Inter and intra annual variation in body condition of the Black Sea anchovy, Engraulis encrasicolus ponticus—Potential causes and consequences

Variations in the relative condition (Kn) of the Black Sea anchovy (Engraulis encrasicolus ponticus) have been evaluated over eleven overwintering seasons (2005–2016). During the study period, a linear decrease was observed in the condition each year. Difference in condition from the onset to end of winter varied between 10% and 20%. Overall however, condition displayed an increasing trend within the time frame studied. Considering the worsening state of the stock during the same period, this increasing trend indicates that condition may be dependent on the fish density. The negative relationship observed between body condition of anchovies and the spawning stock biomass supports the same view and points out that particularly in winter when food supply is limited, interspecies competition could be a considerable factor determining condition. The strong correlation between condition and eddy kinetic energy underlines that velocity of water movement might be an effective factor conserving energy use and consequently supporting maintenance of body condition. Finally, the positive correlation observed between condition loss during winter and number of recruits the following year indicates that how fish overwinter plays an important role in recruitment success rates.