Quantifying the Ocean, Freshwater and Human Effects on Year-to-Year Variability of One-Sea-Winter Atlantic Salmon Angled in Multiple Norwegian Rivers

Many Atlantic salmon, Salmo salar, populations are decreasing throughout the species' distributional range probably due to several factors acting in concert. A number of studies have documented the influence of freshwater and ocean conditions, climate variability and human impacts resulting from impoundment and aquaculture. However, most previous research has focused on analyzing single or only a few populations, and quantified isolated effects rather than handling multiple factors in conjunction. By using a multi-river mixed-effects model we estimated the effects of oceanic and river conditions, as well as human impacts, on year-to-year and between-river variability across 60 time series of recreational catch of one-sea-winter salmon (grilse) from Norwegian rivers over 29 years (1979–2007). Warm coastal temperatures at the time of smolt entrance into the sea and increased water discharge during upstream migration of mature fish were associated with higher rod catches of grilse. When hydropower stations were present in the course of the river systems the strength of the relationship with runoff was reduced. Catches of grilse in the river increased significantly following the reduction of the harvesting of this life-stage at sea. However, an average decreasing temporal trend was still detected and appeared to be stronger in the presence of salmon farms on the migration route of smolts in coastal/fjord areas. These results suggest that both ocean and freshwater conditions in conjunction with various human impacts contribute to shape interannual fluctuations and between-river variability of wild Atlantic salmon in Norwegian rivers. Current global change altering coastal temperature and water flow patterns might have implications for future grilse catches, moreover, positioning of aquaculture facilities as well as the implementation of hydropower schemes or other encroachments should be made with care when implementing management actions and searching for solutions to conserve this species

Start-stop practice in small Norwegian hydropower plants

Start-stop practice was analysed in 256 Norwegian hydropower plants in conjunction to a set of characteristics. The plants were on grid 2005-20014, and production data from 2015. Number of starts were counted for each plant finding a higher number in Kaplan turbines than in Francis and Pelton. Number of starts was not dependent on having a license to practice start-stop, and were related to the annual mean river discharge being negative for Francis, dome-shaped for Pelton, and no association for Kaplan

Start-stop practice in small Norwegian hydropower plants

Start-stop practice was analysed in 256 Norwegian hydropower plants in conjunction to a set of characteristics. The plants were on grid 2005 - 2014, and production data from 2015. Number of starts were counted for each plant finding a higher number in Kaplan turbines than in Francis and Pelton. Number of starts was not dependent on having a license to practice start-stop, and were related to the annual mean river discharge being negative for Francis, dome-shaped for Pelton, and no association for Kaplan

Temporal and spatial variation in recreational catches of anadromous brown trout, Salmo trutta, in Norwegian rivers

15 pages, 1 table, 5 figuresOverall, it has been shown that production of diadromous fishes is declining within the North Atlantic basin reaching the lowest levels in recent years compared to their historic baselines. However, these decreases in abundance, ascribed to numerous factors, are species specific and might differ across each species’ distributional range. Here we used recreational angling catch data for anadromous brown trout Salmo trutta in multiple Norwegian rivers having relatively high annual reported catches to elucidate its spatio-temporal patterns since the late 1960s. Rivers lacking or having very low annual catch reports for various reasons were not included. The catches have increased at a rate of ~15% per decade though trends varied geographically with larger increases at northern latitudes and decreases at more southern latitudes. Larger catches were obtained at elevated levels of runoff during summer and early autumn, and at positive NAO phase during the year preceding the catch. Additionally, higher average catch and more pronounced increasing temporal trends in catches were obtained in larger rivers with shallower slopes, respectively. Furthermore, stronger relationships with runoff occurred in steeper rivers. Other factors such as Gyrodactylosis or fish farming seemed not to have detectable signals in the overall pattern of brown trout catches.This study is part of the Norwegian Research Council Project no 183989/S30. J.O. acknowledges additional funding from the Norwegian Water Resources and Energy Directorate (NVE), and support by a ‘Junta para la Ampliación de Estudios’ fellowship (JAE-Doc programme 2011) from the CSIC and ESF.Peer reviewe

