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Effects of Man on Wild Salmon Population Term Paper

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Updated: Mar 30th, 2019


The protection and restoration of the environment are important duties of every individual if our world wants to continue enjoying the benefits that nature brings. These tasks cannot be left to the government agencies alone because of the people who interact with their habitat everyday.

Research showed that individuals were not conscious enough of the damage they exposed the environment to through their activities. This has led to environmental degradation which has affected various habitats in a number of ways. Some of these habitats that are under a real threat due to this degradation are stream and rivers’ biodiversity and productivity.

Though evolutionary change was noted over the past few generations because various species had disappeared from the ecosystem, human activities have a great impact on the natural ecosystems. According to Williams et al (271), this has affected the earth biota in a number of ways.

This paper will focus on the effect of these activities on the population of salmon fish and seek to find some explanations for this issue. This is because the population of this species has been noted to reduce consistently over the past few decades.

Much of this decline is attributed to human activities which interfered with the physical stream habitat and caused the danger. Such a situation has happened because of high rates of fishing on this species. This affected the population of both the young and adult salmon.

Materials and Methods

In determining the population stability in salmon species, consistent change in environmental conditions was noted as the greatest force behind the decline in populations. Therefore, Measures can be taken to reduce this interference, especially after determining how this occurs.

However, the problem that most of ecologists have found difficult to decide lies in coming up with the appropriate processes that outline the variability in the fish population abundances.

The best time to determine the temporal variability in fish population abundance is spawning which is the most important part of their life because fish is a species that reproduces fast. The reason to take into consideration this period is that there are high rates of mortality in the fish species during the spawning.

According to Einum et al (812), this is determined by trade-offs between egg size and number. During that period, an organism is highly productive, so this fact should reflect in the high mortality from egg to adult life. As a result of the high mortality, even a small level of environmental change may lead to even larger change in adult population abundance during the juvenile stage.

In fact, any changes raise the mortality rate at this stage. On the other hand, such species that lay fewer eggs, but that are larger in size show more stable numbers in their population. This thesis is supported with comparative data received from the month long observation of the population when the egg size was important in unfriendly environmental conditions.

Therefore, adopting other approaches seems to be the best option. This includes such ones as phylogenetic comparative approach which has been adopted by some ecologists due to its ability to compare organisms that have the closest related data.

When this approach was applied in marine fishes where the high rate of productivity was compared with high recruitment variability, the result indicated that there could be a possible relationship between productivity and changes that occurred among fish populations in stability. The changes in fish habitat cause even greater influence on the individual fish species leading to even larger changes in the total population abundance than it was expected.

In determining how population changes affect and result in replenishing breeding habitat of Atlantic salmon, it is necessary to compare those population changes, that is why salmonid fishes are a good choice due to various reasons. First of all, there are some determined data that were created after observation of population sizes during some particular period, these results should be accurate because they are of high importance.

This is because the number of adults can be taken as they rise up their natal river (Einum et al 931). Another reason that makes this method the best for salmonid species is that it is easy to define population of this fish as its representatives do not always fail to go back to their biological river.

In addition, the history of the salmon fishes reveals that there are always a great number of its representatives. This makes it easy to carry out interrelation studies between the characteristics and population dynamics possible and efficient. In an attempt to reinforce the conservation measures of the salmon populations, it is important to understand that fish characteristics affect their dynamics.

While studying the populations of the Salimo salar vary, the Scorff river which is a small coastal river of Southern Brittany was used. The method used to determine and analyze the potential for interactions from human activities to influence evolutionary change in the life history of a threatened salmonid showed that salmon fish has various species which are either found in fresh water or the sea.

For instance, in the Snake River which is the largest tributary of the Columbia River, Chinook salmon is a unique species. This is because its migration approach is different from other existing species which can be highly attributed to anthropogenic interferences.

For instance, the construction and activities at Brownelee Dam has a great effect on the water temperatures between Hells Canynon and the area where the Salmon joins the Snake River (Williams et al. 275). Due to these interferences, the water becomes warmer in the fall and cooler during the spring.

This has affected Chanook salmon spawn in a great way. This is because the fall in the water temperatures could be attributed to the delay in their spawning while the young ones fail to thrive as they are expected.

In addition, the spawning areas that are in the lower part become cooler than the location that is above Brownlee Dam since the water that flows from high elevation tributaries cools the temperatures of the mainstream. As a result, the fry currently surfaces in the extant spawning areas from the gravel in spring later than it was before. After this stage, the juveniles are noticed to take more time to grow than it was earlier.

Such a disorder leads to the delay in the beginning of their seaward movement. These operations have also affected the movement of the Chinook salmon. As Williams et al (274) note, in the past, the peak of the Chinook salmon subyearlings movement via the lower Snake River was in the month of June.

