Funka Bay Research Articles

Hotate (Patinopecten yessoensis) Seeding Technique using Zabutonkago and Marukago Tools with Hanging Method in Funka Bay Hokkaido, Japan

This research focuses on cultivation techniques for Hotate shellfish (Patinopecten yessoensis) during the hatchery phase in Funka Bay, Hokkaido, Japan. Hotate scallops are also called giant ezo scallops, these scallops are cultivated in Japan because they have relatively high productivity. This research aims to determine the best seeding technique for mussels (Patinopecten yessoensis) using the hanging zabuton-kago and maru-kago media. The research method uses observation and interviews with company owners. The results show that the technique for seeding Hotate shellfish (Patinopecten yessoensis) using pearl nets and lantern nets from May to September was carried out in 3 processes, namely chigai, kari-bunsan, and hon-bunsan. The method used is to sort the shells repeatedly until they reach a size of 50 mm – 70 mm during the mimizuri process in March. The hatchery process for cultivating Hotate shellfish can provide the basis for valuable information for sustainable management and maintenance in the future.

Inventory of Pests and Parasites in the Cultivation of Hotate Shellfish (<i>Patinopecten yessoensis</i>) in Funka Bay, Hokkaido, Japan

Hotate Shellfish Cultivation is the largest shellfish cultivation in the world, but many pests and parasites are found. This research aims to inventory the types of pests and parasites found in the cultivation of Hotate Shellfish (Patinopecten yessoensis) in Funka Bay, Hokkaido, Japan. The objects used for this research were 54 Hotate shellfish, consisting of three life stages of shellfish, namely seed shellfish, juvenile shellfish, and adult shellfish. This research was carried out using observation and random sampling methods to determine the types and percentages of pests and parasites present during the research. This research was carried out for seven months from 13 April to 6 December 2022 at the Daisan Matsui Company, Ohama, Oshamambe, Hokkaido, Japan. The results of this research show that there are four types of pests, namely Starfish, Purple Shellfish, Crustaceans, and Sea Pineapples as well as two types of parasites, namely Annelid Worms and Barnacles which attack shellfish cultivation. The percentage of shellfish at three life stages that were attacked by parasites was 75.93%. There are several factors that control the attachment of pests and parasites, including substrate availability, nutrient availability, and environmental considerations. The surfaces and nutrients provided by hotate culture facilities provide adequate conditions for pest settlement and growth.

Effects of Temperature on the Gastric Evacuation Rate and Maintenance Ration of Adult Pointhead Flounder Cleisthenes pinetorum

We investigated the gastric evacuation rate (GER) and maintenance ration (MR) for the adult pointhead flounder Cleisthenes pinetorum (77–421 g) at 4°C, 9°C, and 14°C which reflect the bottom, middle, and surface temperatures of their habitat in early summer. GERs were obtained from gravimetric experiments with 34 flounders fed juvenile walleye pollock Gadus chalcogrammus as prey. A 169‐day feeding experiment for 67 pointhead flounders fed krill Thysanoessa inermis was undertaken to measure MR. The effects of a 10°C temperature increase (Q10) on the GER and the MR were 6.55 and 2.04, respectively, indicating that the effect of temperature was greater on GER than on MR. As a result, the differences between the GER and MR, indicating the maximum amount of food ingestible for growth, were 2.8 and 30.7 cal·g−1 day−1 at 4 and 14°C, respectively. The water temperature on the sea floor generally remained at <4°C from winter through summer, but exceeded 10°C in the surface layer of Funka Bay, where pointhead flounders were sampled. Therefore, their growth rate should be considerably limited if they remain in the bottom layer. The unique ecology of this species among the flatfishes of floating from sea floor and feeding at pelagic zones may represent a strategy to compensate for the physiological limitation of growth at low temperatures.

Morphological Character and Percentage of Hotate Clams (Patinopecten Yessoensis) Meat Weight in the Growing Phase, in Funka Bay, Hokkaido, Japan.

This study focuses on the growth and meat weight percentage of Hotate clams (Patinopecten yessoensis) during the rearing phase in Funka Bay, Hokkaido, Japan. Japan, as a major producer of seafood, including Hotate clams, plays a significant role in global seafood consumption. The objective of this study was to analyze the length-weight relationship of Hotate scallops and assess their meat weight percentage during the rearing phase. The research method involved observations using a random sampling technique during the period from August to October 2022. Samples were taken in Funka Bay, with coordinates between 42°20'-42°40' North and 140°00'-141°00' East at a depth of 43 meters. Results showed that the length-weight relationship of Hotate clams during August to October exhibited a negative allometric growth pattern, with the highest constant reaching 2.640. This means that length growth is faster than body weight. The percentage of Hotate clam (P. yessoensis) meat weight during the rearing phase ranged from 31.03% to 35.70%. This study provides important insights into the growth and meat composition of Hotate clams during critical phases in their culture in Funka Bay, Hokkaido, Japan. It can serve as a valuable information foundation for the management and maintenance of sustainable and productive Hotate clam aquaculture in the future.

