An investigation was carried out in order to compare the performance of constant fishing coefficients maximizing some different objective functions for management of fishery stock in a periodical environment. The stock dynamics are expressed by the generalized stock production model incorporating the periodical changes in carrying capacity. The objective functions to be maximized are the average catch over the unit cycle, and the minimum or maximum catch. The performance of the fishing coefficient at the maximum sustainable yield in a steady environment is also examined. The expressions of the average catch and of the annual variation were mathematically analyzed and numerical calculations were carried out using various values of the growth rate of fishery stock and of the amplitude of periodical changes in the carrying capacity. The models were applied to the Pacific stock of the Japanese pilchard Sardinops melanostictus and the chub mackerel Scomber japonicus. From the results, the fishing coefficient at the maximum sustainable yield mathematically maximizes the generalized mean of catch with the negative of the power coefficient of the production model as the exponent, and is not consistent with that for maximizing the average catch. Interpretation of the results and issues to be resolved in the near future are discussed.
Surveys for upriver migration and conditions around spawning grounds of the ice goby Leucopsarion petersii were conducted in the Mitsuo River, Hiroshima Prefecture, southwestern Japan. A set net fishing for the ice goby was operated near the river mouth from late February to late April 2016. Daily catch of the ice goby was high during the spring tide period and low during the neap tide period. Abundance of egg mass was highest at the sampling site located about 350 m upriver from the river mouth, where salinity was about 0 throughout the day in the neap tide period and increased to about 25 during high tide hours in the spring tide period. In the Mitsuo River, where the maximum tidal amplitude is about 4 m, the spawning ground of ice goby was exposed to higher salinity conditions during the spring tide period compared to other rivers flowing into the Sea of Japan with lower tidal amplitude (<1 m). Exposure to both freshwater and brackish water seems to be an indispensable environmental factor for the formation of the spawning ground of the ice goby in the Mitsuo River.
To assess transportation in the early life history stages in the flathead flounder Hippoglosoides dubius, we measured the specific gravities of the eggs at 9℃ and the larvae and juveniles at 9℃ and 12℃ using density-gradient and density-bottle methods. We also examined the effect of temperature (1, 3, 6, 9, and 12℃) on the duration between fertilization and yolk sac absorption. Eggs in glass beakers had lower specific gravities than the water densities experienced in one of the spawning grounds, Funka Bay. In contrast, the specific gravities were higher than the water densities in Funka Bay in yolk sac larvae, almost the same in early preflexion larvae, and increased with advancing development from the late preflexion larval to juvenile stages. The duration from fertilization to yolk sac period decreased with increasing water temperature. Thus, annual variation in the water temperature in the field combined with transport directions and speeds at various depths may affect the transportation of flounder eggs and larvae.
The causative dinoflagellate blooms of paralytic shellfish toxins (PSTs) and changes in the toxin contents and the profiles in both arc shell Scapharca broughtonii and Japanese cockle Fulvia mutica in Osaka Bay for three years from 2013 to 2015 were investigated. During the investigation, the toxic dinoflagellate Alexandrium tamarense and A. catenella occurred in Osaka Bay. A. tamarense was the most important causative species in contamination of bivalves with PSTs. Contamination and detoxification in arc shell with PSTs were slower than those in Japanese cockle and slight amounts of PSTs remained in the arc shell throughout the year. On the other hand, PSTs in Japanese cockle were not detected after the end of bloom of A. tamarense. The dominant toxins of arc shell were GTX2 and GTX3 and relative ratio of STX in the arc shell increased with decontamination of toxins. In contrast, the dominant toxins in Japanese cockle were C1 and C2. In conclusion, the rate of GTX1 and GTX4 increased during the bloom of A. tamarense in both species. It was suggested that toxins in Japanese cockle were rapidly excreted without any in vivo conversions of toxins from the causative dinoflagellates.
Changes in algal flora by removing the sea urchin Diadema spp. were studied in Haidaura Bay, Mie Prefecture, central Japan in 1999, 2004 and 2014. The algal flora and distribution of seaweed beds and barren ground were surveyed by skin diving at 10 sampling sites. Thirteen species of Chlorophyceae, 30 species of Phaeophyceae and 67 species of Rhodophyceae were observed during the study period. In the mouth of the bay, seaweed beds were stable and the number of algal species did not show remarkable changes from 1999 to 2014. As a result of the recovery of seaweed beds from barren grounds by removing Diadema spp., the number of algal species drastically increased in the inner parts of the bay. Consequently, removing Diadema spp. increased the number of algal species including various small algae in Diadema-dominated barren grounds.
Award-winning paper in 2017
Baird's beaked whale were caught in the summer of 2014, and their red meat was subjected to analysis of proximate composition, mineral contents, and fatty acid composition. Methanolic extract was prepared to determine free amino acids and imidazole dipeptides. There was no significant difference in proximate composition or fatty acid composition depending on sex. Male whale red meat contained significantly higher amounts of Ca, Zn, and Mn than female. Oleic acid was the most predominant fatty acid. Among free amino acids, aspartic acid, serine, glutamic acid, methionine, and histidine were found to be significantly higher in red meat from male whale than female whale. The red meat from male whale had 3170 mg/100 g dry matter of balenine while the meat from female whale had 2980 mg/100 g dry matter of balenine. There was no significant difference in balenine content depending on sex. DPPH radical scavenging and angiotensin converting enzyme inhibitory activities of the methanolic extract were determined, but these activities were far smaller than those of other livestock meat extracts.
In order to confirm the importance of dehydration at low temperature on the quality of wakasakarei, changes in moisture content, extractive components and properties of myofibrillar proteins in muscle of salted willowy flounder with decrease in yield during dehydration were investigated. As a result, evaporation of moisture during dehydration happened mainly at the surface of fish regardless of temperature; on the other hand, the degree of decrease of moisture in muscle was very small. Dehydration at 20℃ and below suppressed degradation of IMP and denaturation of myofibrillar proteins in muscle. Moreover, the water holding capacity of muscle with yield of 85% at 4℃ was higher than that at 20℃, suggesting that reduction of NaCl solubility of myofibrillar proteins by permeation of salt contributed to this result.
Porphyra yezoensis (nori) is consumed as part of the traditional Japanese diet, and some studies have reported antihyperlipidemic effects associated with it. However, there has been no demonstration of the effects of nori on lipid absorption in a rat model. The triglyceride concentration of the serum of rats that were administered nori powder heated with oil (NARO) was higher than that of the control rats in the present study. The present study was undertaken to clarify the lipid proabsorptive effect of NARO. The results showed that nori boiled water extract and 75% ethanol extract did not promote pancreatic lipase activity. A polyethylene glycol solution with the same viscosity as NARO did not promote lipid absorption in the rat serum, and the lipid particle size of NARO was not smaller than that of other foods such as milk. Based on these facts, the reason contributing to the lipid proabsorptive effect of NARO remains unclear.
This study aims to clarify the distribution of marine products from the Batan Estuary in Panay Island, the Philippines, and the relationships between actors in this distribution system. To achieve these objectives, we interviewed 24 seafood distributors located around the Batan Estuary and in Kalibo, using a structured questionnaire, in March and October 2013 and in September 2015. The results showed that the food system of raw marine products from the Batan Estuary is completed within the country. The results of distributors' profit margins indicated that the distributors had not established a monopoly or an oligopoly. They experienced difficulties in procuring and selling products owing to increased competition during product collection. The findings suggested that the rising domestic demand for marine products has led to overfishing, causing resource depletion and consequent decrease in the supply of these products, and that this situation might have deteriorated following intensifying competition among distributors.