Age and growth of Sebastes vulpes in the coastal waters of western Hokkaido, Japan

ABSTRACT:   Age and growth of Sebastes vulpes collected from the coastal waters of western Hokkaido were studied. Observation of the otolith margin verified that annuli (outer margins of the opaque zone) were produced chiefly from July to August. This period was associated with parturition and the birth season. The maximum age estimated by the surface method was 12 years but the oldest fish was aged at 35 years by the cross-section method. The surface method was inadequate for aging of S. vulpes older than 6 years because of the underestimation of age. No significant difference was found in the parameters of the growth equations between both sexes. The von Bertalanffy growth curve combined for both sexes was as follows: SL _t  = 358.6(1 − exp^{−0.156( t +0.820)}), where SL _t is standard length (mm) at age t (after parturition in years). It seems likely that S. vulpes grows slowly and lives longer than previously thought.     

Variability in timing and magnitude of spring bloom in the Oyashio region, the western subarctic Pacific off Hokkaido, Japan

The spring bloom of phytoplankton is a well-established, regular, seasonal event in the western subarctic Pacific and is considered one of the most important conditions of massive production of pelagic fishes. A series of 12 cruises was conducted from 1990 to 1992 to examine the timing and magnitude of the spring phytoplankton bloom in the Oyashio region, the western subarctic Pacific off Hokkaido, Japan. An interannual variability in the bloom events was also analysed. On the basis of hydrographical characteristics, the study area was divided into three water masses: the Oyashio Water Mass, the Mixed Water Mass, and the Coastal Water Mass. Spring blooms were observed first in April in the Oyashio and the Coastal Water Masses, and continued to May in 1991 and 1992. However, no bloom was recorded in the Mixed Water Mass. High nutrient supply into the surface mixed layer during winter is likely to be one of the factors supporting an intense spring bloom in the Oyashio Water Mass. A significant positive relationship between log-transformed surface chlorophyll a concentration and maximum density gradient (MDG) within the euphotic layer was obtained in April, indicating the importance of vertical stability of the water column in the initiation of spring blooms in the Oyashio and the Coastal Water Masses. The spring blooms in 1991 were much more extensive and lasted longer than in 1990. It is suggested that meteorological conditions and abundance of grazers were responsible for this interannual difference.     

Age,growth, maturity,and sex changes of monogrammed monocle bream Scolopsis monogramma in the waters around Okinawa-jima Island,Japan

Age, growth, maturity, and sex changes of the monogrammed monocle bream Scolopsis monogramma were estimated from ca. 500 specimens collected at Okinawa-jima Island in southern Japan. Age was determined from sectioned otoliths: maximum ages were 10 years for females and 9 years for males. Parameters for von Bertalanffy growth functions were L _t  = 206.6{1 ? exp[?0.68(t + 0.81)]} (n = 337) for females and L _t  = 244.4{1 ? exp[?0.93(t + 0.32)]} (n = 130) for males. The spawning season was estimated to last from June to July, with a peak in July. The standard length (SL) and age at 50 % maturity for females were estimated as 186.4 mm SL and 3.3 years, respectively. Intersex individuals appeared from 159.6 to 237.5 mm SL (n = 16) in fish between 1 and six years old, with the highest frequencies occurring at 170 mm SL and 2 years old. Hence, almost all S. monogramma specimens found at Okinawa-jima Island exhibited pre-maturational sex change, although some may have been protogynous hermaphrodites. Biological characteristics such as age at growth, maturation, and spawning season are valuable factors that can inform the resource management of local fisheries.     

Age and growth during immature stages of the mangrove red snapper Lutjanus argentimaculatus in waters around Ishigaki Island, southern Japan

Age and growth during immature stages of the mangrove red snapper Lutjanus argentimaculatus were examined using 129 sectioned otoliths of fish collected in rivers and coastal areas around Ishigaki Island. Monthly changes in the marginal growth index indicated that ring marks (inner edge of opaque zone) are formed once a year around May. Estimated ages of the sampled fish ranged from 0.2 to 4.5 years. The proportion of mangrove red snappers collected in each sampling set in the rivers was associated with age, namely, the older the fish, the smaller the proportion. This result suggests that the mangrove red snapper gradually moves from the river habitat to coastal areas with increasing age between 1 and 3 years. The relationship between standard length (Y; cm) and age (X; year) was expressed by the linear regression Y = 6.30X + 5.41. Both the somatic and otolith growth of age-one and age-two fish collected in coastal areas were faster than those of fish collected in rivers, suggesting that individuals with fast growth leave the rivers earlier than those with slow growth. Whereas the basic growth pattern obtained in this study is similar to that of the mangrove red snapper in waters around Great Barrier Reef, Australia, there is a clear difference in length of time spent in rivers between the two populations, probably associated with the difference in the scale of the rivers used as nursery grounds.     

