| Neon flying squid, Ommastrephes bartramii, is an important commercial squid for China mainland fishery. This species plays a very important role in the marine ecosystem of North Pacific Ocean. North Pacific Fisheries Commission(NPFC) started to manage this species for the sustainable utilization. Ommastrephes bartramii consist of two main geographic populations. Growth, feeding behavior and migration of different stocks were influenced by the variation of oceanographic environment, and also present distinct status between these two stocks. In order to know the role of Ommastrephes bartramii in marine ecosystem and assess and manage this species with scientific method, we should understand its stock discrimination, age and growth, feeding ecology and migration pattern.Beak is the main feeding organ for cephalopod. It contains varies ecological information. In this paper, Ommastrephes bartramii will be investigated completely with the samples from North Pacific Ocean, which caught from May to November in 2010-2012. We used beak as studying material, compared the difference between two stocks based on the morphmetrics, and discriminated the different stocks with the morphmetrics of statolith and beak, the landmark was also used in this analysis. We also counted the number of increments in microstructure of beak, and compared the coefficient variance between the increments in statolith and beak. This study provided a supplemental information for the beak pigementation and made a revision of the criterion of pigmentation stage. The difference of trophic ecology between two stocks was compared through beak stable isotopes. And we also analyzed the composition and concentration of trace elements of beak and compared the sexual difference and ontogenetic stages. At last, we established the relationship between sea surface temperature(SST) and trace elements. The migration route was reconstructed and compared it with the previous study. In this study, the results showed that:(1) Compared the beak morphology between different stocks, beak of females were larger than males’, and the sexual dimorphism in eastern stock is more obvious than western stock. The relationship between beak morphmetrics and mantle length(ML) and body weight(BW) was suitable with linear and exponential model, respectively. Upper hood length(UCL/ML) and upper wing length(UWL/ML) can be the main contributed variable for the principal component analysis. The beak variables had significant difference among different ML groups(P<0.01) and different sex maturity stages(P<0.01). There was no significant difference between stock in females only in stage III.(2) Beak sexual dimorphism was only observed in eastern stock(P<0.05). Most of the beak variables had significant different in western stock(P<0.05). Sexual dimorphism in statolith was very apparent in eastern stock(P<0.05), but had no difference between sexes in western stock(P>0.05). The classification rate of stepwise discriminant analysis(SDA) was 55.7% with six beak variables(URWS, UWLS, LCLS, ULWLS, LRWS, URLS), this rate was 52.8% with five statolith variables(RLS, LDLS, RLLS, RWS, WLS). Combined these two hard strutures, the classification rate of SDA increased to 71.7% with eight beak and statolith variables(URWS, MWS, RLLS, UWLS, LLWLS, DLLS, LCLS, RLS).(3) Geometric morphometrics is a popular method for distinguish different stocks and species. Using this method, we found that beak morphology had significant difference among beak pigmentation stage(PS)(P<0.01), allometric growth between two stocks also had signification difference(P<0.01). First four components explained 60% of the total variance, beak morphology had significant difference among different PS in eastern stock, but only lower beak had significant difference in western stock. The mean shape of each stock was also showed in this study. Considered the different sexes in western stock, the upper beak had no difference between females and males(P>0.05), but had significant difference in lower beak(P<0.01). First four components explained 60.1% of the total variance, beak morphology was kept its size with the body increase, the predicted values for upper and lower beak presented negative correlation and positive correlation respectively. The classification rate of upper beak morphology was 66.5% with nine beak variables(PC6, PC1, PC4, PC12, PC2, PC5, PC20, PC3, PC16), 69.5% for lower beak with eight beak variables(PC3, PC4, PC9, PC2, PC11, PC10, PC14, PC13).(4) The shape of statolith like a drop, consisted of dorsal, lateral, wing and rostrum zone. Most of the previous study used dorsal zone for age estimation. The increments in beak rostrum was obvious and can be easily counted from rostrum tip to hood and crest. The hood is darker than crest for the pigmentation. In 26 samples, the mean±standard deviation(st) was 214±39 d for statolith increments, and 211±40 d for beak increments, coefficient of variance was 1.11% between these two hard structures. The relationship of increments between statolith and beak can be fitted with linear model, the coefficient regression was nearly 1.