Recovery and reconstruction of fisheries from the Great East Japan Earthquake and tsunami disaster on March 11, 2011 was evaluated based on the registration records of fishing boats, and the annual data of catch, number of landing boats and CPUE in 2011 and 2012 to compare the data of pre-disaster from 2008 to 2010 in Iwate Prefecture, the Pacific coast of northeast Japan. The registered number of fishing boats greatly decreased after the earthquake mainly in the small-scale boat class less than 15 GT, and the recovery rate of the boats canceled due to tsunami was relatively low in the class greater than 5 GT among them. Catch of abalone, Haliotis discus hannai, and sea urchin, Strongylocentrotus spp., decreased extremely after the earthquake in 2011, and the extremely low value (less than 50% of the pre-disaster value), caused by direct impact of tsunami on the stock, continued in 2012 for the latter. The number of landing boats in fish markets of Iwate was available for the evaluation of the recovery and reconstruction from the earthquake and the states of recovery were varied among seven types of offshore fisheries, i.e., bottom trawl, set-net, bottom gillnet, pot, squid jigging, stick-held dip net for Pacific saury and boat seine for Pacific krill. In the small-scale offshore fisheries as bottom gillnet and pot, the number of landing boats decreased extremely after the earthquake in 2011 and the low value continued without conspicuous increase of the number of landing boats in 2012. Regional differences were also appeared in the state of recovery and reconstruction in the heavily damaged fisheries types. It will be possibly caused by multiple factors of the regional differences in the damage level by the disaster and the reconstruction rate of the infrastructure of the fisheries.

Coastal artificial structures are demanded for a consideration of environmental protection in recent years. Although gradually sloped seawalls were adopted in various parts of Japan, little is known on the food web of the community around such structures. In the present study, the food web and food source were estimated on the seawalls of artificial islands in Osaka Bay as determined by analyses of carbon and nitrogen stable isotopes. Clustering of δ¹³C and δ¹⁵N values of animals on the seawalls showed five feeding groups: fish, suspended feeders, suspended and surface deposit feeders, carnivores and herbivores. The dual isotope plot of δ¹³C and δ¹⁵N showed that the three food sources (phytoplankton, microbenthic algae and macrobenthic algae) were eaten by herbivores, suspended feeders, surface deposit feeders, and that these animals were ingested by carnivores and fish, both occupying the highest trophic levels.

We compared the long-term fluctuations in fisheries catch of benthic marine resources between two typical enclosed bays, Ise-Mikawa and Tokyo Bays, which face the Pacific Ocean in central Japan. The catch of the Manila clam Ruditapes philippinarum has decreased since the 1970s, when artificial reclamation was massively conducted in both bays. However, the Manila clam catch in Mikawa Bay has increased since the 2000s with improvement in reproductive network due to transplant release of juvenile clams by local fisherman. The fluctuation in the catch of five of eight major species of small bottom trawl fisheries target positively correlated between Ise and Tokyo Bays despite the considerable distance separating the bays. The catches of flounder (Pleuronctidae), Japanese tiger prawn, Marsupenaeus japonicus, and mantis shrimp, Oratosquilla oratoria, have decreased, whereas those of Japanese temperate bass, Lateolabrax japonicus, and cuttle squid, Sepia esculenta, increased in synchrony. Fluctuations in major water quality parameters such as temperature, nutrients, and dissolved oxygen concentration were similar in both bays. These changes in the environment of both bays and climate will affect the drastic and synchronous fluctuations in benthic marine resources among these two separate enclosed bays.

Hatch dates of age-0 yellowtail Seriola quinqueradiata collected by set-nets in the eastern coastal area around the Noto Peninsula in the Sea of Japan between 2005 and 2007 were determined using the otolith daily growth increments. Hatch dates of 1146 individuals in total (range of 96-448 mm in fork length) were estimated by subtracting the number of otolith daily increments from the sampling dates. Estimated hatch dates of the age-0 fish samples indicated a protracted spawning season from late January to mid August. Then hatch month distributions of the recruitment in the whole fishing season were calculated by weighting the total catch by the number of age-0 fish from the set-net fishery in this area. Results showed that 57.7-69.5% of fishes were hatched during the period from March to April in every survey year. This suggests that age-0 fishes caught in the eastern coastal area of the Noto Peninsula mostly originated from the shelf break region of the East China Sea, the main spawning ground of yellowtail. On the other hand, hatch month distributions shifted later in progressive catching periods originating from other spawning grounds. Furthermore, age-0 fishes that hatched from March to April were hardly found in the coastal waters around the Noto Peninsula after December, and may migrate to other areas.

