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Institute of

SF Sea Fisheries

M.Sc. Sabrina Duncan

Thünen Institute of Sea Fisheries

Herwigstraße 31
27572 Bremerhaven
+49 471 94460 385

What I do

Assemblage structure and trophodynam­ics of mesopelagic fishes in the Canary and Benguela Current

Eastern Boundary Upwelling Systems are known as highly productive areas and vital for fisheries. Because these provide about 20% of the global fish catches, it is important to understand the community assemblage and trophic interactions, since factors such as climate change and over-exploitation can have large impacts on these environments. The Benguela and Canary current are two of these highly productive areas that have seen decreases in fish stocks and changes in community composition due to over exploitation of fish. My aim is to gain a better understanding between the differences in assemblage structure and the role mesopelagic fish play in the food webs of these upwelling systems.

Although once thought of as barren and not containing much life, the mesopelagic zone (200-1000 m)  contains the highest biomass of fish in the world’s oceans. Mesopelagic fish are important, as they are  prey for many predatory fish such as sharks, hake, and tuna. Not only are they a vital part of the ocean’s food webs, but they also play a role in the ocean’s biological pump and contribute to the transport of carbon from the epipelagic to the mesopelagic zone. Many families of mesopelagic fish, including lanternfish (Myctophidae) perform diel vertical migrations (DVM), spending the day in deeper waters and going to the surface to feed on krill and other zooplankton at night. Because fish come to the surface to feed, they are ingesting a considerable amount of biomass, which is then transported to the mesopelagic zone. Through excretion and respiration, large amounts of carbon are transported to these deeper water layers. For these reasns, it is important to understand the role mesopelagic fish play in the food webs of these highly productive areas.

The first aim of my pro­ject is to com­pare the as­semblage struc­ture of meso­pela­gic fish in the Ca­nary cur­rent (sec­tions off the coast of Senegal and Maur­it­ania) and the Benguela up­welling sys­tems (north­ern and south­ern Benguela). In or­der to com­pare as­semblage struc­ture, I will use samples col­lec­ted in 2016 in the Ca­nary cur­rent and samples that we will col­lect for the pro­ject TRAFFIC (see below) in the Benguela. Fish will be iden­ti­fied and meas­ured to com­pare com­munity com­pos­i­tion, rich­ness, and the bio­mass size spec­tra for each loc­a­tion. My second aim is to com­pare the role of meso­pela­gic fish in the food web in these four loc­a­tions. To do this, I will per­form stom­ach con­tent ana­lysis and ni­tro­gen and car­bon stable iso­tope ana­lysis (δ15N & δ13C) of dif­fer­ent fish spe­cies and sizes in each loc­a­tion. With these meth­ods I hope to gain a bet­ter un­der­stand­ing of the as­semblage struc­ture and the role meso­pela­gic fish play in the food web of the Ca­nary cur­rent and Benguela up­welling sys­tem.

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