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I am choosing to do migratory patterns for the Anguillia freshwater eels.

Pankhurst N. W. 1982. Relation of Visual Changes to the onset of sexual maturation in the European eel (Anguilla Anguilla L.). Journal of Fish Biol 21: 1287-140 This article discusses the change in the body of the eels due to maturation. The sexual maturity of eels plays an important role for when the eels travel to sea. The eyes of eels change structurally which would be more advantageous for swimming in the ocean.

Tsukamoto K. et al. 2002. Migration, speciation, and the evolution of diadromy in Anguillid eels. Canadian Journal of Fisheries and Aquatic Sciences 59(12): 1989-1998 This article discusses the otolith of the eel, which is a part of the inner ear of the eel. It uses these to help track the migration of eels and the changes of fresh water to sea. It also shows the evolutionary similarities to eels that stay in salt water and those who become fresh water eels.

Boe¨tius I, J. Boe¨tius .1980. Experimental maturation of female silver eels, Anguilla anguilla. Estimates of fecundity and energy reserves for migration and spawning. Dana 1:1–28 This article discusses the maturation process of females and how they change for the ability to reproduce in their bodies and hormones. Briones A. A. et al. 2007. Migratory Pattern and Habitat Use of tropical eels Anguilla Spp. (Teleostei: Anguillidae) In the Philippines, as revealed by otolith microchemistry. The Raffles Bulletin of Zoology 14: 141-149 This article discusses the connection of calcium and strontium in eels migrating and how the levels change when the eels start to migrate. It uses the otolith to help measure these levels.

Ellerby, D.J. et al.2001. Slow muscle power output of yellow- and silver-phase European eels (Anguilla anguilla L.): changes in muscle performance prior to migration. J Exp Biol 204: 1369-1379 This article discusses how the eels change their ability to use their muscles more efficiently when they start to migrate. It talks discusses different life stages and compares their muscle chemistry

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https://en.wikipedia.org/wiki/Anguillidae

Page Improvements

https://en.wikipedia.org/wiki/Eel_life_history

FINAL DRAFT STARTS HERE

Anguilla freshwater eels have been known for their ability to travel between the ocean and fresh

waters. The Anguilla freshwater eels are born in the ocean then travel to fresh waters where they live out

most of their life. Later on these same eels will once again return to the ocean to copulate and create the

next generations. These elusive eels have had little discovered about them, despite their long existence

known to man.The mystery behind eel migration and maturation is a studied subject that includes

many new discoveries. The ability to go between the salty ocean and crisp fresh waters is a feat not

known to many aquatic animals. Anguilla freshwater eels are born in the ocean, but depending on their

adulthood destinations these locations in the ocean change. The origin of an ancient ancestor and

convergent evolution drive many different explanations for various phylogenetic trees. Eels are hatched

into larval stage and eventually use the streams of the ocean to get to the continental shelves. At this point

in an eels life they become known as “glass eels”, called so because they are small clear eels.

maturate in the fresh water triggered by different environmental factors. Shifts in the temperatures and

sun light availabilities jump start the populations into full migration readiness. The eels change things

such as body and eye size and their ability to convert energy. All these things are important due to the fact

that once eels maturate into breeding adults they have only one chance to make it to the sea where they

will copulate and die. All the reproductive success depends on an eels’ proper maturation and migration.

Ancient Ancestor

The eels evolved from a common ancestor known as Eocene, which resided

from western Pacific Ocean. The species supposedly split into two groups and from there evolved from

allopatric speciation due to continental drift. The eels’ migration patterns’ differences can be examined to

give an explanation for differences in patterns and genetic relatedness. Phylogenetic trees are constantly

being updated and changed so that we may infer different things about species and genus. Branching from

the original ancestor, Eocene, in the western pacific, the eels moved in multiple directions giving rise to

many species we now know about. Understanding how these species derived can be seen through

different characteristics and behaviors of these eels. We can infer that there might have been a need for

more space for the eels and possibly better feeding grounds that drove the eels outward from their place

of origin. The currents and temperatures are some of the many things that drive the eels to their different

mating grounds and their maturating habitats of the fresh waters.

Environmental Effects

During eel migration anything below 4o C and above 18o C the eels would mostly not migrate. This suggests a balance between costs and

benefits to the eels for proper migration times. The amount of light during the day time was also a factor

of the eels’ migration. These factors would suggest a possible measure for the proper time of migration

and maturation in the eels influenced by the change of temperature and sun light. Light and temperature

change are largely an indicator of seasonal changes in the north of different seasons and time of year.

