Fish Stock Indicators as Measure for Sustainability: Black Sea Sprat Case

Background

Most abundant planktivorous fish species in the Black Sea are the anchovy and the sprat.

Sprat is the main target for commercial fishery, especially for Bulgarian trawler and fixed gillnet fishery. The rising of the fishing mortality of the pelagic, feeding on zooplankton fish species and the retention of their exploited biomass at comparatively low levels increased the misbalance of the most abundant consumers of plankton (jellyfish and planktivorous fish). Prodanov and Stoyanova (2000) stated that the retention of the biomass of the fish species pointed out, at lower levels as a result of their intense fishing, has brought to the enhancement of the misbalance between the different components of the food web. Initially, the niche of the planktivorous fishes was occupied by the jellyfish Aurelia aurita, which biomass from 50 million tons in 1965 has risen up to 400 million tons. According same authors, strongly exploited fish like anchovy and sprat can recover fastest if the fishing mortality lowered. This in its turn will exert a depressing effect on the abundance and the biomass of the ctenophores since the fishes (sprat and anchovy) seek for their food more actively than jellyfish and ctenophores. Despite of the high “resilience” (stock capability to recover from over fishing) of the sprat population, the peculiarities of ecology and behavior, like variability in recruitment and sensibility to the environmental factors could easily lead to stock degradation. The goal of this paper is to emphasize on the recent state (last decade) harvest policy and to provide some preliminary results in Bulgarian territorial waters of production modeling of the sprat stock. Some previous investigations on the sprat stock assessment Virtual Population analysis (Pope, 1972) were compared with the results of surplus-production modeling and presented in the paper. In the context of fishery management that takes ecological and ecosystem considerations into account, reserves (marine protected areas) play two extremely important roles. First, no-take marine reserve of sufficient size will allow one to maintain a source of baseline data for components of the ecosystem (Goodman et al., 2002) .The same authors stated that a common approach to fishery management around the world has been to monitor and assess the status of individual, commercially exploited species (fish stocks) and to adjust the intended amount of catch, each year. The aim of this approach is to maintain each individual stock at a level that is safe for the stock (allowing it to continue to reproduce effectively in sufficient numbers), and which is biologically productive in an ongoing (sustainable way).