Defining sustainable and precautionary harvest rates for data-limited short-lived stocks: a case study of sprat (Sprattus sprattus) in the English Channel2023

Publication history: Accepted - 3 March 2023; Published - 17 April 2023.Empirical harvest control rules set catch advice based on observed indicators and are increasingly being used worldwide to manage fish stocks that lack formal assessments of stock and exploitation status. Within the International Council for the Exploration of the Sea, trend-based rules that adjust advice according to recent survey observations have been adopted; however, there is increasing evidence that such rules do not work well for short-lived pelagic species that can exhibit large inter-annual fluctuations in stock size. Constant harvest rates, removing a fixed proportion of observed biomass index, have been proposed as a suitable strategy for managing short-lived species. Unknown survey catchability has, however, remained a barrier to reliance on their application on these stocks in the past. We apply simulation testing to define a robust, sustainable constant harvest rate for a data-limited short-lived stock, using the English Channel sprat as a case study. By conditioning a management strategy evaluation framework based on existing and borrowed life-history parameters and precautionary considerations, we test and show that a constant harvest rate outperforms trend-based catch rules, maximizing yields while reducing risks of stock overexploitation, and conclude an 8.6% constant harvest rate provides sufficiently precautionary catch advice for this stock.Part of this work was funded by the UK Department of Environment, Food and Rural Affairs

A multidisciplinary approach to identify priority areas for the monitoring of a vulnerable family of fishes in Spanish Marine National Parks

Background Syngnathid fishes (Actinopterygii, Syngnathidae) are flagship species strongly associated with seaweed and seagrass habitats. Seahorses and pipefishes are highly vulnerable to anthropogenic and environmental disturbances, but most species are currently Data Deficient according to the IUCN (2019), requiring more biological and ecological research. This study provides the first insights into syngnathid populations in the two marine Spanish National Parks (PNIA—Atlantic- and PNAC—Mediterranean). Fishes were collected periodically, marked, morphologically identified, analysed for size, weight, sex and sexual maturity, and sampled for stable isotope and genetic identification. Due the scarcity of previous information, habitat characteristics were also assessed in PNIA. Results Syngnathid diversity and abundance were low, with two species identified in PNIA (Hippocampus guttulatus and Syngnathus acus) and four in PNAC (S. abaster, S. acus, S. typhle and Nerophis maculatus). Syngnathids from both National Parks (NP) differed isotopically, with much lower δ15N in PNAC than in PNIA. The dominant species were S. abaster in PNAC and S. acus in PNIA. Syngnathids preferred less exposed sites in macroalgal assemblages in PNIA and Cymodocea meadows in PNAC. The occurrence of very large specimens, the absence of small-medium sizes and the isotopic comparison with a nearby population suggest that the population of Syngnathus acus (the dominant syngnathid in PNIA) mainly comprised breeders that migrate seasonally. Mitochondrial cytochrome b sequence variants were detected for H. guttulatus, S. acus, and S. abaster, and a novel 16S rDNA haplotype was obtained in N. maculatus. Our data suggest the presence of a cryptic divergent mitochondrial lineage of Syngnathus abaster species in PNAC. Conclusions This is the first multidisciplinary approach to the study of syngnathids in Spanish marine NPs. Habitat preferences and population characteristics in both NPs differed. Further studies are needed to assess the occurrence of a species complex for S. abaster, discarding potential misidentifications of genus Syngnathus in PNAC, and evaluate migratory events in PNIA. We propose several preferential sites in both NPs for future monitoring of syngnathid populations and some recommendations for their conservation.Postprin