The distribution and early growth of juvenile Pacific bluefin tuna Thunnus orientalis around Sado Island in the eastern Sea of Japan

Fisheries Science - The distribution and early growth of juvenile Pacific bluefin tuna (PBF) Thunnus orientalis were studied based on trawl surveys conducted around Sado Island, eastern Sea of...     

Interannual variability in hatching period and early growth of juvenile walleye pollock, Theragra chalcogramma, in the Pacific coastal area of Hokkaido

Juvenile walleye pollock of the Japanese Pacific population were collected from the Funka Bay [spawning ground; 16–64 mm fork length (FL)] in spring and the Doto area (nursery ground; 70–146 mm FL) in summer. Hatch dates were estimated by subtracting the number of otolith daily increments from sampling dates, and their early growth was back‐calculated using otolith radius–somatic length relationships. Interannual change of the hatching period was observed during 2000–02, and the peaks ranged from mid‐February in 2000 to early‐April in 2002. In 2000, when a strong year class occurred, early life history of the surviving juveniles could be characterized by early hatching and slower growth in the larval stage (<22 mm length). Higher growth rate in 2001 and 2002 did not always lead to good survival and recruitment success. Even though their growth was slow in 2000, the larvae hatched early in the season had larger body size on a given date than faster‐growing larvae hatched in later season in 2001 and 2002. Bigger individuals at a certain moment may have advantage for survival. The delay of hatching period may result in higher size‐selective mortality, and as a necessary consequence, back‐calculated growth in 2001 and 2002 could shift towards higher growth rate, although abundance of such a year class would be at the lower level. Variability in spawning period, early growth and their interaction might have a strong relation to larval survival through cumulative predation pressure or ontogenetic changes in food availability.     

Repeated reaching of the harmful algal bloom of Karenia spp. around the Pacific shoreline of Kushiro,eastern Hokkaido,Japan, during autumn 2021

Unprecedented large-scale algal blooms were observed during autumn 2021 around the Katsurakoi fishing port, Kushiro, eastern Hokkaido, Japan. Monitoring of shoreline water showed that chlorophyll a (Chl a) concentrations and the cell density of Karenia spp., dominated by Karenia selliformis, repeatedly increased synchronously between September and November 2021. These increases were associated with a southerly wind-driven current, which transported offshore water on the shelf towards the shoreline at the sea surface. The blooms were prolonged as a result of algal accumulation in the semi-closed fishing port. The maximum Chl a concentration and cell density exceeded 50 µg Chl a/L and 10⁴ cells/mL, respectively. During the autumn bloom of Karenia spp., the nitrate?+?nitrite and phosphate concentrations in the water were lower than those in 2019 and 2020, and the silicate concentration was comparable. The ammonium concentration during the bloom was notably higher than before the bloom period, reaching 15 µM. Mass mortality of several fish species and echinoderms that were cultured using rearing water intake from the same shoreline occurred synchronously with the increase in Karenia spp.

     

Age determination and growth of Pacific bluefin tuna, Thunnus orientalis, off Japan and Taiwan

Age determination of wild captured Pacific bluefin tuna, Thunnus orientalis, was conducted using sagittal otoliths of 806 specimens (47–260 cm in fork length) caught in the waters off Japan and Taiwan. Otoliths were transversely sectioned and the opaque and translucent zones were analyzed. Opaque zones mainly appeared on the otolith edge from April to July, indicating that the opaque zone is formed annually. The opaque zones formed during later life (age 10+) were more distinct than the earlier zones. The estimated ages of specimens ranged from 1 to 26 years. Parameters of the von Bertalanffy growth function were estimated to be 249.6 cm, 0.173, and −0.254 years for L_∞, k, and t₀, respectively. Growth of younger fish was rapid up to 5 years old attaining about 150 cm, and then growth rate decreased. After that, fish attained about 200 cm at 9 years old and about 225 cm (90% of L_∞) at 13 years old (50% of maximum age). This paper updates the biological information on length at age with a large size range to support stock assessment model analyses for this commercially valuable species.     

