The optimal stability `window': a mechanism underlying decadal fluctuations in North Pacific salmon stocks?

While recent evidence suggests that North Pacific salmon stocks are influenced by decadal variability in atmospheric forcing of the ocean, the actual combination of physical and biological processes that determines this linkage has not been identified. This paper describes a possible scenario in which water column stability is the primary factor by which the physical environment influences phytoplankton production, the basis for production at higher trophic levels. Variation in the strength of the wintertime Aleutian Low pressure area affects water column stabilities, hence primary production, along the entire eastern boundary of the North Pacific. The `optimal stability window' explains the qualitative relationship between fish stocks and the strength of the winter Aleutian Low, as well as the observed out-of-phase variation between northern and southern salmon stocks.     

Marine biogeochemical response to a rapid warming in the main stream of the Kuroshio in the western North Pacific

Impact of climate change on marine biogeochemical parameters and ecosystem is one of the important issues of our environment. Direct evidence of marine pelagic ecosystem changes is found with warming of sea water and sea‐level rise in the main stream of the Kuroshio in the East China Sea and the western North Pacific during these three decades based on the analysis of long‐term comprehensive hydrographic observations. In terms of annual mean, the warming rate of surface air temperature and sea surface temperature ranged from 0.15 to 0.21°C per decade in and around the main stream of the Kuroshio in the East China Sea, which exceed the global mean warming rate of 0.128 ± 0.026°C per decade during the period from 1956 to 2005 reported in IPCC 2007. One of the features in this rapid warming region is an increase of number of Pterosagitta draco, a cosmopolitan warm‐water zooplankton. Biogeochemical parameters, such as wet weight of zooplankton, plant pigment and nutrients concentration in the upper 200 m have been decreasing while dissolved oxygen content and seawater temperature have been increasing in the upper 200 m in the main stream of the Kuroshio in the East China Sea. These observed linear trends of the biogeochemical parameters would be foresights for temperate oceans in the future.     

A century and a half of change in the climate of the NE Pacific

Spectral analysis of twenty-one climate records indicates that NE Pacific temperatures and winter wind stress have fluctuated at four dominant time scales in this century: 2–3 years (quasi-biennial oscillation), 5–7 years (El Nio-Southern Oscillation, ENSO), 20–25 years (bidecadal oscillation, BDO), and a poorly resolved, very-low-frequency (VLF) oscillation with a 50–75 year period. Forty-four per cent of the low-frequency variability in British Columbia air temperatures is associated with the strength of the Aleutian Low pressure system in winter. Only 42% of the 'strong' and 25% of the 'moderate' ENSO events in this century have produced large warm anomalies off BC. Interactions between the ENSO, bidecadal and very-low-frequency oscillations produce a pattern of alternating warm and cool climate states, with major warnings every 50 to 75 years. Since 1850 there have been seven warm periods, lasting an average of 11.4 years, and six cool periods lasting an average of 10.8 years. Sharp transitions from cool to warm climate states (as in 1977/78) occur when warming phases of the BDO and VLF oscillations coincide. Recent evidence suggests that the BDO may originate in either the tropical or the subtropical North Pacific. The NE Pacific has experienced a major warming since 1978. A long-range forecast suggests that the BDO and VLF oscillations peaked in 1989 and are currently in a cooling phase. Consequently, coastal temperatures should moderate for the rest of this century. A transition to the next cool climate state could occur about the year 2001. The forecast for moderating temperatures could begin the first phase of the recovery of the southern BC coastal chinook and coho salmon and herring stocks, which are currently at low abundance levels.     

