3. RESULTS
3.1 Catch, hatchery release and life-history parameters ofL. crocea in the
mid-southern ECS
Based on the reported landing information, the overall production ofL. crocea in the ECS has been continuously decline since 1970s.
The variation of landing data indicated that the recent annual catch is
now less than 4400 tons, which have declined by > 90%,
compared with peak yields of the 1970s (Fig. 2A). Meanwhile, several
long-term and large-scale restocking programs have been conducted since
the 1990s. Millions of L. crocea have been released in the
coastal areas of Fujian and Zhejiang provinces by government (Fig. 2B).
The life history parameters
results show that since 1980s. using length-based data, we fit a series
of ELEFAN models and most the workflows were within feasible ranges for
data limited measurement (Hordyk et al. 2015). The best model (ELEFAN
S.A. with bin=10, MA=11, see details in Supporting information Table S3)
exhibited serious overfished status of L. crocea stock in the ECS
(Table 1, Fig. 3C).The most recent assessment found that (i) the average
body length was 130.4 mm, with the body length of the predominant group
being 145 – 155 mm (Fig. 3A), while the average body weight was 34.5 g,
with the dominant group weight being 10 – 50 g; (ii) the growth curve
(Fig. 3C) and maturation proportion (Fig. 3B) shows that juvenileL. crocea and the recruitment population have been the main catch
targets, which the age of first capture and age of probability 95% of
capture is the only 0.37 year and 0.49 year respectively (Fig. 3D);
(iii) the exploitation rate (E ) of stock is now as high as 0.84,
which reveals serious overfished of L. crocea stock.Our results
consist with previous studies that identified species as being smaller,
younger, and maturing faster in ECS due to the overfishing and STE:
Firstly, both size truncation and age truncation have occurred inL. crocea population alongside with decrease of \(L_{\inf}\)(555.4 mm in 1980s vs. 434 mm in 2018 – 2019), trophic level
(∆TL=0.15), maximum age (8 years in 1980s vs. 6 years in 2019),
and predominant body length (144
– 155mm). Also, the increase in body growth rate from the 1980s to the
current study (K : 0.36 vs. 0.43, respectively) is
consistent with advanced and smaller size at maturity
(Lmat : 350 – 400 mm vs.Lmat : 200 – 205 mm, respectively) (Table 1).
Still, the fishing mortality (F) and exploitation rate (E= F/Z )
was predicted to be 1.57 and 0.84, respectively, which are continuously
increasing compared with the 1980s (Table 1).