A huge marine mammal known as Steller’s sea cow once lived in the waters around Bering Island off the coast of Siberia. It was described in 1741 by Georg W. Steller, a naturalist who was among the first Europeans to see one. In 1768 the animal became extinct. The reasons for the extinction are not clear. Here are three theories about the main cause of the extinction.
First, the sea cows may have been overhunted by groups of native Siberian people. If this theory is correct, then the sea cow population would have originally been quite large, but hundreds of years off too much hunting by the native people diminished the number of sea cows. Sea cows were a good source of food in a harsh environment, so overhunting by native people could have been the main cause of extinction.
Second, the sea cow population may have become extinct because of ecosystems disturbances that caused a decline in their main source of food, kelp (a type of sea plant). Kelp populations respond negatively to a number of ecological changes. It is possible that ecological changes near Bering Island some time before 1768 caused a decrease of the kelp that the sea cows depend on.
Third, the main cause of extinction of the sea cows could have been European fur traders who came to the island after 1741. It is recorded that the fur traders caught the last sea cow in 1768. It thus seems reasonable to believe that hunting by European fur traders, who possessed weapons that allowed them to quickly kill a large number of the animals, was the main cause of the sea cow’s extinction.
The article discusses about the Steller's sea cow, a creature who was used to live around Bering Island, and provides three probable explanations of their extinction. However, the professor in the lecture thinks that the main cause is not clear and refutes each of author's reasons.
First, the article states that native Siberian people may have overhunted these animals and caused them to distinct. However, the professor explains that the villages in that area was small and have little population and also the sea cows was giant animals who were more than 9 meters long weigh and 10 tons. He states that one of these animals was sufficient to feed a village for months, hence they did not need to hunt lots of them and cannot be the main reason of their extinction.
Second, the passage claims that ecosystems disturbances which caused their main source of food, the kelp, to decline and as a result the sea cow population has extinct. However, the lecturer refutes this idea by saying that these disturbances of ecosystem must had affected other species in that area too. He avers that there is no evidence that other species in the area such as whales had been affected. So there were no disturbances in the ecosystem that led to their shortage of food.
Third, the reading avers that European fur traders came to the island after 1741 and possessed weapons to kill a large number of them at once and they might contribute to sea cow's extinction. Though, the professor not contradicts that the Europeans came to the island but he claims that they came a years after sea cow's extinction. They were extinct long time ago and the traders could not be the main reason for that.
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Grammar and spelling errors:
Line 7, column 112, Rule ID: LARGE_NUMBER_OF[1]
Message: Specify a number, remove phrase, or simply use 'many' or 'numerous'
Suggestion: many; numerous
...fter 1741 and possessed weapons to kill a large number of them at once and they might contribute ...
^^^^^^^^^^^^^^^^^
Line 7, column 298, Rule ID: A_PLURAL[1]
Message: Don't use indefinite articles with plural words. Did you mean 'a year' or simply 'years'?
Suggestion: a year; years
...the island but he claims that they came a years after sea cows extinction. They were ex...
^^^^^^^
Transition Words or Phrases used:
also, but, first, hence, however, may, second, so, third, such as, as a result
Attributes: Values AverageValues Percentages(Values/AverageValues)% => Comments
Performance on Part of Speech:
To be verbs : 12.0 10.4613686534 115% => OK
Auxiliary verbs: 6.0 5.04856512141 119% => OK
Conjunction : 12.0 7.30242825607 164% => OK
Relative clauses : 18.0 12.0772626932 149% => OK
Pronoun: 33.0 22.412803532 147% => Less pronouns wanted
Preposition: 30.0 30.3222958057 99% => OK
Nominalization: 7.0 5.01324503311 140% => OK
Performance on vocabulary words:
No of characters: 1395.0 1373.03311258 102% => OK
No of words: 292.0 270.72406181 108% => OK
Chars per words: 4.77739726027 5.08290768461 94% => OK
Fourth root words length: 4.13376432452 4.04702891845 102% => OK
Word Length SD: 2.40767551564 2.5805825403 93% => OK
Unique words: 154.0 145.348785872 106% => OK
Unique words percentage: 0.527397260274 0.540411800872 98% => OK
syllable_count: 420.3 419.366225166 100% => OK
avg_syllables_per_word: 1.4 1.55342163355 90% => OK
A sentence (or a clause, phrase) starts by:
Pronoun: 3.0 3.25607064018 92% => OK
Article: 10.0 8.23620309051 121% => OK
Subordination: 0.0 1.25165562914 0% => More adverbial clause wanted.
Conjunction: 1.0 1.51434878587 66% => OK
Preposition: 1.0 2.5761589404 39% => More preposition wanted as sentence beginning.
Performance on sentences:
How many sentences: 12.0 13.0662251656 92% => OK
Sentence length: 24.0 21.2450331126 113% => OK
Sentence length SD: 37.7634266042 49.2860985944 77% => OK
Chars per sentence: 116.25 110.228320801 105% => OK
Words per sentence: 24.3333333333 21.698381199 112% => OK
Discourse Markers: 6.5 7.06452816374 92% => OK
Paragraphs: 4.0 4.09492273731 98% => OK
Language errors: 2.0 4.19205298013 48% => OK
Sentences with positive sentiment : 1.0 4.33554083885 23% => More positive sentences wanted.
Sentences with negative sentiment : 6.0 4.45695364238 135% => OK
Sentences with neutral sentiment: 5.0 4.27373068433 117% => OK
What are sentences with positive/Negative/neutral sentiment?
Coherence and Cohesion:
Essay topic to essay body coherence: 0.183859222954 0.272083759551 68% => OK
Sentence topic coherence: 0.0631097542851 0.0996497079465 63% => OK
Sentence topic coherence SD: 0.074893764796 0.0662205650399 113% => OK
Paragraph topic coherence: 0.115120609644 0.162205337803 71% => OK
Paragraph topic coherence SD: 0.0646485397453 0.0443174109184 146% => OK
Essay readability:
automated_readability_index: 13.2 13.3589403974 99% => OK
flesch_reading_ease: 64.04 53.8541721854 119% => OK
smog_index: 3.1 5.55761589404 56% => Smog_index is low.
flesch_kincaid_grade: 10.3 11.0289183223 93% => OK
coleman_liau_index: 10.74 12.2367328918 88% => OK
dale_chall_readability_score: 7.69 8.42419426049 91% => OK
difficult_words: 53.0 63.6247240618 83% => More difficult words wanted.
linsear_write_formula: 13.5 10.7273730684 126% => OK
gunning_fog: 11.6 10.498013245 110% => OK
text_standard: 14.0 11.2008830022 125% => OK
What are above readability scores?
---------------------
Rates: 78.3333333333 out of 100
Scores by essay e-grader: 23.5 Out of 30
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Note: the e-grader does NOT examine the meaning of words and ideas. VIP users will receive further evaluations by advanced module of e-grader and human graders.