Body Changes

Eels change morphologically when they prepare to migrate back to the ocean. These changes in

the body allow for higher efficiency of swimming long distances and changes in salinity in the ocean. The

ocean is a different environment than rivers, i.e. higher salinity, more predators, different temperature,

and many more other factors. Eels are born and die in the ocean, but spend a majority

of their life span in fresh waters. Eels had to gain the ability to travel back to the ocean in order to

properly reproduce to pass on their genes. It is not known exactly why eels need to travel back to the

ocean to spawn. Many of these things are still under strong observation and studying. Eels have

developed the ability to change their bodies in order to migrate. They grow through changes such as eye

enlargement and thickened, darkened bodies. Eels also change their ability to use muscles in a more

efficient way in order to conserve enough energy for the long migration to their reproducing grounds. This power was observed with respect to that of power of terrestrial animals. This

was done to show when eels can move on land in order to migrate across patches of dry land to get more

water to get to the ocean. Eels evolved these traits to adapt their different environment changes in order to

reproduce.

== Swimming Patterns ==

Eels all over the world migrate long distances to spawning grounds in the ocean. The European

eel was tagged and observed during the early stages of migration in order to track patterns and behaviors

. Tracking this behavior gives us a better understanding of eel migration behaviors

that have for long time been unknown. Eels change their migration patterns in the ocean according to the

time of day whether, the sun was out or not. “When eels moved into mesopelagic zone they all under-took

distinct diel vertical migrations (DVMs), predominantly between depths of 200 and 1000m” <ref>Aarestrup, A. et al. 2009. Oceanic Spawning Migration of the European Eel (Anguilla anguilla).Science 325:1660.

DVMs are basically patterns of behavior the correlate with the different availabilities in 

sunlight in accordance with feeding and risk of predation that can be mathematically calculated.2

DVMs were broken down into two tags one at night where eels stuck to shallow, warmer water and at

dawn they dove into deeper, cooler waters. The warmer water that was more shallow was suggested to

help keep up the high metabolism levels and constant swimming activity. Whereas the cooler deeper

levels during the day light were to avoid predation. Selection for these traits can be explained by the

evolution of eels migrating with respects to predators. The dark bodies of the eels are more likely to be

seen in lighter waters, this would leave them more exposed to predation; though it may be more energy

costly to swim at cooler temperatures. The eels in the night returning to the warmer waters allows for a

more efficient swimming because body regulation is easier in warmer waters, plus the lack of sunlight

allows for easier camouflage at night. These behaviors could give explanations as to why eels migrate at

certain times of the year.Similar tactics of adult migration patterns are used by the larval stages of eels as they drift to their

freshwater homes. The migration begins in autumn and the larval stage is discovered swimming around

July. The area of exact spawning and when the spawning happens is still

unknown. Eels tend to favor 200 m of depth in the ocean. “It probably originates as a comprise by the

organism to avoid slower geostrophic currents deeper in the water column and also southward transport in

the North Atlantic storm track region, where the mean westerly winds un duce southward transport in the

Ekman surface layer” <ref> Marui, M. et al. 2001. Comparison of early life history between New Zealand temperate eels and

Pacific tropical eels revealed by otolith microstructure and microchemistry. Marine Ecology Progress

Series 213: 273-284 . Eel larval migration was suggested to be about two

years for the A. anguilla and less than one year for A. rostarata, both temperate eels. These amount of

times are advantageous to discovering the full life style of the fresh water eels especially in comparison to

the closely, genetically related salt water eels. The variations can be observed to show how the two

species might have originated and if there were any common ancestors. Eels also tend to mix when

reproducing causing genetic recombinations of different sub species and species. This mixing of genes

could allow for new genes to arrive in different populations causing a genetic drift. The new genes could

allow for a new profitable trait for conquering more area and new habitats. The late winter spawning was

also shown as being more gainful to maximize food availability.

References

<ref>Aarestrup, A. et al, "Oceanic Spawning Migration of the European Eel (Anguilla anguilla)", 2009 <ref>Aoyama, J. and K. Tsukamoto, "Evolution of the Freshwater Eels", 1997 <ref>Briones A. A. et al, "Migratory Pattern and Habitat Use of tropical eels Anguilla" Spp. (Teleostei: Anguillidae) In the Philippines, as revealed by otolith microchemistry",2007 <ref>Department of Marine Resources of the state of Maine, [1], "The Maine Eel and Elver Fishery", 2012 <ref>Ellerby, D.J. et al, "Slow muscle power output of yellow- and silver-phase European eels (Anguilla anguilla L.): changes in muscle performance prior to migration',2001 <ref>Jensen Lab Rutgers University, [2], " Diel vertical migration of freshwater fishes and zooplankton", 2013 <ref>Kettle, A.J. and K. Haines, "How does the European eel (Anguilla anguilla) retain its larval migration across the North Atlantic Ocean?", 2006 <ref>Marui, M. et al "Comparison of early life history between New Zealand temperate eels and Pacific tropical eels revealed by otolith microstructure and microchemistry", 2001 <ref> Pankhurst N. W., "Relation of Visual Changes to the onset of sexual maturation in the European eel (Anguilla anguilla L.)", 1982 <ref> Vøllestad, L.A. et al, "Environmental Factors Regulating the Seaward Migration of the European Silver Eels (Anguilla anguilla)", 1986

~~~~Christa Eyster

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