Publication Abstract

The Black Sea fisheries and ecosystem change: discriminating between natural variability and human-related effects

The Black Sea fisheries and ecosystem change: discriminating between natural variability and human-related effects.

G.M Daskalov, K. Prodanov and M. Zengin

The fisheries in the Black Sea have a long history, but they became a major factor in ecosystem dynamics after the intensification of commercial fishing in the late 20^th century. The first major targets of the developing industrial fisheries were the large and middle-size valuable predatory species like marine mammals, sturgeons, tunas, bonito, turbot, and Black Sea mackerel. As a result by the early 1970s most of the predatory fish and marine mammal populations were depleted and some like the Black Sea mackerel and the large horse mackerel disappeared from the Black Sea. The fisheries then oriented mainly towards the small pelagic species like sprat, anchovy and horse mackerel (small variety) and record catches were attained during the 1980s. The lack of effective fisheries management in combination with unfavourable environmental and anthropogenic influences led to systematic overfishing and general fisheries collapse by the early 1990s. Since then, a partial recovery has taken place due mainly to decreased fishing capacity, and improving environmental conditions, but the situation could easily worsen again if effective management based on an understanding of ecosystem functioning is not applied.

The present paper reviews the recent history of the fisheries and ecosystem change attempts to discriminate between effects attributable to the environment, fisheries, and other anthropogenic (eutrophication, alien invasion) factors. It explores the mechanisms that produce transformations in ecosystem structure and function, fisheries collapses, and discuss options for effective management and conservation.

The sustained heavy fishing in combination with natural decrease in fish productivity due to fluctuating ocean climate, was recognised as the main cause of fisheries collapse. The anthropogenic pressure, in terms of deteriorating habitat and alien introductions amplified the problem. Overfishing and alien intrusion at high trophic levels produced trophic cascades down the food web. Interaction between environmental, biological and anthropogenic factors generated feedbacks resulting in massive phytoplankton or jellyfish blooms, hypoxia, and hydrogen sulphide production adversely affecting the ecosystem as a whole and fish stocks in particular.

A variety of fisheries management actions such as quotas, effort reduction, area and season closure of fisheries, can be applied by the authorities to improve the situation.

The main conclusion, in terms of conservation and sustainable use of the living resources, is that the Black Sea ecosystem is strongly inter-connected and the management should account for the linkages and mechanisms behind system dynamics in order protect the ecosystem integrity, function and diversity.

Reference:

G.M. Daskalov, K. Prodanov and M. Zengin (2008) The Black Sea fisheries and ecosystem change: discriminating between natural variability and human-related effects. In review in Proceedings of the Fourth World Fisheries Congress, American Fisheries Society Books (4th World Fisheries Congress, Vancouver. May 2004.

G.M. Daskalov*, K. Prodanov and M. Zengin

In review in Proceedings of the Fourth World Fisheries Congress, American Fisheries Society Books (4th World Fisheries Congress, Vancouver. May 2004.