Ecological effects of regime shifts in the Bering Sea and eastern North Pacific Ocean

Large‐scale shifts occurred in climatic and oceanic conditions in 1925, 1947, 1977, 1989 and possibly 1998. These shifts affected the mix and abundance of suites of coexisting species during each period of relative environmental stability—from primary producers to apex predators. However, the 1989 regime shift was not a simple reversal of the 1977 shift. The regime shifts occurred abruptly and were neither random variations nor simple reversals to the previous conditions. Timing of these anomalous environmental events in the North Pacific Ocean appears to be linked to physical and biological responses in other oceanic regions of the world. Changes in the atmospheric pressure can alter wind patterns that affect oceanic circulation and physical properties such as salinity and depth of the thermocline. This, in turn, affects primary and secondary production. Data from the North Pacific indicate that regime shifts can have opposite effects on species living in different domains, or can affect similar species living within a single domain in opposite ways. Climatic forcing appears to indirectly affect fish and marine mammal populations through changes in the distribution and abundance of their predators and prey. Effects of regime shifts on marine ecosystems are also manifested faster at lower trophic levels. Natural variability in the productivity of fish stocks in association with regime shifts indicates that new approaches to managing fisheries should incorporate climatic as well as fisheries effects.     

Feeding habits of albacore Thunnus alalunga in the transition region of the central North Pacific

ABSTRACT:   The feeding habits of albacore Thunnus alalunga (fork length: 48.9–76.2 cm, n  = 132) were examined from late spring to early autumn in relation to its northward migration in the transition region between the subtropical and subarctic fronts in the central North Pacific. Samples were collected at night using surface gill nets or during daytime pole-and-line surveys in 2001 and 2002. During May and June, albacore fed mainly on Japanese anchovy Engraulis japonicus , which accounted for 27.2%, 67.0%, and 45.5% of the total stomach contents by number ( Cn ), wet weight ( WW ), and frequency of occurrence ( F ), respectively, and secondarily on the subarctic gonatid squid Gonatopsis borealis ( Cn , 15.8%; WW , 10.8%; F , 28.8%). From July to September, albacore continued to depend on Japanese anchovy ( Cn , 48.2–52.8%; WW , 79.9–95.2%; F , 27.8–85.4%). These results corresponded well with the remarkable rebound of the Japanese anchovy stock since the 1990s. Gonatopsis borealis , the main squid prey from May to June, almost disappeared from the stomachs of albacore from July to September, probably due to the northward migration of this squid to subarctic waters in summer. The feeding impact of albacore on the Japanese anchovy stock in the transition region was conservatively estimated to be from 1400 to 2100 tons per day from late spring to early autumn.     

Interdecadal variations of plankton biomass and physical environment in the North Pacific

In the central and western subarctic Pacific, zooplankton biomass and chlorophyll concentrations during the mid 1960s to mid 1970s were a few times higher than in the preceding and following decades, corresponding to higher values of the atmospheric Northern Hemisphere Zonal Index (NHZI). In the Alaskan Gyre, however, it was reported that biomass of zooplankton and nekton doubled after the atmospheric regime shift in the mid 1970s. In the subtropical North Pacific, chlorophyll a concentration decreased drastically after 1980, although a decrease of zooplankton biomass was clearly seen only in the northern part of the subtropical gyre. Chlorophyll concentration in the central subarctic Pacific and zooplankton biomass in the Oyashio have been decreasing since the early 1980s. Additionally, chlorophyll concentration in the western subarctic Pacific and eastern Bering Sea, and zooplankton biomass in the central subarctic Pacific and eastern Bering Sea have also been decreasing since the late 1980s. In these regime-shift situations, there is a general tendency for intensification of wind speed or de-stratification to cause plankton biomass to decrease in regions where the upper mixed layer is deep, such as the western subarctic and north-western subtropical water, whereas in relatively stratified areas, such as in the eastern subarctic and south-western subtropical water, the effect is an increase of plankton biomass.     

Changes in albacore tuna habitat in the northeast Pacific Ocean under anthropogenic warming