Age,growth and maturation of the blackspot snapper <Emphasis Type="Italic">Lutjanus fulviflammus</Emphasis> around Okinawa Island,Japan

ABSTRACT:   The blackspot snapper Lutjanus fulviflammus is one of the most common Lutjanus species landed and consumed on Okinawa Island, Japan. Using 901 fish (29.9–304.2 mm in standard length; SL) obtained from fish markets or caught by angling, the age, growth, maturation size and maturation age were estimated. Each opaque zone formed on the otolith every year correlated with their spawning and was thought to be an annual ring. The main spawning season was estimated to be from April to July, which peaked in May and June, with a few mature fish collected in August and September. Maximum ages were observed as 24 years for both sexes and L_∞ (mm SL), K and t₀ (years) of the von Bertalanffy growth formula were estimated to be 276, 0.144 and −5.22 for females and 247, 0.227 and −3.18 for males, respectively. First maturation size and age were estimated to be 175 mm SL and 2 years for both sexes. A faster growth rate up to 2 years will allow reproduction at a young age and provide many chances for spawning throughout their long life. Furthermore, the possibility exists that populations would easily recover if regulations were established.     

Re-examination of age and growth of daggertooth pike conger Muraenesox cinereus in the western Seto Inland Sea, Japan

Age determination and growth using otolith rings in Muraenesox cinereus was re-examined in the western Seto Inland Sea, Japan. Previous study in this area indicated that new rings were formed annually from March to May, and then from September to October once individuals had achieved four or five rings. In this study, monthly changes in marginal growth rate indicated that the first ring was formed before November in the year following hatching, and from then on another ring was formed annually in July or August. The birth month was determined to be August based on a peak in monthly change in the gonad somatic index. Estimated von Bertalanffy growth functions were L = 806.6{1 ? exp[? 0.33(t + 0.06)]} and L = 1264.0{1 ? exp[? 0.19(t + 0.15)]} for males and females, respectively. Lengths after 3 years of age in this study were 100 mm longer than those in a previous study for both sexes.     

Interdecadal decrease in potential fishing areas for Pacific saury off the southeastern coast of Hokkaido,Japan

We examined interdecadal variations in potential fishing grounds for the Pacific saury, Cololabis saira, off the southeastern coast of Hokkaido, Japan, for the early fishing season of August–September. We applied linear trend analysis to a time series of several oceanographic variables for 1993–2014. Trends in the appearance frequency of sea surface temperatures (SST) of 12–18 °C during August–September indicated an interdecadal reduction in the potential fishing area off the Hokkaido coast. There were localized significant increases of both SST and the sea level anomaly along the Kuril–Kamchatka Trench off the Hokkaido coast. The localized trends coincided with decadal decreases of satellite‐based chlorophyll concentrations after 2002. Analysis of mesoscale eddies revealed that the localized trends were related to clockwise (counterclockwise) eddies that appeared more frequently (less frequently) near the trench in recent years. Moreover, the Oyashio transport on the slope between the coast and the trench decreased significantly and completely disappeared in some recent summers. Interactions between the Oyashio and mesoscale eddies resulted in an interdecadal shift in the cold‐water intrusion along the main stream of the Oyashio from the along‐slope direction to the offshore direction in the upstream region of the Hokkaido coast, and large areas of favorable potential fishing grounds near the Hokkaido coast have disappeared in recent years.     

Influence of volcanic ash sediments on spore adhesion of the red alga Gelidium elegans from the coastal seabed around Miyakejima Island, Japan

The populations of red alga Gelidium elegans along the coast of Miyakejima Island were severely damaged by a volcanic eruption in 2000. The effect of this volcanic eruption has been long lasting, and populations of this red alga still have not recovered. We investigated the effect of seabed sediment particles derived from volcanic ash on the substrate adhesion of G.?elegans spores. The analysis provides evidence that increasing amounts of sediment particles result in lower adhesion rates of G.?elegans spores, and that smaller sediment particles have a greater influence on adhesion. The amount of seabed sediment particles around Miyakejima Island was 9.3?C1815.4?mg/cm². This amount has changed greatly from year to year. The adhesion rate of G.?elegans spores in water around Miyakejima Island was 0?% at all points in 2008 and 2010, but it was estimated as 6.3?C38.6?% in 2009. These results suggest that there is significant inhibition of algal spore adhesion by seabed sediment particles derived from volcanic ash around Miyakejima Island.     

