Marine Trophic Index Research Articles

‘Fishing down marine food webs’ and spatial expansion of coastal fisheries in India, 1950–2000

The worldwide crisis of fisheries, which are usually managed on a single species basis, has led to calls for ‘ecosystem management’, along with the development of various ecosystem indicators. The Marine Trophic Index (MTI) and the related Fishing-in-Balance (FiB) index are two such indicators, which can be used to draw inferences on the sustainability of fisheries, notably those targeting high-trophic level species, in an ecosystem context. These indices are used here to evaluate the status of marine fisheries in India, based on taxonomically and spatially disaggregated time series of catches covering the years 1950, when 0.6 million tonnes were landed to 2000, when 3.3 million tonnes were landed. We show that the MTI is steadily decreasing in all 13 Indian States and Union Territories, at rates averaging 0.058 trophic level per decade, about the same as in other parts of the world. This decline, however, is not due to the sequential addition of newly exploited species of low trophic level to the multi-species catch from which mean trophic level is calculated. Rather, the MTI values were computed after exclusion of species with trophic levels lower than 3.25. Notably, this excluded Indian oil sardine and penaeid shrimps, the catch of which grew enormously in the 1980s. What has to date maintained the landings of higher trophic level fish in India has been the geographic expansion of the fisheries, which, until the early 1970s, exploited only waters immediately under the coast, while they now reaches to the edges of the continental shelf and beyond. This expansion is quantified here through a ‘spatial expansion factor’, based on a re-interpretation of the Fishing-in-Balance index. This index was proposed earlier to analyse, in an ecosystem context, the interrelationship between mean trophic level and magnitude of the catch, and the trophic transfer efficiency among trophic levels of the food web. The FiB index is shown here to allow, under some specific assumptions about productivity of the exploited areas, inferences on the spatial behavior of fisheries. Based on the newly formulated spatial expansion factor, it is suggested that the Indian shelf fisheries, covered by 2000 about 4 times the area they covered in 1970. However, this expansion had apparently met its natural limits, and catches can be expected to stagnate and ultimately decline, with serious consequences for the marine fisheries sector and consumers in India.

TheSea Around UsProject: Documenting and Communicating Global Fisheries Impacts on Marine Ecosystems

The Sea Around Us Project, initiated by the Pew Charitable Trusts in Philadelphia, PA, and located at the Fisheries Centre, University of British Columbia, Vancouver, Canada, started in mid 1999. Its goal was (and still is) to investigate the impact of fisheries on marine ecosystems and to propose policies to mitigate these impacts. Although conceived as a global activity, the project first emphasized the data-rich North Atlantic as a test bed for developing its approaches, which rely on mapping of catch data and indicators of ecosystem health derived from the analysis of long catch time series data. Initial achievements included mapping the decline, throughout the North Atlantic basin, of high-trophic level fishes from 1900 to the present and the presentation of compelling evidence of change in the functioning of the North Atlantic ecosystems, summarized in a 2003 book. The Central and South Atlantic were the next basins to be tackled, with emphasis on the distant-water fleet off West Africa, culminating in a major conference in Dakar, Senegal, in 2002. The project then emphasized the North Pacific, Antarctica, and marine mammals and the multiplicity of tropical Indo-Pacific fisheries before it turned completely global, with all our major analyses and reports (e.g., on the interactions between marine mammals and fisheries, on fuel consumption by fleets, on the catches of small-scale fisheries, on subsidies to fisheries) being based on global studies. Broadly, the work of the project is aimed at a reappraisal of fisheries, from the benign activity that many interested people still perceive them to be, to a realization that they have become the driver for massive loss of biodiversity in the ocean. Moreover, the emphasis on global estimates (rather than local estimates of dubious generality) has allowed the project to contribute to various global initiatives (e.g., developing the Marine Trophic Index for the Convention on Biological Diversity, quantifying marine ecosystem services for the Millennium Ecosystem Assessment), that is, activities that we expect to increase and for which we invite collaboration from academia and environmental nongovernmental organizations.