Anthony S. Ilano

Comparative Population Assessments of Nautilus sp. in the Philippines, Australia, Fiji, and American Samoa Using Baited Remote Underwater Video Systems

The extant species of Nautilus and Allonautilus (Cephalopoda) inhabit fore-reef slope environments across a large geographic area of the tropical western Pacific and eastern Indian Oceans. While many aspects of their biology and behavior are now well-documented, uncertainties concerning their current populations and ecological role in the deeper, fore-reef slope environments remain. Given the historical to current day presence of nautilus fisheries at various locales across the Pacific and Indian Oceans, a comparative assessment of the current state of nautilus populations is critical to determine whether conservation measures are warranted. We used baited remote underwater video systems (BRUVS) to make quantitative photographic records as a means of estimating population abundance of Nautilus sp. at sites in the Philippine Islands, American Samoa, Fiji, and along an approximately 125 km transect on the fore reef slope of the Great Barrier Reef from east of Cairns to east of Lizard Island, Australia. Each site was selected based on its geography, historical abundance, and the presence (Philippines) or absence (other sites) of Nautilus fisheries The results from these observations indicate that there are significantly fewer nautiluses observable with this method in the Philippine Islands site. While there may be multiple possibilities for this difference, the most parsimonious is that the Philippine Islands population has been reduced due to fishing. When compared to historical trap records from the same site the data suggest there have been far more nautiluses at this site in the past. The BRUVS proved to be a valuable tool to measure Nautilus abundance in the deep sea (300–400 m) while reducing our overall footprint on the environment.

Present state of imposex in neptune whelk Neptunea arthritica inhabiting shallow waters around Hokkaido, Japan

The state of imposex in Neptunea arthritica from seven sites along the coast of Hokkaido, Japan was examined in 2002 based on the criteria: (i) relative penis size index (RPSI); (ii) imposex freqeuncy; (iii) stage freqeuncy distribution of imposex in adult and immature whelks; and (iv) sex ratio. RPSI differed from site to site, although values from all sites were low (0.186–5.294). In particular, the RPSI values for four sites were very low (<1.0). In sites where immature whelks were also collected, the frequency of imposex was considerably lower in immature (7.7%–55.6%) than in adult whelks (50%–95.2%) except at one site. The imposex stage frequency distribution also differed among sites, and the trend in the adult whelks corresponded with their RPSI value. Female whelks showing severe imposex (Stage 3 and 3+) were restricted to large individuals.

Effects of imposex and parasite infection on the reproductive features of the Neptune whelk Neptunea arthritica.

Abstract The effects of imposex and parasite infection on the reproductive cycle of Neptunea arthritica as well as sexual maturity size were examined from April 2003 to August 2004 in Saroma Lagoon, Hokkaido, Japan. Samples were sexed and divided into two groups (normal and abnormal), based on the degree of imposex and parasite infection. In normal whelks, males reached sexual maturity at a smaller size (60 mm in shell length) than females (75 mm). Normal whelks copulated from March to August, with a peak between May and July, and spawned from May to August, with a peak in June–July. In all groups, the female ovary and pallial oviduct, and the male seminal vesicle developed synchronously, and inverse to the male testis. Abnormal whelks follow a normal reproductive cycle. However, significantly lower reproductive organ index values, modifications in the number of individuals and periods extension in each developmental stage were observed. Gonads of individuals with severe imposex (stage 3) and parasite infection were reduced to a thin layer of tissue or eliminated. Imposex (stage 3) and parasite infection had serious effects on the population reproductive cycle of N. arthritica, but infection by parasites seemed to be the more disruptive phenomenon according to its proportion (25%).