Albacore tuna are widespread in the North Pacific Ocean and the basis of an important commercial fishery. These fish live mainly within a fairly narrow thermal niche range defined by sea surface temperature (SST) isotherms between 14 and 19°C. Because the fish's thermal range coincides with strong latitudinal temperature gradients off the northwest coast of North America, there is a great deal of seasonal and interannual variability in the distribution of these fish, and a significant potential for a new habitat in this region with anthropogenic climate change. We use historical catch and effort data from the Canadian troll fleet to define the fish's thermal niche, and document observed shifts in distribution associated with interannual climate variability. We then use an ensemble of climate model simulations from the Coupled Model Intercomparison Project to estimate northward extension of the potential habitat under anthropogenic warming scenarios. A potential new habitat is about half a million square kilometres even under a moderate mitigation scenario. Estimates are smaller for some months of the year in which the fishery is conducted, but as well as opening up new regions, the length of season in which the fishery is active may be extended in the northern part of the range. However, much of the potential new habitat will be in oceanic waters with relatively low productivity. Our estimated area of potential habitat is based on the fish's thermal niche and assumes that other biologically important factors such as food will not be limiting.     

Effects of the North Pacific Current on the productivity of 163 Pacific salmon stocks

Horizontal ocean transport can influence the dynamics of higher‐trophic‐level species in coastal ecosystems by altering either physical oceanographic conditions or the advection of food resources into coastal areas. In this study, we investigated whether variability in two North Pacific Current (NPC) indices was associated with changes in productivity of North American Pacific salmon stocks. Specifically, we used Bayesian hierarchical models to estimate the effects of the north‐south location of the NPC bifurcation (BI) and the NPC strength, indexed by the North Pacific Gyre Oscillation (NPGO), on the productivity of 163 pink, chum, and sockeye salmon stocks. We found that for salmon stocks located in Washington (WA) and British Columbia (BC), both the BI and NPGO had significant positive effects on productivity, indicating that a northward‐shifted bifurcation and a stronger NPC are associated with increased salmon productivity. For the WA and BC regions, the estimated NPGO effect was over two times larger than the BI effect for pink and chum salmon, whereas for sockeye salmon the BI effect was 2.4 times higher than the NPGO. In contrast to WA and BC stocks, we found weak effects of both horizontal ocean transport processes on the productivity of salmon stocks in Alaska. Our results indicated that horizontal transport pathways might strongly influence population dynamics of Pacific salmon in the southern part of their North American ranges, but not the northern part, suggesting that different environmental pathways may underlie changes in salmon productivity in northern and southern areas for the species under consideration.     

Potential trophodynamic and environmental drivers of steelhead (Oncorhynchus mykiss) productivity in the North Pacific Ocean

Information on prey availability, diets, and trophic levels of fish predators and their prey provides a link between physical and biological changes in the ecosystem and subsequent productivity (growth and survival) of fish populations. In this study two long‐term data sets on summer diets of steelhead (Oncorhynchus mykiss) in international waters of the central North Pacific Ocean (CNP; 1991–2009) and Gulf of Alaska (GOA; 1993–2002) were evaluated to identify potential drivers of steelhead productivity in the North Pacific. Stable isotopes of steelhead muscle tissue were assessed to corroborate the results of stomach content analysis. We found the composition of steelhead diets varied by ocean age group, region, and year. In both the GOA and CNP, gonatid squid (Berryteuthis anonychus) were the most influential component of steelhead diets, leading to higher prey energy densities and stomach fullness. Stomach contents during an exceptionally warm year in the GOA and CNP (1997) were characterized by high diversity of prey with low energy density, few squid, and a large amount of potentially toxic debris (e.g., plastic). Indicators of good diets (high proportions of squid and high prey energy density) were negatively correlated with abundance of wild populations of eastern Kamchatka pink salmon (O. gorbuscha) in the CNP. In conclusion, interannual variations in climate, abundance of squid, and density‐dependent interactions with highly‐abundant stocks of pink salmon were identified as potential key drivers of steelhead productivity in these ecosystems. Additional research in genetic stock identification is needed to link these potential drivers of productivity to individual populations.     

