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3. Extensive avoidance behaviour of krill from predators and nets.

Author

Christiansen, Svenja, Bråthen, Mabel Pernille, Moksnes, Fredrik Lund, Schmedling, Charlotte Aurora, Thorsby, Sara Jegstad, Titelman, Josefin, and Kaartvedt, Stein

Abstract

We used echosounders to assess krill (Meganyctiphanes norvegica) responses to sampling gear and predators. Towing pelagic trawls above autonomous submerged, upward-looking echosounders revealed instantaneous diving by the krill during daytime but not at night. The krill dived at 10–30 cm s−1 with a near-simultaneous response throughout the krill layer below the gear (>10 m). Traversing the paths of the previous sampling revealed long-lasting voids in the krill distribution during the daytime. Such voids were less apparent at night. Backscatter increased in the wake of the gear during nocturnal sampling, possibly due to changes in individual backscatter related to variation in swimming behaviour. During daytime, krill responded to fish schools with instantaneous coherent diving, spanning tens of meters at speeds of 10–27 cm s−1. Coordinated and far-ranging responses indicate that even loose krill aggregations may facilitate predator avoidance by enabling efficient signal transmission between individuals. The krill antipredator behaviour instigated marked daytime krill patchiness. Krill patchiness will vary relative to the predator regime and reflect recent encounters. [ABSTRACT FROM AUTHOR]

Published
2024
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41. Poleward distribution of mesopelagic fishes is constrained by seasonality in light

Author

Langbehn, Tom J., Aksnes, Dag L., Kaartvedt, Stein, Fiksen, Øyvind, Ljungström, Gabriella, Jørgensen, Christian, and Bates, Amanda

Subjects
0106 biological sciences, Global and Planetary Change, 010504 meteorology & atmospheric sciences, Ecology, 010604 marine biology & hydrobiology, 14. Life underwater, 01 natural sciences, Ecology, Evolution, Behavior and Systematics, 0105 earth and related environmental sciences
Abstract

Aim Mesopelagic fishes have a near-global distribution in the upper 1,000 m from tropical to sub-Arctic oceans across temperature regimes. Yet, their abundance decreases poleward and viable populations seem excluded from high latitudes. Why? Location North Atlantic between 50–85°N, with implications for high-latitude oceans globally. Time period Present-day. Major taxa studied Diel vertically migrating (DVM) mesopelagic fishes. Methods We use a mechanistic, state-dependent life-history model to characterize DVM mesopelagic fishes. This model links light-dependent encounters and temperature-dependent physiology, allowing optimal DVM strategies to emerge. We run the model along a latitudinal gradient with increasing seasonality in light and track individual fitness-related measures, that is, survival and surplus energy, through the annual cycle to make predictions about population consequences. Results Mesopelagic fishes thrive in the oceans’ twilight zone, and many are dependent on periods of darkness for safe foraging near the surface, before migrating back to depth during daytime. When daylight lasts for 24 hr during the Arctic summer, these fish are trapped in deep waters void of prey because it is never safe to forage in the shallow waters where zooplankton prey are found. Hence, they are left with two poor options, starvation at depth or depredation while foraging. Our model predicts surplus energy, vital for reproduction and growth, to halve from 50–85°N and annual survival to drop by two-thirds over a narrow range of 10° of latitude around the Arctic Circle. Thus, low recruitment and high predation mortality during summer make polar waters population sinks for mesopelagic fishes because of the extreme seasonality in light. Main conclusions At high latitudes, foraging mesopelagic fishes are exposed to sunlight in upper waters also at night. This makes them easy prey for visual predators, which limits their poleward distribution. Our findings highlight the importance to think beyond temperature to explain high-latitude range limits. publishedVersion

Published
2022

42. Trophic Structure and Community Stability in an Overfished Ecosystem

Author

Utne-Palm, Anne C., Salvanes, Anne G. V., Currie, Bronwen, Kaartvedt, Stein, Nilsson, Göran E., Braithwaite, Victoria A., Stecyk, Jonathan A. W., Hundt, Matthias, van der Bank, Megan, Flynn, Bradley, Sandvik, Guro K., Klevjer, Thor A., Sweetman, Andrew K., Brüchert, Volker, Pittman, Karin, Peard, Kathleen R., Lunde, Ida G., Strandabø, Rønnaug A. U., and Gibbons, Mark J.

Published
2010

48. Surfacing behavior and gas release of the physostome sprat (Sprattus sprattus) in ice-free and ice-covered waters

Author

Solberg, Ingrid and Kaartvedt, Stein

Subjects
Respiration -- Research, Spatial behavior in animals -- Research, Biological sciences
Abstract

Upward-facing echosounders that provided continuous, long-term measurements were applied to address the surfacing behavior and gas release of the physostome sprat (Sprattus sprattus) throughout an entire winter in a 150-m-deep Norwegian fjord. During ice-free conditions, the sprat surfaced and released gas bubbles at night with an estimated surfacing rate of 3.5 times per fish [day.sup.-1]. The vertical swimming speeds during surfacing were considerably higher (~10 times) than during diel vertical migrations, especially when returning from the surface, and particularly when the fjord was not ice covered. The sprat released gas a few hours after surfacing, suggesting that the sprat gulped atmospheric air during its excursions to the surface. While the surface activity increased after the fjord became ice covered, the records of gas release decreased sharply. The under-ice fish then displayed a behavior interpreted as 'searching for the surface' by repeatedly ascending toward the ice, apparently with limited success of filling the swim bladder. This interpretation was supported by lower acoustic target strength in ice-covered waters. The frequent surfacing behavior demonstrated in this study indicates that gulping of atmospheric air is an important element in the life of sprat. While at least part of the population endured overwintering in the ice-covered habitat, ice covering may constrain those physostome fishes that lack a gas-generating gland in ways that remain to be established., Introduction The clupeid sprat (Sprattus sprattus) is a physostome fish with an open swim bladder. Clupeids have one pneumatic duct connecting the swim bladder to the stomach and one anal [...]

Published
2014
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49. Piscivorous fish patrol krill swarms

Author

Kaartvedt, Stein, Røstad, Anders, Fiksen, Øyvind, Melle, Webjørn, Torgersen, Thomas, Breien, Mari Tiseth, and Klevjer, Thor A.

Published
2005

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