Åbn hovedmenuen

FysiologiRediger

TermoreguleringenRediger

Grønlandssæler kombinere anatomiske og adfærdsmæssige tilgange til at styre deres kropstemperatur, i stedet for at hæve deres stofskifte og energikrav. [1] Et tykt lag af spæk isolerer sin krop og giver energi, når maden er knappe eller under faste. Spæk også strømliner sin krop for en mere effektiv svømning. Brown fedt varmer blod, da det vender tilbage fra kroppens overflade samt skabe energi, vigtigst for kun-fravænnede unger. [1]

Flippers fungere som varmevekslere, opvarmning eller afkøling blodet efter behov. På is, kan seglet trykke på sin foreflippers til sin krop og dens hindflippers sammen for at reducere varmetabet. [1]

SanserRediger

Grønlandssæls øje er forholdsmæssigt stort og har som andre vandlevende dyr en kugleformet linse, der er en tilpasning til syn under vand. Nethinden er domineret af stave, tilpasset monokromatisk (sort/hvidt) syn ved meget lave lysstyrker. Bag [[nethinden findes et reflekterende lag tapetum lucidum, der også øger lysfølsomheden. Dens stænger bedste forstand blå-grøn, mens dens kogler hjælpe med skarpt lys, og kan give lidt farve diskrimination. Dens hornhinden er konstant rive-dækket, for at beskytte den mod salt. Manglende tåre kanalen s, det "skriger" for at fjerne sine tårer. [1] på is, moderen identificerer hendes afkom efter lugten. Denne følelse kan også advare om en nærmer rovdyr. Underwater, denne forsegling lukker sine næsebor og lugte noget. [1] Dens knurhår, kaldet vibrissae, ligger i vandrette rækker på begge sider af dens snude. De kan fastsætte en touch forstand, og under vandet, også svare på lavfrekvente vibrationer, så som bevægelse. [1]

LivshistorieRediger

Grønlandssæler foretrækker at svømme i havet, bruger relativt lidt tid på land. [2] Disse er ekstremt sociale dyr, og de kan være meget støjende så godt. De vil danne store kolonier, hvor de tilbringer en stor del af tiden. Inden for dette løs struktur mindre grupper med deres eget hierarki menes at danne. Nogle gange vil disse store grupper nødt til at gå hver sin vej der. Mange grønlandssæler er i stand til at leve op til 30 år i naturen.

På isen, kalder ungerne deres mødre med "skråle" og "mumle", mens du spiller med andre. Voksne "knurre" og "kvidre" for at advare off andre. Underwater, voksne udtrykke sig med mere end 19 typer opkald i løbet kurtiserer og parring. [1]

ReproduktionRediger

Hunnerne modne seksuelt i alderen fem til seks. Derefter hvert år, de bærer en hvalp, som regel i slutningen af ​​februar. De befrugtede æg vokser ind i et sfærisk foster, at implantater i livmoderen først efter tre eller så måneder, så fødslen kan finde sted, mens tilstrækkelig pakisen er til rådighed. [1]

Nyfødte unger vejer omkring Skabelon:Konvertere og er Skabelon:Konvertere længe. Efter fødslen, kun moderen feeds, som hvalp. I løbet af 12 dage sygepleje periode, har moderen ikke spise, mister op til Skabelon:Konvertere per dag. Harpe sæl mælk indeholder op til 48% fedt, så hvalpene vinde over Skabelon:Konvertere per dag. I løbet af denne tid, vokser den unge er "greycoat" i under den hvide neonatal pels, og det vejer Skabelon:Konvertere. Fravænning er brat; moderen vender sig fra sygepleje til promiskuøs parring, så hvalpen bag på isen. Mens frieri starter på isen, parring finder normalt sted i vandet. [1]

Den strandede hvalp græder i første omgang, og derefter bliver stillesiddende at bevare kropsfedt. Inden for få dage, kaster den sin hvide pels, nå "tæppebanker" fase. [1]

Hvalpene er ude af stand til at svømme eller finde føde indtil syv til otte uger gammel eller indtil isen smelter og efterlader dem sårbare over for isbjørnen s og andre rovdyr. Denne hurtige koster dem op til 50% af deres vægt. Så mange som 30% af ungerne dør i løbet af deres første år, dels på grund af deres tidlige immobilitet, fordi de lærer at svømme kun langsomt.