Understanding the impact of climate change on the oceanic circulation in the Chilean island ecoregions

1. The largest changes in the circulation of the South-eastern Pacific resulting from global warming are associated with the southward shift and intensification of the anticyclone and with coastal surface warming. Coastal upwelling is projected to be increase off central Chile, due to an increase in equatorward winds, although increased oceanic stratification and associated enhanced nearshore turbulence will yield an onshore deepening/flattening of the thermocline.
2. The overall increase in south-easterly trade winds of the South-eastern Pacific in a warmer climate are likely to increase the connectivity pattern between Juan Fernandez and Desventuradas islands, and along the Sala y Gomez ridge, through increasing wind-driven mean ocean currents.
3. Deoxygenation associated with the warmer temperatures and changes in ventilation are likely to modify marine habitat and the respiratory barriers of species in the seamounts located in the vicinity of the limits of the minimum oxygen zone.
4. In the South-eastern Pacific, the prevailing 2D understanding of the responses of marine life to climate change needs to be expanded to 3D approaches, integrating the vertical habitat compression of marine organisms as a result of ocean warming and deoxygenation, as climate velocities for temperature and oxygen have contrasting vertical and horizontal patterns.
5. There is a need for regional biogeochemical-coupled modelling studies dedicated to the Chilean islands in order to provide an integrated view of the impact of anthropogenic stressors (e.g. deoxygenation, increased stratification, and climate shift) at the scale required for addressing socio-ecological interactions.
6. A refined understanding of the large-scale biogeography and spatial dynamics of marine populations through experimentation with high-resolution regional ocean models is a prerequisite for scaling-up regional management planning and optimizing the conservation of interconnected marine ecosystems across large scales.

     

北太平洋鱿钓生产及资源利用

北太平洋鱿钓渔业经过多年发展目前已进入相对稳定的阶段,但中日政府签署渔业协定的生效对鱿钓生产影响很大.作者根据辽渔2000年生产情况对鱿钓生产形势作简单分析,并阐述一些渔场及资源利用等问题,以期对北太平洋鱿钓生产起指导作用.     

Long‐term variation in the abundance of Pacific herring (Clupea pallasii) from the Yellow Sea in the western North Pacific and its relation to climate over the past 590 years

A qualitative understanding of the long‐term variation in the population dynamics of Yellow Sea (YS) herring is particularly important for clarifying the evolutionary processes and driving mechanisms of the YS large marine ecosystem. Unfortunately, because of a lack of long‐term, continuous, and simultaneous monitoring data, the specific driving processes and mechanisms of climate effects on the population dynamics of YS herring remain largely unknown. In response to this scientific issue, we preliminarily propose the idea of reconstructing long‐term changes in YS herring abundance over the past 590 years (AD 1417–2004) based on historical documents and attempt to explore the impacts of climate on the population. Our results show that YS herring abundance maintained at a relatively high level from AD 1417 to 1870 (during the Little Ice Age); in contrast, the population declined significantly from AD 1870 to 2004 at different rates. In addition, we also found that there were strong relationships between the population abundance of YS herring and the Pacific decadal oscillation (PDO) and drought/flood cycles. We suggest that the fluctuations in YS herring abundance may be influenced by ocean–climatic circulation shifts throughout the North Pacific, especially the PDO.     

北太平洋小型中上层鱼类资源对气候–海洋变化的响应研究进展

小型中上层鱼类是北太平洋海域重要的渔业资源,具有生命周期短、生长速度快、高集群性等特点,其资源年间波动显著,且受气候-海洋变化的影响。本文围绕秋刀鱼（Coloabis saira）、鲣（Katsuwonus pelamis）、鲐（Scomber japonicus）、鳀（Engraulis japonious）、竹䇲鱼（Trachurus japonicus）、沙丁鱼（Sardinops sagax）6种主要的小型中上层鱼类,回顾了厄尔尼诺-南方涛动（El Niño/La Niña-southern oscillation,ENSO）、太平洋年代际振荡（the Pacific decadal oscillation,PDO）、黑潮-亲潮（Kuroshio-Oyashio,KR-OY）等关键气候-海洋指数的特点及对鱼类栖息地环境和资源变动的影响。概括了气候-海洋变化对小型中上层鱼类的洄游分布和资源丰度的直接影响过程,以及对亲体繁殖产卵、仔稚体成活率和资源量波动间接的滞后影响过程。建议：（1）在多种气候-海洋指数基础上添加种群动态过程、捕捞方式系数、自然死亡率等参数构建生物量动态模型,揭示气候-海洋变化对渔业资源量的影响过程;（2）结合北太平洋涛动（North Pacific oscillation,NPO）、北极涛动（Arctic oscillation,AO）、北太平洋环流振荡（North Pacific gyre oscillation,NPGO）等其他北太平洋主要气候,基于物理海洋模型及空间耦合水动力学模型研究大尺度海流、中尺度涡旋对小型中上层鱼类影响。     

