Spatio-temporal covariability in coho salmon (Oncorhynchus kisutch) survival,from California to southeast Alaska

One of the motivations of the GLOBEC Northeast Pacific program is to understand the apparent inverse relationship between the increase in salmon catches in the Gulf of Alaska and concurrent declines in the California Current System (CCS). We therefore used coded wire tag (CWT) data to examine the spatial and temporal patterns of covariability in the survival of hatchery coho salmon along the coast from California to southeast Alaska between release years 1980 and 2004. There is substantial covariability in coho salmon survival between neighboring regions along the coast, and there is clear evidence for increased covariability within two main groups – a northern and southern group. The dividing line between the groups lies approximately at the north end of Vancouver Island. However, CWT survivals do not support inverse covariability in hatchery coho salmon survival between southeast Alaska and the CCS over this 25 year time span. Instead, the hatchery coho survival in southeast Alaska is relatively uncorrelated with coho survival in the California Current System on inter-annual time scales. The 50% correlation and e-folding scales (distances at which magnitude of correlations decreases to 50% and e⁻¹ (32.8%), respectively) of pairwise correlations between individual hatcheries were 150 and 217 km, which are smaller than that reported for sockeye, pink, and chum salmon. The 50% correlation scale of coho salmon is also substantially smaller than those reported for upwelling indices and sea surface temperature. There are also periods of 5–10 years with high covariability between adjacent regions on the scale of hundreds of km, which may be of biological and physical significance.     

Linkages between Alaskan sockeye salmon abundance, growth at sea, and climate, 1955–2002

We tested the hypothesis that increased growth of salmon during early marine life contributed to greater survival and abundance of salmon following the 1976/1977 climate regime shift and that this, in turn, led to density-dependent reductions in growth during late marine stages. Annual measurements of Bristol Bay (Bering Sea) and Chignik (Gulf of Alaska) sockeye salmon scale growth from 1955 to 2002 were used as indices of body growth. During the first and second years at sea, growth of both stocks tended to be higher after the 1976–1977 climate shift, whereas growth during the third year and homeward migration was often below average. Multiple regression models indicated that return per spawner of Bristol Bay sockeye salmon and adult abundance of western and central Alaska sockeye salmon were positively correlated with growth during the first 2 years at sea and negatively correlated with growth during later life stages. After accounting for competition between Bristol Bay sockeye and Asian pink salmon, age-specific adult length of Bristol Bay salmon increased after the 1976–1977 regime shift, then decreased after the 1989 climate shift. Late marine growth and age-specific adult length of Bristol Bay salmon was exceptionally low after 1989, possibly reducing their reproductive potential. These findings support the hypothesis that greater marine growth during the first 2 years at sea contributed to greater salmon survival and abundance, which in turn led to density-dependent growth during later life stages when size-related mortality was likely lower. Our findings provide new evidence supporting the importance of bottom-up control in marine ecosystems and highlight the complex dynamics of species interactions that continually change as salmon grow and mature in the ocean.     

A critical size and period hypothesis to explain natural regulation of salmon abundance and the linkage to climate and climate change

We hypothesise that salmon year class strength is determined in two stages during the first year in the ocean. There is an early natural mortality that is mostly related to predation, which is followed by a physiologically-based mortality. Juvenile salmon that fail to reach a critical size by the end of their first marine summer do not survive the following winter. In this study we describe our initial tests of this critical size and critical period hypothesis using data from ocean surveys of juvenile salmon and from experimental feeding studies on coho. Conservative swept volume abundance estimates for juvenile coho, and possibly chinook, indicate that there is high mortality in fall and winter during their first year in the sea. Studies of otolith weight show that the length and otolith-weight relationship for young coho changes in the early fall of their first ocean year. Studies of growth and associated hormone levels in feeding studies show that slow growing juvenile coho are stunted and deficient in an insulin-like growth factor-I (IGF-I). Juvenile coho sampled in September had low IGF-I values, indicative of poor growth. The results of these studies provide evidence for the general hypothesis that growth-related mortality occurs late in the first marine year and may be important in determining the strength of the year class (brood year). The link between total mortality and climate could be operating via the availability of nutrients regulating the food supply and hence competition for food (i.e. bottom–up regulation).     

