Editing Marine mammal (section)

====Habitat loss and degradation====
{{Further|Marine mammals and sonar|Effects of climate change on marine mammals}}
[[File:Polar Bear Habitat.png|thumb|Map from the [[U.S. Geological Survey]] shows projected changes in polar bear habitat from 2005 to 2095. Red areas indicate loss of optimal polar bear habitat; blue areas indicate gain.|alt= The Canadian Basin is blue for the most part, while the rest of the Arctic Basin is mainly red with scattered areas of blue]]
[[Habitat degradation]] is caused by a number of human activities. Marine mammals that live in coastal environments are the most likely to be affected by habitat degradation and loss. Developments such as sewage [[marine outfall]]s, [[mooring (oceanography)|moorings]], [[dredging]], blasting, dumping, [[port]] construction, [[hydroelectric]] projects, and aquaculture both degrade the environment and take up valuable habitat.<ref name=white/> For example, extensive shellfish aquaculture takes up valuable space used by coastal marine mammals for important activities such as breeding, foraging and resting.<ref name=wur/>

[[Contaminant]]s that are [[Effluent|discharged]] into the marine environment accumulate in the bodies of marine mammals when they are stored unintentionally in their blubber along with energy.<ref name=white/> Contaminants that are found in the tissues of marine mammals include [[heavy metals]], such as [[mercury (element)|mercury]] and [[lead]], but also [[organochloride]]s and [[polycyclic aromatic hydrocarbon]]s.<ref name=white/> For example, these can cause disruptive effects on [[endocrine system]]s;<ref name=and/> impair the reproductive system, and lower the immune system of individuals, leading to a higher number of deaths.<ref name=white/> Other pollutants such as [[Crude oil|oil]], [[plastic debris]] and [[sewage]] threaten the livelihood of marine mammals.<ref>{{Cite journal | doi = 10.1016/0006-3207(81)90017-3| title = Otter ''Lutra lutra'' L. Mortality and marine oil pollution| journal = Biological Conservation| volume = 20| issue = 4| pages = 311–321| year = 1981| last1 = Baker | first1 = J. R. | last2 = Jones | first2 = A. M. | last3 = Jones | first3 = T. P. | last4 = Watson | first4 = H. C. | bibcode = 1981BCons..20..311B}}</ref>

[[Noise pollution]] from anthropogenic activities is another major concern for marine mammals. This is a problem because underwater noise pollution interferes with the abilities of some marine mammals to communicate, and locate both predators and prey.<ref>{{cite journal|last=Harwood, J. |year=2001|title=Marine Mammals and their Environment in the Twenty-First Century|journal=Journal of Mammalogy|volume=82|issue=3|pages= 630–640|jstor=1383602|doi=10.1644/1545-1542(2001)082<0630:MMATEI>2.0.CO;2|doi-access=free}}</ref> [[Underwater explosion]]s are used for a variety of purposes including [[military]] activities, construction and [[oceanographic]] or [[geophysical]] research. They can cause injuries such as hemorrhaging of the lungs, and contusion and ulceration of the [[Gut (anatomy)|gastrointestinal tract]].<ref name=clap/> Underwater noise is generated from [[shipping]], the oil and gas industry, [[research]], and military use of [[sonar]] and oceanographic acoustic experimentation. [[Acoustic harassment]] devices and [[acoustic deterrent devices]] used by aquaculture facilities to scare away marine mammals emit loud and noxious underwater sounds.<ref name=wur/>