Gender identification of the horsehair crab, Erimacrus isenbeckii (Brandt, 1848), by image recognition with a deep neural network

Appearance-based gender identification of the horsehair crab [Erimacrus isenbeckii (Brandt, 1848)] is important for preventing indiscriminate fishing of female crabs. Although their gender is easily identified by visual observation of their abdomen because of a difference in the forms of their sex organs, most of the crabs settle with their shell side upward when placed on a floor, making visual gender identification difficult. Our objective is to use deep learning to identify the gender of the horsehair crab on the basis of images of their shell and abdomen sides. Deep learning was applied to a photograph of 60 males and 60 females captured in Funka Bay, Southern Hokkaido, Japan. The deep learning algorithms used the AlexNet, VGG-16, and ResNet-50 convolutional neural networks. The VGG-16 network achieved high accuracy. Heatmaps were enhanced near the forms of the sex organs in the abdomen side (F-1 measure: 98%). The bottom of the shell was enhanced in the heatmap of a male; by contrast, the upper part of the shell was enhanced in the heatmap of a female (F-1 measure: 95%). The image recognition of the shell side based on a deep learning algorithm enabled more precise gender identification than could be achieved by human-eye inspection.

ANALISIS KELAYAKAN BUDIDAYA KERANG HOTATE (MIZUHOPECTEN YESSOENSIS) DI TELUK FUNKA, HOKKAIDO, JEPANG

Cultivation of Hotate clams (Mizuhopecten yessoensis) in Funka Bay, Hokkaido, Japan, has become an attractive option for farmers. This study assessed the feasibility of Hotate clam (Mizuhopecten yessoensis) culture sites in Funka Bay, Hokkaido, Japan based on water quality data such as temperature, salinity and depth. The analysis showed that the site is highly suitable for Hotate clam culture, with water temperature ranging from 11.5°C to 22.3°C, salinity ranging from 31.01 to 32.97 psu, and culture depth up to 25 meters. Optimal temperatures range from 10°C to 15°C, optimal salinities range from 26 to 32 psu, and suitable depths range from 10 to 30 meters. Appropriate water quality management is an important key in achieving successful Hotate clam culture at this site. The results of the analysis indicate that this site has good suitability for Hotate clam culture. Temperature, salinity and water depth were main factors affecting the cultivation of Hottate mussels and the abundance of invasive organisms

Keragaman Morfologi Kerang Hotate (Patinopecten yessoensis) di Teluk Funka Hokkaido Jepang

Hotate scallop are cold water species that can only be cultivated in cold waters. Consumption of Patinopecten yessoensis, Jay 1857 from Japan and other countries shows greater demand, so research related to hotate scallop is important to manage hotate culture and its broodstock to maintain continous supply of this marine product. The purpose of this study is to determine the similarities and dissimilarities morphological characters of hotate scallop in Funka Bay Japan based on landmark characteristics. Data collection technique used was purposive sampling. Morphological measurements was conducted using Image-J software, principle component analysis using PAST software. The results indicate that the level of similarity of hotate scallop in cluster I is 70% and in cluster II is 85%. The principal components of hotate scallop morphometric landmarks is growth line number A20, A21, A22, A23, A25 from total 35 landmarks.

Growth, Toxin Content and Production of Dinophysis Norvegica in Cultured Strains Isolated from Funka Bay (Japan).

