A dynamic optimization model of the diel vertical distribution of a pelagic planktivorous fish

We investigated fine-scale (5m, 4h) species-and stage-specific (N1 to C6) distributions of common copepods at an anchor station in a Swedish fjord during two 24 h periods in October 1997. Generally, both calanoid and cyclopoid nauplii were found near the surface, while copepodids stayed deeper in the water column. No diurnal migration was observed. To analyze the observed distributions, we combined mechanistic models of predation risk from fish and copepods, formulations of temperature-dependent growth and a habitat optimization model, maximizing expected lifetime reproductive output. Motility pattern has implications for encounter rates with copepod predators, and therefore affected optimal vertical positioning in the model. By applying species-and stagespecific motility, and accounting for the ambient copepod predator field, we computed depth profiles of the mortality risk for the observed field situation. Predicted diel and ontogenetic vertical distribution patterns for various levels of fish concentrations were compared with observed distributions, and much of the patterns in the field were explained by the model. While the risk of fish predation governs the deeper habitat selection of the larger copepodids, the risk of copepod predation is probably more important for nauplii and small copepods. In addition, the vertically homogeneous growth profile and dense layers of copepod predators may wipe out potential benefits of diurnal migration.

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“…The solar irradiance at the surface was modeled as a function of h from the measured light level at midday (see Rosland & Giske 1994).…”

Section: Modelmentioning

confidence: 99%

Ontogenetic vertical distribution patterns in small copepods: field observations and model predictions

Titelman

Fiksen²

2004

Mar. Ecol. Prog. Ser.

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“…During the last decade, the risk of mortality has been established as vital for the understanding of habitat choice (Rosland & Giske 1994, Kaartvedt et al 1996, Eiane et al 1997, behavior (Ohman 1990, Fiksen & Giske 1995, Ohman & Wood 1995, De Robertis 2002, and life history (Aksnes & Giske 1990, Verity & Smetacek 1996 of organisms inhabiting the marine pelagial. Without proper estimates of mortality it is very hard, or impossible, to address any of these problems in quantitative terms.…”

Section: Introductionmentioning

confidence: 99%

Stage-specific mortality of Calanus finmarchicus, Pseudocalanus elongatus and Oithona similis on Fladen Ground, North Sea, during a spring bloom

Eiane

Ohman²

2004

Mar. Ecol. Prog. Ser.

110

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We used Woods Population Surface Method to estimate stage-specific mortality rates for populations of Calanus finmarchicus, Pseudocalanus elongatus, and Oithona similis from abundance data obtained during the Fladen Ground Experiment (FLEX 1976) in the northern North Sea. Temperatures from the day and night depth distributions of each developmental stage were used to force temperature functions for the duration of developmental stages. In addition, we considered the influence of potential food-limitation of development, which had only minor effects on the mortality estimates. We show that the risk of mortality changes substantially over the life span of the animals, with notable differences among species. O. similis, in particular, shows negligible losses after naupliar stages 1 and 2, which may account for its numerical dominance in many ocean regions. Differences among taxa are poorly explained by allometry alone and are instead related to species-and stagespecific differences in behavior. The vertical migration behavior of late developmental stages of C. finmarchicus (i.e. their choice of habitat) might help to reduce mortality risk.

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“…Furthermore, field studies on the mesopelagic fish Maurolicus muelleri, an important zooplanktivore in Norwegian fjords, have revealed that both the feeding and the vertical behavior are highly sensitive to the prevailing light conditions of the water column (Giske and Notes Aksnes 1992;Baliño and Aksnes 1993;Rosland andGiske 1994, 1997). According to the model derived by Aksnes and Giske (1993) and Aksnes and Utne (1997), visual feeding rate (f) can be expressed…”

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confidence: 99%

Fish or jellies—a question of visibility?

Eiane

Aksnes

Bagøien

et al. 1999

Limnology & Oceanography

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Light is an important limiting factor for the visual foraging process in fishes, and the light regime may potentially affect the competition between visual and tactile predators. We investigated two equal‐sized fjords of quite different pelagic food web structure. Earlier studies have revealed that the jellyfish Periphylla periphylla dominates Lurefjorden, while fish predators dominate in the other fjord, Masfjorden. Furthermore, the mesozooplankton stock of Lurefjorden is larger in both total biomass and size of the individuals. Hence, earlier hypotheses linking the competitive advantage of tactile gelatinous plankton predators to smaller sized mesozooplankton communities are unable to explain the present phenomenon. To see if the difference in the pelagic biota of the two fjords could be associated with characteristics of the light regime, we measured the light absorbance in the basin water of the two fjords. We found that, due to a slightly stronger influence of coastal water in the basin water of Lurefjorden, the exponential light absorbance coefficient below 100 m is two to three times higher there than in other fjords. This results in a reduction in light flux of several orders of magnitude, effectively reducing the possibility of visual foraging. The tactile mode of predation in jellyfish, however, is not influenced, and we hypothesize that the visibility regime has a decisive role in structuring the pelagic food webs of the two fjords.

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A dynamic optimization model of the diel vertical distribution of a pelagic planktivorous fish

Cited by 74 publications

References 62 publications

Ontogenetic vertical distribution patterns in small copepods: field observations and model predictions

Ontogenetic vertical distribution patterns in small copepods: field observations and model predictions

Stage-specific mortality of Calanus finmarchicus, Pseudocalanus elongatus and Oithona similis on Fladen Ground, North Sea, during a spring bloom

Fish or jellies—a question of visibility?

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