Fisheries Oceanography最新文献

The spatial distribution patterns of Merluccius capensis in the Namibian waters were investigated and related to average environmental conditions during 1996–2020. Fisheries-independent data and simultaneously collected water temperature and dissolved oxygen data were used from austral summer surveys. A geostatistical kriging approach was employed to evaluate the spatial structure of hakes. Links to environmental conditions were explored via data-driven generalized additive models (GAMs). M. capensis generally exhibited average patch sizes between 40 and 50 nm at depths between 180 and 280 m. During the extreme episodic water warming in 2011 related to a Benguela-Niño, the hake patches shrank up to a historical minimum of about 13 nm and moved offshore showing maximum densities at unusual deeper bottoms between 260 and 320 m. The deepening and size reduction of aggregations did not alter the biomass estimates (570 kt) that remained within historical ranges (249–811 kt). Although other extremely warm and cold summers were reported during the study period, no significant impact on the M. capensis patch size was detected. Maximum M. capensis densities were linked to optimal bottom temperature range between 10.1 and 11.8°C, dissolved oxygen values close to zero nearshore, and between 0.8 and 1.4 ml/L offshore. Potential changes of biomass produced by extreme environmental events remained undetected within the interannual biomass ranges, suggesting a high resilience capacity to episodic extreme environmental events.

This study has considered anchoveta acoustic data from the Pelagic Resources Hydroacoustic Assessment Surveys carried out by the Peruvian Sea Institute (IMARPE) and free access satellite data (HYCOM and MODIS from the USA) of some oceanographic variables between the period 2011 and 2021, to know the oceanographic conditions, characteristics of schools and size structure in the optimum zone (OZ) and in the physiological stress zone (PSZ), of their total distribution. The OZ is determined by the extent of the Cold Coastal Waters (CCW), and the PSZ is determined by the mixing of waters, to the north by the CCW-ESW (Equatorial Surface Waters) and to the west between the CCW-SSW (Subtropical Surface Waters). The range of sea surface temperature and salinity in the PSZ (16.1–25.0°C and 34.65–35.29, respectively) was wider than in the OZ (14.5–24.0°C and 34.65–35.20, respectively), where a higher number of schools were recorded. Our analyses showed that the morphometric and energetic acoustic descriptors of anchoveta schools in the summer were higher during summers compared to springs. In terms of positional characteristics, the mean depth of the schools in the PSZ was slightly greater than in the OZ. The total size structure of anchoveta in the OZ consisted mainly of juvenile specimens (less than 12 cm total length) in the summer of 2011 and 2013–2014 and in the spring between 2014–2017 and 2021. In the PSZ, adult specimens (greater than 12 cm total length) predominated in summer between 2011–2013, 2015, 2018, and 2021 and in spring between 2011–2013, 2015, and between 2018–2021. However, specimens greater than 10 cm in total length were found in the PSZ. Knowledge of the location of this zone away from the coast will allow a high probability of anchoveta capture of adult specimens during fishing periods.

The North Sea is one of the busiest and most exploited marine areas on Earth and is home to many highly migratory and economically important species. At the northern boundary, a 300-km corridor between Norway and Shetland forms a major egress point from the North Sea to the Norwegian Sea and broader Atlantic Ocean, which is known to be used by many focal species including Atlantic salmon, European eel, European sturgeon, Atlantic bluefin tuna, basking shark, Atlantic mackerel, spiny dogfish, among others. We argue that this relatively shallow 300-km corridor is a critical area for ecological and oceanographic research in the North Sea to understand species distribution, migratory patterns, responses to climate, fisheries, and more. Instrumentation of the Bergen-Shetland Corridor with a line of oceanographic and biological tracking infrastructure would help capture the spatiotemporal dynamics of the ocean and its major fauna between the North Sea and Norwegian Sea, a boundary between management areas from ICES and OSPAR.