The successful cultivation of Dinophysis norvegica Claparède & Lachmann, 1859, isolated from Japanese coastal waters, is presented in this study, which also includes an examination of its toxin content and production for the first time. Maintaining the strains at a high abundance (>2000 cells per mL-1) for more than 20 months was achieved by feeding them with the ciliate Mesodinium rubrum Lohmann, 1908, along with the addition of the cryptophyte Teleaulax amphioxeia (W.Conrad) D.R.A.Hill, 1992. Toxin production was examined using seven established strains. At the end of the one-month incubation period, the total amounts of pectenotoxin-2 (PTX2) and dinophysistoxin-1 (DTX1) ranged between 132.0 and 375.0 ng per mL-1 (n = 7), and 0.7 and 3.6 ng per mL-1 (n = 3), respectively. Furthermore, only one strain was found to contain a trace level of okadaic acid (OA). Similarly, the cell quota of pectenotoxin-2 (PTX2) and dinophysistoxin-1 (DTX1) ranged from 60.6 to 152.4 pg per cell-1 (n = 7) and 0.5 to 1.2 pg per cell-1 (n = 3), respectively. The results of this study indicate that toxin production in this species is subject to variation depending on the strain. According to the growth experiment, D. norvegica exhibited a long lag phase, as suggested by the slow growth observed during the first 12 days. In the growth experiment, D. norvegica grew very slowly for the first 12 days, suggesting they had a long lag phase. However, after that, they grew exponentially, with a maximum growth rate of 0.56 divisions per day (during Days 24-27), reaching a maximum concentration of 3000 cells per mL-1 at the end of the incubation (Day 36). In the toxin production study, the concentration of DTX1 and PTX2 increased following their vegetative growth, but the toxin production still increased exponentially on Day 36 (1.3 ng per mL-1 and 154.7 ng per mL-1 of DTX1 and PTX2, respectively). The concentration of OA remained below detectable levels (≤0.010 ng per mL-1) during the 36-day incubation period, with the exception of Day 6. This study presents new information on the toxin production and content of D. norvegica, as well as insights into the maintenance and culturing of this species.

Significant nutrient consumption in the dark subsurface layer during a diatom bloom: a case study on Funka Bay, Hokkaido, Japan

Abstract. We conducted repetitive observations in Funka Bay, Hokkaido, Japan, on 15 February, 4 and 15 March, and 14 April 2019. The diatom spring bloom peaked on 4 March and started declining on 15 March. Funka Bay winter water remained below 30 m depth, which was below the surface mixed-layer and dark-layer depth (0.1 % of the surface photosynthetically active radiation, PAR, depth) on 4 and 15 March. In the subsurface layer at depths of 30–50 m, concentrations of NO3-, PO43-, and Si(OH)4 decreased by half between these dates, even in the dark. Incubation experiments using the diatom Thalassiosira nordenskioeldii showed that this diatom could consume added nutrients in the dark at substantial rates after pre-culturing to deplete nutrients. Incubation experiments using natural seawater collected in the growing phase of the bloom on 8 March 2022 also showed that nutrient-depleted phytoplankton could consume added nutrients in the dark. We excluded three physical process – water mixing, diffusive transport, and subduction – as possible main reasons for the decrease in nutrients in the subsurface layer. We conclude that the nutrient reduction in the subsurface layer (30–50 m) between 4 and 15 March 2019 could be explained by nutrient consumption by diatoms in the dark in that layer.

Intrusion of Coastal Oyashio water to Funka Bay and Tsugaru Strait occasionally disturbed by Kuroshio-originating warm core ring

Intrusion of Coastal Oyashio water to Funka Bay and Tsugaru Strait occasionally disturbed by Kuroshio-originating warm core ring

Seasonal changes in taxonomic, size composition, and Normalised Biomass Size Spectra (NBSS) of mesozooplankton communities in the Funka Bay, southwestern Hokkaido: Insights from ZooScan analysis

Knowledge about the taxonomic and size composition of mesozooplankton is of critical importance for both fisheries and oceanography. In this study, we collected an annual time series of mesozooplankton samples in Funka Bay and analysed them using ZooScan to reveal the seasonal changes in taxonomic and size structure. Both zooplankton abundance and biovolume peaked in April and were dominated by an appendicularian Oikopleura labradoriensis which has been reported as being are being important food source for flatfish larvae. Furthermore, Noctiluca scintillans was abundant from September to December. The occurrence of this species may be related to the recent increase in the transport of Tsugaru Warm Current water into the bay. The Normalized Biomass Size Spectra (NBSS) was significant for 16 of 21 sampling dates. Insignificant NBSS, with an extremely flat slope, was observed for January–March. Significant NBSS with a flat slope was observed in April. Then, the relatively steep slopes of the NBSS were the case from mid-May to December. These seasonal changes in the slope of NBSS suggest that the energy transfer efficiency for higher trophic levels varied seasonally. The observed slopes of the NBSS in Funka Bay ranged from −1.09 to −0.30, which was flatter than the theoretical value (−1) and the previously reported values for the oceanic region of the western North Pacific. This suggests that the energy transfer efficiency to organisms at higher trophic levels in the Funka Bay is higher than in the adjacent oceanic region.

