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BI 3063 J. Mork H08

Genetic and biologic stock management

Evolution of the gadoid Evolution of the gadoid fish familyfish family

miocene ---> presentmiocene ---> present

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BI 3063 J. Mork H08

Genetic and biologic stock management

Setting the stage...

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BI 3063 J. Mork H08

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Earth history mapped to 24 hours

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BI 3063 J. Mork H08

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EVOLUTIONARY TIME LINE

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BI 3063 J. Mork H08

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EVOLUTIONARY TIME LINE

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THE EOCENE WARM EPOCHTHE EOCENE WARM EPOCH

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BI 3063 J. Mork H08

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EOCENE CONTINENTS

Global paleogeographic reconstruction of the Earth in the middle Paleogene (Eocene) period 50 million years ago.

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BI 3063 J. Mork H08

Genetic and biologic stock management

Prorastomus, an early sirenian

EOCENE ANIMALS

The Grande Coupure, or "great break" in continuity with a major European turnover in mammalian fauna about 33.5 Ma, marks the end of the last phase of Eocene assemblages, and the arrival in Europe of Asian immigrants. The Grande Coupure is characterized by widespread extinctions and allopatric speciation in small isolated relict populations.

The Grande Coupure of Eocene

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Genetic and biologic stock management

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BI 3063 J. Mork H08

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After the warm Eocene comes the Oligocene and then the Miocene, which marks the start of a general cooling of the earth.

East Antarctica had some glaciers during the early Miocene (23-15 million years ago). Oceans cooled partly due the formation of the Antarctic Circumpolar Current, and about 15 million years ago the ice cap in the southern hemisphere started to grow to its present form.

The Greenland ice cap developed later, in Pliocene time, about 3 million years ago.

The MIOCENE cooling epochThe MIOCENE cooling epoch

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BI 3063 J. Mork H08

Genetic and biologic stock management

Middle Miocene ocean map

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BI 3063 J. Mork H08

Genetic and biologic stock management

The Middle Miocene extinction peak, refers to a wave of extinctions of terrestrial and aquatic life forms that occurred around the middle of the Miocene Epoch, c. 14.8 to 14.5 million years ago, during the Langhian stage of the Miocene.

Researchers dispute the full extent of the extinctions in the middle Miocene; the most extreme estimates assert that 30% of the mammalian genera of the early Miocene epoch went extinct in the disruption — though other scientists rate the event much less severe. Possible causes are still speculative: the attention of some researchers has focused on the consequences of the bolide (meteorite) impact that created the Nördlinger Ries crater in southwestern Germany, which is dated in the relevant era. Volcanic action has also been considered; global volcanic ash output reached an extreme at the time, notably from the Rift Valley of East Africa, with consequent cooling of global climate and an advance in the East Antarctic Ice Sheet.

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BI 3063 J. Mork H08

Genetic and biologic stock management

The gadoid family is, together with the clupeoid family, among the few of current fish families that have had the main part of their differentiation into current species in the Atlantic.

From an ancestrous forefather in the North Pole basin, in a warmer period with substantially higher (i.e. > 20º C) oceanic temperatures than today, the gadoids inhabited, populated and differentiated into their various niches made available when the Atlantic opened up.

The northern polar areas have undergone large temperature fluctuations in the past. For example, in the period known as the "Palaeocene-Eocene thermal maximum", a period that occurred around 55 million years ago, the polar climate was sub-tropic with massive carbon depositions on the seabed and increased CO2 concentrations in the air. Today the seabed deposits are evident from deep-sea core drillings at 500 m depth near the geographical north pole.

The main gadoid species differentiation is assumed to have taken place during the:

Oligocene (34 - 23 mya) Miocene (23 - 5 mya) Pliocene (5 mya --)

Paleogeography and gadoid evolutionPaleogeography and gadoid evolution

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Genetic and biologic stock management

Warm and cold periods in geological time

[Espen Sjulstad Powerpoint presentation]

&

Late Oligocene climatic changes: Evidence from calcareous nannofossils at Kerguelen Plateau Site 748 (Southern Ocean) Giuliana Villa and Davide Persico]Palaeogeography, Palaeoclimatology, Palaeoecology Volume 231, Issues 1-2, 9 February 2006, Pages 110-119 Antarctic Climate Evolution: geological records from the margin and modelling]

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Genetic and biologic stock management

The gadoid family todayThe gadoid family today

Norwegian marine waters:Silvery pout (Gadiculus argenteus)

Cod (Gadus morhua)Haddock (Melanogrammus aeglefinus)Whiting (Merlangius merlangus)Pollack (Pollachius pollachius)Saithe (Pollachius virens)Tusk (Brosme brosme)Ling (Molva molva)Blue whiting (Micromesistius poutassou)Norway pout (Trisopterus esmarkii)Poor cod (Trisopterus minutus)

Fresh water:Burbot (Lota lota) - circumpolar distribution

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(From Bakke & Johansen)

For comparison, the time since divergence between Atlantic cod and Pacific cod is probably arond half a million years.

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Today, the different gadoid species are very variable in size, longeivity, temperature preferences and latitudinal distribution. They are thus characterised by a variety of habitate preferences;

• pelagic and benthic, • shallow and deep, • polar, northern and temperate latitudes

Nutritionwise, they are mostly carnivorous. Evolutionary, the gadoid family has beeen a success story.

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