ESR 25:197-207 (2014)  -  DOI: https://doi.org/10.3354/esr00582

Patterns of extirpation. I. Changes in habitat use by thornback rays Raja clavata in the German Bight for 1902-1908, 1930-1932, and 1991-2009

Heino O. Fock*

Th√ľnen-Institute of Sea Fisheries, Palmaille 9, 22767 Hamburg, Germany
*Corresponding author:

ABSTRACT: Abundance trends and distribution were analyzed for thornback rays Raja clavata in the German Bight (eastern central North Sea) for 3 periods: 1902-1908, 1930-1932, and 1991-2009. Abundances declined until 1932, and after 1991 only 4 specimens were encountered in the area during standard fisheries surveys. During the first period, thornback rays inhabited almost the entire German Bight, while a range reduction was observed for the second period and again after 1991. In the first period, thornback rays were negatively associated with gravel and mud, while no sediment parameter appeared to be significant in the 1930-1932 period. Temporal differences are interpreted as differential impacts of fisheries. At low fishing pressure, habitat associated with feeding grounds was occupied by thornback rays, while with increasing fishing pressure, in accordance with the interference hypothesis, less risky habitat was occupied and as such was less associated with feeding grounds, before fishing pressure ultimately caused extirpation. Local fishing mortality observed in all 3 periods exceeded the extinction level mortality (Fext = 0.84). The shift in habitat use is discussed with respect to the designation of marine protected areas based on distributions of species already under pressure.


KEY WORDS: Natura 2000 · North Sea · Trophic cascades · German Bight · Historic time series · Elasmobranchs


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Cite this article as: Fock HO (2014) Patterns of extirpation. I. Changes in habitat use by thornback rays Raja clavata in the German Bight for 1902-1908, 1930-1932, and 1991-2009. Endang Species Res 25:197-207. https://doi.org/10.3354/esr00582

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