Marine sediment as a likely source of methyl and ethyl iodides in subpolar and polar seas

The surface ocean is an important source of longer-lived volatile organic iodine compounds, such as methyl and ethyl iodide. However, their production in deep waters is poorly constrained. Here, we combine shipborne seawater and sediment core analyses to investigate the temporal and vertical distribution of methyl and ethyl iodide concentrations in the Bering and Chukchi Seas in July 2017 and 2018, and Funka Bay, Japan, between March 2018 and December 2019. We find the highest methyl and ethyl iodide concentrations in sediment porewaters and at the sediment surface. In Funka Bay, concentrations in the sediment and bottom waters strongly increased following the spring bloom and subsequent settling of phytodetritus to the seafloor. Dark incubation experiments suggest that diatom aggregates are a source of methyl and ethyl iodide to the ambient water. Our findings suggest that phytodetritus at the seafloor is a potential source of volatile organic iodine compounds to the water column in polar and subpolar coastal oceans.

Effect of egg size on the growth rate and survival of wild walleye pollock Gadus chalcogrammus larvae

AbstractTo clarify the survival process of walleye pollock larvae of the Japan Pacific stock in relation to the individual egg size, we estimated the original relative egg diameter from the diameter of the hatch check formed on larval sagittal otoliths. Significant positive correlations were obtained between egg diameter and embryonic body length, yolk sac volume, and lapillar otolith diameter in 3‐year groups (2013–2015 year classes) collected with a plankton net in Funka Bay. Embryos before hatching were without a check; however, checks were observed on all larval otoliths just after hatching. The check diameters showed significant positive regressions to age at collection (days after hatching) in 2014 and 2015 year classes, however not in the 2013 year class. Diameters of eggs collected with a ring net in Funka Bay gradually increased from 2013 to 2015 year classes. During the 2013–2015 spawning seasons, the proportion of adult females of the 2007 and 2009 year classes, which had relatively high abundances, gradually increased to higher proportions with age (43%, 57%, and <73%, respectively), indicating that the mechanism by which the eggs gradually became larger. The low water temperature experienced by the spawners ca. 2 months earlier, advancement in spawner age, and increase of repeat spawners (at least twice in their life time) would contribute to the increase in egg size and growth and survival rate of walleye pollock larvae.

Isoprene production in the water column and sediment in Funka Bay, Hokkaido, Japan

Isoprene production in the water column and sediment in Funka Bay, Hokkaido, Japan

In situ broadband acoustic measurements of age-0 walleye pollock and pointhead flounder in Funka Bay, Hokkaido, Japan

Measurements of the broadband acoustic backscattering from fish should improve acoustic discrimination between species. The pulse compression processing of broadband systems can be used to measure acoustic backscattering with high range resolution and improve signal-to-noise ratio. This may increase opportunities for in situ target strength (TS) measurements, the preferred method of collecting TS data. To evaluate the availability of TS spectra for acoustic discrimination, three Simrad EK80 wideband transceivers and split-beam transducers of 70, 120, and 200 kHz were used to collect in situ frequency responses of TS from age-0 juvenile walleye pollock and pointhead flounder, a swimbladderless flat-fish, distributed in and around Funka Bay, Hokkaido, Japan. The single echoes were extracted from backscattering data, and the TS spectra of the two species were obtained. However, processing of the broadband acoustic data is under discussion. To ensure the reliability of our data, the TS spectra of standard targets were also calculated. The measured TS spectra of the standard targets were close to the theoretical TS spectra. The individual TS spectra of two species included complex frequency response; however, the mean TS spectrum was relatively stable. The different characteristics of the frequency responses observed for the two species were in good agreement with reported observations. The results available for the acoustic discrimination were similar to the multi-frequency method, which uses two or more single frequencies. The raw TS spectra should aid in not only discriminating between species but also Q3 estimating the size of the fish.

Age and growth of Pacific rainbow smelt Osmerus dentex estimated from scales and otoliths in Funka Bay and the Yamazaki River, Japan

Age and growth of Pacific rainbow smelt <I>Osmerus dentex</I> estimated from scales and otoliths in Funka Bay and the Yamazaki River, Japan

Numerical modeling of the interaction between submerged floating tunnel and surface waves