As the impacts of climate change become more severe throughout the global oceans, fisheries managers will be increasingly challenged to rebuild stocks exhibiting declining productivity. In such cases, detailed knowledge of species life history will be necessary to both restrict harvest and manage other environmental conditions, where possible, that impact survivorship. A current example of these challenges, the Southern New England/Mid-Atlantic Bight winter flounder stock remains in a persistently depleted state due to a combination of past harvest and the effects of climate change mediated through increased predation. To explore the recovery capacity of a subpopulation of this stock, a life-cycle model was fit to 29 year classes of stage-specific winter flounder data from surveys conducted in Narragansett Bay, Rhode Island and used to project future subpopulation abundance. Supporting a prevailing hypothesis, the results indicated that environmental factors influencing juvenile mortality were largely responsible for inhibiting recovery. Furthermore, recovery of the subpopulation to past levels of abundance was determined to be unlikely even under optimistic future conditions resulting from aggressive management interventions. Taken together, the findings of this work pose important questions regarding the realism of assessing climate-challenged populations against biological reference points set under past environmental regimes and the degree to which harvest restrictions to promote recovery of such stocks should be allowed to limit warm-water fisheries thriving in a warming ocean.

This study reviews the evidence for warming climate impacts on ocean migration, growth, and survival of southern populations of Pacific salmon (Oncorhynchus spp.), in particular, Japanese chum salmon (O. keta). In this century, productivity of Asian and North American Pacific salmon declined in southern areas but increased in northern areas owing to a warming climate. Japanese chum salmon, mainly hatchery-produced fish, are roughly divided into two populations: warm-current populations (WCPs) affected by the Tsushima warm current and cold-current populations (CCPs) affected by the Oyashio cold current. Their population size and survival rate have declined in Honshu since the late 1990s and in Hokkaido since the late 2000s. The decrease in population size of CCPs is greater than that of WCPs, suggesting that WCPs are relatively adaptable to global warming. A decline in survival rate and insufficient growth of juveniles in coastal habitats due to a shortened duration of coastal stay as a consequence of global warming was identified as the factor affecting the reduced production of Japanese chum salmon. The current situation of chum salmon is approaching that of the Jomon transgression period in Japan (7–5.5 kyr before present). Therefore, it is necessary to establish sustainable conservation management for southern populations of Pacific salmon under a warming climate regime.

The vertical distribution of species richness, abundance and biomass of planktonic ostracods down to a depth of 1000 m were studied in the northeastern South China Sea (NESCS) during March and in the central South China Sea (CTSCS) during September 2016. A total of 47 species of halocyprids were identified, with 46 species recorded in the NESCS and 28 species in the CTSCS. Most of the species observed were concentrated in the mesopelagic zone (200–1000 m), but the majority of species abundance and biomass occurred in the 25 m to 300 m water column. Results of statistical analysis showed that the vertical distribution of planktonic ostracods was associated with chlorophyll a concentration and sampling depth. The high abundance and species richness of ostracods in the NESCS were probably influenced by the Kuroshio intrusion and eddies leading to high levels of chlorophyll a concentration. The biomass of large-sized individuals with low abundance is equal to or larger than, the extremely small-sized individuals with high abundance, particularly in deep layers. The body sizes of planktonic ostracods were found to increase from surface to deeper water layers, indicating a trend of greater body length and higher biomass of ostracods in deep sea.

Ichthyoplankton assemblages in the south central Tyrrhenian Sea are not known in spite of this being an intensely fished area. There are two large canyons in this region: Dohrn, in the Gulf of Naples, and Cuma, at the south end of the Gulf of Gaeta. In this study, we provide the first description of summer ichthyoplankton assemblages in the vicinity of the two canyons and present the physical features and Lagrangian particle tracking analyses at the time of the sampling. We identified fish larvae of 19 families and fish eggs of 8 families. The most abundant species was Engraulis encrasicolus, which was found at densities comparable to other known spawning grounds of the western Mediterranean. Mesopelagic species, such as Gonostomatidae and Myctophidae, were also abundant, especially at the Cuma Canyon. The notochord and standard length of the E. encrasicolus larvae ranged from 2.06 to 10.47 mm and was significantly smaller at the Cuma stations than at the Dohrn stations, suggesting the presence of sub-populations with different spawning phenologies. The passive particle tracking analyses and the examination of currents confirmed distinct circulation features between the two sampled regions and in relation to depth and proximity to the canyon heads. These results uncover previously unknown rich assemblages of fish eggs and larvae and have conservation and management implications given the proximity of these canyons to a marine protected area and to an intensely fished continental shelf.

