A review of burrow counting as an alternative to other typical methods of assessment of Norway lobster populations

14 páginas, 4 figuras, 2 tablas

The diurnal and seasonal regulation of the complex burrowing behavior of Nephrops norvegicus complicates population assessment for this species. Population assessment is traditionally carried out by Virtual Population Analysis (Length Cohort Analysis; LCA) and swept area density estimations from catch data. However, burrow counting from visual surveys has also acquired increasing importance in recent years as an alternative and apparently efficient method. All these approaches produced non-equivalent assessment results in the literature, and therefore, a comparison and critical discussion of these methods is warranted. In this review, we pursued this goal by using already published and unpublished fishery data for a commercially exploited western Mediterranean shelf (60–100 m) population as an example. The cross-assessment was carried out by LCA, the swept area method and burrow counting in different seasons (spring-summer and autumn–winter) to highlight biases in abundance estimations in relation to Nephrops behavior. We also used novel trawl density data for other fish and decapod species in the area because the burrowing behavior of these species may deeply bias Nephrops abundance in visual surveys. LCA provided intermediate assessment values when compared to the swept area and photographic estimates, which over- and underestimated the abundance, respectively. We reviewed the problems related to the peculiar burrowing behavior of the species that generate assessment estimations of such different magnitude

The present work was carried out within the framework of the following projects: NERIT (CICYTMAR/98/0935), NORIT (CICYT-CTM/2005/02034), RITFIM (CTM2010-16274), MONITORING CONTRACT (Generalitat de Catalunya); and finally, EUROLEON (REN2002-11216E). The authors would like to thank: Prof. M. Canals (Univ. Barcelona-UB), Dr. J.B. Company and Mr. Ramirez-Llorda (ICM-CSIC). J. Aguzzi is a Postdoctoral Fellow of the Ramon y Cajal Program, funded by the Spanish Ministry of Science and Innovation (MICINN)

Peer reviewed