Recent changes in the spawning grounds of Black Sea anchovy, Engraulis encrasicolus

Abstract

Towards the end of the 1980s, when the spawning grounds in the northwestern shelf (NWS) of the Black Sea were lingering with the effects of eutrophication and of an exotic invasive ctenophore, a series of basin‐wide international ichthyoplankton surveys pointed out an increase in the anchovies spawning in the southern half of the Black Sea. Later, with the help of international conservation efforts, several key littoral ecosystem components within the anchovy's historical spawning grounds showed signs of recovery. However, the fate of the spawning stock anchovy in the south remained unanswered. In order to present the current situation in the southern Black Sea after two decades, an ichthyoplankton survey adopting the same methodology as previously used was undertaken during the peak spawning season of the Black Sea anchovy (BSa). The survey showed that the density of eggs was by far greater than for any of the surveys conducted previously. A wider geographical distribution of the eggs indicated an increase in the number of vagrants which had drifted away from the known spawning grounds. In contrast, the increased reproductive activity in the south signifies existence of a growing, non‐migrating southern BS stock. This stock seems to utilize the coastal hydrographic features associated with the rim current facilitating escape (loophole) from gelatinous predators such as Mnemiopsis leidyi and Aurelia aurata.

Understanding the Impact of Environmental Variability on Anchovy Overwintering Migration in the Black Sea and its Implications for the Fishing Industry

“…We hypothesize that if anchovy from the NWS cannot migrate successfully to the overwintering area in great numbers, but aggregations of migrating anchovy continue to arrive and are fished annually, this may mean that anchovy in the eastern Black Sea spawn successful enough to be able to sustain this overwintering population. This is also supported by studies indicating anchovy spawn successfully over much of the southern Black Sea (Einarsson and Gürtürk, 1960;Niermann et al, 1994;Kideys et al, 1999;Gucu et al, 2016).…”

“…m −2 ) and larvae densities (3-359 ind. m −2 ) to be considerably higher than in previous studies (Gucu et al, 2016). Unfortunately, these surveys were not conducted continuously and over longer time scales, however they suggest anchovy spawning is not restricted to the northwestern shelf but occurs over much of the Black Sea with more or less success.…”

“…Model results are compared to available data on anchovy overwintering migration (Chashchin, 1996;Chashchin et al, 2015) as well as anchovy distribution along the Black Sea coast from recent, multi-year, acoustic and landing surveys (Gucu et al, 2016(Gucu et al, , 2017. However, the lack of available, longterm anchovy spatial distribution data and anchovy migration observations make it difficult to perform an in-depth model validation.…”

“…As anchovy is a fast-growing and short-lived species, the influence of environmental drivers may regulate survival rate of the early life stages (Guraslan et al, 2014;Gucu et al, 2016). Of these factors, eutrophication, climate variability (Oguz et al, 2008a,b) and the invasion of an alien ctenophore (Mnemiopsis leidyi) have been stated to be of crucial influence.…”

“…Gucu et al (2016) hypothesize that there is a southern stock of anchovy that reproduces in the area and is non-migrating.…”