(5) Based on the beak increments, the age range of female samples was 107-322 d with average 203 d, age range for males was 107-320 d with average 180 d. The peak hatching time of females was from January to April derived from the back-calculation, account for 72.7% of the total females, February to April was the male hatching time that account for 74.7% of total males. Most of the sample squids belonged to winter-spring cohort. The instantaneous relative growth rate(G) of males was faster than females in early life stage, females will grow faster in latter period. The ML, BW and URL had no significant difference between sexes(P>0.05). The relationship between ML/BW and age was fitted with exponential model, URL and age fitted with linear model.(6) Because of the body size difference, we defined seven PS for females and five PS for males. The most pointed part for pigmentation was the hood, lateral wall of upper beak and shoulder, wing of lower beak. Females had no significant difference between PS 3 and 4 except for LWL(P>0.05), and also had no difference between PS 5, 6 and 7(P>0.05). Males had significant difference among all the PSs(P<0.01) except for PS 1 and 2(P>0.05).(7) Pigmentation stage increased with the month, but PS 2 still had the highest proportion. ML also influenced the pigmentation. Most individuals in PS 1 of females ranged from 200-250 mm, 200-350 mm for PS 2. ML from 300-400 mm belonged to PS 3 and 4. The ML of squid was larger 400 mm in PS 6 and 7. BW also had similar distribution. The relationship between pigmentation stage and ML or BW was fitted with logarithm model. Females grows faster than males. All the beak morphometrics had logarithm relations with PS except for LRL. The growth of LHL and LWL was faster than other parts.(8) All the stable isotopes(?13C and ?15N) had significant difference between eastern and western stock(P<0.01) except for C/N. The trophic position was largely overlapped in two stocks. It was more concentrated in western stock. Trophic position was varied from low ?13C and ?15N to high ?13C and ?15N. Large sized samples in eastern stock had similar trophic position with western stock. Small sized samples in eastern stock had lower trophic position than others. ?13C and ?15N values changed from 0.5 to 0.8‰ and 3 to 3.5‰ respectively in different ML groups for eastern stock. ?13C value kept constant and ?15N increased 1.5 to 2.0‰ in different ML groups for western stock. In eastern stock, Latitude and ML were two main variable to explain the ?13C variation, and decreased with latitude increase, kept constant with ML increase. ML was the only variable to explain the ?15N in GAM and increased with the ML increase. We also found ?15N was level off between 350 to 400 mm. In western stock, none of any variable can explain the ?13C variation. ?15N was increased with ML increase and level off between ML 300 to 350 mm.(9) There were 18 main trace elements in beak: Pb, Li, Na, Mg, Al, P, K, Ca, Mn, Co, Ni, Cu, Zn, Sr, Ag, Ba and U. Ca had the highest concentration, and Mg was the second, P was the third. Most of these trace elements had no significant difference between sexes(P>0.05). Na/Ca, Cu/Ca and K/Ca were increased in juvenile and sub-adult, and deceased in adult stage. P/Ca and Zn/Ca increased in juvenile and deceased in sub-adult, then increased again in adult. Only Cu/Ca had significant difference between different life stages(P<0.01) based on the ANOVA results. The samples was consisted of winter spawning cohort and spring spawning cohort. There was no difference between two spawning cohorts(P>0.05).(10) Na/Ca,P/Ca and Zn/Ca can be best fitted with SST for the lowest AIC value. The age range was 21- 32 d, 48-70 d, 110-139 d and 144-180 d for embryonic, paralarve, juvenile, sub-adult and adult respectively, the corresponding hatching month was January to March, February to April, May to July and June to August, respectively. Using R to calculate the probability of occurred area, we conclude the migration route of Ommastrephes bartramii for winter-spring cohort as following: eggs hatched in 25°-30°N during December to February in the next year, and migrate northeastward along with the Kuroshio during February to April. Then experienced paralarve and juvenile in 140°-145°E, 30°-32°N and 145°-155°E, 30°-35°N, and continue migrated northward to 150°-155°E, 35°-40°N, and swam to the feeding ground(150°-160°E, 40°-45°N) for growth. This result is similar with the previous study, and also give us a new way to analyze the migration pattern of cephalopod. |
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