Resolving the Trophic Relations of Cryptic Species: An Example Using Stable Isotope Analysis of Dolphin Teeth

Understanding the foraging ecology and diet of animals can play a crucial role in conservation of a species. This is particularly true where species are cryptic and coexist in environments where observing feeding behaviour directly is difficult. Here we present the first information on the foraging ecology of a recently identified species of dolphin (Southern Australian bottlenose dolphin (SABD)) and comparisons to the common bottlenose dolphin (CBD) in Victoria, Australia, using stable isotope analysis of teeth. Stable isotope signatures differed significantly between SABD and CBD for both δ13C (−14.4‰ vs. −15.5‰ respectively) and δ15N (15.9‰ vs. 15.0‰ respectively), suggesting that the two species forage in different areas and consume different prey. This finding supports genetic and morphological data indicating that SABD are distinct from CBD. In Victoria, the SABD is divided into two distinct populations, one in the large drowned river system of Port Phillip Bay and the other in a series of coastal lakes and lagoons called the Gippsland Lakes. Within the SABD species, population differences were apparent. The Port Phillip Bay population displayed a significantly higher δ15N than the Gippsland Lakes population (17.0‰ vs. 15.5‰), suggesting that the Port Phillip Bay population may feed at a higher trophic level - a result which is supported by analysis of local food chains. Important future work is required to further understand the foraging ecology and diet of this newly described, endemic, and potentially endangered species of dolphin

Direct observation of ¹³⁴Cs and ¹³⁷Cs in surface seawater in the western and central North Pacific after the Fukushima Dai-ichi nuclear power plant accident

The horizontal distribution of radioactive cesium (Cs) derived from the Fukushima Dai-ichi nuclear power plant (FNPP) in the North Pacific is still unclear due to the limitation of direct measurement of the seawater in the open ocean. We present the result of direct observation of radioactive Cs in surface seawater collected from a broad area in the western and central North Pacific in July 2011, October 2011 and July 2012. We also conducted a simple particle tracking experiment to estimate the qualitative spatial distribution of radioactive Cs in the North Pacific. ¹³⁴Cs was detected at 94 stations out of 123 stations, and ¹³⁷Cs was detected at all stations. High ¹³⁴Cs and ¹³⁷Cs concentrations more than 10 m Bq kg⁻¹ were observed in the area of the northern part of Kuroshio Extension at 144° E and 155° E in July 2011, in the area 147–175° E around 40° N in October 2011, and the northern part of Kuroshio Extension at 155° E and 175°30´ E in July 2012. Combining the result of direct observations and particle tracking experiment, the radioactive Cs derived from the FNPP had been dispersed eastward to the central North Pacific during 2011. It was considered from the horizontal distribution that radioactive Cs was dispersed not only eastward but also north- and southward in the central North Pacific. Pronounced dilution process of radioactive Cs from the FNPP during study period is suggested from temporal change in the activity ratio of ¹³⁴Cs / ¹³⁷Cs, which was decay-corrected on 6 April 2011, and relationships between radioactive Cs and temperature

Size distribution of the hard remains of prey in the digestive tract of northern fur seal (Callorhinus ursinus) and related biases in diet estimation by scat analysis.

Distributions of fish otoliths and squid beaks in the stomach, small intestine, and large intestine of northern fur seal (Callorhinus ursinus) were examined to assess their relevance to biases in diet estimation by scat analysis. The contents of the digestive tracts of 51 seals collected in the western North Pacific off northern Japan were inspected. The large intestines contained more fish otoliths and squid beaks than either the stomachs or the small intestines. The prey composition estimated from hard parts in the small intestines was similar to the large intestines, but there was a greater dominance of squid in the stomachs. Squid beaks found in the digestive tracts ranged from 2.26-22.20 mm in wing length, although large beaks (?10 mm) were found only in the stomachs. In addition, there were significant differences in the sizes of fish otoliths found in the stomachs and the large intestines. The difference of the prey composition and the size may have resulted from the limited passage of large particles at the pyloric end of the stomach. In order to improve the accuracy of scat analysis, we must investigate to restrict passing the large particles