Gakushi Ishimura

Development of Bayesian production models for assessing the North Pacific swordfish population

Bayesian surplus production models were developed for assessing the North Pacific swordfish population under alternative scenarios: a single-stock scenario and a two-stock scenario with subareas that represented the western central and eastern Pacific Ocean regions. Biomass production was modeled with a three-parameter production model that allowed production to vary from the symmetric Schaefer curve using an estimated shape parameter. Lognormal prior distributions for intrinsic growth rate and carrying capacity were assumed. Goodness-of-fit diagnostics were developed for comparing the fits of alternative model configurations based on the root-mean squared error of catch per unit effort (CPUE) fits and the standardized CPUE residuals. Production model fits for 1952–2006 indicated that the Japanese longline CPUE numbers were influential under each stock scenario because these scenarios were the longest time series of relative abundance indices. Model results also indicated that assumptions about the prior means for intrinsic growth rate and carrying capacity may be important based on the model configuration.

The market value of freshness: observations from the swordfish and blue shark longline fishery

One important component in determining the market value of fish is freshness, essentially the time period from capture to consumer. By shortening the time from harvest to landing, freshness can be improved and thus the market value may increase. The opportunistic nature of the marine capture fisheries sector, however, can encourage fishers to extend their time at sea to catch additional fish, while retaining already harvested fish. Here, fishers face a tradeoff: extending the duration of their operations, but compromising their ability to maintain product freshness. This study estimates the freshness premium for two fish species, swordfish and blue shark, landed at Kesennuma, Japan. Swordfish is generally destined for the raw market, while blue shark is first processed into several products. Our results suggest substantial heterogeneity in the freshness premium, depending on the likelihood of a product being consumed fresh or after processing. This work is an important investigation in the Kesennuma region, which suffered devastating damage from the tsunami following the Tohoku Earthquake.

Baseline assessment of total fisheries-related biomass removal from Japan’s Exclusive Economic Zones: 1950–2010

The rise and fall of Japan’s marine fisheries have been well documented and are clearly evident in official landings statistics. However, the extent of illegal, unreported and unregulated fisheries, including recreational fisheries, and the discarding of unwanted catch in Japanese waters, both of which may have significant implications on the success of management regimes, have yet to be closely examined. This study reassessed the impact of fisheries on the marine ecosystems of Japan’s Exclusive Economic Zones (EEZ) by estimating the total marine biomass removed through the use of an established catch reconstruction approach. Since 1950, 368 million t of marine biomass have been extracted from the Japanese EEZ as commercial catch, recreational catch, illegal catch and discards. Commercial catch accounted for 87xa0% of the total, while discards accounted for an additional 8xa0%. The disparity between the estimated biomass removals and the reported commercial catch is 48 million t, or 15xa0% of the reported catch. The difference is not as large as observed in similar studies of other regions. Nonetheless, the reconstructed biomass removals represent a better baseline for the management of fisheries in the Japanese EEZ, particularly if Japan is to move forward with implementation of output control management.

Combined effect of superchilling and tea polyphenols on the preservation quality of hairtail (Trichiurus haumela)

ABSTRACT The combined effect of superchilling and tea polyphenols on the preservation quality of hairtails was assessed in terms of pH, electrical conductivity, K value, TVB-N, TBARS, total plate count, and sensory assessment. Hairtail blocks were subjected to three treatments: frozen at −18°C, superchilling at −3°C, and superchilling at −3°C after immersed in a 6.0 g/L tea polyphenols solution, respectively. For storage of 30 days, the TBARS value of hairtails increased steadily from 0.41 mg/100 g to 1.83, 1.38, 1.14 mg/100 g (p < 0.05) in the samples that were superchilled at −3°C, frozen at −18°C, and superchilled at −3°C with tea polyphenols, respectively. The TVB-N, microbial growth, electrical conductivity, and K values also exhibited an increasing trend (p < 0.05), similar to that obtained with the TBARS values, whereas the stability of sensory scores decreased (p < 0.05). Compared with superchilling samples, all these quality indicators have been improved in combined treated samples. Indicators such as pH, TVBN, and TBARS in combined treated samples even showed better results than those in frozen samples. These results suggested that superchilling with tea polyphenols provided an effective approach for inhibiting lipid oxidation and microbial growth, retarding the deterioration, and maintaining the inherent and fresh quality of hairtails.

Does trade openness reduce a domestic fisheries catch

Although trade liberalization may increase a country’s welfare, its specific effect on a country’s fishing industry has not been well studied. By decomposing the effect of international trade into four parts, i.e., scale-technique effects (ST), the indirect trade-induced composition effectxa0(IC), the indirect effect of trade intensity through income (ITC), and the direct effect of trade intensityxa0(DTC), this study empirically investigates the effect of trade openness on country-level fisheries production. To take into account the endogeneity of trade openness and income, we adopt the instrumental variable approach. We find that a rise in trade openness reduces fisheries catch on average. In particular, the long-run effect is large. This result implies that future production is affected by current overfishing through stock dynamics. Our decomposed elasticities indicate that the ST and ITC dominate in the trade elasticity of fisheries catch. While ST implies that overfishing would be affected by trade, ITC may either establish an “overfishing haven”, similar to a “pollution haven” in the environmental literature, or production shift of fisheries to countries with lax regulation to pass stringent regulation, which is more likely to occur in high-income countries.

