Biometric Measures Indicating Sexual Dimorphism in Stenella coeruleoalba (Meyen, 1833) (Delphinidae) in the North-Central Tyrrhenian Sea

Abstract

Since 1985, the Centro Studi Cetacei (Cetacean Study Centre) in Italy has been committed to the recovery of cetaceans stranded along the Italian coastlines to estimate the abundance of species present and to identify causes of death, disease, and other information useful to the study of cetaceans. The current study analyzed some external morphometric parameters of striped dolphin (Stenella coeruleoalba), the most abundant small cetacean in the Mediterranean Sea, to identify features indicating sexual dimorphism. Identification and measurement of external dimorphic characteristics allowed for determination of the sex of those specimens for which gender was not immediately evident due to decomposition of their external genital organs. Specifically, a total of 37 specimens (19 males, 15 females, and 3 unsexed) of S. coeruleoalba that stranded along the north-central Tyrrhenian Sea coasts (Italy) from 1983 to 1991 were measured; 28 parameters of external morphology were examined; and values were analyzed using the parametric Student t-test and were subsequently validated by stepwise discriminant analysis. According to the data, the total length reached by individuals, which is greater in female specimens, was not a statistically significant parameter leading to gender confirmation-that is, the length reached by individuals was independent of sex. However, the distance between the genital slit and anus (greater in males as in other small odontocetes) and the distance between the umbilicus and anus (greater in females) were found to be statistically significant dimorphic characters. The distance between the genital slit and the median notch of the flukes, which is longer in males, was identified as significant by discriminant analysis only. Thus, it may be considered as a feature indicating sexual dimorphism, but further investigation is required.

Mercury and cadmium in striped dolphins (Stenella coeruleoalba) stranded along the Southern Tyrrhenian and Western Ionian coasts

“…The mean length of the females was 166.4 ± 41.0 cm and that of the males 153.5 ± 49.5 cm; the mean weight of the females was 52.7 ± 29.1 kg and that of the males 51.8 ± 37.0 kg. These results were similar to those reported in other studies on Mediterranean dolphins (Carlini et al, 2014;Monaci et al, 1998). A positive correlation between the length and weight of the 35 specimens was found (R 2 =0.83).…”

“…For each specimen, the following key biometric parameters were recorded: body weight, body length, sex and life stage ( Table 1). The life stage of each dolphin was determined from the total body length (BL): newborn (BL<100cm), juvenile (100≤BL≤190cm) and adult (BL>191 cm), in accordance with biometric measurement criteria (Carlini et al, 2014). The age of each animal was confirmed by counting growth-layer groups in sections of its teeth.…”

Stranding patterns of the striped dolphin (Stenella coeruleoalba, Meyen 1833, Delphinidae) along the Sicilian coast (Mediterranean Sea)

“…Following Carlini et al . () and references therein, the individuals were divided into three life stage categories on the basis of total body length: (1) newborns <100 cm, (2) juveniles from 100 cm to 190 cm, and (3) adults >191 cm.…”

“…, Carlini et al . ), 13 females, 5 males, and 5 of indeterminate sex had a total length (TL) >190 cm, the typical size of adult individuals. 11 dolphins were <100 cm, corresponding to newborn animals, which were only a few days old, with 39 specimens measuring between 101 cm and 190 cm (Fig.…”

“…() in the western Mediterranean but it is similar to those observed by Carlini et al . () in the north‐central Tyrrhenian Sea. Moreover, our data confirmed that adults were represented by approximately one third of the sample, while the remaining part is made up of young/immature individuals.…”