who can complete this assignment by Thursday, April 16th, 2020 by 11:00pm?

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A Scientific Review of the Physiology of Pacific Salmon Migration

B. C. McKinney1

1 Department of Natural Sciences, University of South Carolina Beaufort, One University

Boulevard, Bluffton, South Carolina 29909, USA

Abstract For many generations, humans have altered practically every

ecosystem in the entire world. The footprint humans leave behind on ecosystems

on Earth has continuously matted the ecosystems and critical habitat in which all

species on Earth depend on for survival. When considering Pacific and Atlantic

salmon populations, the array of human caused stressors is responsible for the

population depletions across the United States and Canada. This review will

coordinate the impacts of river impoundments (i.e., hydropower systems) on

upstream and downstream migration as well as visit the impacts of natural and

human caused change on the quality of habitat in which salmonids inhabit through

all life stages.

Introduction

A variety of teleost species are classified within the Family Salmonidae under the Order

Salmoniformes. Salmonidae is comprised of a variety of trouts (Salmo spp.), chars (Salvelinus

spp.), graylings (Thymallus spp.), taimen (Parahucho spp.), and salmons (Salmo &

Oncorhynchus spp.). The anatomy of this family is similar to other ray-finned fish having

dorsal, pelvic, pectoral, anal, and dorsal fins, however they possess an additional fin posterior to

the dorsal called the adipose fin.

Salmonid lifecycles are very complex and have been a topic of research for many

generations (Briggs, 1953; Holmes & Stainer 1966; Vronskiy, 1972; Thompson & Sargent, 1977;

Healy, 1980; McCormick &Saunders, 1987; Murray & Rosenau, 1989; Nehlson et al., 1991). In

recent findings, the introduction of telemetry techniques and field sampling routines have given

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researchers insight about the duration, timing, and patterns of homing and staying (Healy, 1980;

Giorgi et al., 1997; Walker et al., 2016). Through the protection of the Endangered Species Act

(ESA) select Pacific salmon populations have been granted protection by federal regulations in

relation to the habitat that is essential to their survival (USNMFS 1995). In this review, relevant

available published literature will be compiled to discuss a variety of explanations towards the

physiology and morphological complexities associated with Pacific salmon.!

Overview of Salmon Biology

In this section, emphasis will focus on the evolutionary history of Salmon (see Groot &

Margolis, 1991, Hendry et al., 2000, and Waples et al., 2007 for more details). North America’s

populations of Pacific Salmon consist of five distinct species: chinook salmon (Onchorhynchus

tshawytscha), pink salmon (O. gorbusha), chum salmon (O. keta), coho salmon (O. kisutch), and

sockeye salmon (O. nerka). Pacific salmon are uniquely characterized as anadromous

(migratory) and semelaparous (i.e., die after spawning) species. This life strategy is opposite of

their cousin, steelhead are the anadromous form of rainbow trout (O. mykiss), which are

iteroparus (i.e., spawn more than once).

Spawning adults (spawn and die within 2 weeks) must migrate far enough upriver to an

area there has good water quality and low predation rates, seeking this habitat is essential to the

survival of their offspring as eggs (i.e., 0-3 months), alevin (i.e., feed off yolk sac for 1-2 weeks),

fry (i.e., 5-10 weeks), and parr (i.e., 1-2 months old). Yearling smolt will reside in the brackish

estuary for weeks, months, or even years before moving offshore depending on the species and

their ability to osmoregulate to increasing salinities. Their voyage into the ocean occurs next,

migrating to more productive water for growth will last for multiple years (i.e., 1-3 depending on

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the species) until sexual maturity (i.e., 3-8 years old) when the homing phase will be initiated.

Shoji et al. (2003) and Hara (1992) investigated an essential mechanism for successful homing to

the natal grounds; explaining the dependency on olfactory organs to electro-physically respond

to dissolved chemicals (i.e., amino acids, steroids, bile acids, and prostaglandins) queues in

rivers and streams which they were born. Salmon face a variety of physical and morphological

obstacles along the way, for example, sockeye salmon morph from their silver (i.e., offshore)

coloration into a vibrant reddish/pink color and the formation of a hooked snout (i.e., kype)

(Groot and Margolis, 1991; McCormick & Saunders, 1987).

Effects of Hydropower Systems

The implication of hydropower systems in the United States and Canada has significantly

affected the passage of spawning salmon. Due to their vast size, salmon are often times limited

in terms of upstream distance traveled (Anderson & Salinger, 2006). Brett (1995) further

explains that because salmonids do not feed during upstream migration, the flow velocity of the

river is essential. Brett (1995); Anderson & Salinger (2006); and Tillotson & Quinn (2017) all

contribute reasons why hydropower systems are responsible for pre-natal spawning and pre-

spawn death.