Abundance,distribution, and feeding patterns of juvenile coho salmon (Oncorhynchus kisutch) in the Juan de Fuca Eddy

The Juan de Fuca Eddy is a seasonal, counter-clockwise gyre off the mouth of the Strait of Juan de Fuca between Washington, USA and British Columbia, Canada that may provide favorable feeding habitat for juvenile coho salmon (Oncorhynchus kisutch) during their early marine existence. In late September 2002, physical and biological sampling was conducted along two transects of the eddy region. Surface rope trawling was conducted to capture juvenile salmon and other nekton, along with bongo and neuston net tows to examine potential mesozooplanktonic salmon prey. Presence of the Juan de Fuca Eddy was confirmed with vertical water profiles. In addition, nutrient and chlorophyll a concentrations collected from 3-m depth were within the range observed in previous studies within the eddy region. In the mesozooplankton community, euphausiids, chaetognaths, and decapod megalopae were common. In the diet of juvenile coho salmon, euphausiids and decapod megalopae were dominant by percent number, and larval and juvenile fish were dominant by percent weight. Feeding intensity (percent body weight) based on stomach contents was variable, but not significantly different among stations. To compare the Juan de Fuca Eddy region with an upwelling area, we sampled along a transect off La Push (LP), Washington, USA which is south of the eddy. The eddy region was found to be less productive than the LP transect. Nutrients were lower, chlorophyll a concentrations were higher, and zooplankton abundance was generally higher along the LP transect than in the eddy region. In addition, more juvenile coho salmon were captured from the LP transect than the eddy region. Prey items in stomachs of salmon from the LP transect were heterogeneous compared to those from the eddy region. Feeding intensity along the LP transect was slightly lower and more variable than in the eddy region, and differences in feeding intensity among LP stations were significant. In addition, feeding intensities among stations nested within regions were significantly different.     

Bioenergetic model estimates of interannual and spatial patterns in consumption demand and growth potential of juvenile pink salmon (Oncorhynchus gorbuscha) in the Gulf of Alaska

A bioenergetic model of juvenile pink salmon (Oncorhynchus gorbuscha) was used to estimate daily prey consumption and growth potential of four ocean habitats in the Gulf of Alaska during 2001 and 2002. Growth potential was not significantly higher in 2002 than in 2001 at an alpha level of 0.05 (P=0.073). Average differences in growth potential across habitats were minimal (slope habitat=0.844 g d⁻¹, shelf habitat=0.806 g d⁻¹, offshore habitat=0.820 g d⁻¹, and nearshore habitat=0.703 g d⁻¹) and not significantly different (P=0.630). Consumption demand differed significantly between hatchery and wild stocks (P=0.035) when examined within year due to the interaction between hatchery verses wild origin and year. However, the overall effect of origin across years was not significant (P=0.705) due to similar total amounts of prey consumed by all juvenile pink salmon in both study years. We anticipated that years in which ocean survival was high would have had high growth potential, but this relationship did not prove to be true. Therefore, modeled growth potential may not be useful as a tool for forecasting survival of Prince William Sound hatchery pink salmon stocks. Significant differences in consumption demand and a two-fold difference in nearshore abundance during 2001 of hatchery and wild pink salmon confirmed the existence of strong and variable interannual competition and the importance of the nearshore region as being a potential competitive bottleneck.     

Pilchard distribution in South African waters, 1983–1985

Seasonal movements of South African pilchard Sardinops ocellatus in the relatively abundant 1982/83 year-class are inferred by means of length frequency information from predator diet analyses and from commercial and research catches in various localities. Pilchard of approximately one year of age were most abundant in the vicinity of Algoa Bay on the south-eastern Cape coast in the summer of 1983/84. The pilchard length frequency distribution in gannet diet and research midwater trawl samples in this area provided a clear linkage, through the known juvenile growth rate, with fish of an average 6 months of age, which were abundant off the West Coast during May 1983. Pilchard in this year-class were subsequently found to be widely distributed over the Agulhas Bank, with a tendency for them to inhabit deeper water towards the shelf edge as they reached the age of first spawning (about 18 months). During 1985, a noticeable increase in the abundance of large, two-year-old and older pilchard in the diet of West Coast gannets and in West Coast commercial catches indicated a movement of 1982/83 year-class fish into that area. The changes in distribution of pilchard in this year-class are discussed in relation to seasonal differences in the marine environment off South Africa.     

