3. Collect
Sources of environmental data
Users of this web site who are interested in understanding mechanisms behind changes in monitored salmon variables also need to have data on physical and biological factors that affect salmon. Knowledge of mechanisms would help identify appropriate management actions to reduce detrimental impacts on salmon. However, as noted in the section, "Causal mechanisms: Basic questions", definitive conclusions about causes of particular observed changes in salmon are not generally possible because aquatic systems that contain salmon are subject to disturbances that are caused by many simultaneously acting sources. Those sources include ecological dynamics of predators and prey of salmon, short- and long-term weather/climate-driven oceanographic processes, and human-derived changes in salmon habitats that affect growth and survival of spawners, fry, smolts, and returning adults. Thus, at best in ideal circumstances, we can estimate the relative importance to salmon of those different sources of change. However, to do so, reliable and usually extensive data are required on indicators that reflect those postulated mechanisms. Such indicators include physical and biological variables in both freshwater and marine environments of salmon.
For example, depending on the salmon species and location, many decades of research show that freshwater conditions that affect salmon include summer-low-flows, area of spawning gravels, silt load in those gravels, extreme water temperatures in winter and summer, and density of predators of juvenile salmon, among other factors. All of these are known to affect survival rate, abundance, and/or spatial distribution of salmon at various life stages in fresh water (Knudsen and Michael 2009).
Analogous indicators of the marine environment are also needed for exploring hypotheses about causes of changes in salmon. Such indicators that have been well-documented to affect salmon growth, survival rates, and/or spatial distribution include early ocean sea-surface temperature, strengths and directions of ocean currents, timing of the spring transition, abundance of predators such as squid and marine mammals, food supply for salmon, and abundance of competitors for food (Beamish 1995). A brief annotated summary of research on marine as well as freshwater variables that affect salmon can be viewed here.
Some types of these environmental data are gathered as part of other routine operations and thus do not need to be incorporated into designs of monitoring programs for salmon. For instance, many government agencies use automatic sensors placed at strategically chosen locations to monitor freshwater conditions such as flow rates, water levels, and air/water temperatures. The resulting data are recorded in data bases that are available on web sites. Similarly, government agencies and researchers use a combination of satellites, ocean-based sampling devices, and regular research cruises to monitor marine conditions such as sea-surface temperature, conditions of winds and currents, chlorophyll (a measure of phytoplankton density), salinity, temperatures at various depths, and other biological and physical oceanographic variables. These freshwater and marine data are usually readily available on various web pages; click here for data on Canada and here for the United States.
There is an important caveat about using such freshwater or marine databases. Scientists often find that data that are collected for one purpose are not necessarily appropriate for other purposes. This could be due to the original sampling method being too imprecise or too infrequent in space or time to answer detailed questions. Users of such pre-existing databases should therefore carefully determine their appropriateness.