Water Quality:

Ever since the introduction of hydropower systems, (Waples et al., 2007; Regetz, 2003)

strongly suggest that the redirection of water for agricultural use is the major reason for pour

water quality (i.e., lower dissolved oxygen, higher water temperatures, salinity, sedimentation,

and contaminants from pesticides and fertilizers) in the lakes and streams of the Pacific

Northwest.

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Physical Conditions:

Brett (1995) explains that the ocean phase before upstream migration is essential to

migration because this is the period in which the salmon consume their last bit of energy.

Semaloparous salmon begin to deteriorate and transform during this migration, their mouth

structure changes significantly, which limits their ability to consume food during migration.

Evolutionary Significance

Egg Phase:

During a spawning event, gravid females will create a spawning bed (i.e., redd); this

structure is often variable in size depending on the surface area and flow velocity of the river

(Vronskiy, 1972). In Healy’s (1980) review of Utilization of the Naniamo River Estuary By

Figure 1. Sockeye Salmon (O. nerka) Spawning Phase can be observed by the change in coloration from silver (ocean phase) to reddish/pink during spawning. Males (top) show significant morphological changes: the hump in front of the dorsal fin and kype of the jaw structure. (Photo credit: Washington Department of Fish & Wildlife)

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Juvenile Chinook Salmon, (Briggs, 1953) observed that chinook salmon tended to deposit eggs in

gravel substrate at a mean depth of 20-36 cm in a small steam located in California. In contrast,

Vronskiy (1972) observed deposition in the same substrate characteristics but at a more variable

depth (i.e., 10-80 cm).

The incubation (1-3 months) of eggs in the spawning bed is variable among Pacific

salmonids; however, a factor that affects development into alevin and fry is stream quality.

Severe flooding in rivers during the time of incubation is noted as a major cause of mortality; in

addition, the flow of water (percolation) through the spawning bed is another factor that

promotes mortality of eggs and larvae (Gangmark & Bakkala, 1960)

Juvenile Phase:

The emergence of fry from the spawning beds occurs mostly at night; from here they will

be dispersed downstream into the estuary or may occupy a slack pool (less current) or stream for

a short period of time (Reimers, 1971). The progeny of fry that emerge from spawning beds are

faced with a variety of challenges which determine their survival, in today’s era, scientists are

developing a better understanding about survival rates, abundance, and growth rates of juvenile

salmon through telemetry research as well as intensive sampling of river and estuary habitats

(see Downstream Migration).

Downstream Migration:

Healy (1980) established a sampling routine in the Nanaimo River, Canada to

establishing an understanding about duration of residency of juvenile chinook salmon in

freshwater before migrating to the estuary and the duration of residency in the estuary before

migrating offshore. Healy’s sampling protocol focused on sampling fry in freshwater stream

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channels (i.e., incline plane fry traps), estuarine intertidal mud flats (i.e., beach seine) and marine

rivers/creeks (i.e., beach and purse seine). Healy (1980) recorded fork length (FL), weight of

total catch, and weight of stomach content from a subset (i.e., 10-15 individuals) of the total

collection. In conclusion, his findings from sampling fresh and saline habitats revealed that

juveniles reside in the freshwater and the estuary of Nanaimo River for a year before migrating

offshore, respectively (Healy, 1980).

Giorgi et al. (1997) estimated the downstream migration rate of juvenile chinook salmon

throughout 259-km of river between the Rock Island Dam (RI) and McNary Dam (McN) of the

Columbia River. In 1997, Giorgi implanted 14,723 chinook smolts (47-171 mm) with a Passive

intergraded transponder (PIT) tag which allowed him to collect telemetry data about the timing

of downstream migration by an electronic scanner attached to various smolt by-passes.

.

Years later in 2016, Walker et al. investigated the size threshold which juvenile chinook

salmon were capable of bearing a passive integrated transponder tag (PIT). This study focused

on minimalizing the size of the tag so that the implantation of this telemetry transmitter would

Figure 2. Passive Internal Transponder (PIT) illustrating the size comparison of old technology (A-B) vs. new technology (C-D) (Walker et al., 2016).!

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have no negative effect on juveniles during development and migration. Walker et al. (2016)

conducted swimming performance and predator avoidance simulations to gain insight about the

effects of adding additional weight (i.e., 0.22g in air; 0.11g in water) to the fish during

development. Through these experiments, he was able to conclude that implantation of internal

tags for telemetry research in fact has no negative impacts on the fish during his study.

