Taxonomic Notes
De Buen (1931) described two subspecies of Aphia minuta: Aphia minuta atlantica, the larger Atlantic subspecies, and Aphia minuta mediterranea, the smaller Mediterranean subspecies (Miller 1986). However, A. minuta mediterranea should be considered a synonym of A. minuta minuta (Risso 1826), on the basis of the International Code of Zoological Nomenclature (La Mesa et al. 2005).
Justification
This nearshore and estuarine species is widely distributed and short-lived with a high reproductive capacity. It is targeted by a small-scale, seasonal fishery in the Mediterranean Sea and localized population declines have been observed in the past. Some fishing regulations are in place to regulate effort. A global level decline approaching 30% over a three generation period (10 years), is not suspected at this time; therefore, it is listed as Least Concern with a recommendation to monitor populations where fishing effort is high.
Geographic Range Information
This species is distributed in the northeastern Atlantic from Norway and the western Baltic Sea south to the Strait of Gibraltar in Morocco, the Mediterranean Sea from Gibraltar east to Egypt and Israel, the Black Sea, and the Azov Sea (Kovačić et al. 2015, Kovačić et al. 2022). The depth range is 0-100 m (Kovačić et al. 2022).
Population Information
No estimation of size and trend of the global population of this species has been published, however some data are available from the Mediterranean, where the species is subject to fishery exploitation (Kovačić et al. 2015).
The sub-population in the Tyrrhenian Sea was estimated as fairly stable with an annual variation of 40-60 tonnes (Auteri et al. 2000). The subpopulation in the Alboran Sea (western Mediterranean) was drastically reduced by fishing, and as result of this population collapse, the species' fishery is prohibited in this area (Iglesias and Morales-Nin 2001). The species is only fished in the Mediterranean (in Spanish and Italian waters), and here the populations have been reported to have declined (La Mesa et al. 2005) as a result of fishing. In recent years, this species has become less abundant off Mallorca Island (Morales-Nin et al. 2022). There is ongoing monitoring in Italian waters but these data are not available (Kovačić et al. 2015).
It is not an abundant species off the coast of Portugal (Da Cunha and Antunes 2008).
Habitat and Ecology Information
This transparent, pelagic and neritic species inhabits eelgrass (Zostera marina), seagrass (Posidonia oceanica), and large thalus algae (Cystoseira) beds in inshore and estuarine waters over sand or mud bottoms (La Mesa et al. 2005, Kovačić et al. 2022). It lives for up to one year and attains a maximum total length of 5.8 cm in the Mediterranean (Kovačić et al. 2022, Morales-Nin et al. 2022) and 7.9 cm in the Atlantic (Arruda et al. 1993).
It has two distinct spawning seasons, occurring from December to April in shallow bays and shoals, and from September to October in deeper waters (Morales-Nin et al. 2022). Just after spawning, all breeders quickly die probably as a consequence of the degeneration of the intestinal epithelium by apoptosis, marking the end of the entire cohort. This species reaches sexual maturity between 2.8-4.5 cm total length (Kovačić et al. 2015), and 4 to 5 months of age (Morales-Nin et al. 2022). In the Mediterranean, the average total length at maturity for females is 3.8 cm and 3.4 cm for males (Tsikliras and Stergiou 2014). The range of absolute fecundity is approximately between 900 and 7,000 oocytes per female (Kovačić et al. 2015).
Spending most of its life in the water column, it is a planktotrophic feeder, relying mainly on small copepods (Kovačić et al. 2015). In turn the transparent goby is preyed on by several species of fish and larger cephalopods (Kovačić et al. 2015). During ontogenesis, three phases characterize the species: a ‘pelagic phase’, composed of larval stages hatched from demersal eggs that inhabit shallow coastal waters; an ‘aggregated phase’, composed of juveniles that gather in schools in shallow waters during winter; finally, a ‘demersal phase’, composed of adults that in spring migrate offshore with a more dispersed distribution in proximity of the bottom (La Mesa et al. 2005).
Threats Information
This species is locally threatened by fisheries in the western Mediterranean (Spain and Italy) (Morales-Nin et al. 2022).
In Spain, the total catches of this species generally account for less than 100 tonnes per year (Kovačić et al. 2015). In Italy, total catches are about 160 tonnes per year, most of them in the southern Adriatic, and the fishing fleet is constituted of about 400 vessels (La Mesa et al. 2005). The trend of total landings per fishing season is annually highly variable, being strongly affected by the strength of recruitment (La Mesa et al. 2005). The overexploitation of this species by the fishery or environmental disturbances negatively affecting recruitment can cause, in the very short-term (i.e., in the next fishing season), a rapid collapse of the stock biomass available to the fishery (Kovačić et al. 2015).
