| The Indo-Pacific humpback dolphin(Sousa chinensis;hereafter referred as "humpback dolphin")is a species of viviparous higher vertebrate that lives in water all its life,nursing,and breathing with its lungs.As the first-class national protected wild animal,it mainly distributes in estuaries and inshore waters south of the Yangtze River.Because the habitat range highly overlaps the area of human activities,it is vulnerable to the interference and threats from human activities.In order to protect this precious marine living resource,various research work have been carried out.Based on the photographs obtained from April 2012 to September 2021 and UAV video data from September 2018 to September 2021 in the field survey of humpback dolphins in Jiangmen coastal waters,this paper updates the individual identification database of humpback dolphin in Jiangmen coastal waters,and collates the relatively complete reproductive behavior videos of 113 nursing groups and 35 mating groups.According to it,this paper calculates the reproductive parameters,describes and analyzes the reproductive behavior,reflecting the reproductive ecology feature of the population.The reproductive behavior of humpback dolphins in Jiangmen coastal waters mainly includes lactation,protection,assisting breathing,cooperative nursing and other nursing behaviors,courtship,mixed mating,coercion,competition for mating rights and other mating behaviors.In the aspect of nursing behavior,(1)the average individual number in nursing groups is 4.50±2.47,the average mother-calf pair number is 1.48±0.77,while group nursing is the main nursing method of humpback dolphins in Jiangmen coastal waters,and cooperative nursing is the main group nursing mode;(2)there are different preferences on nursing method among nursing individual at different ages;(3)the females who assist nursing play an important role in cooperative nursing,and underage females are also an important force in assisting raising calf.In the aspect of mating behavior,(1)the average individual number of mating groups is 7.97±4.05,the overall male-to-female ratio is 1:2.92,mixed and coerced mating take place frequently in Jiangmen coastal water;(2)the overall mating success rate is lower than 50 percent,while there is an average mating number of 8.31 ±7.41 occur in the groups of successful mating,and the average duration of a mating is 11.86±6.24S;(3)compared to non-coercion mating,coercive mating has larger clusters,higher proportion of males,and lower mating success rate,and when mating occurs,there are more mating times and shorter time for each mating;(4)individuals at different ages behave differently in mating;meanwhile;(5)the intention of female dolphins during the nursery period to refuse mating is more obvious.During the decade,the number of born calves in each year fluctuate greatly,and the main reproductive parameters are as follows.(1)The calves are mainly born in spring and summer,from April to September,also there are calves born in the rest of the year;(2)the inter-birth interval(IBI)of dolphin mother is mainly from 3.08 to 4.50 years,and the average is 3.72±0.79 years;(3)the mother fecundity in the population is 0.169±0.017;(4)the crude birth rate is 0.075±0.007,and the calf survival rate of 1 year old is 0.890±0.099,which is higher than the other comparable waters.To increase reproduction success rate of humpback dolphins in Jiangmen coastal waters,this paper raises three protection suggestions as follows:create a good reproductive environment,strengthen the maritime management of the calving season,and carry out special investigations and research. |
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