Intercalibrating SCOR, NORPAC and bongo nets and the consequences for interpreting decadal-scale variation in zooplankton biomass in the Gulf of Alaska

The Canadian weathership time series of zooplankton wet weight biomass, collected at Ocean Station Papa in the Gulf of Alaska from 1956 to 1981, is one of the most comprehensive of its kind in marine science. In 1966, the sampling gear changed from a white North Pacific (NORPAC) net to a black Scientific Committee on Oceanic Research (SCOR) net and it was recently discovered that insufficient intercalibration samples were collected to understand how their sampling properties differed. A Canada‐GLOBEC project to redo the intercalibration of these net types and to understand how they relate to current sampling gear (bongo net) started in 1997. Seventy replicates of the three net types were collected in deep water in the Gulf of Alaska. The major finding is that all nets have similar sampling characteristics, whereas earlier reports indicated that NORPAC biomass values should be multiplied by a factor of 1.538 to be equivalent to the SCOR net. It now appears that this factor arose because flowmeters were not used in the original 1956–81 sampling (volume filtered was estimated from tow length × mouth area). A positive bias was introduced into the SCOR values because relatively more water passed through the SCOR net (undetected without a flow meter) than through the NORPAC net. This means that the unmetered NORPAC samples from 1956 to 1966 should not be adjusted and the unmetered SCOR values should be reduced by a factor that is related to wire angle. The general effect on the entire series is to lower the average biomass estimates, but more so for the early portion of the series than the later years.     

Biogeography of pelagic food webs in the North Pacific

The tufted puffin (Fratercula cirrhata) is a generalist seabird that breeds throughout the North Pacific and eats more than 75 different prey species. Using puffins as samplers, we characterized the geographic variability in pelagic food webs across the subarctic North Pacific from the composition of ~10,000 tufted puffin meals (~56,000 prey items) collected at 35 colonies in the Gulf of Alaska (GoA) and Aleutian Archipelago. Cluster analysis of diet species composition suggested three distinct forage fish communities: (i) in the northern GoA, multiple age‐classes of coastal and shelf residents such as capelin, sand lance and herring dominated the food web, (ii) in the western GoA to eastern Aleutians, the shelf community was dominated by transient age‐0 walleye pollock, and (iii) in the western Aleutians, shelf‐edge and mesopelagic forage species such as squid, lanternfish, and Atka mackerel were prevalent. Geographic patterns of abundance of capelin and sand lance in tufted puffin diets were corroborated by independent research fisheries and diets of piscivorous fish, indicating that puffin diets reflect the local abundance of forage species, not just selection of favored species. Generalized additive models showed that habitat characteristics predict, in a non‐linear fashion, forage species distribution and abundance across two large marine ecosystems. We conclude that major biogeographic patterns in forage fish distribution follow gradients in key habitat features, and puffin diets reflect those patterns.     

Turtles on the edge: movement of loggerhead turtles (Caretta caretta) along oceanic fronts, spanning longline fishing grounds in the central North Pacific, 1997–1998

