Abstract
The status of fishery resources in the Mediterranean Sea is critical: most of the fish and shellfish stocks are in overexploitation and only half of them are routinely assessed. This manuscript presents the use of Surplus Production Models (SPMs) as a valid option to increase the number of assessed stocks, with specific attention to the Adriatic basin. Particularly, the stock of European sprat (Sprattus sprattus), Mediterranean horse mackerel (Trachurus mediterraneus), and Atlantic horse mackerel (Trachurus trachurus) living in the Adriatic Sea have been evaluated comparing three SPMs: Catch Maximum Sustainable Yields (CMSY), Stochastic surplus Production model in Continuous Time (SPiCT), and Abundance Maximum Sustainable Yields (AMSY). The different approaches present some variations; however, they generally agree on describing all the stocks close to the reference values for both biomass and fishing mortality in the most recent year. For the European sprat, AMSY results are the most robust model for this species’ survey data allow depicting a clearer picture of the history of this stock. Indeed, for the horse mackerel species, CMSY or SPiCT results are the preferred models, since for these species landings are not negligible. Notwithstanding, age-structured assessments remain the most powerful approach for evaluating the status of resources, but SPMs have proved to be a powerful tool in a data-limited context.
Highlights
The status of fishing resources in the Mediterranean Sea is critical: less than 50% of the fish and shellfish stocks inhabiting the basin are routinely assessed and the majority of them are considered overexploited (European Environment Agency (EEA), 2019)
Based on the information included in the European Union—Data Collection Framework (EU-DCF), which can be defined as the European database grouping fisheries data from all member states, the pelagic vessels fishing in the Adriatic Sea report catches of other species, such as Mugilidae, European sprat (Sprattus sprattus), mackerels (Scombrus spp.), horse mackerels (Trachurus spp.), and others (source EU-DCF database 2019; European Commission (EC), 2017)
Regarding the status of this stock, Catch Maximum Sustainable Yield model (CMSY) and surplus Production model in Continuous Time (SPiCT) describe a similar situation: biomass results above the reference points for the first years, while since 2007 for CMSY and 2011 for SPiCT it moves below the reference point describing an increasing trend in the last years reaching the value of B/BMSY equal to 0.867 and 0.902 in 2019, respectively, for the CMSY and the SPiCT models (Figure 5 bottom right panel and Table 3)
Summary
The status of fishing resources in the Mediterranean Sea is critical: less than 50% of the fish and shellfish stocks inhabiting the basin are routinely assessed and the majority of them are considered overexploited (European Environment Agency (EEA), 2019). Surplus Production Models (SPMs) represent a valid option to produce stock assessments This type of model requires limited information, such as a time series of catch and, if available, an abundance index or effort data, and can estimate population biomass and produce evaluations of maximum sustainable yield (MSY), that is the maximum yield that the stock can sustain without affecting its long-term productivity (Sparre and Venema, 1998). These models provide fishing mortality and biomass at the corresponding MSY level (FMSY and BMSY ), which are useful to address the management objectives. In these situations of data-limited context, the use of historical catch and survey or effort data is advisable (Jackson et al, 2001; Branch et al, 2011.); this will favor a truthful description of the status of the stock, as well as improving targets and limited reference points’ estimates (Gabriel and Mace, 1999)
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