However, this has been changed because the movement via this location is observed in the early or even mid July nowadays. In Chinook salmon species, juveniles are known to either start relocating into the sea after emerging in the spring or sometimes taking a whole year in fresh water to venture into the sea as yearlings.


The obtained results reflected major disparities among species. The variation in annual population went down with the mean population size. In addition, there was annually a decrease in the size of the population.

After examining and analyzing how various species differed from each other as far as their marginal means were concerned, it was established “that Atlantic, Chinook and Coho salmon were less variable than sockeye and pink salmon, and with chum being more similar to sockeye and pink. For detrended variation, a similar pattern emerged” (Einum et al 939).

The results of the potential for disruptions from human activities to influence evolutionary change in the life history of a threatened salmonid were reached after coming up with estimates. After receiving the proper data of the relative fitness of the yearling and subyearling movement strategies, there were modeling functions that could be undertaken.

The modeling functions that were used in the study were based on demographic data that had been gathered from Snake River fall Chinook salmon that had been intercepted at the adult trap at Lower Granite Dam between 1999 and 2006. The gender and the length of each fish were noted, and the scales were also tested during their period at the hatchery.

Based on subsequent scale reading, natural fish were distinguished from hatchery fish, total age was identified, and the age at ocean entry was determined. Up to seventy percent of spawners made the population of Lyons Ferry Hatchery which was taken into the Snake River while thirty percent were destined for the Clearwater River.

Using samples extracted from mature fish in Cleanwater where spawning took place, the distribution of age and class for the mature fish was determined. This was narrowed to cover the young juveniles which had moved into the area. This appeared to coincide with samples taken from Lyons Ferry Hatchery.

Nevertheless, seventy-six percent of these included young fish that were one year old. Taking these figures into account, it is possible to find out the representation of adults that were in Cleanwater River at that period.

While exploring the evolutionary mechanisms that were experienced in wild Salimo salar found in the Atlantic, the results showing the comparison of posterior to prior distributions suggested that the information contained in the data led to considerable updating of the prior distributions.

In predicting population responses to replenishment of habitat in Atlantic salmon where breeding took place, results showed that the intensity of reliance on density differed strongly between size classes in a given environment and across habitat availability scenarios for a given size class. Severe competition ensued due to limited breeding areas, thus exacerbated dependence on density.

In the end, the parr population heightened since only a limited number of fry matured to parr. The result of reduced competition weakened density dependence. One can therefore conclude that survival of fry directly determined the survival of parr.

A rise in breeding dispersion among the fry in a certain habitat led to reduced reliance on fry density and increased dependence on density among parr. Reliance on density was the same in the populations that were influenced by density as well as those which were not influenced by it at all.

In terms of numbers, one can explain significant disparities that occur when analyzing data of deaths because of density dependency and the cases which were not influenced by dependency. If density increases, there is a chance that a number of deaths will grow for fry and reduce for parr. This happened because of decrease in parr body size is of higher importance than deaths because of density-dependent increase.

It would be correct to conclude that movement of parr in the smolt stage led to an increase in adult population. Consequently, more eggs were deposited considering the limitation of habitat for fry population. To sum everything up, deaths in fry increased due to the growth in density


It was identified that the population of salmon did not vary greatly each year. Even where population varied, a link between this variation and the number of eggs deposited were not established. From the findings that were determined, the strongest one was that increasing population sizes appeared to lend stability to the dynamics.

An increase in the population of salmon had the effect of reducing population variation. The authors, however, substantiate that variability in this case was independently related to population size. In salmonids, as far as population size is concerned, varying negative relationships are biologically explainable.

Since large populations are spatially distributed in a complex manner, negative correlations are unavoidable. This fact differ it from small species where the entire population changes are synchronously.

That is why, “such spatial structuring may be stabilizing if the relative successes of different segments of a population vary from year to year because the effect of exogenous forces on the total population is averaged out during years” (Buoro, Prevost and Gimenez 2634).

It was also hypothesized that high variability existed in small populations since environmental variance was very high in such populations. Consequently, as far as spatial distribution is concerned, varying population size is affected by other factors that consider variations in environmental conditions as a constant.

Such factors include quality of the environment as well as the available habitat. If a number of species reduce, demographic randomicity may affect other levels of populations different in size.

The results for the potential for anthropogenic disturbances salmonid showed that the first method that was applied in this analysis was aimed at identifying the range of survival probabilities that in their diversity would be of benefit to individuals who adopted the yearling and subyearling smolt-migration tactics.

