Growth variation and rational utilization of small yellow croaker (Larimichthys polyactis) in artificial reef areas of Shengsi, Zhejiang Province

Artificial reefs are natural or manmade objects deployed purposely on the seafloors to influence physical, biological or socioeconomic processes related to marine resources. It gainfully bears the characteristics of rehabilitation and restoration of marine environment by protecting and reserving fishery resources. Based on the data (spanning from Oct. 2004 to Sep. 2007) of small yellow croaker (Larimichthys polyactis) in artificial reefs of Shengsi, Zhejiang Province, changes in mean body length, and weight, and in length and weigh frequencies were analyzed. Comparing the background data for Oct. 2004, (i.e., the time prior to artificial reef deployment) with the track data for 2005, 2006 and 2007 (i.e., the time after artificial reef deployment), the length-weight formula, Von Bertalanffy growth function, and population biomass of small yellow croaker in artificial reefs were analyzed using FISAT. The results are as follows: 1) mean length and weight tend to increase while dominant length and weight groups are noted to be increasing from Oct. 2004 to Sep. 2007; 2) by using length-weight formula, calculated weight value at the same length is higher for track-data than that for background-data; 3) growth parameters of L∞, W∞ and K respectively increase from 140.5 mm, 36.5 g and 0.28 a^-1 to 186.0 mm, 118.5 g and 0.36 a^-1 after artificial reef deployment; 4) appreciable increases are noted in body length and weight growth rate after artificial reef deployment, and inflexion age of weight growth increases from 2.55 to 2.58 years after artificial reef deployment; 5) there is an increase in critical biomass age from 3.21 to 3.77 years after artificial reef deployment; 6) there is a decrease in total instantaneous population mortality from 1.065 to 0.75 per year after artificial reef deployment; and 7) the overall population biomass of small yellow croaker stands at 131.5 tons. Furthermore, the growth characteristics and rational utilization are discussed.