Large-Scale Disturbance and the Structure of Marine Systems: Fishery Impacts on Georges Bank

Abstract

Georges Bank, a shallow submarine plateau located off the New England coast, has supported valuable commercial fisheries for several centuries. The region is characterized by high levels of primary productivity and, historically, high levels of fish production. Within the last four decades Georges Bank has been subjected to major perturbations that have profoundly altered levels of catch, abundance, and species composition. The arrival of distant water fleets during the early 1960s resulted in dramatic increases in effective fishing effort and the subsequent commercial collapse of several fish populations. Total fish biomass is estimated to have declined by >50% on Georges Bank during the period of operation of the distant water fleets. The implementation of extended jurisdiction (the 200‐mile [370.4‐km] limit) in 1977 was followed by modernization and increased capacity of the domestic fleet, resulting in a second perturbation to the system that resulted in further declines in groundfish populations to historically low levels. A subsequent increase in the abundance of species of low commercial value was documented, with an apparent replacement of gadid and flounder species by small elasmobranchs (including dogfish sharks and skates). Examination of feeding guild structure suggests that this switch in species dominance may have been linked to a competitive release. The small elasmobranchs, notably dogfish sharks, also prey on species of commercial importance (primarily small pelagics, including herring and mackerel). The cumulative impacts on the groundfish populations as a result of intense exploitation and predation pressure may have been further exacerbated by effects of fishing gear on the physical structure of the habitat. Implications for the development of an ecosystem‐based management approach are described.

Trophic Relations of Lesser-Spotted Catshark (Scyliorhinus canicula) and Blackmouth Catshark (Galeus melastomus) in the Cantabrian Sea

“…However, in the case of these catsharks, trawling in the Cantabrian Sea may have made them more abundant because fishing activity has supplemented their food with offal and discards. Previous studies have documented similar increases in abundance of catshark and small sharks that have accompanied the decline of commercial species (Fogarty and Murawsky, 1998;Rogers and Ellis, 2000). In most cases, the reasons for these increases are unknown.…”

Rapid Effects of Marine Reserves via Larval Dispersal

“…Fishing can also have indirect effects on predatory fish communities. For example, removal of large-bodied predators may have allowed smaller ones to increase in abundance due to release from competition or predation [30,61,62]. Indeed, the relatively unfished trumpetfish, and the two smallest species of both grouper (i.e., graysby and coney) and snapper (i.e., lane and mahogany snappers) were found to increase in presence with decreasing presence of large predators (Table 3, Figs.…”

Measuring marine fish biodiversity: temporal changes in abundance, life history and demography

“…increased abundance of shrimp and small pelagic fish (Choi et al 2004) following the collapse of Atlantic cod, increased abundance of flatfish following the collapse of demersal species . On Georges Bank, changes in the abundance of elasmobranchs and sand lance following declines by ground-fish and herring/mackerel, respectively, have also been attributed to reduced competition and predation (Fogarty & Murawski 1998). Thus, a multi-species index for marine fish that combines pelagic and demersal species, both high-and lowtrophic level predators, has great potential to provide inaccurate reflections of the current state of marine fish biodiversity (see also Pauly & Watson 2005).…”