Use and Trade Information
Despite its small size, this species is exploited by local small-scale fisheries mainly in the western and central Mediterranean (Kovačić et al. 2015). The fishing fleets, harboured in several sites in Spain and Italy, are generally composed of small vessels (Kovačić et al. 2015). Most of them use very selective gear such as purse-seine nets to catch schools of the transparent goby during winter (Kovačić et al. 2015). In Mallorca, Spain, individuals ranging from 2 to 8 months of age are targeted, and can be legally harvested from mid-December to late April (Morales-Nin et al. 2022).
For these artisanal fisheries, the transparent goby represents, although seasonally, a very important source of income, yielding locally up to more than 100 tonnes per fishing season and 75 kg/vessel/day (La Mesa et al. 2005). The main fishing areas are in the Alboran Sea, Mar Menor, Balearic Sea, Catalan Sea, Ligurian Sea, Tyrrhenian Sea and in the central and south Adriatic (Iglesias and Morales-Nin 2001). The data on the fishery were summarized in La Mesa et al. (2005). In the Alboran Sea, fishing gear comprised both semi-pelagic and small bottom trawls, but the fishery collapsed in 1980 and is prohibited (La Mesa et al. 2005, anon. pers. comm. 2014).
The gear in Mar Menor is a small mesh seine net (Kovačić et al. 2015). Fishing operations consist of a preliminary search of schools using an echosounder, which are then surrounded by the net and hauled onboard the vessel (Kovačić et al. 2015). The fishing fleet has 26 vessels and total annual landings of this species ranged from 7.2 to 23.1 tonnes (1986-1991). In the Catalan Sea, the species is captured by a local type of seine net used by 11 vessels and there were no published data on catches (in 2001) (Kovačić et al. 2015).
In the Balearic Sea, the species is captured by a type of boat seine net hauled over the bottom (Kovačić et al. 2015). Between 1982 and 1994, the fishing fleet was composed of 30-53 vessels and total landings of this species ranged between 4.8 and 79 tonnes per season (Kovačić et al. 2015). From 2001 to 2019, the fishing fleet was composed of 297 vessels and total landings were reduced to 4.4 to 40.1 tonnes per season (Morales-Nin et al. 2022). In the Ligurian Sea, the fleet consists of 80 vessels and the fishery is conducted by purse seine with small mesh size (5 mm) (Kovačić et al. 2015). Official statistics of total annual landings of 0.5-2.5 tons (1993-1997) were probably largely underestimated (Kovačić et al. 2015). In the Tyrrhenian Sea, two types of fishing activities are present (Kovačić et al. 2015). The bottom trawl fishery fleet was composed of 15 vessels and has probably underestimated total landings reported by the official statistics of between 1-4 tonnes per season (Kovačić et al. 2015). The other fishery is conducted by means of a special Danish purse seine with about 30 vessels involved and total landings are quite variable during the fishing season, ranging approximately between 5 and 29 tons (1980-1999) (Kovačić et al. 2015).
In the Southern Adriatic Sea, two types of semi-pelagic trawls are used, the data for season 1990-1991 reported 299 vessels and total landings of 119 tonnes (Kovačić et al. 2015). In the Central Adriatic Sea, the small-mesh semi-pelagic trawl is used with 8-10 vessels and total landings ranged from 4.4 to 4.7 tons (1996-1997) (Kovačić et al. 2015). Market prices can be high, from 20-40 Euros per kg (La Mesa et al. 2005).
Conservation Actions Information
Conservation measures for this species are mainly based on regulation of fishing activities (e.g., Murcia Region Ministry of Agriculture and Water 2012). A Survey Commission for the Balearic Islands currently follows European Union fishing regulations, one of which calls for the reduction of fishing effort when previous monthly catch thresholds are not met (Morales-Nin et al. 2022). Further research is required to estimate the size and trends of various populations (Kovačić et al. 2015). Considering the biological characteristics of the species, fishing effort should be decided locally and seasonally, possibly on the basis of previous biomass estimates at sea made before the fishing season (La Mesa et al. 2005). Daily catches of this species are limited to 25 kg per day in Mallorca, though local fishers advocate for 20 kg per day quotas (Morales-Nin et al. 2022). The fishery is currently permitted in the Balearics with ongoing monitoring (Kovačić et al. 2015). Although the species has a short generation length with a high reproductive capacity, ongoing monitoring of population and harvest trends is suggested (Kovačić et al. 2015).
This species was assessed as Least Concern in a 2014 Europe regional Red List assessment (Kovačić et al. 2015).
