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.

The reproductive cycle and size at sexual maturity of the commercial whelk Buccinum isaotakii in Funka Bay, southern Hokkaido, Japan, was examined using monthly samples of individuals collected from May 1999 until October 2000. Female and male sexual maturity was determined based on reproductive organ sizes and histological examination, and sex ratios did not differ from parity. There were parallel annual cycles in the size of the ovary and pallial oviduct, and an inverse cycle for the digestive gland. The testis and seminal vesicle showed inverse cycles. The peak in seminal vesicle size was at the same time as the peak in ovary and pallial oviduct. The size of the male digestive gland exhibited no evident cycle. Males were mature from May to October 1999 and from April to October 2000, and spent individuals first appeared in September 1999 and then decreased in numbers until June 2000. Sperm content and epithelium in seminal vesicle indicated that the copulating period started in March and lasted until August 2000. Ovarian maturation and oogenesis occurred from October 1999 onwards and peaked in January 2000, with egg laying occurring from May until September. An increase in temperature coincided with the advancement of spermatogenesis and the egg laying while the transfer of the sperm from the testis to the seminal vesicle in males and the maturation of ovaries in females coincided with a decrease in temperature.

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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 frequency; (iii) stage frequency 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.

The effects of imposex and parasite infection on the reproductive cycle of Neptunea arthritica as well as sexual maturity size were examined from

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Abstract:The Snout Otter Clam, Lutraria philippinarum is a regularly harvested bivalve species for food and also as a source of income in the Philippines. For sustainable supply of this resource in the wild, efficient and effective management strategies are needed, and the evaluation of its reproductive biology and fishery are required. In this study, the reproductive biology and fishery of L. philippinarum in the Philippines were examined monthly from January to December 2010 in North Bais Bay, Manjuyod, Negros Oriental and Philippines. For reproductive biology, otter clams were sampled, and sex ratio (by microscopic observation), size at sexual maturity, shell length (with a vernier caliper), gonad development (by histological examination as resting, developing, mature, spawning and spent) and spawning season were determined. Other information such as water temperature, salinity, pH and dissolved oxygen were also measured. To obtain information on the L. philippinarum fishery, interviews were conducted in Negros Oriental, Bohol, Cebu and Sarangani. A total of 677 snout otter clams were sampled. The study showed that L. philippinarum sex ratio was 1:1.15 and showed no significant difference from 1:1 ratio. Males attained its first sexual maturity at 43mm shell length while the females at 46mm. Histological examination on gonad development indicated that gametogenesis, maturation and spawning season of L. philippinarum occurred throughout the year with two spawning peaks, January and June. Changes in water temperature in North Bais Bay may have influenced the spawning peaks of L. philippinarum. Data on the fishery of L. philippinarum revealed that the Catch Per Unit Effort of L. philippinarum in the Philippines ranged from 0.2kg/hr-man to 1.25kg/hr-man suggesting low shell catch. We recommend that some mature individuals have to be left in the population to allow in situ breeding. Rev. Biol. Trop. 60 (4): 1807-1818. Epub 2012 December 01.