Full report - Conservation Gateway

Chapter 9 - Large Pelagic Fisha 50% probability of the stockrebuilding by 2009 (ICCAT2008). Within United Statespopulations, ICCAT catchper unit effort (CPUE) datafor swordfish has dropped byabout fifty percent since the1980s, but is currently rebuilding.IUCN’s (2007) Review ofChondrichthyan Fishes indicatesthat all of the sharks listed hereare a “harvest threat.” Porbeaglepopulation size is estimated to be10-20% of the 1961 population(Campana et al. 2003).In sum, most large pelagic speciesare in trouble. Substantialadditional detail on populationstatus and current managementstrategies for the fourteen targetspecies and several other largepelagics is contained within thedocuments reviewed for this section (SAFE for AtlanticHighly Migratory Species; IUCN Shark Specialist Group2000; White Marlin Status Review Team 2002; Mahonand McConney 2004; NMFS Final Consolidated HMSFishery Management Plan 2006; IUCN Red List 2008).Additionally, ICCAT provides catch per unit effort statistics,size statistics, observer data, and nominal catchstatistics. The Northwest Atlantic Fisheries Organization(NAFO) also provides catch statistics. A global atlas oftuna and billfish catch, from 1950 onward, is availablethrough the Food and Agriculture Organization website.Ecosystem Interactions andEcological DependenciesLarge pelagic fish are an essential component of theNorthwest Atlantic pelagic food web, thus play a keyrole in the ecosystem. Many of the selected target speciesfeed broadly and opportunistically across the food chain.However, regionally and at certain times, a given age classmay focus their feeding on just a few species (Cayré etFigure 9-1. An example of the complex food web that large pelagic species occupy inthe ecosystem (FAO 2010).al. 1988). Tunas and billfishes prey on squid, smaller fish,and crustaceans (Logan et al. 2006). The larger individualsfeed on pelagic fishes, and are at the top of the trophicweb (Figure 1). Smaller individuals (e.g., juvenile tunasand billfishes) prey on zooplankton (mainly crustaceans).Smaller individuals of all fourteen target species arepreyed upon by sharks, cetaceans or larger fish like mackerels,tunas, and swordfishes.Adults of all of the fourteen target species function asapex predators - large animals at the top of complexfood webs without significant predators except humans.Consequently, they play a critical role in energy flowthrough marine food webs (NOAA 2009) and are sometimesconsidered to be keystone species with disproportionateinfluence on ecosystem structure. Their presence(or absence) can affect ecosystem patterns and processes atmultiple trophic levels and potentially lead to fundamentallyaltered ecosystem state conditions (Baum and Worm2009).Northwest Atlantic Marine Ecoregional Assessment • Phase 1 Report 9-