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[Davyen]

http://www.abcnyheter.no/node/97198

[Chironomus]

TIllet meg å sitere artikkelen i sin heilhet:

European eels (Anguilla anguilla) under- take a ~5000-km spawning migration from Europe to the Sargasso Sea (1), although details of the migration remain unknown. Satellite tracking enables investigation of migratory be- havior of large ocean-dwelling animals (2), but tag sizes have precluded tracking smaller animals like European eels. Here, we present information about the spawning migration of European eels based on a miniaturized pop-up satellite archival transmitter (PSAT). The experiment fell short of revealing the full migration to the Sargasso Sea, but the tags tracked eels up to 1300 km from release and provided unique behavioral insights.

Transmissions were received from 14 of 22 tagged silver eels released on the west coast of Ireland in October and November 2006 (table S1). Eels migrated southwest, suggesting a route against the prevailing shelf edge and Atlantic drift currents and toward the Canary and Azores current systems (Fig. 1A). The horizontal net migration speed varied from 5 to 25 km day–1 (mean of 13.8 km day–1), much lower than re- quired [35 km day–1 (1)] to reach the SargassoSea for spawning in April (table S1). This may reflect drag from the PSAT. However, the in- ferred speed corresponded to results from eels tagged with much smaller archival or acoustic tags in coastal areas (1) and to PSAT studies of much larger long-finned eels (A. dieffenbachii) in the Pacific Ocean (3). In consequence, our data are consistent with a hypothesis (4) suggesting that eels gain speed and increase travel efficiency by entering the south- and west-flowing currents that begin west of Africa and continue as part of the subtropical gyre system to the Caribbean.

The habitat use revealed by depth and tem- perature data showed that migrating eels encoun- tered a diverse range of environments (fig. S1), consistent with ARGO data collected from the same region and time period (fig. S2). When eels moved into the mesopelagic zone they all under- took distinct diel vertical migrations (DVMs), pre- dominantly between depths of 200 and 1000 m. DVM was typified by two tag records (Fig. 1B; all following results refer to these tags). During night, eels occupied shallow warm water (daily average = 282 T 138 m, 11.68° T 0.48°C). Atdawn, eels made a steep dive into the cool dis- photic zone (daily average = 564 T 125 m, 10.12° T 0.89°C, minimum observed = 7.1°C). At night, they ascended steeply back into the upper layer.

DVM allows pelagic organisms to avoid ex- posure to predators during the day and maximize feeding time at night (5). Predator avoidance may explain the deeper depths during the day, but eels do not feed during the spawning migration. We hypothesize that the observed DVM reflects thermoregulation. The daily ascent into shallower warm water may serve to maintain sufficiently high metabolism and swimming activity (1), whereas descent to deeper waters may permit the eels to keep their average temperature below 11°C, delaying gonadal development (6) until reaching the Sargasso Sea. This potential delay of the maturation may prove especially important when eels encounter higher surface temperatures during later stages of the migration.

Further technical improvements of PSAT tags render it realistic to record the entire spawning migration to the Sargasso Sea.

Fullversjon: http://fiskevatn.no/foto/arkiv/36406/91292.jpg

Levert av: http://fiskevatn.no/foto/

References and Notes

1. F. Tesch, The Eel (Blackwell, Oxford, 2003), pp. 1–408.

2. B. A. Block et al., Science 293, 1310 (2001). 3. D. Jellyman, K. Tsukamoto, Mar. Ecol. Prog. Ser. 286,

261 (2005). 4. H. Fricke, R. Kaese, Naturwissenschaften 82, 32 (1995). 5. Y. Iwasa, Am. Nat. 120, 171 (1982). 6. I. Boetius, J. Boetius, Medd. Dan. Fisk.- Havunders.

N.S. 4, 339 (1967). 7. Materials and methods are available as supporting

material on Science Online. 8. This work was funded by the Villum Kann Rasmussen

Foundation, Elisabeth and Knud Petersen’s Foundation, and the European Union FP7 (EELIAD, grant no. 212133). This is paper no. 40 of the Danish Galathea 3 Expedition.

[piscator]

oi oi oi, dette var en kjempespennende artikkel. Nærmere enn dette har vi aldri vært i å få bekreftet det vi egentlig har forstått men ikke tidligere observert, at den europeiske ålen klarer vandringen tilbake til Sargassohavet, og således at den europeiske ålen ikke er samme art eller en underart av amerikansk ål, og ikke avhengig av denne for å reprodusere. At både den amerikanske og den europeiske ålen gyter i det samme området, er jo en indikasjon på at de har samme opphav, hvilket jo er evolusjonært konsistent. Samtidig er det nå slik at begge arter sliter og er truet med utryddelse. Man kan peke på mange av de samme årsakene på begge sider av Atlanterhavet, kraftverksdammer, overbeskatning osv, men kanskje man også kan spore problemene tilbake til forhold der begge artene reproduserer, altså i Sargassohavet? Ikke vet jeg, det er bare en tanke...