Anchovy, Engraulis encrasicolus (LINNAEUS,1758): biology, population dynamics and fisheries case study

Abstract

    The biological and population dynamics parameters, population structure, length and age distribution, sex ratio, reproduction, age and growth, mortality, migration, estimation of population size and maximum sustainable yield as well as exploitation of the anchovy, Engraulis encrasicolus (n = 20 910 ) were studied from sampling undertaken in the Middle and partly in the North Adriatic Sea (Dalmatia) during 1974-1990 period. The overall anchovy length from both the coastal and the open sea water samples ranged between 7.5 and 18.7 cm. Samples of catches from the open sea waters comprised the anchovy of greater mean lengths than those from the coastal waters. The differences in mean lengths between sexes were small. The overall ratio of male and female was almost 1 : 1.

      Spring months represent prematurity and summer months the period of anchovy maximum sexual activity. Winter is the inactivity period in its sexual cycle. In the prematurity stage male gonads were found to be in slightly more advanced stages than those of females.

     Anchovy started to spawn earlier in the open sea waters and reached the spawning maximum sooner than in the coastal waters. Female gonad weight values as well as the values of gono-somatic index were greater than in males. Sexual evolution in bigger anchovy specimens from the open sea waters took place earlier than in smaller ones from the coastal water areas.

     The length-weight relationship for all fish was described by the following parameters: a = 0.0040 ; b = 3.0.

     Anchovy aged 0 to 4+ years old were present in the samples. Age groups 1+ and 2+ were the most prominent. They reach the asymptotic length of 19.4 cm. The fastest growth in anchovy occurs during the first three years of life. The von Bertalanffy growth parameters for all fish were L_∞=19.4 cm; W_∞= 34.8 g ; K = 17.57 yr^-1 and t_o = - 0.5 yr^-1.

     Overlapping of lengths are most evident in age groups 2+ and 3+.

    The highest total mortality rate (Z) was found in the youngest anchovy individuals, whereas their survival rate was the lowest. The average annual mortality (A) was 61 %. The relatively high total mortality coefficient value Z = 1.183 is evident. Natural mortality of anchovy population is M = 0.65. Fishing mortality (F= 0.53) has a lesser influence on total mortality. The exploitation rate was E = 0.45.

     The estimation of anchovy population size and maximum sustainable yield (MSY) shows that this species could have been exploited more than they had been exploited in some years of the investigation period.