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 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 ofL. 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 juvenile L. 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 in L. croceapopulation alongside with decrease of \(L\) (555.4 mm in 1980svs. 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).