Ecological impacts of fishing

This is an important issue to read. Fishes are a great resource of protein and food to human kind, but with the increase of population and development of technology and economy the fisheries industries became a huge threaten for marine fishes populations and the destruction of many habitats in coastal and marine regions around the world. Read bellow the precious informations about it; published by Pauly et al. (2002) in Nature.

Simone Marques

Text extract from Pauly et al (2002). Towards sustainability in world fisheries

Historically, marine fishery resources were assumed to be almost limitless, and fishing was thought to have little impact on fish stocks and marine ecosystems. However, during recent decades, concern about the condition of fisheries has increased. Since 1989 world harvests have apparently leveled off. Many fisheries experts and commercial and recreational fishermen now recognize that fishing can have profound effects on marine fish stocks and the ecosystems they inhabit. Fishing and fisheries makes it abundantly clear that humans have had for thousands of years a major impact on target species and their supporting ecosystems. The fishing process became industrialized in the early nineteenth century when English fishers started operating steam trawlers, soon rendered more effective by power winches and, after the First World War, diesel engines. The Second World War added another ‘peace dividend’ to the industrialization of fishing: freezer trawlers, radar and acoustic fish finders. The fleets of the Northern Hemisphere were ready to take on the world. 

Rather the fisheries expanded their reach, both offshore, by fishing deeper waters and remote sea mounts, and by moving onto the then untapped resources of West Africa, southeast Asia, and other low-latitude and Southern Hemispheric regions. In 1950, the newly founded Food and Agriculture Organization (FAO) of the United Nations began collection of global statistics. Fisheries in the early 1950s were at the onset of a period of extremely rapid growth, both in the Northern Hemisphere and along the coast of the countries of what is now known as the developing world. Everywhere that industrial-scale fishing (mainly trawling, but also purse seining and long-lining) was introduced, it competed with small-scale, or artisanal fisheries. This is especially true for tropical shallow waters (10–100 m), where artisanal fisheries targeting food fish for local consumption, and trawlers targeting shrimps for export, and discarding the associated by-catch, compete for the same resource. Fisheries tend at first to remove large, slower-growing fishes, and thus reduce the mean TL of the fish remaining in an ecosystem. This eventually leads to declining trends of mean TL in the catches extracted from that ecosystem, a process now known as ‘fishing down marine food webs.

Fonte: Pauly et al. (2012). Towards sustainabilityin world fisheries. Nature 418: 689-695.

The principal, direct impact of fishing is that it reduces the abundance of target species. the past few decades have witnessed a growing awareness that fishes can not only be severely depleted, but also be threatened with extinction through overexploitation. Fisheries may also change the evolutionary characteristics of populations by selectively removing the larger, fast-growing individuals, and one important research question is whether this induces irreversible changes in the gene pool. Overall, this has implications for research, monitoring and management, and it points to the need for incorporating ecological consideration in fisheries management, as exemplified by the development of quantitative guidelines to avoid local extinctions

 Globally, 75% of coral reefs occur in developing countries where human populations are still increasing rapidly. Although coral reefs account for only 0.1% of the world’s ocean, their fisheries resources provide tens of millions of people with food and livelihood. Clearly, maintaining the biodiversity that is a characteristic of healthy reefs is the key to maintaining sustainable reef fisheries. Yet coral reefs throughout the world are being degraded rapidly, especially in developing countries. Concerns regarding overexploitation of reef fisheries are widespread. The entry of new, non-traditional fishers into reef fisheries has led to intense competition and the use of destructive fishing implements, such as explosives and poisons, a process known as ‘malthusian overfishing. Another major problem is the growing international trade for live reef fish, often associated with mobile fleets using cyanide fishing, and targeting species that often have limited ranges of movements. This leads to serial depletion of large coral reef fishes, notably the humphead wrasse (Cheilinus undulatus Labridae), groupers (Serranidae) and snappers (Lutjanidae), and to reefs devastated by the cyanide applications.

Cheilinus undulatus. Photo by Simone Marques

These fisheries, which destroy the habitat of the species upon which they rely, are inherently unsustainable. It can be expected that they will have to cease operating within a few decades, that is, before warm surface waters and sea-level rise overcome what may be left of the world’s coral reefs.

Rebuilding of marine systems is needed, and we foresee a practical restoration ecology for the oceans that can take place alongside the extraction of marine resources for human food. Reconciling these apparently dissonant goals provides a major challenge for fisheries ecologists, for the public, for management agencies and for the fishing industry.

Given the high level of uncertainty facing the management of fisheries, which induced several collapses, it has been suggested by numerous authors that closing a part of the fishing grounds would prevent overexploitation by setting an upper limit on fishing mortality. Marine protected areas (MPAs), with no-take reserves at their core, combined with a strongly limited effort in the remaining fishable areas, have been shown to have positive effects in helping to rebuild depleted stocks. In most cases, the successful MPAs were used to protect rather sedentary species, rebuild their biomass, and eventually sustain the fishery outside the reserves by exporting juveniles or adults. Although migrating species would not benefit from the local reduction in fishing mortality caused by an MPA, the MPA would still help some of these species by rebuilding the complexity of their habitat destroyed by trawling, and thus decrease mortality of their juveniles.

To know more read the paper: Pauly et al. (2012). Towards sustainability in world fisheries. Nature 418: 689-695.