På omkring 13-14 måneder gamle, hvalpen molts igen at blive et "bedlamer". Ungerne molt flere gange, hvilket giver en "plettede harpe", før de voksnes harpe-mærket skind fuldt dukker op efter flere år (eller ikke alle hos kvinder). [1]

Sæler samles årligt på isen for at fælde før der migrerer til sommer fourageringsområder. Deres levetid strækker sig for omkring 20 år. [1]

DistributionRediger

Harpen sælbestanden er fundet i tre adskilte populationer, som hver især bruger en bestemt yngleområde. Den vestlige nordatlantiske bestand, som er det største, ligger ved det østlige Canada. Denne population er yderligere opdelt i to separate besætninger baseret på opdræt placering. The Front besætning racer ud for kyst af Labrador og Newfoundland, og Golfen besætning racer nær Magdalen Islands i midten af ​​Golfen af St. Lawrence. En anden bestand yngler på "West Ice" fra det østlige Grønland. En tredje bestand yngler på "East Is" i Hvidehavet, som er ud for kysten af ​​Rusland. Avl sker mellem midten af ​​februar og april, og varierer lidt for hver bestand.

Migration og løsgængeriRediger

Grønlandssæler er stærkt vandrende. Nordvest befolkning regelmæssigt bevæger sig op til 4000 km nordøst uden for ynglesæsonen; Fodnotefejl: Afsluttende </ref> mangler for <ref>-tag

BioakustikRediger

In general three different types of sounds are produced by dolphins (and other toothed whales). These are click trains, which are a series of individual clicks, usually broadband signals with a rapid rise time,[3] burst pulses, which are individual clicks whose repetition is so high that they are heard by humans only as a buzzing sound[4] and whistles, which are pure-tone, narrow-banded frequency modulated signals which vary in frequency with time. Dusky dolphins have been recorded to make all three sounds but most commonly make burst pulses.[4] Whistling is more common when dusky dolphins mingled with other dolphin species like common dolphins.[5]:79 Dusky dolphins project broadband short-duration echolocation signals similar to that of other whistle-producing toothed whales.[5]:95 Most of the species' echolocation signals have bi-modal frequency spectra with a low-frequency peak between 40 and 50 kHz and a high-frequency peak between 80 and 110 kHz.[6] The levels of the echolocation signals are about 9–12 dB lower than for the larger white-beaked dolphin which belongs to the same genus but is over twice as heavy as the dusky dolphins.[6]

FødesøgningRediger

 
A dusky dolphin pair

Dusky dolphins prey consume a variety of fish and squid species. Common fish species eaten include anchovies, lantern fish, pilchards, sculpins, hakes, horse mackerel, hoki and red cod.[7] They are generally coordinate hunters. These dolphins have very flexible foraging strategies that can change depending on the environment.[8] In certain parts of New Zealand, were deep oceanic waters meet the shore, dusky dolphins forage in deep scattering layers at night.[8] They arrive at the hunting site individually but form groups when in the layer.[8] The dolphins use their echolocation to detect and isolate an individual prey.[6] Groups of foraging dolphins tend to increase when the layer is near the surface and decrease when it descends.[8]

When hunting in shallower waters in New Zealand and Argentina, dusky dolphins tend to forage during the day. The dolphins chase schools of fish or squid and herd them into stationary balls.[9] They may control the school by using light reflected from their white bellies.[10] Dolphins herd prey against the surface but also horizontally against the shore, a point of land or the hull of a boat.[9] During these times, it is believed that dusky dolphins increase prey availability for other predators including other dolphins, seabirds, sharks and pinnipeds. In Argentina, dusky dolphins may use bird aggregations to coordinate foraging efforts.[11] On the other hand, pinnipeds and sharks take advantage of the dolphin hunts which leave almost no advantage to the dolphins.[12] Dusky dolphins are themselves preyed on by killer whales and large sharks. Dolphins avoid killer whales by swimming into shallower water.[11] Dusky dolphins are also susceptible to parasitism by certain nematode, cestode and trematode species, mostly Nasitrema sp., Anisakis sp., Phyllobothrium delphini, Braunina cordiformis and Pholeter gasterophilus.[13]

