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Understanding Cephalopod catch and discard rates from fishery-dependent and independent data in north Iberian waters

AuthorsValeiras, J.; Abad, Esther ; Pennino, Maria Grazia; Velasco, Eva ; Punzón, Antonio ; Velasco, Francisco ; Pierce, Graham J.
Issue Date2019
CitationIMBeR Future Oceans 2 (2019)
AbstractCephalopod species are an important marine resource in the fisheries of Northern Spain and in particular for the otter bottom trawl fleet. This fleet prosecutes a mixed fishery which takes place throughout the year and although targets mainly fish, several cephalopod species are also landed by this commercial fleet. These landings have been relatively poorly documented in the past. However, a standardized scientific on-board observer program is carried out monthly to collect quantitative spatio-temporal data on both catches and discards for use in stock assessment. Such data provide long time series, covering the whole year each year, and information on a large variety of cephalopod species. However, this kind of data can be biased due to constraints imposed by management and the deliberate misreporting of catches. Furthermore, another issue arises because the sampled fishing locations are often repeated and tend to be associated with high abundances of target species because fishing fleets are commercially driven. Nevertheless, in the northern shelf of the Iberian Peninsula (ICES divisions 8c and 9a north), cephalopod species data are also collected through the annual bottom trawl scientific survey IBTS-DEMERSALES, performed by the Instituto Español de Oceanografía (IEO). This type of fishery-independent dataset is considered to be of superior quality because it is independent of fisher behaviour and management measures, standardized fishing methods are used, and both sampling statistics and the biological information can be taken into consideration. The disadvantage of these surveys is that they have limited space-time coverage, as they are performed over relatively short periods of time (autumn season). Comparing and combining observations from different fishery data sources could provide a useful tool with which to bridge some gaps in our cephalopod species knowledge. In this context, the aim of this study is to characterize catches and discards of cephalopod species along the northern continental shelf of the Iberian Peninsula, taking advantage of these two different data sources and to relate distribution and abundance to environmental variables. In particular, species data were analyzed with Bayesian hierarchical spatial-temporal models considering, as environmental variables, Sea Surface Temperature, Sea Surface Salinity, bathymetry and rugosity of the seabed. Spatio-temporal patterns obtained with the two sources were then compared using similarity and prediction statistics. Results highlight that the main cephalopod species in catch biomass terms, in order of decreasing abundance, were: curled octopus (Eledone cirrhosa), broadtail shortfin squid (Illex coindetii), lesser flying squid (Todaropsis eblanae), long finned squid (Loligo forbesi), common squid (Loligo vulgaris), European flying squid (Todarodes sagittatus), pink cuttlefish (Sepia orbignyana), common cuttlefish (Sepia officinalis) and elegant cuttlefish (Sepia elegans). Spatio-temporal patterns of occurrence of each species, based on the two data-sources, obtained with Bayesian models were generally similar, although the agreement is closer for some species than others. Finally, we argue that the approach applied in this study could help fishery managers to better define survey designs and analyses, as the obtained results help to improve understanding of patterns in the catches and discards cephalopods along the northern continental shelf of the Iberian Peninsula
DescriptionIMBeR Future Oceans 2, 17-21 June 2019, Brest, France
Appears in Collections:(IIM) Comunicaciones congresos
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