Nine juvenile loggerhead sea turtles tracked during 1997 and 1998 in the central North Pacific by satellite telemetry all travelled westward, against prevailing currents, along two convergent fronts identified by satellite remotely sensed data on sea surface temperature (SST), chlorophyll and geostrophic currents. These fronts are characterized by gradients in sea surface height that produce an eastward geostrophic current, with gradients in surface chlorophyll and SST. Six of the turtles were associated with a front characterized by 17°C SST, surface chlorophyll of about 0.2 mg m^–3, and eastward geostrophic current of about 4 cm s^–1, while the other three turtles were associated with a front with 20°C SST, surface chlorophyll of about 0.1 mg m^–3, and eastward geostrophic flow of about 7 cm s^–1. These results appear to explain why incidental catch rates of loggerheads in the Hawaii longline fishery are highest when gear is set at 17°C and 20°C, SST. Further, from the seasonal distribution of longline effort relative to these fronts, it appears that the surface longline fishing ground lies largely between these two fronts during the first quarter and well to the south of the 17°C front, but including the 20°C front, in the second quarter. These findings suggest seasonal or area closures of the longline fishery that could be tested to reduce incidental catches of loggerheads. Finally, these results illustrate the insights which can be achieved by combining data on movement of pelagic animals with concurrent remotely sensed environmental data.     

北太平洋东部柔鱼群体角质颚生长特性分析

角质颚是头足类重要的硬组织,蕴含着丰富的生态信息。本文根据2010年5~6月和2012年5~7月我国鱿钓船在北太平洋海域(170°E~172°W、38°N~41°N)采集的柔鱼(Ommastrephes bartramii)样本,对柔鱼东部群体的角质颚形态特征进行分析,并结合利用耳石推测的柔鱼日龄建立其生长方程。主成分分析认为,上头盖长(UHL)、上脊突长(UCL)和上侧壁长(ULWL)为柔鱼上颚的主要形态参数,下喙长(LRL)、下喙宽(LRW)和下侧壁长(LLWL)为柔鱼下颚的主要形态参数。AIC(Akaike’s information criterion)准则认为,6项角质颚主要参数与日龄的关系均以自然对数建立的生长方程为最适。分析发现,上颚生长方程的系数均大于下颚,说明上颚的生长速度大于下颚,而喙部生长方程的系数相近且最小,说明喙部生长速度较慢;上下颚比较发现,上颚头盖脊突较下颚的生长快,而喙部和翼部的生长相似。     

北太平洋公海秋刀鱼生物学特性初步研究

根据2004年7～11月西北太平洋秋刀鱼探捕调查的生物学数据,通过统计回归方法分析了秋刀鱼的性腺成熟度,摄食等级,性比,叉长分布,叉长和体重、净重关系。结果为:性成熟度为Ⅱ期的占52．96％;摄食等级主要为2级和3级,占72．91％;性比接近1:1;体长范围为186～340mm,优势体长组为220～280mm;雌性的叉长略大于雄性;群体可能属于2个不同群体,生长参数大于3。     

Seasonal potential fishing ground prediction of neon flying squid (Ommastrephes bartramii) in the western and central North Pacific

We explored the seasonal potential fishing grounds of neon flying squid (Ommastrephes bartramii) in the western and central North Pacific using maximum entropy (MaxEnt) models fitted with squid fishery data as response and environmental factors from remotely sensed [sea surface temperature (SST), sea surface height (SSH), eddy kinetic energy (EKE), wind stress curl (WSC) and numerical model‐derived sea surface salinity (SSS)] covariates. The potential squid fishing grounds from January–February (winter) and June–July (summer) 2001–2004 were simulated separately and covered the near‐coast (winter) and offshore (summer) forage areas off the Kuroshio–Oyashio transition and subarctic frontal zones. The oceanographic conditions differed between regions and were regulated by the inherent seasonal variability and prevailing basin dynamics. The seasonal and spatial extents of potential squid fishing grounds were largely explained by SST (7–17°C in the winter and 11–18°C in the summer) and SSS (33.8–34.8 in the winter and 33.7–34.3 in the summer). These ocean properties are water mass tracers and define the boundaries of the North Pacific hydrographic provinces. Mesoscale variability in the upper ocean inferred from SSH and EKE were also influential to squid potential fishing grounds and are presumably linked to the augmented primary productivity from nutrient enhancement and entrainment of passive plankton. WSC, however, has the least model contribution to squid potential fishing habitat relative to the other environmental factors examined. Findings of this work underpin the importance of SST and SSS as robust predictors of the seasonal squid potential fishing grounds in the western and central North Pacific and highlight MaxEnt's potential for operational fishery application.