More on Habitat Mapping for EBM: Daily Updated Maps to Manage Migratory Species

The December 2011/January 2012 issue of MEAM examined how detailed mapping of the sea floor has informed marine EBM (MEAM 5:3). Because benthic habitat maps show where particular plants and animals are likely to live, such maps can be invaluable for conserving certain species or for assigning specific uses to compatible areas.

Habitats can comprise more than just the sea floor, of course. In the upper water column, dynamic features such as water temperature and food availability can also determine where species are likely to be at any point in time. These features can shift from year to year or even day to day, and some marine species follow these shifts. In cases where management must track the movement of migratory species, detailed maps of dynamic ocean processes may be very helpful.

An EU research team has suggested that daily maps of temperature and chlorophyll concentration at the sea surface (the latter represents food availability) could help in managing the Mediterranean's dwindling stock of bluefin tuna. In an October 2011 article in the journal Marine Ecology Progress Series, a team led by Jean-Noël Druon of the European Commission's Joint Research Centre* showed the region's bluefin tuna closely follow temperature gradients and chlorophyll fronts, both of which are trackable with satellite data. They suggested that regularly updated maps of probable bluefin habitat could be used to restrict fishing grounds (through what would amount to mobile, or dynamic, MPAs) or to direct fishing activity to certain areas – either for greater fishing efficiency or to ease enforcement. Journal articles on the habitat modeling and its potential use in fisheries management are available at http://fishreg.jrc.ec.europa.eu/fish-habitat. Druon discusses the research below.

MEAM: Your bluefin tuna habitat maps could be used to restrict fishing grounds or to prompt fishers toward favorable areas. Which of these strategies would you prefer to see applied with your maps?

Jean-Noël Druon: Those two strategies are not exclusive or incompatible. One strategy we have suggested would be to close bluefin tuna fisheries in the spawning grounds and direct fishermen toward the feeding grounds. [Editor's note: Spawning and feeding grounds are associated with different characteristics of temperatures and chlorophyll concentrations.] This strategy would help protect the spawners to ensure sufficient reproduction, while decreasing illegal fishing by concentrating the fleet and making enforcement more efficient.

The choice of management or enforcement strategies should be driven by the chance of success when implemented. The practical aspects range from equity of fishing opportunities among fishermen to compatibility with current legislation. Managed areas that are open to bluefin tuna fishing, for example, should be well distributed in the Mediterranean Sea to provide comparable fishing opportunities to fishermen from all countries possessing a fishing quota. We have also proposed that some fishing could be allowed in spawning grounds but only in the second half of the favorable period (spawning lasts regionally for 15-20 days), allowing the adult fish to spawn several times before potential capture. Whatever the management measure, it should be evaluated carefully by the various stakeholders involved – fishery scientists, control authorities, fishery technical experts – prior to implementation.

MEAM: The International Commission for the Conservation of Atlantic Tunas (ICCAT), which manages Atlantic bluefin tuna, has not indicated it intends to implement your proposed strategy. As you point out in your research, the chlorophyll and temperature data are freely available. Is it possible that fishers – including illegal ones – could use the data to produce their own tuna maps?

Druon: We may work with the ICCAT Scientific Committee on spatial analysis combining their aerial surveys with our habitat maps in order to better characterize the effective spawning grounds. In the meantime, our maps of mean fortnight habitat have been provided to the European Fisheries Control Agency to better plan the EU joint control. And our real-time maps have been sent to several national control authorities during the fishing season to help guide at-sea enforcement in the favorable spawning grounds.

Because of the high variability of the potential spawning habitat, only the real-time maps are useful to fishermen for increasing their catch. Such maps are not publicly available nor are they easy to produce by non-experts. Purse seiners targeting bluefin in the Mediterranean Sea do not even use satellite-derived temperature or chlorophyll content, in contrast to their colleagues who target other tuna species in tropical latitudes. Therefore the habitat information is in the appropriate hands for combating illegal fishing. A good collaboration between scientists and control authorities (in addition to ongoing enforcement and fleet reduction) should help reduce effective catches to quota levels that enable Atlantic bluefin tuna recovery, as well as re-establishing fairness among fishermen.

* In collaboration with Jean-Marc Fromentin of the French Research Institute for Exploration of the Sea (IFREMER).

For more information:

Jean-Noël Druon, Maritime Affairs Unit, Joint Research Centre of the European Commission, Ispra, Italy. E-mail: jean-noel.druon@jrc.ec.europa.eu