Foregone harvests and neoliberal policies: Creating opportunities for rural,small-scale,community-based fisheries in southern Alaskan coastal villages

Neoliberal policies of effort limitation and privatization have reduced commercial salmon and other fishing opportunities available to the coastal, predominantly Alaska Native, villages of southern Alaska. However, there are a variety of circumstances, including the manner in which the current commercial fishery is prosecuted, that lead to surpluses of unharvested salmon, and potentially other species, available in certain areas. This paper will define the concept of “foregone harvests”, discuss the environmental and managerial conditions that lead to “foregone harvests” and describe the possibilities such conditions create for the development of small-scale, local and community-based fisheries. Case studies of possible Huna Tlingit (Hoonah) and Kaigani Haida (Hydaburg) salmon fisheries will be presented. Alternative arrangements of salmon fisheries and institutions in southeast Alaska are presented through case studies of the villages of Yakutat and Metlakatla. These examples demonstrate how such fisheries could be built on local and traditional knowledge, as well as currently used subsistence technologies resulting in new economic opportunities compatible with local cultural patterns and interests and buttressing local identities and commitments.     

Influence of the sea surface temperature conditions in the Pacific subarctic frontal zone on the pink salmon’s winter survival ability

Similar to other high-latitude ocean basins, the subarctic Pacific exhibits strong seasonal and inter-annual variations in the abiotic factors of the environment, which, in turn, strongly influence biological objects. One of the principal factors of this kind is the temperature regime. For our research, we chose pink salmon because more than 90% of its natural mortality occurs precisely during the wintering period. The lifetime of pink salmon is only one year, and the conditions of their populations reflect the thermal regime of the given year. The main wintering area of Asian pink salmon is the part of the subarctic frontal zone located south of the Aleutian Islands (43°–46°N). This region features sufficiently high wintertime concentrations of chlorophyll a and temperature conditions favorable for pink salmon wintering. The interannual temperature variability in the frontal zone is close to zero, and the width of the frontal zone may significantly change depending on the winter severity. In “milder” winters, the area of wintering extends, while, in “severe” winters, it is rather narrow, the forage base for fish decreases, they become more accessible for predators, and their survival rates sharply drop.     

Escaping the corporate net: Pragmatics of small boat direct marketing in the U.S. Salmon fishing industry of the Northeastern pacific

This article considers corporate power in the fishing industry of southeast Alaska and Puget Sound, Washington State, USA, as experienced by direct marketing salmon gillnet fishermen. Tracing the evolution of a small family-based fish business, this paper examines survival strategies of independent fishermen in a context of concentrated corporate power. Topics addressed include corporate domination of the fishing industry, “niche” alternatives to the commodity system, alliance with the farmers’ market movement, obstacles to direct sales and the critical role of family participation.     

Juvenile fish condition in estuarine nurseries along the Portuguese coast

Connectivity between estuarine fish nurseries and coastal adult habitats can be affected by variations in juvenile growth and survival. Condition indices are renowned proxies of juvenile nutritional status and growth rates and are valuable tools to assess habitat quality. Biochemical (RNA:DNA ratio) and morphometric (Fulton's condition factor K) condition indices were determined in juveniles of Solea solea, Solea senegalensis, Platichthys flesus, Diplodus vulgaris and Dicentrarchus labrax collected in putative nursery areas of nine estuaries along the Portuguese coast (Minho, Douro, Ria de Aveiro, Mondego, Tejo, Sado, Mira, Ria Formosa and Guadiana) in the Spring and Summer of two consecutive years (2005 and 2006) with distinct climatic characteristics. Individual condition showed significant variation amongst species. The combined use of both condition indices highlighted the low correlation between them and that RNA:DNA had a higher sensitivity. RNA:DNA varied between years but overall the site relative patterns in condition were maintained from one year to the other. Higher RNA:DNA values were found in Spring than in Summer in most species. Intra-estuarine variation also occurred in several cases. Species specific trends in the variability of condition amongst estuaries were highlighted. Some estuaries had higher juvenile condition for more than one species but results did not reveal an identical trend for all species and sites, hindering the hypotheses of one estuarine nursery promoting superior growth for all present species. Significant correlations were found between condition indices, juvenile densities and environmental variables (water temperature, salinity and depth) in the estuarine nurseries. These influenced juvenile nutritional condition and growth, contributing to the variability in estuarine nursery habitat quality. Management and conservation wise, interest in multi-species approaches is reinforced as assessments based on a single species may not reflect the overall nursery habitat quality.     

