Marine Ökologie

Quantification of eel mortality in German inland waters

Funded by the German Federal Ministry of Food, Agriculture and Consumer Protection

PD Dr. Reinhold Hanel, Dr. Lasse Marohn, Enno Prigge

 

European eel (Anguilla anguilla) recruitment experienced a sharp decline since the 1970s and the stock is considered to be out of safe biological limits. Reasons for this appear to be divers including anthropogenic impacts during the continental growth phase and climatic changes affecting the oceanic egg and larvae stages. A proper quantification of mortality causes, however, is lacking.

This three-year project aims at identifying and quantifying mortality causes of European eels in an exemplary freshwater system, the Schwentine River. This system provides ideal conditions to monitor eel mortality since it is blocked by two hydropower stations and exclusively relies on restocking. The combination of data analyses (restocking data and landing statistics (commercial and recreational fisheries)) and the extensive monitoring of silver eels migrating out of the system provides the basis for a precise estimation of natural mortality. To further identify and quantify specific mortality causes, the health status of individual eels is assessed (condition, parasites, viral diseases) and an extensive predator-monitoring is conducted (fish and birds).

 

 

 

North Sea squid

Cephalopod landings have increased globally since the 1950s from about 500,000 tons to 4 million tons in 2007, and there are indications that some of their stock sizes increase in areas where stock sizes of commercially valuable fishes decrease. Therefore, we started to study the long-term abundance and distribution of cephalopods in heavily exploited areas such as the North Sea (Oesterwind et al., 2010). We will also include studies on the cephalopods’ diet in order to document their role as consumers of fish and invertebrates and the likely effects on the recruitment of economically important fish species (Oesterwind and Piatkowski, in prep.).

 

The four figures above demonstrate distribution patterns of the European common squid Alloteuthis subulata in the North Sea during summer 2007, winter 2008, summer 2008, and winter 2009. The data show an ontogenetic migration and suggest that the predator impact of the squid changes in place and time with consequences for its prey – the early life stages of exploited fish stocks.

We further contribute to current transnational work on distribution, fisheries, ecology and conservation of European cephalopods and are members of the ICES Working Group on Cephalopod Fisheries and Life History (WGCEPH) (e.g., Pierce et al. 2010).

 

This research was funded by the environmental foundation Deutsche Bundesstiftung Umwelt (DBU), the Federal Ministry of Food, Agriculture and Consumer Protection, and by institutional resources.

 

Hastie LC, Pierce GJ, Wang J, Bruno I, Moreno A, Piatkowski U, Robin JP (2009) Cephalopods in the north-eastern Atlantic: Species, biogeography, ecology, exploitation and conservation. Oceanogr Mar Biol 47:111-190

Oesterwind D, ter Hofstede R, Harley B, Brendelberger H, Piatkowski U (2010) Biology and meso-scale distribution patterns of North Sea cephalopods. Fish Res 106:141-150

Pierce GJ, Valavanis VD, Guerra A, Jereb P, Orsi-Relini L, Bellido JM, Katara I, Piatkowski U, Pereira JMF, Balguerias E, Sobrino I, Lefkaditou E, Wang J, Santurtun M, Boyle PR, Hastie LC, MacLeod CD, Smith JM, Viana M, Gonzalez AF, Zur AF (2008) A review of cephalopod - environment interactions in European Seas. Hydrobiologia 612:49-70

Pierce GJ, Allcock L, Bruno I, Bustamante P, Gonzalez A, Guerra A, Jereb P, Lefkaditou E, Malham S, Moreno A, Pereira J, Piatkowski U, Rasero M, Sanchez P, Santos B, Santurtun M, Seixas S, Villanueva R (2010) (eds.) Cephalopod biology and fisheries in Europe. ICES Cooperative Research Report 303:1-175

 

Contact:

Daniel Oesterwind

Uwe Piatkowski

 

OEKOFISCHMAN

OEKOFISCHMAN (Ecosystem Based Fisheries Management in the German Exclusive Economic Zone EEZ)

Funded by the German Federal Office for Nature Conservation

Dr. Rainer Froese, Dr. Silvia Opitz, Cristina Garilao

Oekofischman forms part of a more extended cluster on fisheries hosted at the German Federal Office for Nature Conservation – outpost Vilm. This three-year project, which started in March 2013 aims to investigate the impact of fisheries on Natura 2000 habitat types and species and other  European aspects related to fisheries and environmental protection  and to develop a technical basis for the implementation of ecosystem based fishery management plans.

 

 

 

 

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