The stock parameter of anchovy (Engraulis encrasicolus) population on the coasts of the eastern black sea: Reason and implications in declining of anchovy population during the 2004-2005 and 2005-2006 fishing seasons

Abstract

Some basic characteristics of anchovy (Engraulis encrasicolus) population in the Eastern Black Sea coasts were estimated in order to explain the differences seen in the catch of anchovy during the fishing seasons of 2004-2005 and 2005-2006. The samplings were carried out from October to April in both fishing seasons on board of commercial fishing vessels. A total of 1499 and 1485 individuals were examined during 2004-2005 and 2005-2006 fishing seasons, respectively. Weight- length relationship and von Bertalanffy growth equations were calculated as W = 0.0101 L 2.7948 and Lt = 16.114 (1 - e -0.2919 (t + 2.56262)) and W = 0.0055 L3.0425 and Lt= 15.272 (1 - e -0.284(t+3.530)) for the 2004-2005 and 2005-2006 fishing seasons, respectively. Total (Z), natural (M) and fishing mortality rates (F) of 2004-2005 fishing season were calculated as Z = 0.99 year-1, M = 0.45 year-1, and F = 0.54 year-1, respectively. Corresponding rates for 2005-2006 season, on the other hand, were calculated as Z =1.56 year-1, M =0.54 year-1 and F = 1.02 year-1. There were remarkable differences in some growth parameters including weight (9.27 vs. 6.80), length (11.36 vs. 10.05), percentage of fish having a length less than 9 cm (4.39 vs. 34.08), percentage of immature individuals (4 vs. 16) and condition factor (1.02 vs. 0.49) between 2004-2005 and 2005-2006 fishing season, respectively. The changes in these parameters suggested that environmental or biological factors could not be suitable for anchovy especially during the 2005-2006 fishing season. The results of higher natural mortality rate, lower weight, length, and condition factor for the 2005-2006 fishing season and higher catches of bonito during this fishing season (12 times greater than previous season) suggested that bonito, one of the natural enemies of anchovy, could affect anchovy through predation or by preventing anchovy to freely forage in feeding areas (i.e., anti-predator behavior). In addition to the effect due to presence of bonito, extreme changes in the other biological and physical conditions could have operated together with bonito causing population parameters of anchovy to decline during the 2005-2006 fishing season.