Socialadfærd og reproduktionRediger

Fil:Duskyd.jpg
A pair of dusky dolphins breaching

Dusky dolphins live in a fission-fusion society with most group size increases occurring during foraging and decreases in group sizes occurring during resting and traveling. In the Golfo San José off the Valdes Peninsula, dolphins encounter a variety of associates by switching between small traveling groups and large socio-sexual groups. Studies of dolphins off Kaikoura, New Zealand show that dolphins normally live in large groups that split into smaller sub-groups.[12] These sub-groups are composed of mating adults (mating groups), mothers with calves (nursery groups) and non-breeding adults.[12] Dusky dolphins have a promiscuous mating system in which both males and females mate with multiple partners. Mating groups are generally made of around ten males and a single female.[12] These mating groups can be found in both shallow and deep water but more often gather near shore.[14]:162

In the mating groups, the males pursue the female in high speed chases. Male reproductive success seems to be determined by speed and agility rather than size, strength or aggression.[14]:164 :175 Females exercise their choice in sexual partners by extending the chase as long as possible.[15] Females may opt to evade males that fail to demonstrate vigor or social skill.[14]:170 It is also possible that males may form alliances to catch females.[14]:167–69 Unlike male bottlenose dolphins, male dusky dolphins can't monopolize females.[14]:166 The time when female dusky dolphins first reproduce varies between regions. New Zealand dolphins first reproduce at about 7–8 years with 6–7 years for Argentine dolphins. A study of dusky dolphins off the coast of Peru showed the reproductive cycle to be around 28.6 months, mother dolphins would be pregnant for 12.9 months, lactate for a further 12 months and rest for 3.7 months before beginning the cycle again.[16] During copulation, females tend to be on the top.[14]:170 As with all species where females mate with multiple partners, male dusky dolphins have large testicles for sperm competition.[14]:166 Dusky dolphins sometimes engage in sexual behavior for reasons other than reproduction, perhaps in greeting or communication. Homosexual behavior between males has been observed.[12] Social sexual behavior tends to be more relaxed.[14]:175

Females with calves tend to gather in nursery groups in shallow water. Nursery groups likely provide calves protection from predators and marauding males as well as benefits such as resting, foraging, socializing and social learning. [17] The formation of nursery groups may grant mothers and calves increased time for rest which is important for growing calves and females which face increased energetic constraints due to lactation. While the behaviors of nursery groups vary by month, resting is the predominant behavior during most months. [17]:188 The formation of nursery groups in shallow waters also allow members to exploit prey species other than those found in deep scattering layers. Both adults and calves have been observed to chase and catch fish and the adults may be teaching the calves how to hunt. [17]:188-89 In contrast to shallower waters, hunting in deep water at night may be too dangerous for calves. [17]:189 Calves are particularly vulnerable to predators like killer whales and use of shallow water by nursery groups may be a predator avoidance strategy. [17]:183 Nursery groups tend to avoid mating groups. [14]:174 Adult males in these groups will aggressively herd and chase single females. This may create a dangerous situation for calves has they may become separated from their mothers and may themselves become subjects of adult male harassment. [17]:185 Calves may also become exhausted, disorientated and more vulnerable to predation. [17]:185 Mother dolphins may look after calves that are not their own.[17]:192