In this method, life tables separated the age-specific survival probabilities and fecundity for individuals adopting either the subyearling or yearling tactic and returning to spawn at sea after 1, 2 or 3 years.

Without considering the tactics that was chosen, individuals are assumed to have the same survival probabilities from the egg stage to the time they emigrate from the Snake River and in the ocean as subadults. The tables differ in such cases.

The first is the term Sriver that represents the probability that a smolt survives the period during which it resides in freshwater. The measurement value had to be no less than 0.2 or greater than 0.8. The life tables also showed that differences existed as far as chances of survival in the migration period when the smolts were headed to the sea coming from Columbia River.

This parameter, Smigration, was 0.05 on the lower side and 0.25 on the higher side for subyearling smolts. Among yearling smolts, their larger size may be associated with higher survival immediately prior to and/or shortly after entry to the ocean, Smigration was increased by factors ranging between 1 and 3.

To bind the range of survival probabilities, the researchers used estimated smolt-to-adult return ratios (SARs) developed from fall Chinook salmon tagged with PITs and released between 1995–2000 for a study to evaluate juvenile migration, survival and timing. Data from fishes that were PIT-tagged in 2001 and released similarly to the earlier studies were also used.

There was grouping of juvenile detections at Lower Snake River dams into three categories. Firstly, there were fish detected between June and August; the second ones were detected in September and October, and the third case when the species were detected the following spring.

Mature fish that had a PIT tag detected at Lower Granite Dam were assigned to their respective years when they migrated during their young stages. Geometric means of these annual PIT-tag estimates were also used to develop relative rates of return for fish migrating as juveniles during the three different time periods.

In predicting population responses to restoration of breeding habitat in Atlantic salmon, the success of restoration strategies is thought to depend on details of the ecology and behavior of individuals. For example, increase of anadromous salmonids population is the main target that all the scientists pursue trying to restore a natural balance.

Because of many conditions, growth in population resulted in decrease of local competition for distribution during the juvenile period. It is nonetheless recognized that thriving of the fish is strongly dependent on the habitat at different stages. During early stages of life, it was particularly recognized that this is the time when breeding dispersion was the most widespread in intermediate habitats.

This explains why a rise in breeding dispersion will lead to differing population effects. At the young stage of life, the fish will experience abundance in their habitat since competition is not severe.

While investigating the evolutionary trade-offs in wild populations of the Atlantic salmon (Salimo salar), the use of Bayesian state space modeling approach made it possible to represent the whole life-history process of Atlantic salmon and establish evolutionary changes.

The results did not rely on differences in traits in the lives of the fish. It should be noted that the traits that were under investigation were not fully observed since likelihood of detecting the traits were not more than one.

To come up with factors that would determine the selection criteria during the stages of observing and detecting changes, magnetic resonance studies were exploited. It is important to note that these were to be determined in under natal conditions.

However, magnetic resonance was noted to have its shortcomings, especially in detecting body mass. The results helped the authors to utilize detection probabilities, thus they were able to establish relationships between fish traits in relation to the history of the fish. The stage in the life of the fish was a contributing factor as far as a detection of body mass was concerned.

In changes which are related to revolution as well as differences among individuals, interest is piqued in regards to explaining the differences among individuals. This holds a great promise in conducting studies in evolutionary changes.

The modeling platform is not fixed, and hence options are available on how to bring together the aspects of individual differences in order to emerge with a uniform model. By knowing that differences between individual exist, it becomes possible to determine what other factors may influence these differences. Although this is based on probability, it comes in handy in knowing what numbers of parr will smolt to adults.

Works Cited

Buoro, Mathieu, Prevost, Etienne, and Olivier Gimenez. “Investigating Evolutionary Trade-offs in Wild Populations of Atlantic Salmon (Salmo salar): Incorporating Detection Probabilities and Individual Heterogeneity.” Evolution 64.9 (2010): 2629-2642. Print.

Einum, Sigurd, Fleming, Ian A., Cote, Isabelle M., and John D. Reynolds. “Population Stability in Salmon Species: Effects of Population Size and Female Reproductive Allocation.” Journal of Animal Ecology 72 (2003): 811–821. Print.

Einum, Sigurd, Nislow, Keith H., Reynolds, John D., and William J. Sutherland “Predicting Population Responses to Restoration of Breeding Habitat in Atlantic Salmon.” Journal of Applied Ecology, 45 (2008): 930–938. Print.

Williams, John G., Zabel, Richard W., Waples, Robin S., Hutchings, Jeffrey A., and Connor William P. “Potential for anthropogenic disturbances to influence evolutionary change in the life history of a threatened salmonid.” Evolutionary Applications 1 (2008): 271–285. Print.

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