Oceanic frontal zones have been shown to deeply influence the distribution of primary producers and, at the other extreme of the trophic web, top predators. However, the relationship between these structures and intermediate trophic levels is much more obscure.
Myctophids, or lanternfish, are one of the most abundant groups of mesopelagic fish. They are present in the oceans worldwide and constitute one the largest portions of world fish biomass. They represent important prey items for numerous predators and are reported to play a central role in the carbon export to deep sea depths, possibly affecting the climate. Constituting a potentially massive harvestable resource, they are threatened to be exploited in the near future. However, their description in trophic models should be improved, and a better understanding of the mechanisms regulating their biomass is pivotal for fisheries management and sound marine spatial planning.
The paper Fine-scale structures as spots of increased fish concentration in the open ocean compares acoustic measurements of mesopelagic fish concentration to satellite-derived fine-scale Lagrangian Coherent Structures in the Indian Sector of the Southern Ocean. The paper demonstrates that higher fish concentrations occur more frequently in correspondence with strong Lagrangian Coherent Structures. However, not all the Lagrangian Coherent Structures are associated with a strong fish biomass, as other factors affect fish distribution. In this regard, the authors showed that, when only chlorophyll‐rich Lagrangian Coherent Structures are considered, their intensity modulates significantly the local fish concentration.
The paper also presents a model representing fish movement along Lagrangian features, specifically built for mid‐trophic levels. Its results, obtained with realistic parameters, are qualitatively consistent with the observations and the spatio‐temporal scales analyzed. Overall, these findings may help to integrate intermediate trophic levels in trophic models, which can ultimately support management and conservation policies.
Future satellite missions, such as the Surface Water and Ocean Topography (SWOT) altimetry satellite will possibly help to improve this type of models by helping the assimilation scheme to better reconstruct the three dimensional dynamics, and in particular providing information on vertical velocities of the ocean, for which there is currently a lack of observational information. At the same time, they will also improve satellite resolution, providing a more precise location of fine-scale fronts.
The work contributed to CNES/TOSCA and LEFE project KERTREND and BIOSWOT, and was partly funded by the Copernicus Marine Environment Monitoring Service (CMEMS) Sea Level Thematic Assembly Centre (SL-TAC). This work was supported financially and logistically by the Agence Nationale de la Recherche (ANR MyctO-3D-MAP, Programme Blanc SVSE 7 2011, Y. Cherel), the Institut Polaire Français Paul Emile Vic- tor, and the Terres Australes et Antarctiques Françaises and benefited from ANR-11-IDEX-0004-17-EURE-0006.
FOR MORE INFORMATION
Baudena, A., Ser-Giacomi, E., D’Onofrio, D. et al. Fine-scale structures as spots of increased fish concentration in the open ocean. Sci Rep 11, 15805 (2021). https://doi.org/10.1038/s41598-021-94368-1