Reluctantly, Walker et al. (2016) concluded these results because the use of telemetry had

previously been used for centuries before his experiments (e.g. Giorgi et al., 1997).

Early Ocean Phase:

McCormick & Saunders (1987) describes the transformation of stream-dwelling parr to

the seaward-migrating smolt (i.e., smoltification) as a significant stage of life, which is essential

for the survivorship of various salmon species. Morphological changes of parr transformation is

described (Folmar & Dickhoff, 1980) to have dark bars that are perpendicular to the lateral line

and as the parr grow into smolts, these bars tend to disappear through the accumulation of purine

amino acids (i.e., guanine and hypoxanthine), which change the coloration into a reflective silver

appearance (Folmar & Dickhoff, 1980). Physiological changes are also important to migrating

smolts; changes in ionic composition by the gills and the excretory and endocrine systems. (see

Osmoregulation)

Adult migration phase:

Quinn et al. (2001) believed that populations of migrant and spawning salmon were

repeatedly differed in that the time of spawning is a product of adaptation and spatial isolation

of populations to facilitate and accelerate divergence in traits. The timing of spawning migrations

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is temporally and spatially different among salmonids, however, there is a common link in

phenotypic size and growth of the expected progeny (Quinn et al., 2001).

Shoji et al. (2003) investigated the ability of salmon to recognize stream-specific

chemical composition (i.e., amino acids, steroids, bile acids, and prostaglandins) during the

homing phase. During this study Shoji used mature chum salmon from the Osaru River, Japan

where he then simulated an environment that had two inputs of water: on one side of the test tank

had inflow of artificial stream water which was a mixture of Osaru River water and artificial

freshwater (0.5 mM NaCl, 0.05 mM KCl, 0.4 mM CaCl2 and 0.2 mM MaHCO3, pH 6.9) and on

the opposite side was natural lake water. Both water types were added to the test tank over a

nine-hour period, fish movement was monitored by a remote camera system (T-water 2000C,

Tukamoto Musen Co., Mie) and then the selection to each arm was recorded. During his

experiment, of the forty-four total chum salmon, twenty-eight (64%) showed upstream

movement (i.e., selecting the left of right arm), 24% of fish were recorded selecting the arm

which had an inflow of artificial water and 15% of fish chose the natural lake water. From these

results, it is plausible to implicate the olfactory capabilities of salmon to smell the chemical

composition of water for successful migration to their natal grounds (Shoji et al., 2003).!

Physiological Adaptations

Osmoregulation:

Spawned salmonids reside in freshwater for a short period of time (i.e., 1-2 weeks) before

they migrate into the estuary where the water becomes more saline (Healy, 1980; McCormick &

Saunders, 1987). The gill structure in teleost fish is the primary organ that physiologically

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transforms during migration; gill Na+, K+-ATPase activity increases as the salt concentration

increases from fresh into salt water systems (Epstein et al., 1967).

Loretz et al. (1982) concluded that during the downstream migration of coho smolts,

chloride cell abundance and size increase proportionally to the size of the fish. In addition,

during this osmoregulation process, the internal medium of ionic salt concentration must be

regulated, (Holmes & Stainer, 1966) found that the excretory system is responsible for this

change. Kidney Na+, K+-ATPase activity of the Atlantic salmon is highly variable in the

estuary in regards to seasonal fluctuations of freshwater input from the streams during the rainy

season and visa versa during the dry seasons (Loretz et al., 1982).

In conclusion, salmonids have a “strategy” for osmoregulation, which entails a

continuous migration event from fresh to saltwater (i.e., juvenile migration) and salt to

freshwater (i.e., adult migration) (Thompson & Sargent, 1977), whereas euryhaline species (e.g.,

fundulus spp.) have a “strategy” for osmoregulation, which entails multiple migration events

from fresh to saltwater or salt to freshwater.

Growth:

The Nanaimo estuary is an important habitat for the growth of chinook salmon, (Healy,

1980) found that the length of juvenile in the estuary was slightly greater than those found in the

stream surveys. Healy (1980) concluded that the average length of juvenile chinook in the

estuary was 70 mm fork length at the end of the downstream fry run. During 1975-1977, Healy

(1980) concluded that there were differences in size class in the different years however there

was not a significant difference, in conclusion the average size threshold, which leaves the

estuary in migration to the ocean, was 70 mm fork length, respectively.

