Abstract:
There are no previous records on the sexual size dimorphism in the sea snake
Hydrophis spiralis (Shaw 1802). However, there are reports that head shape
differences in sea snakes are related to differences in consumed prey type or
prey shape. The aim of the present study was to find out sexual dimorphism in
external morphology and some aspects of feeding of H. Spiralis (Elapidae) in
the waters of Vadamaradchi division of the Jaffna Peninsula. Sea snakes were
collected from fisheries by-catch once a week from December 2011 to July
2012. Out of a total of 75 specimens of H. spiralis collected, 31 were males and
44 were females. Various head and body measurements were taken (mm) and
morphological differences between the male and female snakes were compared
by t-test. The degree of size dimorphism between males and females of adults
pertaining to head, body lengths and scale counts were quantified by the sexual
size dimorphism index (SDI). To find out the feeding differences among sexes,
the stomach of every snake was pressed gently to release the prey items. The
number of fish present in the gut, status of feed and direction of prey were
recorded. Chi-square test was employed to both sexes to find out the food intake
pattern, proportion of having empty stomach and head size of the snake against
the prey items. Seven out of 13 morphological characters were significantly
different (t- test, P<0.05) between adult males and females (total length, head
width, length between snout-eye, inter-orbital, eye-width, inter-nostril lengths
and number of ventrals). Four out of 13 characters namely vent-tail length, inter nostril, eye-width and sub-caudal count showed male-biased and the rest were
female biased SDI value, and the mean degree of sexual size dimorphism of H.
spiralis is 0.2953. Analysis of feeding revealed that the preys composed of two
fish families namely Muranidae and Congridae. There were no significant
differences between the proportion of males and females with empty stomach or
the direction of food intake and head size with the prey type among sexes (Chi
square test). Both sexes consume fishes with the same shape. In conclusion, this
study reveals that adult females of H. spiralis are 29.53% times longer than
adult males. Even though sexual size dimorphism is prominent in H. spiralis, no
significant differences were observed in the feeding of male and female snakes.
