnets, longlines, and trawlers. For kleptoparasites and scavengers, to trail a fishing vessel exacts a cost but also confers a benefit; they are occasionally killed by fishing gear, but a potentially reliable food source may outweigh that risk. Also, the costs and benefits are direct. In contrast, pursuit-divers do not benefit from fisheries nearly as much and bear both direct and indirect costs—direct in that divers are caught in fishing gear, and indirect in that discards may lead to increases in populations of kleptoparasites and scavengers, which prey on pursuit-divers, their eggs, and their young at breeding colonies.