Marine Environmental Variables Research Articles

Consideration of ocean conditions in the management of salmon

An ecologically based conceptual foundation is presented as a way to incorporate environmental variability in salmon management. The argument addresses the problem of accommodating marine environment variability through actions in freshwater. We argue for an approach that considers marine and freshwater environments as integral components of a larger salmonid ecosystem. This contrasts with previous propositions that either relied heavily on technological fixes in the freshwater environment or questioned the value of any recovery effort designed to withstand overwhelming ocean forces. Salmon management requires a more holistic approach incorporating modern understanding of the salmonid ecosystem and its variability. We suggest two strategies. The first calls for deliberate improvement of estuarine and nearshore ocean conditions through regulation of upstream flows, river operations, hatchery production, and other actions. The second calls for improving the resilience of salmon to a variable environment. This requires relaxing anthropogenic factors that hinder the natural range of salmon life history diversity within and between populations, a survival mechanism that evolved in response to changing conditions. These strategies recognize that although the ocean primarily determines overall salmon abundance, management actions, particularly in freshwater, are critical to the ability of salmon to cope with a variable ocean environment.

Long‐term changes in the sea‐age at maturity and seasonal time of return of salmon, Salmo salar L., to Scottish rivers

Abstract Using catch data, changes in salmon, Salmo salar L., sea‐age and seasonal return time were compared between several Scottish east coast rivers over the last 150–200 years. Parallel long‐term trends were found, suggesting common influences affecting salmon at sea. Long‐term associations with marine environmental factors were investigated by literature review and comparisons with an index of Icelandic sea‐ice abundance. Apparent associations were shown to exist since about 1900, although the cause was not demonstrated. However, over a longer timescale, the same associations were not apparent. Unique gradual marine changes since 1900 may have resulted in perceptible associations with salmon data which may otherwise be imperceptible when short‐term marine environmental variability is greater than long‐term variability. Marine factors must affect salmon, but the complexity of the marine environment and controls on age at maturity and time of return mean that a retrospective analysis cannot be expected to identify the causal factors.

Criteria for the evaluation of alternative environmental monitoring variables: Theory and an application using winter flounder (Pleuronectes americanus) and Dover sole (Microstomus pacificus)

The design of environmental monitoring programs is frequently hampered by a lack of objective, quantitative criteria for evaluating alternative monitoring variables. In this paper we describe two such criteria, which we call samples required - the number of samples required to detect a given change in value - and information imparted - the amount of environmental information revealed by the monitoring variable. We then use these criteria to evaluate fin erosion in winter flounder (Pleuronectes americanus) and Dover sole (Microstomus pacificus) as marine environmental monitoring variables. Two methods for determining the samples required use contaminated and reference areas to estimate the sample statistics of a hypothetical impacted population. The first method is based on the overall difference in the proportions of diseased fish in the reference and hypothetical populations. The second treats the proportion of diseased fish in individual trawls as the variate and determines the samples required based on the mean and variance of the reference and contaminated populations. We use both methods to predict the number of trawls needed to detect an increase of 200% in fin erosion in the reference population. The first method had greater statistical power but assumes spatially homogeneous populations. The second method accounts for environmental patchiness. For Dover sole it predicted 1661 trawls would be needed to detect the 200% increase. An estuarine winter flounder population would require 74 trawls, and an oceanic winter flounder population would require 142.5 trawls. It appears that fin erosion in winter flounder may be a useful indicator of environmental contamination, but several stipulations apply. Migration may inflate the number of diseased fish observed in the reference population, and a more detailed etiology of the disease is required, including an understanding of what contaminants are responsible for manifestation of the disease.

Does History Have a Future? Forecasting Climate Change Effects on Fisheries by Analogy

Abstract Fisheries represent an important aspect of economic, social, political, and cultural life in developed as well as developing societies. The relationship between biological productivity in the marine environment and climate variability and change has not been adequately addressed. There are many instances in recent times in which climate-related environmental stress (or analogies to such stress) combined to varying degrees with current fisheries management practices to bring about adverse changes in biological productivity. Changes in sea surface temperature, for example, can cause a reduction in biomass or a shift in the location of fish stocks, creating local, national, and international political, economic, and social problems. Assessing societal responses to recent instances of decline in specific fisheries can serve to identify weaknesses as well as strengths that may exist in society's ability to cope with anomalies in biological productivity in the marine environment. Important fisheries fr...

Aspects of marine environmental variability near Cape Town, 1960–1985

Time-series of atmospheric pressure, winds, sea surface temperature, sea level and the Southern Oscillation Index are analysed in order to document aspects of marine environmental variability of and to provide suitable environmental indices for the nearshore southern Benguela system. The circannual cycle dominated, but a high degree of month-to-month and interannual variability was evident. Two contrasting environmental scenarios are postulated, representing extended summer or winter conditions respectively and probably related to decadal changes in the mean position of the South Atlantic Anticyclone. Principal components analysis pointed to possible teleconnections between the Pacific El Nino and the associated Southern Oscillation, and local environmental conditions.