Biomass and taxonomic composition of micronekton in the western tropical–subtropical Pacific

The biomass distribution, community structure and species composition of the dominant micronektonic animals were determined in the western tropical Pacific, using day/night sampling from upper 200 m depth with a commercial midwater otter trawl in fall‐winter of 1994, 1995 and 1997. Night‐time micronekton biomass was significantly higher than daytime biomass except for a few cases. All the night‐time catches had similar taxonomic composition, dominated by myctophid fishes, small squids, shrimps and euphausiids. Night‐time micronekton biomass in the upper 200 m was assumed to be higher in the North Equatorial Counter Current than in the North Equatorial Current, reflecting the zooplankton biomass distribution which micronektons feed on at night. A total of 42 species of myctophid fishes, 34 species of squids, 27 species of shrimps and six species of euphausiids were collected. Community types of each dominant taxonomic group were classified by cluster analysis based on the species composition. A station located north of the subtropical convergence zone was distinct from other tropical stations south of the convergence zone, having significantly different species composition in three of the four dominant taxonomic groups (myctophids, squids and shrimps). The interaction between the larvae of commercially important fishes and micronektonic animals is discussed.     

东太平洋大青鲨年龄与生长的研究

根据2003年7~11月在东太平洋海域(03°~17°S、96°~146°W)金枪鱼延绳钓生产调查中兼捕获取的89 ind大青鲨样本,通过对大青鲨脊椎骨年轮的观察及其生物学特征数据的记录,研究了大青鲨的年龄与生长。结果表明,大青鲨的最大寿命为17.1龄;von Bertalanffy生长参数L∞=292 cm,K=0.16/yr,t0=-1.6yr;大青鲨的生长拐点年龄为5.3yr,拐点体重为55.8kg,拐点叉长为195 cm。     

Larval growth rates differ in response to seasonal temperature variations among clupeoid species inhabiting the Pacific coastal waters of Japan

Growth rates of round herring Etrumeus teres, Japanese anchovy Engraulis japonicus, and Japanese sardine Sardinops melanostictus larvae respond differently to seasonal temperature variations in Sagami Bay on the Pacific coast of central Japan. Larvae of these three clupeoid species were collected from small seine net catches between February 2008 and April 2009. Correlations between otolith growth increment widths and ambient temperatures were examined at five body sizes and indexed to otolith radii of 50–175 μm, which corresponded to notochord lengths of 15–24 mm. Round herring larvae showed positive correlations between growth rate and habitat temperature at all five body sizes. In contrast, Japanese sardine larvae did not show significant correlations between growth rate and ambient temperature at any of the five body sizes. Japanese anchovy larvae showed significant but weaker correlations between growth rate and temperature than round herring. Although these three species share habitats with some differences in seasonal occurrence in the bay, they showed different species-specific responses to seasonal habitat temperature variations. These differences in response to temperature variations may constitute an ecological basis for different migration patterns among the three species.     

Quantitative mapping of kelp forests (Laminaria spp.) before and after harvest in coastal waters of the Shiretoko Peninsula,Hokkaido, Japan

In the Shiretoko Peninsula, a World Natural Heritage site, the sustainable management of kelp forests has drawn public attention because of the economic and ecological importance of kelp. We spatially estimated the distributions of kelp forests in the Shiretoko Peninsula before and after harvest. Field surveys were conducted in coastal waters (23.74 km²) at the ends of July and August 2008, immediately before and after harvest. Data on the presence or absence and thickness of the kelp forests were collected via acoustic observation. The data were interpolated using geostatistical methods. Before harvest, the kelp forests were continuously distributed over 5.64 km² (thickness 33–132 cm), especially near the north part of the study area. After harvest, they were sparsely distributed over 2.73 km² (thickness 35–105 cm). In the southern part of the study area, the influence of harvests was observed as declines in forest area. In addition, relatively thickly forested areas formed the majority of the part most likely to be harvested. Selective harvesting for area and size was confirmed though quantitative mapping of kelp forests. The quantitative mapping of both the distribution and harvest of kelp forests was successful.