γ-PGA and MTGase improve the formation of ε-(γ-glutamyl) lysine cross-links within hairtail (Trichiurus haumela) surimi protein

The present study investigated the mechanism of ε-(γ-glutamyl) lysine cross-links within hairtail (Trichiurus haumela) surimi protein via γ-polyglutamic acid (γ-PGA) and MTGase. The results indicated that the addition of MTGase and γ-PGA markedly improved the gelation properties of hairtail surimi protein, including its maximum breaking force and deformation, water holding capacity and gel strength. The maximum improvements were achieved by adding 0.5units MTGase/g meat paste in combination with 0.06% γ-PGA. SDS-PAGE showed that the band intensity of cross-linked proteins increased, whereas that of myosin heavy chain decreased after treatments. Further scanning electron microscopy (SEM) analysis showed the formation of a denser gel matrix, which was caused by much stronger and more inter- and intra-molecular cross-linking of proteins, via MTGase catalysing ε-(γ-glutamyl) lysine cross-links formed between lysine residues in the gel protein and glutamic residues in the hydrolytic γ-PGA. The results provide reliable guidance for the improvement of hairtail surimi protein gelation properties.

Protein denaturation and oxidation in chilled hairtail (Trichiutus haumela) as affected by electrolyzed oxidizing water and chitosan treatment

ABSTRACT The effect of chitosan (CH) coating combined with electrolyzed oxidizing water (EOW) on microbiological and physicochemical of hairtail (Trichiutus haumela) was evaluated during 15 days of storage at −3°C. Hairtail samples treated by EOW combined with 1.5% (w/v) CH were compared with samples soaked in single material. For storage of 15 days, the thiobarbituric acid value of hairtails increased steadily to 1.79, 1.52, 1.48 mg/100g (p < 0.05) in the EOW, CH, and EOW+CH group, respectively. All of these were significantly lower than that of the control group (2.01 ± 0.04 mg malonaldehyde/100g; p < 0.05). Microbiological results, total volatile basic nitrogen, pH, and peroxide value also revealed that EOW and CH significantly retarded hairtail spoilage. The sodium dodecyl sulfate–polyacrylamide gel electrophoresis pattern of sarcoplasmic proteins revealed CH+EOW could slow down the protein deterioration of fillet. In this study, CH coating combined with EOW effectively extended the shelf life of hairtail to 6–7 days.

Euryphorus brachypterus (Copepoda: Caligidae) on wild pacific bluefin tuna from the Tsugaru Strait, northern Japan.

Parasitic copepods infecting large scombrid fishes have been known for a long time because their hosts are economically important. Most studies, however, have focused on their morphology or their infection status in aquaculture from pathological viewpoints, and very few quantitative surveys have been conducted under conditions in the wild. This study therefore investigated the prevalence of Euryphorus brachypterus (Caligidae) in wild Pacific bluefin tuna (PBF). Results of sampling from August to September 2014 at the western area of the Tsugaru Strait, Japan showed that 13.2% of the PBF individuals (n = 1978) were infected with this copepod. The prevalence of infections was highest in larger fish but varied among landing dates, which were classified into three clusters and in all smaller fish, the prevalence of infections was zero. This suggests that E. brachypterus mainly uses the larger PBF, which becomes sources of further infections in other seas, and that at least two host populations with different infection statuses at the strait.

Economic valuation of critical habitat closures

We developed methods to estimate the spatial variation in economic values of ocean fisheries, and applied the methods to estimate the cost of closing groundfish fisheries in Steller sea lion Critical Habitat in the Bering Sea and Gulf of Alaska. The research addressed two related goals: (1) explicitly linking spatial variability of fisheries biomass and profitability over time to environmental variables; and (2) developing estimates of opportunity costs of time and area closures to the fishing industry at scales relevant to management. The approach involved two stages of statistical analyses. First, environmental conditions measured at 3 km and 9 km spatial scales and two-week and one-month intervals were used to predict fish biomass and fisheries catch per unit of effort (CPUE). Environmental variables included bathymetry, remotely sensed physical and biological observations, and output from a physical oceanographic circulation model. Second, we used predicted CPUE and spatial regulatory and cost factors to explain the spatial distribution of fishing effort over time. Our results suggested that 2001 Critical Habitat closures cost the North Pacific groundfish trawl fisheries 5-40 percent of their total potential net earnings. The improved methods for estimating opportunity costs of fisheries closures we present have direct applications to evaluating boundary changes to marine protected areas and other spatial management decisions. Limitations include the extensive data requirements and the need to bootstrap confidence intervals. If further research demonstrates the robustness and stability of the estimated relationships over time, the methods could project spatial fishery effects of climate variability and change, leading to dynamic spatial models linking fisheries with ecosystems. Economic Valuation Of Critical Habitat Closures, Berman et al. 3

Developing joint educational programs in sustainability science across different universities: a case study from Japan

The challenge for sustainability educational programs lies in how to imbue students with the strong motivation necessary to move the world in a more sustainable direction. Five universities in Japan have mutually collaborated in the design and development of a unique curriculum and education system for sustainability science since 2008. Specifically, they have developed a common and remote lecture system called the “Frontier of sustainability science” (FSS). This paper discusses the concepts and challenges of FSS and how it was organized to teach students to actively learn how to work with people of various disciplines to realize interdisciplinarity.