Genetic stock identification of immature chum salmon (<Emphasis Type="Italic">Oncorhynchus keta</Emphasis>) in the western Bering Sea, 2004

Genetic stock identification studies have been widely applied to Pacific salmon species to estimate stock composition of complex mixed-stock fisheries. In a September-October 2004 survey, 739 chum salmon (Oncorhynchus keta) specimens were collected from 23 stations in the western Bering Sea. We determined the genetic stock composition of immature chum salmon based on the previous mitochondria DNA baseline. Each regional estimate was computed based on the conditional maximum likelihood method using 1,000 bootstrap resampling and then pooled to the major regional groups: Korea - Japan - Primorie (KJP) / Russia (RU) / Northwest Alaska (NWA) / Alaska Peninsula - Southcentral Alaska - Southeast Alaska - British Columbia - Washington (ONA). The stock composition of immature chum salmon in the western Bering Sea was a mix of 0.424 KJP, 0.421 RU, 0.116 NWA, and 0.039 ONA stocks. During the study period, the contribution of Asian chum salmon stocks gradually changed from RU to KJP stock. In addition, North American populations from NWA and ONA were small but present near the vicinity of the Russian coast and the Commander Islands, suggesting that the study areas in the western Bering Sea were an important migration route for Pacific chum salmon originating both from Asia and North America during the months of September and October. These results make it possible to better understand the chum salmon stock composition of the mixed-stock fisheries in the western Bering Sea and the stock-specific distribution pattern of chum salmon on the high-seas.     

Abundance and distribution of pelagic piscivorous fishes in the Columbia River plume during spring/early summer 1998-2003: Relationship to oceanographic conditions, forage fishes, and juvenile salmonids

From 1998 to 2003, we observed large fluctuations in the abundance and distribution of four pelagic predatory (piscivorous) fishes off northern Oregon and southern Washington, USA. Fluctuations in predatory fish species composition and abundance were strongly linked to the date of the spring transition and to ocean temperatures. Predatory fishes, forage fishes, and juvenile salmonids had distinct spatial distributions, with predators distributed primarily offshore and forage fish and salmonids onshore, but this varied depending on ocean conditions. We suggest that predatory and forage fish distributions respond to ocean temperatures, predator/prey interactions, and possibly turbidity. A shift in ocean conditions in 1999 decreased overall predator fish abundance in the Columbia River plume, particularly for Pacific hake. Marine survival of juvenile salmon started to increase in 1999, and forage fish densities increased in 2000, lagging by one year.     

气候变化对鲑鱼丰富度和繁殖影响的研究进展

鲑鱼是人类重要的食品来源之一,具有巨大的经济价值。同时,鲑鱼资源通过输送营养物质对维持溪流和陆地生态系统的结构、功能和过程等有重要作用。而鲑鱼是对温度极为敏感的冷水性鱼类,对气候变化的反应尤为明显。作者通过文献综述法梳理相关研究,从气候变化引起的温度变化、淡水和海洋环境的变化以及鱼病传播4个方面探讨对鲑鱼丰富度和繁殖的影响,并提出研究展望。研究显示:温度变化对鲑鱼的产卵和迁徙有较大影响;溪流和河流流量的改变会影响鲑鱼的迁徙和幼年鲑鱼的存活数量;温度和二氧化碳浓度的变化使海洋食物供应减少,鲑鱼丰富度降低;水温的升高使病原体增加,鲑鱼死亡率增加。本研究成果可为鲑鱼种群应对气候变化的研究及管理提供一定的理论支持。     

Variability in scale growth rates of chum salmon (Oncorhynchus keta) in relation to climate changes in the late 1980s