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Metabolism:

Oxygen consumption changes in proportion to the rate of growth in juveniles in the

smoltification phase, here, coho salmon tend to decrease blood glucose levels were as Atlantic

salmon increase blood glucose levels during development (McCormick & Saunders, 1987).

Creatine composition in juveniles during the smoltification phase is significantly correlated with

downstream migration to the estuary and also during seaward migration; Cowey & Parry (1963)

concluded that this 30% increase is due to the increased muscle mass needed the future

migration.

Competition and Predation:

Salmon are an important step in the food web complex for a variety of reasons. Predation

on adult salmon by brown bears (Ursus arctos) in Karluk Lake, Alaska was significant in 1964

(Gard, 1971). The timing of upstream migration by sockeye salmon in relation to predation by

bears was experimented by visual surveys; this evaluation concluded that the bears killed up to

79 % of the migrant sockeye population in 1964 (Gard, 1971). This predation is a natural

behavior that has been occurring for many generations, conversely, Gard (1971) also estimated

bear predation was only a part of the loss of eggs during a spawn, the estimates made in this

experiment explained that bears killed 1000 adults which is not many considering the total death

of adults was estimated to be 8000, respectively.

Tillotson & Quinn (2017) evaluated the conspecific density trigger for pre-spawning

mortality of sockeye salmon in the Fraser River, Canada was a combination of predation by

terrestrial animals, anthropogenic impacts, fishing pressure, and competition for habitable

freshwater.

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Collateral Damage / Sustainability:

Since the late 1970s, the economic value of wild salmon has been decreasing due to the

introductioun of fish farms in Canada (Noakes et al., 2000; Carr!&!Whoriskey, 2006) and years

later in the U.S. Noakes (2000) explained the escape of farmed salmon by human error and

natural events is a factor that decreased wild salmon stocks in British Columbia. Hybrid species

of salmon have impacted the migration and developmental life stages of wild coho and chinook

salmon stocks, however, these are only a small piece of the puzzle which further is completed

with the impacts of climate change, overfishing, and the loss of critical freshwater habitat

(Noakes et al., 2000).!

Climate Change:

Climate fluctuation has been a relevant topic of research for many generations, Perry et

al., (2005) investigated Climate Change and Distribution Shifts in Marine Fishes in the North

Sea, his findings promote that water temperatures are increasing with increased latitude. Perry et

al. (2005) concluded that shifts in distribution would eventually result in a loss of species

through habitat loss. His concept can be applied to many other water bodies around the world.

Beamish et al. (1997; 1999) used the Aleutian Pressure Index (ALPI) to estimate the

regime concept and natural trends in the production of Pacific salmon. Beamish et al. (1997)

investigated the effects of the seven el Niño events from 1960 to 1993, concluding that the smolt

production during three events (1965-1966, 1969-1970, and 1982-1983) on average was

significantly higher than in two other events (1972-1973 and 1992-1993).

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Conclusions

Pacific salmon and Atlantic salmon have been studied for many generations through

physiological, morphological, and behavioral experiments. These findings have discovered

many different critical life stages, which conservation efforts need to be focused. The spatial and

temporal distribution of anadromous and semelparous species occurs in a variety of rivers,

estuaries, and oceans around the world. The development of hydropower systems is a critical

bottleneck, which has depleted many populations of salmon, thus, pacific salmon specifically

have been continuously degreasing for many generations. The Endangered Species Act (ESA)

enforces conservation of distinct populations of pacific salmon in iconic rivers and streams of the

Pacific Northwest (USNMFS, 1995). Through the distinction of specific salmon populations by

the ESA, restrictions and regulations for recreation have been assessed and enforced by many

state agencies. Climate change is also depleting many populations of salmon, the warming of the

atmosphere, is melting snow and ice on mountains which flows down the mountain into the

rivers creating increased flow and greater surface area (flooding). The increased flow is in part a

reason for lack of survival of avelin and fry during the emergence of spawning beds; however,

the decreased flow of rivers from the introduction of dams has also created situations that affect

the survival of juveniles migrating downstream. The effects of global warming in relation to

increased water temperatures around the world has also had significant negative effects on

spawning and migration.

Salmon have incredible evolutionary significance for osmo-conformity and regulation.

The resilience and evolution of salmon is fascinating, their life cycle is complex in that there are

many different critical aspects of development and survival. Thus, it has been challenging for

scientists to fully understand their complexity. Finally, protection efforts help with conservation,

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however, even with all the protection, salmon populations will continue to decrease to a point of

no return if humans don’t step up and promote awareness of pollution, deforestation, and the

introduction of water control systems in respect to salmon and more importantly all forms of life

that humans cherish.

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