Water column habitats of key marine species
at large scale
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The water column is the most widespread habitat of the planet and is entirely heterogeneous. The presence of gyres, eddies, fronts, temporary currents etc. defines specific conditions that are conducive to different expressions of ecosystem functioning (European Marine Board, 2013). The objective of this project is to identify the daily habitat of key marine species, mainly fish of market value, using satellite-derived data of the sea surface in support of the management and control of fisheries and the implementation of spatial protection measures.
The target species are currently the Atlantic bluefin tuna, the European hake (recruits) and fin whale in the Mediterranean Sea as well as the yellowfin and skipjack tuna species in the tropical Atlantic and Indian Ocean. However a more generic index of productive pelagic habitats at the European scale is also in preparation to monitor the influences of climate and nutrient run-off on the productivity of marine food webs. The productivity pelagic habitat index shall also be used to provide a classification pelagic habitats at the European scale.
The feeding habitat is derived for all species while the spawning habitat is computed only for tuna species. The period covered is from March 2000 or August 2003 depending on the sensors used to yesterday (near real time).
The chosen modelling approach of species distribution relies on the niche theory, which utilizes existing knowledge of environmental and ecological processes to select a limited set of predictors and improve model interpretability. The relevant information for the habitat of specific marine species which is contained in the daily variability of surface oceans is presently fully exploited.
The potential feeding habitat was mainly derived from the occurrence of productive oceanic fronts of satellite-derived sea surface chlorophyll-a content. The potential spawning habitat was mostly inferred from the heating of surface waters (daily temperature difference in a floating window of 30 days) and surface currents. A specific range of chlorophyll content for each habitat was also shown to be discriminant. Hake nurseries were inferred using also physical limitations such as a restricted range of bottom temperature and maximum value for bottom currents since age-0 hake have limited if no mobility.
Potential habitat of the Atlantic bluefin tuna in near-real time (with a one month delay for preventing any use for fishing, 3-day composite):
The aims of the research project may vary with the target species but generally are:
- to improve the assessment of fish stocks (standardization of Catch Per Unit Effort),
- to improve fisheries management (prediction of catch and abundance, of harvest rules based on environmental variation and regime shifts) or species protection (identification of Essential Fish Habitat or Marine Protected Areas),
- to increase knowledge on behaviour and migration patterns (for instance bluefin tuna migration in the Mediterranean Sea for spawning),
- to rise the efficiency of fisheries control (using near-real time maps).
Two main behaviours are recognized in most fish: feeding and spawning. The JRC habitat model uses satellite data of Sea Surface Temperature (SST) and surface chlorophyll content (CHL) from Modis-Terra (SST) and SeaWiFS (CHL) since March 2000 and from MODIS-Aqua sensor (NASA) since July 2002 to compute daily habitats. The use of two independent sets of satellite data observing the surface ocean at different time allows increasing the habitat coverage since SST and CHL are not sensed through clouds.
The methodology used for mapping the potential habitat is a multi-criteria evaluation with specific parameter values for each species. Water depth is a habitat criteria only for the fin whale (minimum depth) and for hake (maximum depth). The feeding habitat was mainly traced by horizontal changes of surface chlorophyll content created by currents (CHL fronts), while the spawning habitat (tuna species) was mostly inferred from the heating of surface waters. Generally, higher CHL contents were found to be preferred for the feeding and a minimum temperature was found to be preferred for the spawning habitat (tuna species).
Both habitats were defined by the presence of relevant oceanographic features (CHL fronts in relation to nutrition and formation of thermal stratification in relation to reproduction) and are therefore potential and functionally-linked habitats, as opposite to effective habitats which are always difficult to produce for marine animals, especially highly migratory ones such as tunas or whales.
The daily maps of bluefin tuna potential habitats were calibrated and validated with geo-located observations from scientific surveys or fisheries operations. An independent calibration is performed for each used couple of satellite data (SST/CHL). Monthly, seasonal and annual maps of potential feeding and spawning habitat were then computed from daily maps for the last decade.