Fish scales were used to investigate the interannual variability in chum salmon growth rates at specific ages in relation to climatic/environmental changes during the 1980s–1990s. Scales were obtained from adult salmon returning to the east coast of Korea between 1984 and 1998. Assuming proportionality between scale size increments and fish length, distances between scale annuli were regarded as the growth conditions in different habitat areas with respect to the life stages of chum salmon. In estuarine and coastal areas, growth rates of fingerling salmon were higher in the 1990s than in the 1980s. Zooplankton abundance off the east coast of Korea increased after the late 1980s, which may have provided favorable growth conditions for young salmon in the 1990s. Growth of juvenile chum salmon during the first summer (Okhotsk Sea) was relatively stable, and neither SST nor zooplankton biomass fluctuated significantly during the study period. However, in the Bering Sea, salmon growth rates between age-2 and age-4 (i.e. ocean-phase immature salmon) were higher in the 1980s than in the 1990s. Variability in salmon growth in the Bering Sea was correlated to zooplankton biomass. These results suggest that the climate regime shift of 1988/1989 in the subarctic North Pacific affected salmon growth mediated by changes of zooplankton biomass, revealing a bottom-up process.     

Stable isotope analysis of Pacific salmon: insight into trophic status and oceanographic conditions over the last 30 years

Food web interactions and the response of Pacific salmon to physical processes in the North Pacific Ocean over interannual and interdecadal timescales are explored using naturally occurring stable isotope ratios of carbon (¹³C/¹²C) and nitrogen (¹⁵N/¹⁴N). Stable isotope analyses of five species of sexually mature North Pacific salmon from Alaska (Oncorhynchus spp.) cluster into three groups: chinook salmon (O. tshawytscha) have the highest values, followed by coho (O. kisutch), with chum (O. keta), sockeye (O. nerka), and pink (O. gorbuscha) together having the lowest values. Although detailed isotopic data on salmon prey are lacking, there are limited data on relevant prey items from areas in which they are found in high abundance. These data suggest that the characteristics of the sockeye, pink and chum we have analyzed are compatible with their diets including open ocean squid and zooplankton, which are in general agreement with stomach content analyses. Isotope relationships between muscle and scale show consistent relationships for both δ¹³C (R²=0.98) and δ¹⁵N (R²=0.90). Thus, scales, which have been routinely archived for many systems, can be used for retrospective analyses. Archived sockeye salmon scales spanning 1966–1999 from Red Lake, Kodiak Island, Alaska were analyzed for their stable isotope ratios of carbon and nitrogen. The δ¹⁵N record displays a decreasing trend of ˜3‰ from 1969–1982 and an increasing trend of ˜3‰ from 1982–1992, while the variations in δ¹³C are relatively minor. These trends may result from factors such as shifts in trophic level of feeding and/or feeding location, or may originate at the base of the food web via changes in processes such as nutrient cycling or primary productivity. Detailed studies on prey isotopic variability and its controls are needed to distinguish between these factors, and thus to improve the use of stable isotope analysis as a tool to learn more about present and past ecosystem change in the North Pacific and its relation to climatic change.     

Recruitment of shrimp (Pandalus borealis) in the Barents Sea related to spawning stock and environment

The shrimp spawn in autumn, and the females carry their eggs as out roe until spring when the larvae hatch. Within a period of 2 months the shrimp larvae settle to the bottom. It has been claimed that the year-class strength probably is determined during the larval phase. Today's assessment and forecast of the shrimp stock productivity and potential fishing yields are weak. This is partly due to poor knowledge on population dynamics from hatching until the shrimp are caught in the fishery at the age of 3 or 4 years. We, therefore, here identify the most important abiotic and biotic factors that affect recruitment in addition to spawning stock biomass. Since 1995, a net attached to the underbelly of the survey trawl used at the annual cruise in the Barents Sea has caught juvenile shrimp. The abundance of settled shrimp larvae varies in time and space. The recruitment to the fishery has been quite stable with the exception of the 1996 year-class, which was observed as 1-year-olds but has not been registered since. The temporal pattern of the three youngest year-classes is studied in relation to abiotic factors such as sea temperature, ice index and North Atlantic Oscillation, as well as biotic factors such as spawning stock biomass and presence of copepods, euphausiids and predating cod. Recruitment indices and factors identified by the Spearmann correlation to be significantly correlated with recruitment were used as input in a principal component analysis (PCA) and a generalized additive model (GAM) was applied. Abundance of 1-year-old shrimp is positively correlated to spawning stock biomass the previous year and to temperature of the previous winter, and negatively correlated with the number of 1-year-old cod. Two-year-old shrimp show significant correlation with temperature, whereas there is a strong negative correlation with euphausiids. Three-year-old shrimp are significantly correlated with the number of 2-year-old shrimp the previous year but negatively correlated to temperature at sampling time. This is probably due to less overlap with the main predator cod when cold. Ricker functions indicate an increased density-dependent mortality with age. When predicting the recruitment of shrimp to the fishery, the spawning stock biomass, the abundance of cod and euphausiids, as well as the temperature should be included.     