Japanese Spanish mackerel Scomberomorus niphonius and Japanese anchovy Engraulis japonicus are typical predator and prey species, respectively, with high commercial values in the China seas. However, the interspecific interaction, particularly the relationship between the two species during early life stages, is unclear. Here, based on ichthyoplankton surveys in the coastal Yellow Sea during 2013–2018, we analyzed the relationship between the two species based on egg occurrence and abundance in the context of species interaction. Spawning optimal temperature were examined for anchovy (13.0–18.0°C) and mackerel (15.0–20.0°C) based on egg occurrences and abundances in relation to sea surface temperature. We confirmed the peak spawning periods (May and June) and primary spawning areas (Haizhou Bay) for both mackerel and anchovy based on spatiotemporal distributions of two species eggs. Mackerel showed a high spawning overlap with anchovy, and anchovy egg abundance were also higher in overlap areas. Anchovy egg abundance may be more important for mackerel spawning than environmental variables, suggesting the significance of prey for predators during early recruitment. The temperature also has important effects on mackerel spawning and could be a threshold affecting mackerel spawning activity. Mackerel might have evolved a spawning strategy of short-term spawning timed to coincide with the peak spawning of anchovy in the coastal Yellow Sea. These results highlight the effects of interspecific relationships on spawning strategy of anchovy and mackerel in the coastal Yellow Sea and may provide some insights for early recruitment studies of piscivorous fishes in the context of the match–mismatch hypothesis.

Mackerel is an important commercial pelagic species present in the western and eastern North Atlantic. The Northeast Atlantic Mackerel (NEAM) stock has its southernmost spawning area mainly located western Iberian Peninsula and southern Biscay. This species performs extensive annual migrations. The present study is focused on the distribution of this species along the Cantabrian Sea, an essential area of the South Spawning Component (SSC), and the environmental drivers that can affect its migration phenology. We have used data from Vessel Monitoring System and Logbooks of the hand line fishery to estimate the catch per unit of effort (CPUE) as a proxy of its distribution and abundance. CPUEs data of fisheries targeting NEAM provided us with a tool to discriminate the most important predictors for both its prespawning and the postspawning behavior. Among the drivers that can affect mackerel migration, we have analyzed wind speed and direction, temperature at surface (SST) and at 200 m depth, chlorophyll a, mixed layer depth, upwelling intensity, and the most representative geographical variables: depth, slope of the seafloor, and distance to coast. We used generalize additive models to highlight the predictors most closely related to the phenology of the species and to shape the spatial–temporal abundance of NEAM in the southern Bay of Biscay waters. Temperature and wind speed and direction are the most important factors that affect prespawning and postspawning migration of NEAM SSC and shape its niche tracking leading to a gradual advance of the spawning season.

In the waters off Japan, the patterns of the Kuroshio Current (KC) and its bifurcations are highly variable, which significantly affect the physical and biological environments. Knowledge about species' habitats of marine apex predators such as cetaceans and their variability is fundamental to understand not only their population structures but also their ecosystem structures related through bottom-up and top-down trophic linkages. In dynamic ocean environments, however, such crucial information has not been provided adequately by snapshot-based conventional approaches, such as sighting surveys. Spatiotemporal habitat utilization patterns of the common bottlenose dolphin (Tursiops truncatus) were investigated using fin-mounted Advanced Research and Global Observation Satellite (ARGOS) tags. Behavioral states at each tracking location were categorized into transiting- or area-restricted searching (ARS) modes based on Bayesian state-space model. Twelve satellite-tracked dolphins showed different movement patterns. Their habitat ranges were estimated by minimum convex polygons (MCPs), and movement patterns were classified into three types (four animals each of eastward, offshore, and westward movements) based on MCP overlapping among tagged dolphins. The animals that restricted their habitat to the coastward side of the KC (CSKC) tended to show ARS modes more frequently. Estimated locations of these animals corresponded well with cold coastal waters. On the other hand, offshore movements corresponded well with clockwise flow generated by the bifurcation of the KC, and those dolphins were likely straying into less productive waters. These patterns suggest that common bottlenose dolphins off the southern coast of Japan mainly utilize productive CSKC waters but occasionally move to offshore waters.