Two changes to the global [[atmosphere]] due to anthropogenic activity threaten marine mammals. The first is increases in [[ultraviolet radiation]] due to [[ozone depletion]], and this mainly affects the [[Antarctic]] and other areas of the [[Southern Hemisphere]].<ref name=white/> An increase in ultraviolet radiation has the capacity to decrease phytoplankton abundance, which forms the basis of the food chain in the ocean.<ref>{{Cite journal |doi=10.1016/S1011-1344(98)00182-1 |title=Changes in biologically active ultraviolet radiation reaching the Earth's surface |journal=Journal of Photochemistry and Photobiology B: Biology |volume=46 |issue=1–3 |pages=5–19 |year=1998 |last1=Madronich |first1=S. |last2=McKenzie |first2=R. L. |last3=Björn |first3=L. O. |last4=Caldwell |first4=M. M. |pmid=9894350 |citeseerx=10.1.1.319.3101 }}</ref> The second effect of [[global climate change]] is [[global warming]] due to increased [[carbon dioxide]] levels in the atmosphere. Raised sea levels, rising sea temperatures and changed currents are expected to affect marine mammals by altering the distribution of important prey species, and changing the suitability of breeding sites and migratory routes.<ref>{{Cite journal |doi=10.1017/S0030605307001524 |title=The impacts of climate change on marine mammals: Early signs of significant problems |journal=Oryx |volume=41 |page=19 |year=2007 |last1=Simmonds |first1=M. P. |last2=Isaac |first2=S. J. |doi-access=free}}</ref> The Arctic food chain would be disrupted by the near extinction or migration of polar bears. Arctic sea ice is the polar bear's habitat. It has been declining at a rate of 13% per decade because the temperature is rising at twice the rate of the rest of the world.<ref name=apex1>{{cite journal|first1=Nicholas J.|last1=Lunn|first2=Sabrina|last2=Servanty| first3=Eric V.|last3=Regehr|first4=Sarah J.|last4=Converse|first5=Evan|last5=Richardson|first6=Ian|last6=Stirling|year=2016|title=Demography of an apex predator at the edge of its range – impacts of changing sea ice on polar bears in Hudson Bay|journal=Ecological Applications|doi=10.1890/15-1256|pmid=27755745|volume=26|issue=5|pages=1302–1320|bibcode=2016EcoAp..26.1302L }}</ref><ref>{{cite journal |last1=Stirling |first1=Ian |last2=Lunn |first2=N. J. |last3=Iacozza |first3=J. |date=September 1999 |title=Long-term trends in the population ecology of polar bears in Western Hudson Bay in relation to climatic change |journal=Arctic |volume=52 |issue=3 |pages=294–306 |url=http://pubs.aina.ucalgary.ca/arctic/Arctic52-3-294.pdf |doi=10.14430/arctic935 |access-date=2016-06-13 |archive-date=2019-09-28 |archive-url=https://web.archive.org/web/20190928135003/http://pubs.aina.ucalgary.ca/arctic/Arctic52-3-294.pdf |url-status=dead }}{{open access}}</ref> By the year 2050, up to two-thirds of the world's polar bears may vanish if the sea ice continues to melt at its current rate.<ref>{{Cite book|url=https://alaska.usgs.gov/products/pubs/2008/2008_Amstrup_Marcot_Douglas_AGU_Ch14.pdf|last1=Amstrup|first1=S. C. |volume=180|last2=Marcot|first2=B. G.|last3=Douglas|first3=D. C.|title=Arctic Sea Ice Decline: Observations, Projections, Mechanisms, and Implications |chapter=A Bayesian Network Modeling Approach to Forecasting the 21st Century Worldwide Status of Polar Bears |series=Geophysical Monograph Series |year=2008|editor1-first=Eric L.|editor1-last=DeWeaver|editor2-first=Cecilia M.|editor2-last=Bitz|editor3-first=L.-Bruno|editor3-last=Tremblay|doi=10.1029/180GM14|bibcode=2008GMS...180..213A|pages=213–268|isbn=9781118666470|access-date=2017-09-04|archive-date=2017-02-22|archive-url=https://web.archive.org/web/20170222072632/https://alaska.usgs.gov/products/pubs/2008/2008_Amstrup_Marcot_Douglas_AGU_Ch14.pdf|url-status=dead}}{{open access}}</ref>

A study by evolutionary biologists at the [[University of Pittsburgh School of Medicine|University of Pittsburgh]] showed that the ancestors of many marine mammals stopped producing a certain enzyme that today protects against some neurotoxic chemicals called [[organophosphate]]s,<ref name=":0">{{Cite news|url=https://www.nytimes.com/2018/08/09/science/marine-mammals-pesticides.html|title=Marine Mammals Have Lost a Gene That Now They May Desperately Need|newspaper=The New York Times |date=9 August 2018 |access-date=2018-08-13|language=en|last1=Zimmer |first1=Carl }}</ref> including those found in the widely used pesticides chlorpyrifos and diazinon.<ref>{{Cite journal|last1=Meyer|first1=Wynn K.|last2=Jamison|first2=Jerrica|last3=Richter|first3=Rebecca|last4=Woods|first4=Stacy E.|last5=Partha|first5=Raghavendran|last6=Kowalczyk|first6=Amanda|last7=Kronk|first7=Charles|last8=Chikina|first8=Maria|last9=Bonde|first9=Robert K.|last10=Crocker|first10=Daniel|last11=Gaspard|first11=Joseph|last12=Lanyon|first12=Janet|last13=Marsillach|first13=Judit|last14=Furlong|first14=Clement|last15=Clark|first15=Nathan|date=2018-08-10|title=Ancient convergent losses of Paraoxonase 1 yield potential risks for modern marine mammals|journal=Science|language=en|volume=361|issue=6402|pages=591–594|doi=10.1126/science.aap7714|issn=0036-8075|pmid=30093596|pmc=6317340|bibcode=2018Sci...361..591M}}</ref> Marine mammals may be increasingly exposed to these compounds due to agricultural runoff reaching the world's oceans.