Metabolic conversion of cyclohexane by Pacific salmon microsomal preparations

Hydrocarbons are being introduced into the marine environment from a variety of sources including combustion processes, crude oil spills, fuel oil spills, and controlled disposal such as processed ballast water. Even in the relatively clean waters of Alaska hydrocarbons are being released at an alarming rate. The purpose of this study was to determine the optimum conditions for the metabolism of a representative hydrocarbon by Coho Salmon Oncorhynchus kisutch liver microsomes. The product of cyclohexane metabolism in the salmon microsomal system was identified by gas chromatography-mass spectrometry as cyclohexanol. Conditions of the microsome incubation were varied systematically to determine the optimum temperature, pH, and ionic strength for cyclohexanol production. Cyclohexanol was quantified by capillary column gas chromatography. Maximum cyclohexanol formation was achieved at 20°C, a pH of 8·0–8·5 and an ionic strength of 0·026. A linear rate of cyclohexanol formation is seen from 0–60 min of incubation and there is an apparent decrease in the rate from 60–90 min. Poor stability of the microsomal preparation from the species studied was also identified and several stability studies have been undertaken using cyclohexane metabolism as a monitor.     

Pacific Basin climate variability and patterns of Northeast Pacific marine fish production

A review of oceanographic and climate data from the North Pacific and Bering Sea has revealed climate events that occur on two principal time scales: a) 2–7 years (i.e. El Niño Southern Oscillation, ENSO), and b) inter-decadal (i.e. Pacific Decadal Oscillation, PDO). The timing of ENSO events and of related oceanic changes at higher latitudes were examined. The frequency of ENSO was high in the 1980s. Evidence of ENSO forcing on ocean conditions in the North Pacific (Niño North conditions) showed ENSO events were more frequently observed along the West Coast than in the western Gulf of Alaska (GOA) and Eastern Bering Sea (EBS). Time series of catches for 30 region/species groups of salmon, and recruitment data for 29 groundfish and 5 non-salmonid pelagic species, were examined for evidence of a statistical relationship with any of the time scales associated with Niño North conditions or the PDO. Some flatfish stocks exhibited high autocorrelation in recruitment coupled with a significant step in recruitment in 1977 suggesting a relationship between PDO forcing and recruitment success. Five of the dominant gadid stocks (EBS and GOA Pacific cod, Pacific hake and EBS and GOA walleye pollock) exhibited low autocorrelation in recruitment. Of these, Pacific hake, GOA walleye pollock and GOA Pacific cod exhibited significantly higher incidence of strong year classes in years associated with Niño North conditions. These findings suggest that the PDO and ENSO may play an important role in governing year-class strength of several Northeast Pacific marine fish stocks.     

Recruitment variability in dab (Limanda limanda) in the southeastern North Sea

Data from three annual surveys, covering inshore and offshore waters of the southeastern North Sea, were analysed to study recruitment variability in dab (Limanda limanda) over the period 1978–1997. Geometric mean abundance of 0- to 5-group dab was estimated using general linear models. Juvenile dab (0- and 1-group) were found over the entire area, from inside the estuaries to 50 m depth offshore. Environmental conditions (water temperature, wind stress, turbidity) affected the catch rates. The potential errors in the estimates of year-class strength, caused by differences in catchability, are discussed. The inter-annual pattern of year-class strength appeared to be established between ages 1 and 2, suggesting that factors determining recruitment are not restricted to the pelagic early life phase only, but also operate during the demersal juvenile phase. Recruitment variability at age 2 was in the order of 50–60% and appears to be equal to, or lower than, recruitment variability in plaice and sole. These results contradict expectations based on the concentration hypothesis, which states that the degree of variation in recruitment is inversely related to the degree of concentration during early life phases.