Evaluation de l’état des populations de raie bouclée

• Main Author: Marandel, Florianne
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: Agrocampus Ouest 2018
• Subjects: Schaefer; Northeast Atlantic
• Online Access: https://archimer.ifremer.fr/doc/00471/58268/60788.pdf; https://archimer.ifremer.fr/doc/00471/58268/

During the 20th century, several skates and rays species in European waters declined because of fishing. Conservation of these species is a major objective of the management of marine resources. The thornback ray (Raja clavata) is the most widespread species of the North-Est Atlantic. Its management is based on a nonspecific quota and lay on observations only as no stock assessment is available. Thus this thesis aims to compare the available stock assessments methods for this species and to apply them to empiric data. Two types of methods are investigated: methods based on population demography and methods based on population genetics. The thesis is separated in three parts: 1) assessment of management units; 2) assessment of the state of the thornback ray populations; 3) comparison of the thornback ray population’s states with the other rays species of the Northeast Atlantic. Management units for thornback ray are currently mainly based on administrative limits but results of a simulation study show that studying the demographic connectivity of this species could be useful for its management. However, genetic connectivity doesn’t appear relevant for management but for conservation as it informs on long term and large scale population structure. Assessment of the demographic state of thornback ray populations is feasible thanks to stochastics modelling. A Bayesian State Space model was developed using the production function of Schaefer. Results in the Bay of Biscay show a stabilization of the species at a very low level (7% of its carrying capacity). Studying the genetic state of thornback ray populations could a priori refine these results by studying the effective population size (Ne). Thus genetic markers (SNPs) were simulated within large thornback ray populations. Effective population sizes of these populations were estimated using different estimators (Linkage Disequilibrium and the Temporal Method adapted for overlapping generations). First results show a systematic bias and a low precision which cannot ...