Patterns of extirpation. II. The role of connectivity in the decline and recovery of elasmobranch populations in the German Bight as inferred from survey data

• Published in: Endangered Species Research
• Main Authors: Fock, Heino Ove, Probst, Wolfgang Nikolaus, Schaber, Matthias
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2014
• Subjects: article; Text; meta-population models; North Sea; fish diversity; historic time series; Common skate; Dipturus batis; spiny dogfish; Squalus acanthias
• Online Access: https://doi.org/10.3354/esr00583; https://www.openagrar.de/receive/timport_mods_00032805; https://www.openagrar.de/servlets/MCRFileNodeServlet/timport_derivate_00032805/dn054031.pdf

Abundance trends and distribution patterns from 1902 to 1932 for 7 elasmobranch species in the German Bight (eastern central North Sea) were analyzed and compared to survey trends for 1991 to 2009. Abundances of thornback ray Raja clavata, common skate Dipturus batis, smoothhound Mustelus spp., tope shark Galeorhinus galeus, and spiny dogfish Squalus acanthias declined and common skate was extirpated, while abundances of starry ray Amblyraja radiata and lesser spotted dogfish Scyliorhinus canicula increased. A meta-population approach was developed to analyze connectivity in terms of the surrogate parameter Cˆ representing donor population Nj, separation distance Di,j, and migration range parameter a. As populations declined, connectivity between sub-populations was lost before resident populations finally collapsed. The loss of connectivity was caused by both a loss of sub-populations and a subsequent increase in the distance separating the remaining sub-populations. For lesser spotted dogfish, an increase in the donor population fostered the establishment of a local sub-population after 2000. For starry rays, an apparent increase in Nj due to a concentration of the donor population near the study area increased connectivity with the local sub-population. The interpretation of local abundances in terms of meta-population dynamics demonstrates the importance of seasonally resolved survey information for conservation planning.