This study was carried out to obtain correct ecological information for the resources management of Muraenesox cinereus in the Korean waters.
Comparison of distribution and morphological characteristics differences between M. cinereus and M. bagio were investigated based on the specimens collected in the Korean waters by danish seine and coastal longline fisheries between May 2018 to April 2019. A total of 529 specimens were collected; 469 specimens (89%) were M. cinereus and 60 specimens (11%) were M. bagio. The abundance of M. bagio was higher than M. cinereus in relatively lower latitudes. Otolith (sagitta) shape between M. cinereus and M. bagio differed from each other as they have a different anterior, posterior, dorsal, ventral margin. The relative growth of preanus length and total length, preanus length and total weight, total length and total weight has significant difference between M. cinereus and M. bagio (P<0.001).
Spawning ecology of M. cinereus were investigated based on the specimens collected in the Korean waters by danish seine and coastal longline fisheries between May 2018 to April 2019. A total of 463 specimens was collected (306 females and 157 males) during the study period. The rate of Female M. cinereus in ripe and spent stage was highest from August to September 2018. The gonadosomatic index of female reached the maximum in April 2019. The spawning period was from April to September. The size at 50%, 75% and 100% sexual maturity females was estimated at 64.3 cm, 80.0 cm and 88.1 cm TL, respectively.
The age and growth of M. cinereus were estimated using sagittal otoliths of fish samples in the Korean waters by danish seine and coastal longline fisheries between May 2018 to April 2019. Otoliths of 343 fish were observed under reflected light, and the edges of the opaque zone considered to be otolith ring. The precision of age estimates was relatively high. Monthly changes in marginal index indicated that rings (opaque zones) were formed once a year from June to July. The estimated von Bertalanffy growth function was TL=138.37(1-e-0.18(t+0.79)) for females and TL=99.00(1-e-0.13(t+3.99)) for males. The oldest M. cinereus was 12 years in Female, and 8 years in male.
Condition factor and proximate composition of M. cinereus off the southern coast of Korea were investigated, caught by costal longline fisheries from June to October 2018. The mean total length was 60.0 cm, which was less than L50, indicating that the individuals were mostly immature. Sex ratio (M/F) is 0.07, we captured 382 females and 29 males, which produced a significantly different ratio (P<0.05). Condition factor remained constant over the study period. The proximate composition of M. cinereus individuals was analyzed. No significant differences in moisture, crude lipid, crude protein, and ash content were observed between individuals caught in summer and those caught in fall.
The longline hook and bait selectivity for Muraenesox cinereus were investigated in the southern coast of Korea during 2-16 June 2019. Four sizes of hooks and two sizes of bait were tested in seven and three fishing trials, respectively. The survival rate and hook shedding rate after cutting the line were observed during the study period. Our results revealed that there was no significant size selectivity effect for hook size (P>0.05), but small bait improved capture efficiency and caught smaller fish (P<0.05). Even if survival was 100%, the hook shedding was 28.6%.