Demographic changes in Chinook salmon across the Northeast Pacific Ocean (original) (raw)
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Changes in Size and Age of Chinook Salmon Oncorhynchus tshawytscha Returning to Alaska
PloS one, 2015
The average sizes of Pacific salmon have declined in some areas in the Northeast Pacific over the past few decades, but the extent and geographic distribution of these declines in Alaska is uncertain. Here, we used regression analyses to quantify decadal trends in length and age at maturity in ten datasets from commercial harvests, weirs, and spawner abundance surveys of Chinook salmon Oncorhynchus tshawytscha throughout Alaska. We found that on average these fish have become smaller over the past 30 years (~6 generations), because of a decline in the predominant age at maturity and because of a decrease in age-specific length. The proportion of older and larger 4-ocean age fish in the population declined significantly (P < 0.05) in all stocks examined by return year or brood year. Our analyses also indicated that the age-specific lengths of 4-ocean fish (9 of 10 stocks) and of 3-ocean fish (5 of 10 stocks) have declined significantly (P < 0.05). Size-selective harvest may be ...
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The abundance of many Chinook salmon ( Oncorhynchus tshawytscha) stocks has declined despite reductions in harvest. We used state-space models parameterized with data from 57 Chinook salmon indicator stocks, ranging from coastal Oregon to southeast Alaska, to quantify long-term (since 1972 release year) changes in juvenile marine survival rate and mean age-at-maturity, as well as identify stock groupings with coherent dynamics. We found that juvenile marine distribution—rather than freshwater life history, run timing, or adult marine distribution—was the best predictor of trends in both survival and age. Only subyearling stocks that enter the Strait of Georgia showed evidence of transitioning to a low juvenile survival period, other groupings exhibited low and stable or cyclical patterns in survival. Conversely, declines in mean age-at-maturity were widespread and do not appear to have stabilized, suggesting that future declines in Chinook salmon population productivity may be influ...
Climate , Growth and Population Dynamics of Yukon River Chinook Salmon
2009
Harvests of Yukon Chinook salmon increased in the mid-1970s, then declined during 1998 to 2007 in response to fewer returning salmon. We examined annual growth of age-1.3 and age-1.4 Yukon Chinook salmon scales, 1965–2004, and tested the hypothesis that shifts in Chinook salmon abundance were related to annual growth at sea. Annual scale growth trends were not significantly correlated with salmon abundance indices, sea surface temperature, or climate indices, although growth during the first year at sea appeared to have been affected by the 1977 and 1989 ocean regime shifts. Chinook salmon scale growth was dependent on growth during the previous year, a factor that may have confounded detection of relationships among growth, environmental conditions, and abundance. Scale growth during the second year at sea was greater in oddnumbered years compared with even-numbered years, leading to greater adult length of age-1.3 salmon in oddnumbered years. The alternating-year pattern in Chinoo...
Conservation …, 2006
The viability of populations is influenced by driving forces such as density dependence and climate variability, but most population viability analyses (PVAs) ignore these factors because of data limitations. Additionally, simplified PVAs produce limited measures of population viability such as annual population growth rate ( λ) or extinction risk. Here we developed a "mechanistic" PVA of threatened Chinook salmon (Oncorhynchus tshawytscha) in which, based on 40 years of detailed data, we related freshwater recruitment of juveniles to density of spawners, and third-year survival in the ocean to monthly indices of broad-scale ocean and climate conditions. Including climate variability in the model produced important effects: estimated population viability was very sensitive to assumptions of future climate conditions and the autocorrelation contained in the climate signal increased mean population abundance while increasing probability of quasi extinction. Because of the presence of density dependence in the model, however, we could not distinguish among alternative climate scenarios through mean λ values, emphasizing the importance of considering multiple measures to elucidate population viability. Our sensitivity analyses demonstrated that the importance of particular parameters varied across models and depended on which viability measure was the response variable. The density-dependent parameter associated with freshwater recruitment was consistently the most important, regardless of viability measure, suggesting that increasing juvenile carrying capacity is important for recovery.
Evolution of age and length at maturation of Alaskan salmon under size-selective harvest
Evolutionary applications, 2014
Spatial and temporal trends and variation in life-history traits, including age and length at maturation, can be influenced by environmental and anthropogenic processes, including size-selective exploitation. Spawning adults in many wild Alaskan sockeye salmon populations have become shorter at a given age over the past half-century, but their age composition has not changed. These fish have been exploited by a gillnet fishery since the late 1800s that has tended to remove the larger fish. Using a rare, long-term dataset, we estimated probabilistic maturation reaction norms (PMRNs) for males and females in nine populations in two basins and correlated these changes with fishery size selection and intensity to determine whether such selection contributed to microevolutionary changes in maturation length. PMRN midpoints decreased in six of nine populations for both sexes, consistent with the harvest. These results support the hypothesis that environmental changes in the ocean (likely ...
Ecology, 2010
We empirically assess the relationship between population growth rate (k, a parameter central to ecology) and effective population size (N e , a key parameter in evolutionary biology). Recent theoretical and numerical studies indicate that in semelparous species with variable age at maturity (such as Pacific salmon, many monocarpic plants, and various other species), differences in mean reproductive success among individuals reproducing in different years leads to variation in k, and this in turn can reduce N e . However, this phenomenon has received little empirical evaluation. We examined time series of abundance data for 56 populations of chinook salmon (Onchorhynchus tshawytscha) from the northwestern United States and compared N e (calculated from demographic data) with the total number of spawners each generation (N T ). Important results include: (1) The mean multigenerational ratioÑ e /Ñ T was 0.64 (median ¼ 0.67), indicating that annual variation in k reduces effective population size in chinook salmon by an average of ;35%. These reductions are independent of, and in addition to, factors that reduce N e within individual cohorts (uneven sex ratio and greater-than-random variance in reproductive success). (2) The coefficient of variation of k was the most important factor associated with reductions in N e , explaining up to two-thirds of the variance inÑ e /Ñ T . (3) Within individual generations, N e was lower when there was a negative correlation between annual N i and k, i.e., when relatively few breeders produced relatively high numbers of offspring. Our results thus highlight an important and little-studied eco-evolutionary trade-off: density-dependent compensation has generally favorable ecological consequences (promoting stability and long-term viability) but incurs an evolutionary cost (reducing N e because a few individuals make a disproportionate genetic contribution). (4) For chinook salmon,N eH (an estimator based on the harmonic mean number of breeders per year) is generally a good proxy for true N e and requires much less data to calculate.
Fish and Fisheries, 2019
Successful management of wildlife involves an understanding of fluctuations in abundance, survival, productivity, and body size or condition. Demographic metrics are shaped by a wide range of factors related to environmental conditions, interactions with humans and population dynamics related to density, interactions with other species and other factors. Multidecadal, accurate, species-specific accounting of these metrics enables managers to compare them to environmental and anthropogenic conditions to accurately forecast future abundance and viability (