© 2004 by ICES/CIEM International Council for the Exploration of the Sea/Conseil International pour l'Exploration de la Mer
Recruitment indices of European hake, Merluccius merluccius (Linnaeus 1758), in the Northwest Mediterranean based on landings from bottom-trawl multispecies fisheries
a Instituto Español de Oceanografía, Centro Oceanográfico de Baleares Apartado 291, 07080 Palma de Mallorca, Spain
b University of Michigan School of Natural Resources and the Environment, 138 Museum Annex, 1109 N. University, Ann Arbor, MI, USA
c Instituto Español de Oceanografía Avenida de Brasil, 31, 28020 Madrid, Spain
d Instituto de Ciencias del Mar, CMIMA–CSIC Paseo Marítimo Barceloneta, 37–49, 08039 Barcelona, Spain
e Universitá di Pisa, Dipartimento di Scienze dell'Uomo e dell'Ambiente Via A, Volta 6, Pisa, Italy
*Correspondence to R. Goñi: tel: +34 971 401561; fax: +34 971 404945. e-mail: raquel.goni{at}ba.ieo.es.
Temporal and spatial variation in Merluccius merluccius recruitment in the Northwest Mediterranean is examined, and recruitment indices are derived from monthly M. merluccius catch rates of four bottom-trawl fleets operating in Spanish and Italian waters during the period 1991–1999. Where M. merluccius catches were not recorded by size category, multivariate techniques were applied to species proportions in order to identify catch records most representative of recruit abundance. Selected catch rates were analysed by generalized linear models (GLMs) to estimate recruitment indices. The GLMs explain large proportions of the variation in recruit abundance (50–84%) and indicate significant annual and seasonal variation in recruitment strength. Vessel was by far the most important factor affecting catch rates of recruits, stressing the need to account for vessel characteristics when analysing commercial catch data for stock assessment. Seasonal patterns of recruitment reveal similarities among the study areas and interannual variations within areas. One major recruitment peak was identified in each area during either spring/summer or late summer/winter. In most areas, recruitment between 1991 and 1999 seemed to decline, but this could not be confirmed owing to high interannual variability. The coherence of annual fluctuations in recruitment indices with those of MEDITS surveys supports the present results.
Keywords: catch rates, generalized linear models, Merluccius merluccius, multivariate analysis, Northwest Mediterranean, recruitment trends
Received 25 November 2003; accepted 21 April 2004.