A Comparative Study On Morphology Of Otoliths,Age And Growth And Habitat Environment Between Sardine And Round Sardinella In Waters Near Mauritania

Sardine?Sardina pilchardus?and round sardinella?Sardinella aurita?are two of the dominated catch species in the Mauritania exclusive economic zone?EEZ?.As the important fish species with high biomass in the pelagic ecosystem of the Atlantic,the study on otolith morphology,age and growth,trace elements in otolith and habitat environment are important for the protection and sustainable exploitation of sardine and round sardinella in Mauritania EEZ.The otoliths of sardine and round sardinella were collected from the survey in Mauritania EEZ from September 2018 to January 2019 were used to study the otolith morphology,age and growth,trace elements,and habitat environment.We collected219 sardine and 95 round sardinella samples.Firstly,the total length,maximum width,back length,back width,belly length and wing leaf length of otoliths were measured as morphological data of otolith,and the main factors affecting the otolith morphology were analyzed by principal component analysis.Secondly,the relationship between otolith morphological parameters and biological data of each fish species was analyzed by single factor analysis.Then,Von Bertalanffy growth function was applied to study the age and growth of sardine and round sardinella,and the trace elements in otolith at each age stage were measured by laser ablation inductively coupled plasma mass spectrometry?LA-ICP-MS?.The difference of trace element in otoliths of sardine and round sardinella was tested by one-way ANOVA in order to speculate the habitat environment of the two fish species.Finally,the correlations between the ratio of trace elements to Ca at the edge of otolith and the sea surface temperature?SST?and sea surface salinity?SSS?were studied by one-way ANOVA to figure out the trace elements that were significantly correlated with SST and SSS.The results are as follows:?1?the total length and width of sardine otolith range from 1.468 to 2.602mm and from 0.704 to 1.165mm,respectively.For the round sardinella,the total length and width of otolith range from 1.678 to 2.656mm and from 0.740 to1.130mm,respectively.?2?for sardine,the otolith length contributes the highest explain rate in the six morphological parameters,and their cumulative contribution rate is 84.002%.The otolith length of sardine was positively correlated with fork length and body weight.The equation between otolith length and fork length is y=0.1364x^0.9278,R²=0.8967;and the equation between otolith length and body weight is y=0.5839x^0.2823,R²=0.893.?3?for round sardinella,the otolith length contributes the highest explain rate of63.363%in the six otolith morphological parameters,followed by the maximum width of 19.350%,and the cumulative contribution rate of the former two was82.712%.With the growth of round sardinella fork length and weight,the total length and width of round sardinella otolith increased.The equation between the sum of otolith length and maximum width and fork length for round sardinella was y=0.0804x^1.2221,R²=0.5161.The equation between the sum of otolith length and maximum width and body weight for round sardinella was y=0.6408x^0.3388,R²=0.4056.With the age and growth,the fitness of relationship equations between otolith morphology parameters and fork length or maximum width for sardine was better than that of round sardinella.?4?sardine has the power function form of the full length and the maximum width of the otoliths,the relationship was y=1.2287x^0.8656?R²=0.7774?;the relationship between otolith full length and maximum width of round sardinella were presented as power function forms,and the relationship was y=9.1542x^0.6052?R ²=0.4459?.With the age and growth,the growth trend of sardine otolith length and the maximum width was more obvious than that of the round sardinella.?5?the samples of 219 sardine were collected,including 95 males and 124females,with a fork length of 13.2cm?23.7cm and an average fork length of 19.41cm.The weight range was 29g?237g,and the average weight was 109.36g.The samples of 95 round sardinella were collected,including 47 males and 48 females.The fork length ranged from 11.5cm to 23.2cm,and the average fork length was 20.8cm.The body weight ranged 10g-184g,and the average weight was 127.0g.The relationship between fork length and weight for sardine was a power function:W=7.4×10^-3L^3.2086?R²=0.973,n=220?.The relationship between fork length and weight for round sardinella was a power function:W=5.1×10^-3L^3.5122?R²=0.95684,n=98?.The growth trend of two fish species was very similar and it can be found from the trend of the power function above.?6?the growth equation between age and fork length for sardine was L_t=22.8[1194[1-e^{-0.41?t+0.29?}].The growth equation between age and fork length for roundweight for round sardinellawas W_t=219[1-e^{-0.43?t+0.15?}].The growth trend between age and fork length for sardine was similar to that of round sardinella,and the growth trend between age and weight for sardine was similar to that of round sardinella.The theoretical fork length of sardine and round sardinella were in close agreement with the trend line of weight.From 1 to 2 years old,the fork length and body weight of round sardinella were higher than that of the sardine.?7?the Fe,Sr,Mg,Ca,Li element concentration fluctuation trends of sardine and round sardinella in 0-2 age were basically the same,while Ba element concentration fluctuation trend was inconsistent.According to the coefficient of variation,Ca,Sr and Na were selected as the main indicator elements.The Sr:Ca and Na:Ca values of sardine showed a consistent trend.The Sr:Ca and Na:Ca ratios of the sardine from 0to 1 years gradually decreased,and the ratios at 2 years reached the lowest level,and showed the increasing trend in the edge.The Sr:Ca and Na:Ca values of round sardinella fluctuated greatly.The Sr:Ca ratio decreased from 0 to 2 years,and the ratio at 2 years reached the lowest level.The Sr:Ca ratio from 2 years stage to the edge showed the increasing trend.?8?the hatchery of sardine and round sardinella with the other ages were different from the 0 age sardine,and the hatchery of 1 year old sardine was different from that of the 2 years old sardine;the hatchery of 1 year old sardine was the same as that of the 1 year old round sardinella;the hatchery of 2 years old sardine was the same as that of the 2 years old round sardinella;the hatchery of 0 year round sardinella was different from that of the 1 year round sardinella;the hatchery of 1 year old round sardinella was the same as that of the 2 years old round sardinella;the hatchery of 2 years old round sardinella was the same as that of the 0 year old round sardinella.?9?the inhabited sea area of 1 year old stage of sardine was the same as that of 2years old stage of sardine for the 2 years old sardine,and there was no migration behavior.There were the migration behavior for the other years old stage of sardine;There were the migration behavior for the 0 year,1 year and 2 years old round sardinella.The inhabited sea area of 1 year old sardine was different from that of the 1year old round sardinella.The inhabited sea area of 1 year old stage of 2 years old sardine was different from that of the 1 year old stage of 2 years old round sardinella.The inhabited sea area of 2 years old stage of 2 years old sardine was different from that of the 2 years old stage of 2 years old round sardinella.?10?the fluctuation of Fe:Ca and Na:Ca ratios can be used to indicate the fluctuation of sea surface salinity and sea surface temperature,respectively when sardine were captured.?11?the fluctuation of Fe:Ca and Mg:Ca ratios can be used to indicate the fluctuation of sea surface temperature and sea surface salinity,respectively when round sardinella were captured.