We developed a method for evaluating the color tone of raw nori (Pyropia yezoensis) by using a digital camera and image analysis. The RGB values of raw nori were derived from images taken using a digital camera, and then image analysis was performed using the freeware Lia32 (http://www.agr.nagoya-u.ac.jp/~shinkan/LIA32/index.html). As a result, the RGB values obtained using 2 different digital cameras were highly correlated. The G value derived using this method was highly correlated with the L* value, which is the measured colorimeter value, and nitrogen content of nori (L*: r=-0.865, nitrogen content: r=0.528). We converted the L* values into G values, and the G values into nitrogen contents using regression equations. As a result, G values below 20 and nitrogen contents below 47 μg・mg DW-1 were determined to indicate discoloration of nori.

In Japan, gross reduction of water quality-related substances has been conducted to achieve the environmental standard levels for chemical oxygen demand, total nitrogen, and total phosphorus in bay areas. However, damage to fisheries, such as catch decline, is still a serious problem. Therefore, establishment of a new environmental standard for dissolved oxygen concentration (DO) in the bottom layers of bay areas is currently being discussed by the government of Japan. Unfortunately, there have been only a few studies on the adverse effects of hypoxic water on fishes, crustaceans, and mollusks, particularly on their fries, larvae, and juveniles; these stages of the organisms are required to determine DO standard values. Therefore, we performed laboratory experiments to investigate potential behavior relation to hypoxic water by using the early life stages of the Japanese littleneck clam, Ruditapes philippinarum, as the representative species in bay areas. The following stages of the Japanese littleneck clam showed the highest sedimentation percentages in hypoxic water: pedi veliger>umbonal veliger>D-shaped veliger. The sedimentation percentages in hypoxic water were increased by decreasing the DO percentage in the same stage. The following stages of the Japanese littleneck clam showed the highest lethality percentages in hypoxic water: D-shaped veliger>umbonal veliger>pedi veliger. The lethality percentages for hypoxia were increased by decreasing the DO percentage in the same stage. On the basis of the results, we formulated their sedimentation and lethality values against low DO for understanding the effects of hypoxic water on the pelagic larvae of the Japanese littleneck clam in marine environments. A DO of 3 mg・l^-1 or more is required in the bottom layers of the bay areas to prevent the influence of hypoxia on the clam larvae. In addition, a DO of at least 2.5 mg・l^-1 or more is required in the bottom layers in order to preserve about 90% of the clam larvae.

Distribution patterns of juveniles of Japanese sardine Sardinops melanostictus in the Kuroshio–Oyashio transition region were examined in relation to the dynamics of the Kuroshio Extension. The juveniles were collected using a pelagic trawl during 1996–2009. Index for juvenile abundance estimated in the current survey showed decreasing trends during 1996–2000, extremely low levels during 2001–2004, and fluctuating trends during 2005–2009. Mean standard length (SL) and age in days of juveniles collected in May ranged from 33.5–43.6 mm and from 46.2–56.6 days after hatching, respectively. The May-caught juveniles during 1996–2000 had significantly larger body size and older age in days than those during 2001–2004 and 2005–2009. Juveniles<40 mm SL occurred predominantly in waters west of 150°E during the decreasing (1996–2000) and fluctuating (2005–2009) periods, meanwhile the small juveniles appeared in waters east of 150°E during the extremely low period (2001–2004). Previous studies have demonstrated that the axis of the Kuroshio Extension showed a meandering path (unstable state) during 1996–2000 and 2005–2009 but a non-meandering path (stable state) during 2001–2004. This suggests that since smaller and younger juveniles were swiftly transported to the downstream waters east of 150°E, they could not stay in the favorable environment for their growth and survival during 2001–2005 resulting in extremely low recruitment.

We tried to produce a daily map of sea surface oceanic conditions in Hyuga-Nada by using temperature and current data measured by fishing boats. The map has been distributed since January 2013. The map of the surface layer was produced by a combination of the horizontal distribution of temperature and that of current. Horizontal distribution of temperature is produced by the surface temperature of round haul-net fishing boats, trolling-line fishing boats and Japan Meteorological Agency product. Horizontal distribution of current is described by the space-averaged current of round haul-net fishing boats in 1/6° latitude. The temperature and current data by fishing boats enable the daily map to depict a detailed temperature and current field at front in the coastal area that would be difficult to recognize by using an existing map. If problems such as the introduction of mechanisms to evaluate the map’s quality by fishermen and improvement of objective space-time interpolation method can be solved, the daily map gives more effective information for the coastal fishermen who pay attention to temperature front.