- Atlantic bluefin tuna (Mediterranean Sea)
- 15 days
- Multi-annual composite
- Annual anomaly
- 15 days climatology
- Monthly (spawning season)
- Multi-annual composite
- Annual anomaly
- Atlantic bluefin tuna (Gulf of Mexico and North Atlantic, end 2014)
- Fin whale (Western Mediterranean Sea) VERSION 2! (see below the modifications from the published version1)
- 15 days
- Multi-annual composite
- Annual anomaly
~~~~~~~~~~~~~~~~ Modifications from version1 (published) to version 2 of the fin whale potential habitat: The new optimized set of parameters are the following (CHL from MODIS-Aqua sensor):
- Hake nurseries (Mediterranean Sea, mid 2014)
- Yellowfin tuna (2015)
- Skipjack tuna (2015)
- Small pelagics (anchovy or sardine, 2016)
- Productive pelagic habitat index (European Seas, 2015)
- CHL gradient > 0.0015 mgCHL/m3/km
- 0.100 < CHL concentration < 0.326 mg/m3
- Water depth > 90 m The main changes are the following:
- the satellite SST front computation was removed since it created somehow either noise and/or a fragmentation of the habitat and a substantial loss of coverage. The CHL fronts are thus the main tracer of the favourable feeding habitat (with a specific CHL range). The satellite CHL is quite stable compared to the SST since it constitutes an optical observation of several metres of the surface waters instead of few microns for the thermal observation.
- because MODIS-Aqua is showing more and more stripes on the CHL data, an increased smoothing was also performed to remove them in the new scheme as they resulted in small linear and totally artificial fronts of low intensity.
- the filter size for computing the fronts (horizontal gradient) is smaller than before (3 instead of 5 pixels) so that the habitat is now available substantially closer to the coast. - Non-habitat is furthermore defined outside the favourable range so that, notably, winter coverage has increased and the overall habitat size decreased in relative value of the basin surface (%). The consequence of these changes is that the favourable feeding habitat is much more continuous and less fragmented than before. The oceanic features (productive fronts) are substantially more continuous and visible than before and the fronts are somehow wider due to the smoothing. The back side of reducing the fragmentation is that the mean closest distance to habitat is about double than for version 1 but it is believed that at least part of this apparent decrease of performance is due to the increased fragmentation and noise which was in the version 1 when using the satellite SST. Therefore, the predictability is likely to be similar, with a higher focus on hot spots of preferred habitat.
This research initiatives are performed with the full collaboration of numerous research institutes across Europe.
- Atlantic bluefin tuna: After an intitial collaboration with IFREMER (France), the current extension of the habitat over the North Atlantic and the Gulf of Mexico is performed within an international collaboration of scientific experts from Mexico, the USA, Canada, Portugal, Spain, France, Italy, Croatia, Greece, Turkey, Denmark and Japan.
- Tropical tunas species: IRD - France
- European Hake: MEDITS scientific community - Italy: COISPA, SIBM-Genova University, CIBM, UNICA, Rome University, CNR-IAMC, Bari University. France: IFREMER. Spain: IEO. Malta: MRRA. Greece: IMBC, HCMR.
- Fin whale: Italy: TETHYS, ISPRA, CETUS, CIMA Foundation. France: ÉcoOcéan, GIS3M, GREC, Souffleurs d'Écume, WWF-France, La Rochelle University, IFREMER. Spain: ALNITAK, CIRCÉ. Switzerland: Swiss Cetacean Society. International: NATO-NURC.
Druon JN, Panigada S, David L, Gannier A, Mayol P, Arcangeli A, Cañadas A, Laran S, Di Méglio N and P Gauffier (2012)
Potential feeding habitat of fin whales in the western Mediterranean Sea: an environmental niche model. Mar Ecol Prog Ser 464:289-306 | Full text and complement in pdf format
Druon JN, Fromentin JM, Aulanier F, Heikkonen J (2011)
Potential feeding and spawning habitats of Atlantic bluefin tuna in the Mediterranean Sea
MEPS 439:223-240 | Full text in pdf format | See Press release
Druon JN (2010)
Habitat Mapping of the Atlantic Bluefin Tuna Derived from Satellite Data: Its Potential as a Tool for the Sustainable Management of Fisheries. Marine Policy;34(2):293-297 | Full text in pdf format (not open access)
Vaes T, Druon J-N (2013)
Mapping of potential risk of ship strike with fin whales in the Western Mediterranean Sea. A scientific and technical review using the potential habitat of fin whales and the effective vessel density. European Commission Report (EUR 25847 EN), doi: 10.2788/8520 | Full text in pdf format | See JRC Headline
Aulanier F, Druon J-N (2010)
The habitat model of marine species using satellite remote sensing: technical aspects. European Commission Report (EUR 23790 EN), doi:10.2788/20881 | Full text in pdf format
Druon J-N (2009)
Environmental analysis of Bluefin Tuna: Identifying its preferred habitat in the Mediterranean Sea. European Commission Report (EUR 23790 EN), doi: 10.2788/20881 | Full text in pdf format