 
Dusky dolphins leaping

AkrobatikRediger

Dusky dolphins perform a number of aerial displays. Displays include leaps, backslaps, headslaps, tailslaps, spins and noseouts.[11] The dolphins also perform head-over-tail leaps which is considered the most "acrobatic" of the displays.[11] A headfirst re-entry is performed when a dolphin leaps clear out of the water and then arches its back strongly while flipping the tail to make a headfirst re-entry. In "humping", the same motion occurs expect the snout and tail do not leave the water during the arch.[11] Leaps, head-over-tail leaps, backslaps, headslaps, tailslaps and spins often occur in groups. One dolphin starts a particular leap and then continues it 3–20 times.[11] Young dusky dolphins apparently are not born with the ability to perform the leaps and must learn to master each one.[17]:190 Calves appear to first learn how to perform noisy leaps, followed by head first re-entries, coordinated leaps and finall acrobatic leaps.[17]:190–91 Adult dusky dolphins may perform different leaps in different contexts and calves may independently learn how to perform leaps but learn when to perform with interactions with others.[17]:191


Mussel farmingRediger

The effect of mussel farming on dusky dolphins has been studied in Admiralty Bay, New Zealand. Regular seasonal migration of dusky dolphins and frequent feeding associations with other apex predators make management of marine farming a wider socio-economic and ecological issue.[18] Dusky dolphins are most often encountered during the winter in Admiralty Bay, the area with the greatest density of proposed farming activity in the region. The dolphins rarely used areas in existing farms and few are observed to enter the boundaries of them.[18] Dolphins that enter mussel farms move rapidly up the lanes between rows of lines and floats.[18]

TourismRediger

 
Dusky dolphin tours off New Zealand's South Island

Dusky dolphins are popular attractions for whale-watching tours. Since 1997, dolphin watching activities have increased in Patagonia, with dusky dolphins (along with Commerson's dolphins) as the target species.[19] For dusky dolphins, the number of tourists increased from 1,393 in 1997 to 1,840 in 2000. The encounter rate grew from 25% during 1999 to 90% in 2001. Most of the groups observed ranged from 50–100 animals.[19] Dolphin watching in this areas started as an alternative to whale watching, mostly based on that of the southern right whale.[19] Dusky dolphin watching is also popular in New Zealand, whose dolphin watching industry begin in the late 1980s. Whale and dolphin watching tours have grown in since then, with the number of permitted dolphin tour operators increasing from none to over 75 since the late 1980s.[20]:235 New Zealand has several locations to view and swim with dusky dolphins, notably in Marlborough Sounds.[20]:236

While dusky dolphin tourism is a larger industry in New Zealand than it is in Argentina, the effects of tourism on the dolphins seem to be lower in the former than the latter.[20]:241 New Zealand tours are operated under permits, whose numbers are limited and are accompanied by conditions and guidelines related to approach procedures and swim operations.[20]:241 By contrast, there is no direct regulation of dolphin watching in Argentina.[19] As such, dolphin activities are often disturbed by touring vessels.[20]:233-35


