The Mesopelagic Fish Guide: shedding light on 550 fish species in one of the largest ecosystems on earth
Within the pelagic zone – the ecological realm that includes the entire ocean water column – the mesopelagic zone is an intermediate ocean layer that extends between depths of 200 and 1 000 m below the ocean surface, and is one of the largest ecosystems on earth. Mesopelagic fish are key components of this ecosystem and although they are abundant within mesopelagic depths during daytime, they ascend to feed, in most cases into the epipelagic zone (0-200 m), shortly before sunset. Through this act referred to as "diel vertical migration", mesopelagic fish contribute to the "biological pump", which facilitates carbon transfer from the surface to the deep ocean. Without this pump, the partial pressure of atmospheric CO2 would be twice its current value. Moreover, as predators on plankton and prey for large fishes, marine mammals, seabirds and others, mesopelagic fish are also a direct link between plankton and high-level predators, many of which are commercially fished.
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The mesopelagic zone is one of the largest marine ecosystems on earth. ©FAO |
Sternoptyx pseudodiaphana, a mesopelagic fish species found in the Atlantic Ocean. ©FAO |
Several recent studies have estimated the mesopelagic fish to be the largest vertebrate group in the world (in terms of biomass), and this has attracted the attention of the fishing industry, seeking sources of fishmeal and oils, which are in great demand from the expanding aquaculture and the livestock sectors. The potential exploitation of this resource may cause repercussions on the structure and functioning of the mesopelagic ecosystem (and wider ocean), but a thorough understanding of the ecological role played by this community, as well as of its species" biology, ecology and abundance, is still lacking.
For this reason, research on mesopelagic ecosystems has been included in the EAF-Nansen Programme"s Science Plan as part of a dedicated theme (Theme 3). The necessary foundation of any research activity is the accurate identification of the species, but mesopelagic fish species identification is a challenging task due to a number of reasons such as the often slight morphological differences within and among species, their soft bodies that are easily damaged in the nets, and the lack of comprehensive keys to species and specific training in their use. In the central and south- east Atlantic Ocean, one of the EAF-Nansen Programme"s focus areas, existing identification tools were either outdated, had a limited geographical coverage or did not include keys to the identification of many mesopelagic fish taxa. To address this issue, the EAF-Nansen Programme set up a project to take on the challenge of producing a fully illustrated identification guide to mesopelagic fish species.
Renowned taxonomists, scientific illustrator, experts and editors take on the challenge of mesopelagic fish identification
FAO has a 50-year history of producing identification tools for fishery purposes through its FishFinder Programme. This Programme has set high-level standards and contributed to the field by involving world-renowned taxonomists, professional scientific illustrators, and dedicated technical and scientific editors. "Understanding the needs and level of expertise of the technical or scientific staff that will be using the identification tool is central to our work" said Edoardo Mostarda, EAF-Nansen Programme consultant, and scientific editor of the mesopelagic-fish guide project. "When the project was conceptualized in early 2018, due to the well-known complexity of identifying mesopelagic fish, we realized that the only way to make the guide really user-friendly was to base it entirely on fully illustrated dichotomous keys to all taxa", he continued.
In order to accomplish this difficult task, a team of experts led by Tracey T. Sutton (Nova Southeastern University, Florida, USA), and lantern fish taxonomists P. Alexander Hulley (Iziko-South African Museum, South Africa) and Dr John R. Paxton (Australian Museum, Australia), as well as scientists with specific expertise in the study area, such as Rupert Wienerroither and Diana Zaera-Perez (Institute of Marine Research, Norway), were brought together.
The team was also joined by the FAO FishFinder Programme scientific illustrator, Ms Emanuela D'Antoni, who has contributed to building one of the largest archives of illustrations focusing on marine and freshwater species. These illustrations are not only FAO's heritage, but are also made available to the scientific community and interested public. In fact, FAO receives countless requests from all over the world every year, for the permission to use its illustrations from scientists willing to develop their own identification tools, thus contributing to improving knowledge on marine biodiversity.
The work on the new guide started in 2018, with a first team meeting, during which the authors defined criteria for the selection of the species, such as the geographical and depth limits of the species. This resulted in a list of more than 550 species, and with this established, the work on the identification keys could finally begin.
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Eustomias. The 35 species occurring in the area can only be identified by looking at their |
Hygophum taaningi (Taning's lanternfish, Myctophidae). The identification of lanternfishes |
After one year of hard work, a draft of the guide was ready, and it was time to for scientists from Western African countries to test it in the field. In early 2019, the EAF-Nansen Programme's Research Vessel (R/V) Dr Fridtjof Nansen carried out a mesopelagic fish survey off Namibia and a scientist on board, José Gonzalez from the Spanish Institute of Oceanography (IEO) was tasked with testing the guide and collecting specimens for a training workshop later that year.
"I usually analyze the Identification Guides in depth", said José Gonzalez, who has more than 30 years of experience in fisheries research. "I use them constantly and I am always trying to adapt them so that they can be as practical as possible" he said, and explained that: "The survey was a good test to fine-tune the Mesopelagic fish guide, as it was carried out on a boat that is very well prepared for this type of work, along with a very professional crew."
The training workshop, that was held in Swakopmund, Namibia, in June 2019, was attended by 16 scientists who were not familiar with the identification of the mesopelagic fish species. All participants struggled at first, but after five days of work under the guidance of Alexander Hulley and José Gonzalez, their capacity to identify the species increased. The workshop was also an opportunity to improve the identification guide, based on the scientists' comments during its use. Reflecting on the experience and the final product, José Gonzales said: "The Mesopelagic Guide will provide an enormous contribution to the knowledge and identification of such complex ichthyological fauna."
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Participants of the training workshop in Namibia, |
The Identification Guide to the Mesopelagic Fishes |
The guide was finalized in July 2020, released online in August 2020, and will be printed and distributed to the main marine research institutions of West Africa by the end of 2020.
Useful links:
- Identification guide to the mesopelagic fishes of the central and south east Atlantic Ocean (FAO Publication)
- FAO FishFinder (FAO Species Identification and Data Programme)
- EAF-Nansen Programme Science Plan (FAO Publication)
For more information:
[email protected]