ATLANTIC SALMON VARIABILITY: THE EFFECTS OF OCEAN, FRESHWATER AND HUMAN IMPACTS USING MULTIPLE TIME-SERIES OF ROD CATCHES FROM NORWEGIAN AND SCOTTISH RIVERS

participantAtlantic salmon (Salmo salar) fishing is one of the most important recreational fisheries in both Norway and Scotland and it has become an important factor in outdoor activities, with salmon angling estimated annual value to be approximately 1 billion NOK in Norway and £70 million in Scotland. The Atlantic salmon is a charismatic anadromous fish utilizing freshwater habitats for spawning and early development, and marine habitats for its main somatic growth. This species is fairly long-lived and is exposed to a large number of human encroachments both in freshwaters and in the sea. It has experienced strong declines worldwide during the last century, although many viable populations remain in the central and northern parts of the species' range. The largest component of natural mortality in the marine environment occurs during the first year at sea, indeed, survival has often been associated with sea surface temperature, which presumably modulates growth rates and controls recruitment. Moreover, yearly fluctuations of one-sea-winter fish are related with sea temperature. Furthermore, the current ocean warming in the foraging areas contributes to delay maturation and decreases growth conditions. In addition, local extinction or strong reductions in production have been partly attributed to acidification and other kinds of pollution, damming, exotic parasites and the effects of increased aquaculture. Understanding the complexity on how within and among river factors affect the dynamics of Atlantic salmon populations will improve our ability to manage the wild resource effectively in the face of current changes in environmental trends

Basin-scale phenology and effects of climate variability on global timing of initial seaward migration of Atlantic salmon (Salmo salar)

Migrations between different habitats are key events in the lives of many organisms. Such movements involve annually recurring travel over long distances usually triggered by seasonal changes in the environment. Often, the migration is associated with travel to or from reproduction areas to regions of growth. Young anadromous Atlantic salmon (Salmo salar) emigrate from freshwater nursery areas during spring and early summer to feed and grow in the North Atlantic Ocean. The transition from the freshwater (parr') stage to the migratory stage where they descend streams and enter salt water (smolt') is characterized by morphological, physiological and behavioural changes where the timing of this parr-smolt transition is cued by photoperiod and water temperature. Environmental conditions in the freshwater habitat control the downstream migration and contribute to within- and among-river variation in migratory timing. Moreover, the timing of the freshwater emigration has likely evolved to meet environmental conditions in the ocean as these affect growth and survival of the post-smolts. Using generalized additive mixed-effects modelling, we analysed spatio-temporal variations in the dates of downstream smolt migration in 67 rivers throughout the North Atlantic during the last five decades and found that migrations were earlier in populations in the east than the west. After accounting for this spatial effect, the initiation of the downstream migration among rivers was positively associated with freshwater temperatures, up to about 10 degrees C and levelling off at higher values, and with sea-surface temperatures. Earlier migration occurred when river discharge levels were low but increasing. On average, the initiation of the smolt seaward migration has occurred 2.5days earlier per decade throughout the basin of the North Atlantic. This shift in phenology matches changes in air, river, and ocean temperatures, suggesting that Atlantic salmon emigration is responding to the current global climate changes