ReferencesRediger

  1. ^ a b c d e f g h i j k l Fodnotefejl: Ugyldigt <ref>-tag; ingen tekst er angivet for referencer med navnet emm
  2. ^ Nationalgeographic.com
  3. ^ Caldwell, M.C; Caldwell D.K (1971) "Underwater pulsed sounds produced by captive spotted dolphins, Stenella plagiodon", Cetology 1:1–7.
  4. ^ a b SE Yin (1999) "Movement patterns, behaviors, and whistle sounds of dolphin groups off Kaikoura, New Zealand", A Thesis, Texas A&M University, College Station, TX.
  5. ^ a b Au, W.W.L.; Lammer, M.O; Yin, S."Acoustics of Dusky Dolphin (Lagenorhynchus obscurus)". Pp. 75–98 in: Würsig, B., and Würsig, M., editors. The Dusky Dolphin: Master Acrobat off Different Shores. Academic Press. (2010) ISBN 0-12-373723-0
  6. ^ a b c Au, WW; Würsig, B (2004). "Echolocation signals of dusky dolphins (Lagenorhynchus obscurus) in Kaikoura, New Zealand.". The Journal of the Acoustical Society of America. 115 (5 Pt 1): 2307–13. PMID 15139642. 
  7. ^ Fodnotefejl: Ugyldigt <ref>-tag; ingen tekst er angivet for referencer med navnet Perrin
  8. ^ a b c d Benoit-Bird, K.J., Würsig, B., and McFadden, C.J. 2004. "Dusky dolphin (Lagenorhynchus obscurus) foraging in two different habitats: active acoustic detection of dolphins and their prey." Marine Mammal Science 20(2): 215–31.
  9. ^ a b McFadden, C. J. (2003). "Behavioral flexibility of feeding dusky dolphins (Lagenorhynchus obscurus) in Admiralty Bay, New Zealand." M.Sc. thesis, Texas A&M University, College Station , TX.
  10. ^ Würsig, B.; Kieckhefer, T. R.; Jefferson, T. A. (1990). "Visual displays for communication in cetaceans". I Thomas, J.; Kastelein, R. Sensory Abilities of Cetaceans. Plenum Press. s. 545–59. ISBN 0306436957. 
  11. ^ a b c d e f Würsig, B.; Würsig, M. (1980) "Behavior and ecology of the dusky dolphin, Lagenorhynchus obscurus, in the South Atlantic". Fishery Bulletin 77: 871–90.
  12. ^ a b c d e Markowitz, T.M. (2004). "Social organization of the New Zealand dusky dolphin". Ph.D . dissertation, Texas A&M University, College Station.
  13. ^ Van Waerebeek K, Reyes JC, Alfaro J (1993) "Helminth parasites and phoronts of dusky dolphins Lagenorhynchus obscurus (Gray, 1828) from Peru". Aquat Mamm 19(3):159–69.
  14. ^ a b c d e f g h i Markowitz, T.M.; Markowitz, W.J.; and Morton, L.M. "Mating habits of New Zealand dusky dolphins". Pp. 151–76 in: Würsig, B., and Würsig, M., editors. The Dusky Dolphin: Master Acrobat off Different Shores. Academic Press. (2010) ISBN 0-12-373723-0.
  15. ^ Whitehead, H.; and Mann, J. (2000). "Female reproductive strategies of cetaceans". In Cetacean Societies. Mann, J., editior. University of Chicago Press, pp. 219–246. ISBN 0-226-50341-0
  16. ^ Fodnotefejl: Ugyldigt <ref>-tag; ingen tekst er angivet for referencer med navnet HMM
  17. ^ a b c d e f g h i j k Weir, J.; Deutsch, S.; and Pearson, H.C. "Dusky Dolphin Calf Rearing". Pp. 177–94 in: Würsig, B.; and Würsig, M., editors. The Dusky Dolphin: Master Acrobat off Different Shores. Academic Press. (2010) ISBN 0-12-373723-0.
  18. ^ a b c Markowitz, Tim M.; Harlin, April D.; Würsig, Bernd; McFadden, Cynthia J. (2004). "Dusky dolphin foraging habitat: overlap with aquaculture in New Zealand". Aquatic Conservation: Marine and Freshwater Ecosystems. 14: 133–49. doi:10.1002/aqc.602. 
  19. ^ a b c d Coscarella, M. A, Dans, S. L, Crespo, E. A, Pedraza, S. N. (2003) "Potential impact of unregulated dolphin watching activities in Patagonia". J Cetacean Res Manag 5: 77–84. Abstract
  20. ^ a b c d e Markowitz, T.M.; Dans, S.L.; Crespo, E.A.; Lundquist, D.L.; and Duprey, N.M.T. "Human interactions with dusky dolphins: harvest, fisheries, habitat alteration, and tourism". Pp. 211–44 in: Würsig, B., and Würsig, M., editors. The Dusky Dolphin: Master Acrobat off Different Shores. Academic Press. (2010) ISBN 0-12-373723-0.
  1. LeDuc, R.G., Perrin, W.F., Dizon, A.E. (1999). Phylogenetic relationships among the delphinid cetaceans based on full cytochrome b sequences. Marine Mammal Science 15, 619–648.
  2. May-Collado, L., Agnarsson, I. (2006). Cytochrome b and Bayesian inference of whale phylogeny. Molecular Phylogenetics and Evolution 38, 344-354.
  3. Schevill, W.E., Watkins, W.A. (1971). Pulsed sounds of the porpoise Lagenorhynchus australis. Breviora 366, 1–10.

Skabelon:Cetacea

BiologiRediger

Den spættede sæl kan blive 15-20 år eller ældre. De lever næsten udelukkende af fisk.


