Gilthead seabream ( Sparus aurata) is an important commercial species, greatly appreciated for consumption and one of the most used fishes in aquaculture (Jouvenel and Pollard 2001). Offshore aquaculture is a growing industry trying to face the increasing demand for seafood, however, fish escapes are cause for concern as they can represent a threat to the marine environment, especially in locations where the farmed species were not previously present (Ramirez et al. 2015). Although this seabream is native in the North-eastern Atlantic it is considered a non-indigenous species (NIS) in Madeira archipelago (Alves and Alves 2002). In Madeira Island , this species was introduced in 1997 for aquaculture purposes (Alves and Alves 2002) which currently hosts three open-ocean aquaculture farms breeding and producing S. aurata. Three years after introducing the species in the archipelago, a first sighting of 5 individuals in the wild was reported in the south coast of Madeira (Alves and Alves, 2002). Generally, unwanted escaping of fish from offshore cages often results from equipment malfunction, accidents and storms. As such, depending on the frequency and severity of such accidental incidents, the number of fishes escaping to the wild could result in the establishment of a local population. Recent studies highlight the presence of wild S. aurata along the coast of Madeira , being caught by recreational spearfishers from 2004 (Martinez-Escauriaza et al. 2020a) and representing the sixteenth most caught fish species by recreational shore anglers in 2017 (Martinez-Escauriaza et al. 2020b). In this context, this study aims to better understand the distribution and occurrence of S. aurata in Madeira coastal habitats and assess their invasiveness in the archipelago.
Material and Methods
Information on captures (i.e. , species, date, location and size) during sport fishing contests held in Madeira between 2010 and 2019 (n=443) were compiled and analysed to assess S. aurata occurrences, distribution and trends. In addition, a custom designed online survey questionnaire targeting stakeholders from three maritime activities (1- SCUBA diving; 2 -spearfishing; and, 3 -fishing) was developed to assess the presence of Sparus aurata in the coastal waters of the Madeira archipelago. The survey was designed using the application ‘Maptionnaire’ (www.maptionnaire.com), that allows users to interact and report georeferenced data through a web-based interface. Data were later analysed and plotted with ArcGIS and IBS SPSS version 27. Finally, a risk analysis was conducted to assess invasiveness and evaluate possible impacts of S. aurata in Madeira habitats, under current and future climate change scenarios, using the Aquatic Species Invasiveness Screening Kit (AS-ISK, Coop et al 2016). Co ncerted scores for Basic Risk Assessment (BRA), Climate Change Assessment (CCA) and BRA+CCA were estimated from multiple screenings by users with different expertise. Concerted BRA and BRA+CCA scores were compared with thresholds for marine fishes in both temperate and tropical regions to assess invasiveness risk.
Sport fishing contest data from 2010 confirmed the presence of S. aurata in the wild with capture in both south and north coasts of the island; whereas data from 2018 showcase that S. aurata specimens were captured almost every month. Similarly, the 73 validated respondents of the online survey reported sightings and captures in 120 sites around the island, most of which reporting small groups of 5 individuals (57%) but with larger groups of more than 20 individuals also being reported (14%). Moreover, respondents’ perception is that seabream sightings in Madeira have been increasing since 2015. Concerted BRA and BRA+CCA scores rank high despite ranging confidence intervals, with average scores above thresholds for marine fishes in both tropical and temperate regions.
Considering the spatial distribution of S. aurata sightings and captures around Madeira I sland, with reports from sites distant from aquaculture farms, and increasing trends in captures and sightings, it is reasonable that it has successfully established a local population . This is not surprising considering that Madeira island environmental conditions are within the range of conditions suitable for S. aurata . In addition, S. aurata averaged BRA and BRA+CCA scores are above the threshold for marine fishes, suggesting it may be a high or medium risk species. Such scores are not surprising as well , due to the high adaptability in food and habitat (Balart et al., 2009), S. aurata can potentially become a fierce competitor of local native species (e.g., Pagrus spp., Diplodus spp.). Overall, findings of this study warrant further investigations into local S. aurata , specifically to confirm its reproduction in the wild and assess impacts from its behaviour and feeding habits.
Alves FMA, Alves CMA (2002) Two new records of seabreams (pisces : sparidae ) from the madeira archipelago. Arquipélago Life and Marine Science 19 A: 107-111
Balart E F, Pérez-Urbiola J C, Campos-Dávila L, Monteforte M, Ortega-Rubio A (2009). On the first record of a potentially harmful fish, Sparus aurata in the Gulf of California. Biological invasions, 11(3), 547-550.
Copp GH, Vilizzi L, Tidbury H, Stebbing PD, Tarkan AS, Miossec L, Goulletquer P (2016) Development of a generic decision-support tool for identifying potentially invasive aquatic taxa: AS-ISK. Management of Bioogical Invasions 7:343–350. Doi: 10.3391/mbi.2016.7.4.04
Jardas I (1996) The Adriatic ichthyofauna . Školska knjiga, Zagreb, 535pp. Croatian with English abstract.
Jouvenel J Y, Pollard D A (2001) Some effects of marine reserve protection on the population structure of two spearfishing target fish species, Dicentrarchus labrax (Moronidae ) and Sparus aurata (Sparidae ), in shallow inshore waters, along a rocky coast in the northwestern Mediterranean Sea. Aquatic Conservations 11, 1–9.
Martínez-Escauriaza R, Vieira C, Gouveia L, Gouveia N, Hermida M (2020a) Characterization and evolution of spearfishing in Madeira archipelago, Eastern Atlantic. Aquatic Living Resources, 33, 15.
Martínez-Escauriaza R, Hermida M, Villasante S, Gouveia L, Gouveia N, Pita P (2020b) Importance of recreational shore angling in the archipelago of Madeira, Portugal (northeast Atlantic). Scientia Marina, 84(4), 331-341.
Toledo-Guedes K, Sánchez-Jerez P, González-Lorenzo G, Hernández AB (2009) Detecting the degree of establishment of a non-indigenous species in coastal ecosystems: sea bass Dicentrarchus labrax escapes from sea cages in Canary Islands (Northeastern Central Atlantic). Hydrobiologia, 623(1), 203-212.
Ramirez B, Ortega L, Montero D, Tuya F, Haroun R (2015) Monitoring a massive escape of European sea bass (Dicentrarchus labrax) at an oceanic island: potential species establishment. Journal of Aquaculture Research and Development . Vol. 6. doi: 10.4172/2155-9546.1000339.