Global Climate

In 2021, both social and economic activities began to return towards the levels preceding the COVID-19 pandemic for some parts of the globe, with others still experiencing restrictions. Meanwhile, the climate has continued to respond to the ongoing increase in greenhouse gases and resulting warming. La Niña, a phenomenon which tends to depress global temperatures while changing rainfall patterns in many regions, prevailed for all but two months of the year. Despite this, 2021 was one of the six-warmest years on record as measured by global mean surface temperature with an anomaly of between +0.21° and +0.28°C above the 1991–2020 climatology. Lake surface temperatures were their highest on record during 2021. The number of warm days over land also reached a new record high. Exceptional heat waves struck the Pacific Coast of North America, leading to a new Canadian maximum temperature of 49.6°C at Lytton, British Columbia, on 29 June, breaking the previous national record by over 4°C. In Death Valley, California, the peak temperature reached 54.4°C on 9 July, equaling the temperature measured in 2020, and the highest temperature recorded anywhere on the globe since at least the 1930s. Over the Mediterranean, a provisional new European record of 48.8°C was set in Sicily on 11 August. In the atmosphere, the annual mean tropospheric temperature was among the 10 highest on record, while the stratosphere continued to cool. While La Niña was present except for June and July, likely influencing Australia’s coolest year since 2012 and wettest since 2016, other modes of variability played important roles. A negative Indian Ocean dipole event became established during July, associated with a warmer east and cooler west Indian Ocean. Northern Hemisphere winters were affected by a negative phase of the North Atlantic Oscillation at both the beginning and end of 2021. In the Southern Hemisphere, a very strong positive Southern Annular Mode (also known as the Antarctic Oscillation) contributed to New Zealand’s record warm year and to very cold temperatures over Antarctica. Land surface winds continued a slow reversal from the multi-decadal stilling, and over the ocean wind speeds were at their highest in almost a decade. La Niña conditions had a clear influence on the regional patterns of many hydrological variables. Surface specific humidity and total column water vapor over land and ocean were higher than average in almost all datasets. Relative humidity over land reached record or near-record low saturation depending on the dataset, but with mixed signals over the ocean. Satellite measurements showed that 2021 was the third cloudiest in the 19-year record. The story for precipitation was mixed, with just below-average mean precipitation falling over land and below-average mean precipitation falling over the ocean, while extreme precipitation was generally more frequent, but less intense, than average. Differences between means and extremes can be due to several factors, including using different indices, observing periods, climatological base reference periods, and levels of spatial completeness. The sharp increase in global drought area that began in mid-2019 continued in 2021, reaching a peak in August with 32% of global land area experiencing moderate or worse drought, and declining slightly thereafter. Arctic permafrost temperatures continued to rise, reaching record values at many sites, and the thickness of the layer which seasonally thaws and freezes also increased over 2020 values in a number of regions. It was the 34th-consecutive year of mass balance loss for alpine glaciers in mountainous regions, with glaciers on average 25 m thinner than in the late 1970s. And the duration of lake ice in the Northern Hemisphere was the fourth lowest in situ record dating back to 1991. The atmospheric concentrations of the major long-lived greenhouse gases, CO2, CH4, and N2O, all reached levels not seen in at least the last million years and grew at near-record rates in 2021. La Niña conditions did not appear to have any appreciable impact on their growth rates. The growth rate for CH4, of 17 ppb yr−1, was similar to that for 2020 and set yet another record, although the causes for this post-2019 acceleration are unknown presently. Overall, CO2 growth continues to dominate the increase in global radiative forcing, which increased from 3.19 to 3.23 W m−2 (watts per square meter) during the year. In 2021, stratospheric ozone did not exhibit large negative anomalies, especially near the poles, unlike 2020, where large ozone depletions appeared, mainly from dynamical effects. The positive impact of reductions in emissions of ozone depleting substances can be seen most clearly in the upper stratosphere, where such dynamical effects are less pronounced. It was the fourth-lowest fire year since global records began in 2003, though extreme regional fire activity was again seen in North America and also in Siberia; as in 2020, the effects of wildfires in these two regions led to locally large regional positive anomalies in tropospheric aerosol and carbon monoxide abundance. Vegetation is responding to the higher global mean temperatures, with the satellite-derived measures for the Northern Hemisphere for 2021 rated among the earliest starts of the growing season and the latest end of the season on record. The first bloom date for cherry trees in Kyoto, Japan, broke a 600-year record set in 1409. This year we welcome a sidebar on the global distribution of lightning, which has been recently declared an essential climate variable (ECV) by the Global Climate Observing System (GCOS). Time series and anomaly maps from many of the variables described in this chapter can be found in Plates 1.1 and 2.1. As with other chapters, many of the sections have moved from the previous 1981–2010 to the new 1991–2020 climatological reference period, in line with WMO recommendations (see Chapter 1). This is not possible for all datasets, as it is dependent on their length of record or legacy processing methods. While anomalies from the new climatology period are not so easily comparable with previous editions of this report, they more clearly highlight deviations from more recent conditions