FormeringRediger

Spættet sæl føder én unge omkring juni måned. Fødslen foregår på land på afsidesliggende sandbanker eller sten. Ungen fødes med voksenpelsen i modsætning til mange arter, der yngler på is, hvor ungen fødes med en hvid, tyk fosterpels (lanugo). Ungen er i stand til at svømme med det samme, hvilket gør det muligt for spættet sæl at føde unger på sandbanker, der overskylles ved højvande. Det er i modsætning til f.eks. gråsæl, der er afhængig af en tør banke til at efterlade ungen på.

SanserRediger

Spættet sæls sanser er som hos alle havpattedyr tilpasset til at fungere under vand. Tilpasningen er dog ikke total, som hos f.eks. hvaler, idet sælerne er afhængige af at gå på land for at hvile og yngle.

HørelseRediger

Sælen hører meget fint, og den kan høre lyd op til 60.000 Hz. Mennesket kan kun høre op til 20.000 Hz. Den får ikke vand i ørerne ved dykning, for den kan lukke ørerne så ingenting kommer ind. Sælen har gode øjne og ser temmelig langt. På land er den bedst til at registrere bevægelser. Den spiser fisk og har i Danmark ikke nogen andre fjender end mennesket.

SynRediger

KnurhårRediger

Andre sanserRediger

Det har været foreslået at sæler biosonar|ekkolokaliserer]] på samme måde som tandhvaler[1], men der er tvivl om resultaternes gyldighed[2]. Der er således almindelig enighed om at sæler ikke bruger biosonar til orientering og byttefangst[3]. Det er ligeledes foreslået at sæler er i stand til at sanse jordens magnetfelt (magnetisk sans eller magnetoreception)[4], men de eksperimentelle resultater er ikke overbevisende og det er derfor et åbent spørgsmål om sæler besidder denne evne.

DykkefysiologiRediger

SælpestRediger

JagtRediger

ReferencerRediger

  1. ^ D. Renouf and M. B. Davis (1982). Evidence that seals may use echolocation. Nature 300:625-637.
  2. ^ D. Wartzok, R. J. Schusterman, and J. Gailey-Phipps (1984). Seal echolocation? Nature 308 (5961):753.
  3. ^ R. J. Schusterman, D. H. Levenson, C. J. Reichmuth, and B. L. Southall (2000). Why pinnipeds don't echolocate. J.Acoust.Soc.Am. 107 (4):2256-2264.
  4. ^ D. Renouf (1989). Sensory function in the habor seal. Sci.Am. April:62-67.

[[Kategori:Oceanic dolphins]] [[Kategori:Mammals of South America]] [[Kategori:Mammals of Argentina]] [[Kategori:Mammals of Chile]] [[Kategori:Mammals of Peru]] [[Kategori:Mammals of Africa]] [[Kategori:Mammals of New Zealand]] [[Kategori:Cetaceans of Australia]] [[Kategori:Fauna of the Pacific Ocean]] [[Kategori:Cetaceans]] [[Kategori:Whale products]] [[Kategori:Toothed whales]] [[bg:Балена]] [[ca:Lagenorhynchus]] [[de:Kurzschnauzendelfine]] [[en:Lagenorhynchus]] [[eo:Balenlameno]] [[es:Lagenorhynchus]] [[fi:Valkokuvedelfiinit]] [[fr:Lagenorhynchus]] [[hr:Usi]] [[hu:Lagenorhynchus]] [[ik:Suqqaq]] [[io:Barto]] [[is:Skíði (hvalir)]] [[it:Lagenorhynchus]] [[ja:カマイルカ属]] [[ka:ვეშაპის ულვაში]] [[nl:Lagenorhynchus]] [[no:Hvalbarde]] [[pl:Lagenorhynchus]] [[pt:Lagenorhynchus]] [[ru:Китовый ус]] [[sh:Usi]] [[sr:Lagenorhynchus obscurus]] [[sv:Barder]] [[tr:Lagenorhynchus]] [[zh-min-nan:Keng-chhiu]]