Study On The Biology And Population Dynamics Of Oxygymnocypris Stewartii

To investigate the biology and population dynamics of O. stewartii, a total of712individuals were captured from the Yarlung Zangbo River and its tributary (Xiang Qu) monthly from August2008to August2009. Furthermore, Age and growth of round goby Neogobius melanostomus at three areas of Lake Michigan were studied by otolith analysis from a sample of666specimens collected from2008to2012. The main results are as follows:1. Otoliths and vertebrae of O. stewartii showed the typical annulus pattern, which was characterized by alternative wide zones and narrow zones. Annuli of otoliths formed from March to June once a year, while annuli of vertebrae formed from March to May once a year. Comparing with vertebrae, annual growth increments in otoliths were more distinct. Otoliths were the more accurate and precise calcified structure for age estimation of O. stewartii, followed by vertebrae.2. The standard length (SL) of O. stewartii ranged between116mm and587mm for female, between167mm and455mm for male and between45mm and260mm for undetermined, respectively. The estimated age ranged from2years to25year for female, from3year to17year for male and from1year to6year for undetermined, respectively. The standard length-body weight relationships were described as BW=6.108×10-6SL3.126for female, BW=9.872×10-6SL3.052for male and BW=3.203×10-5SL2.821for undetermined. The von Bertalanffy growth equations were Lt=618.2[1-e-0.106(t-0.315)] and Wt=3065.9[1-e-1.106(t-0.315)]3.126for female, and Lt=526.8[1-e-0.141(t-0.491)] and Wt=1868.4[1-e-0.141(t-0.491)]3.052for male. The estimated inflexion points were11.1years for female and8.4years for male, respectively.3. In non-spawning season, the external morphology of individual were same for matured female and matured male; In spawning season, pearl organs could be observed on matured male, but not on matured female. Gonads were assigned to five macroscopic maturity stages. Based on the histological analysis, gonads were assigned to six microscopic maturity stages and oocytes were assigned to seven stages. The estimated the first maturity size were357mm for female and273mm for male, respectively. The estimated first maturity age were7.3years for female and5.1years for male, respectively. O. stewartii, which spawns once a year from March to April, was a single spawner. The estimated fecundity ranged between11017eggs per fish and56907eggs per fish. The relative fecundity was between15.8eggs/g and40.2eggs/g of fish body weight. The fecundity increased linearly with standard length and body weight, while fecundity was not significantly correlated with age and ovary weight.4. The feeding intensity of O. stewartii varied significantly over month (P<0.05), which indicated that the feeding intensity was low in Septermber and high in February and March. According to the IRJ,%W and%F, fish was the most important prey, while based on the%N, aquatic insect was the most important prey. O. stewartii is a generalized predator, which relies upon a wide trophic spectrum at the population level, and is characterized by a strong individual feeding specialization. The noticeable variations were observed in O. stewartii diet composition with fish size and season, but not with gender. The range of absolute prey sizes eaten expanded with increasing body size of O. stewartii. The lower limit of prey-size remained at almost the same level, but the upper limit increased with fish size. O. stewartii showed a significant increase in maximum prey size consumed. Overall, prey size increased linearly with increasing predator size. The structure of digestive organs was fit to the feeding habits of O. stewartii.5. The estimated annual total mortality were0.40year-1for female and0.77year-1for male, respectively; The natural mortality were0.19year-1for female and0.26year-1for male, respectively; The fishing mortality were0.21year-1for female and0.51year-1for male, respectively. Under the current management policy, the spawning potential ratio of O. stewartii were9%for female and3%for male, indicating that O. stewartii population was overfished, with a high chance of recruitment failure in the future. Through evaluating six management scenarios, the sixth management scenario might be the better management policy for O. stewartii. The life history type of O. stewartii tends to the k-selection model. Based on the life history type of O. stewartii, we suggested some management policies.6. Total length (TL) of round goby ranged from48mm to131mm for Sturgeon Bay, from50mm to125mm for Waukegan, and from54mm to129mm for Sleeping Bear Dunes. Estimated ages of round goby ranged from2years to7years for Sturgeon Bay, from2years to5years for Waukegan, and from2years to6years for Sleeping Bear Dunes. Body-otolith relationships were calculated for each combination of area and sex. Logarithm of TL was accurately described as a linear function of logarithm of otolith radius. Back-calculated TL at age from the otolith analysis was used to fit a von Bertalanffy growth model for each combination of area and sex. For both sexes, round gobies at Sleeping Bear Dunes and Waukegan grew significantly faster than those at Sturgeon Bay. However, round goby growth did not significantly differ between Sleeping Bear Dunes and Waukegan for either sex. At all three areas of Lake Michigan, males grew significantly faster than females. Based on catch curve analysis, estimates of annual mortality rates ranged from75%to84%. These relatively high mortality rates suggested that round gobies may be under predatory control in Lake Michigan.