This paper presents a numerical model for analyzing the nonlinear interaction between the moored Submerged Floating Tunnel (SFT) and surface waves. The mechanics model of the moored floating body driven by wave forces is built, and an efficient mesh update method is employed to dynamically configure the computational meshes solving the Navier-Stokes equations for viscous and incompressible free surface flows with the volume of fluid (VOF) method. Two laboratory experiments are used for validating the numerical model in terms of surface elevations, motion responses and mooring forces of the SFT, indicating the proposed model is capable of simulating the dynamics of the moored floating body under the wave action. This hydrodynamic model is then utilized to simulate the wave-structure interaction of the prototype SFT designed for Funka Bay, Hokkaido located in Japan. A total of 49 cases are designed for the numerical simulation to investigate the characteristics of the wave-tunnel interaction for different hydrodynamic parameters, including wave height, wave period, immersion depth and buoyancy-weight ratio (BWR). The numerical experiments not only shed light on the mooring forces, as well as pitch, sway and heave responses of the SFT in different wave conditions, but also provide guidance for the choice of BWR in engineering design. A medium value of BWR is suggested to be suitable, which is useful for avoiding the happening of snap forces in mooring chains and preventing SFT from experiencing large movement under external forces in severe wave conditions. As the correlation between the motion responses and BWR is not merely linear or quadratic but parabolic with a peak value, the design of BWR should avoid the case where peak motion responses of SFT happen.

Identification of timing of scallop morphological deformity and mortality from shell oxygen isotope records

The Yesso scallop, Patinopecten yessoensis (Jay), is one of the most important bivalve species in the Japanese and Chinese mariculture industry. In recent years, however, high incidences of scallop shell deformity and mortality have occurred with increasing frequency, but timing of onset and underlying causes are often unclear. Here, we proposed a promising δ18Oshell-based method for constraining the onset of shell deformity and mortality of P. yessoensis. Following six months of intermediate suspension culture in Funka Bay, Northern Japan, shells from healthy, deformed and dead scallops were randomly sampled. High-resolution seawater temperature time-series computed from healthy scallop shell δ18O profiles were precisely and temporally aligned to the instrumental temperature curve, thus allowing δ18Oshell-derived temperature time-series from deformed and dead scallops to be contextualized and allowing timing of scallop deformity and death to be retrieved. Irrespective of scallop shell length, onsets of deformity were anchored in February, and since then deformed scallops grew slowly in comparison to healthy individuals. Without exception, however, dead scallops had already ceased their shell building and died before February, indicating different underlying causes of scallop deformity and mortality. Perhaps most promisingly, considering that shells do not have any isotopic turn-over and once formed, temperature information is locked in. Thus, this approach holds great promise for identifying time anchor points (onsets of deformity and death) in archived scallops collected over different time scales, especially during massive mortality events.

Impact of Climate Extremes on Suitability Dynamics for Japanese Scallop Aquaculture in Shandong, China and Funka Bay, Japan

The assessment of extreme weather events on suitable sites for aquaculture could help in establishing sustainable coastal environmental resource management. Japanese scallop culture is an economically important marine farming activity in the coastal communities of Shandong, China and Funka Bay, Japan. In this study, we improved the suitable aquaculture site-selection model (SASSM) by using Geostationary Ocean Color Imager (GOCI) data instead of Moderate Resolution Imaging Spectroradiometer (MODIS) data, as a complementary source for higher temporal and spatial resolution data that are useful for monitoring fine-scale coastal and oceanic processes. We also applied the newly developed SASSM to the Japanese scallop production site along the Shandong coast. Finally, we analyzed the correlations between environmental factors (chlorophyll a concentration, sea surface temperature (SST), and total suspended sediment), meteorological factors (precipitation, temperature, and wind), and climatic events (winter East Asian monsoon (EAM) and El Niño/La Niña Southern Oscillation), and the impacts of climate events on suitable zones for scallop aquaculture. The new SASSM maps show that GOCI products have the potential for oceanographic investigations in Shandong, China and Funka Bay, Japan. Our results highlighted higher aquaculture site suitability for scallop in Funka Bay than in Shandong coast. During the winter with a strong EAM (2011), the suitable area for Japanese scallop aquaculture increased. Conversely, in the winter during a strong El Niño (2016), we found fewer areas that were highly suitable for scallop aquaculture in Funka Bay. SST was extremely low in Funka Bay during spring and summer 2017, which caused fewer highly suitable areas (scores of 7 and 8) for scallop aquaculture relative to other years. These findings suggest that extreme climatic events significantly impact the availability of suitable sites for marine farming and thus, should be considered in the development and design of coastal aquaculture sites.

Feeding habits of larval yellow goosefish Lophius litulon around the Shimokita Peninsula and in Funka Bay, Japan

Feeding habits of larval yellow goosefish <I>Lophius litulon</I> around the Shimokita Peninsula and in Funka Bay, Japan