Analysis of Bycatches of Two Related Anadromous Shad Species in Fisheries along the Galician Atlantic Coast (NW Iberian Peninsula, Southwest Europe)

Allis shad, Alosa alosa (Linnaeus, 1758) and Twaite shad, Alosa fallax (Lacépède, 1803) are two anadromous Clupeidae species that spend most of their life cycle in the marine environment, where they have a coastal distribution, entering the rivers only during the spawning migration. There is no commercial shad fishery at sea; however, due to their gregarious, shoal-forming behaviour close to the shore, they are frequently caught as “bycatch” along with the “intentional catches”. In fact, both species have been arriving at Galician fish markets (NW Iberian Peninsula) for several decades. Hence, it was necessary to conduct a study in order to gain a deeper understanding of the extent of this phenomenon. To this end, we analysed the statistics on first-sale fishing in the Galician Fishing Platform. In addition, specimens of the genus Alosa (N = 345, sold in first sales not as A. alosa) were acquired at the A Guarda, Malpica and Coruña fish markets, from January to March 2021, in order to determine their specific identity. Finally, additional information regarding the capture of the specimens (precise location of capture, bathymetry, fishing method, target species, etc.) was requested from fishermen. There are records of catches of specimens of the genus Alosa in 14 Galician fish markets, from 1997 to 2020. Catches of A. alosa were regular throughout the period 1997–2020, amounting to a total of 23,956 kg. Regarding A. fallax, it is surprising to note the virtual absence of records throughout the period studied and the high pulses in certain years, with truly exceptional catches (5950 kilos in 1998 or 7320 kilos in 2018). Examination of the number of gill rakers, showed that 59% (N = 203) of the acquired specimens were not A. alosa. Of these 203 misidentified specimens, 81% (N = 164) were A. fallax and 19% (N = 39) were hybrids. Most of the shads were caught in the midst of flatfish, hake or sea bass fisheries, with driftnets being the main fishing gear, and the fishing vessels involved were of different sizes (from large vessels to traditional boats).