U potrazi za plijenom: pojava psine lisice, Alopias vulpinus (Bonnaterre, 1788) u sjevernom Jadranu i njegove interakcije s ribarstvom

The common thresher shark, Alopias vulpinus, has shown a marked decline in abundance in the Mediterranean Sea. Through the analysis of long-term fishery time series (1966–2013), this study highlights that an important driver of the presence of A. vulpinus in the northern Adriatic Sea, one of the most exploited basins of the Mediterranean, is the abundance of its prey, the sardine Sardina pilchardus. From 1997-2013, an annual average of 14 thresher sharks was landed at Chioggia (Italy), the main fish market in the area, mainly from July to October. More than 75% of the landed thresher sharks were sexually immature, with some specimens weighing less than 10 kg, indicating that a high proportion of the catch was composed of small young and newborn individuals. These results support the occurrence of a nursery area in the northern Adriatic Sea, highlighting the need for proper management of A. vulpinus catch in this area.Zabilježen je značajan pad zastupljenosti psa lisice, Alopias vulpinus, u Sredozemnom moru. Analizom dugoročnog vremenskog niza podataka u ribarstvu (1966-2013), ovo istraživanje pokazuje da je važan pokretač prisutnosti A. vulpinus, u sjevernom Jadranu kao jednom od najiskorištenijih bazena na Sredozemlju, obilje njegova plijena srdele, Sardina pilchardus. U razdoblju 1997.-2013. godišnji prosjek ulova psine lisice je iznosio 14 primjeraka donesenih na glavnu ribarnicu u mjestu Chioggia (Italija) i to poglavito od srpnja do listopada. Više od 75% primjeraka ulovljenog psa lisice bili su spolno nezreli, od kojih su neki primjerci imali manje od 10 kg, što ukazuje da je visok udio ulova bio sastavljen od malih nedoraslih jedniki i mlađi. Ovi rezultati podupiru pojavu rastilišta u sjevernom Jadranu, ujedno naglašavajući potrebu pravilnog upravljanja ulovom A. vulpinus u ovom području

U potrazi za plijenom: pojava psine lisice, Alopias vulpinus (Bonnaterre, 1788) u sjevernom Jadranu i njegove interakcije s ribarstvom

The common thresher shark, Alopias vulpinus, has shown a marked decline in abundance in the Mediterranean Sea. Through the analysis of long-term fishery time series (1966–2013), this study highlights that an important driver of the presence of A. vulpinus in the northern Adriatic Sea, one of the most exploited basins of the Mediterranean, is the abundance of its prey, the sardine Sardina pilchardus. From 1997-2013, an annual average of 14 thresher sharks was landed at Chioggia (Italy), the main fish market in the area, mainly from July to October. More than 75% of the landed thresher sharks were sexually immature, with some specimens weighing less than 10 kg, indicating that a high proportion of the catch was composed of small young and newborn individuals. These results support the occurrence of a nursery area in the northern Adriatic Sea, highlighting the need for proper management of A. vulpinus catch in this area.Zabilježen je značajan pad zastupljenosti psa lisice, Alopias vulpinus, u Sredozemnom moru. Analizom dugoročnog vremenskog niza podataka u ribarstvu (1966-2013), ovo istraživanje pokazuje da je važan pokretač prisutnosti A. vulpinus, u sjevernom Jadranu kao jednom od najiskorištenijih bazena na Sredozemlju, obilje njegova plijena srdele, Sardina pilchardus. U razdoblju 1997.-2013. godišnji prosjek ulova psine lisice je iznosio 14 primjeraka donesenih na glavnu ribarnicu u mjestu Chioggia (Italija) i to poglavito od srpnja do listopada. Više od 75% primjeraka ulovljenog psa lisice bili su spolno nezreli, od kojih su neki primjerci imali manje od 10 kg, što ukazuje da je visok udio ulova bio sastavljen od malih nedoraslih jedniki i mlađi. Ovi rezultati podupiru pojavu rastilišta u sjevernom Jadranu, ujedno naglašavajući potrebu pravilnog upravljanja ulovom A. vulpinus u ovom području

The influence of mating system on seminal vesicle variability among gobies (Teleostei, Gobiidae)

A variety of sexual selection mechanisms have been implicated to drive the variability of the male reproductive tract in internal fertilizers, while studies on external fertilizers have been largely limited to exploring the influence of sperm competition on testis size and sperm number. Males in the Gobiidae, a speciose teleost family of demersal spawners with external fertilization, are known to be characterized by accessory structures to the sperm duct called seminal vesicles. These seminal vesicles secrete a mucus-enriched seminal fluid. Seminal vesicle size and function have been demonstrated to be influenced by sperm competition at the intraspecific level. With the aim to test the factors influencing the development of these male organs at the interspecific level, an independent contrast analysis was performed on 12 species, differing in mating system type, sperm competition risk, and duration of egg deposition. The type of mating system appears to be the main factor significantly affecting development of seminal vesicles, with males of monogamous species completely lacking or having extremely reduced organs. Riassunto Nelle specie a fecondazione interna e stato ampiamente dimostrato il ruolo di diversi meccanismi di selezione sessuale nel modellare l'estrema variabilita delle strutture genitali maschili. Nelle specie a fecondazione esterna le informazioni sono, invece, limitate principalmente all'influenza della competizione spermatica sulle dimensioni dei testicoli e sul numero di spermi. Nei Gobiidae, famiglia di pesci teleostei caratterizzata da un elevato numero di specie e dalla produzione di uova demerse, i maschi presentano strutture accessorie allo spermidotto, chiamate vescicole seminali, che secernono un liquido seminale particolarmente ricco di mucine. A livello intraspecifico e stato dimostrato come le dimensioni e la funzione delle vescicole seminali sia influenzata dalla competizione spermatica. Con lo scopo di studiare quali fattori a livello interspecifico influenzino lo sviluppo di questi organi, e stata applicata l'analisi comparativa dei contrasti indipendenti a 12 specie di gobidi che differiscono nel sistema riproduttivo, nel livello di competizione spermatica e nella durata della deposizione. L'unico fattore che influenza significativamente lo sviluppo delle vescicole seminali e risultato essere il sistema riproduttivo, infatti nelle specie monogame i maschi non hanno, o hanno estremamente ridotte, vescicole seminali

Multiple paternity and hybridization in two smooth-hound sharks

Multiple paternity appears to be a common trait of elasmobranch mating systems, with its occurrence likely driven by convenience, due to females seeking to minimize the stress of male harassment. Here we use molecular markers to analyse the frequency of multiple paternity in two related viviparous sharks, Mustelus mustelus and Mustelus punctulatus. We first applied molecular methods to assign pregnant females, embryos and additional reference adults (N\u2009=\u2009792) to one of the two species. Paternity analysis was performed using a total of 9 polymorphic microsatellites on 19 females and 204 embryos of M. mustelus, and on 13 females and 303 embryos of M. punctulatus. Multiple paternity occurs in both species, with 47% of M. mustelus and 54% of M. punctulatus litters sired by at least two fathers. Female fecundity is not influenced by multiple mating and in 56% of polyandrous litters paternity is skewed, with one male siring most of the pups. Genetic analyses also revealed hybridization between the two species, with a M. punctulatus female bearing pups sired by a M. mustelus male. The frequency of polyandrous litters in these species is consistent with aspects of their reproductive biology, such as synchronous ovulation and possible occurrence of breeding aggregations

Recovery trends of commercial fish: the case of an underperforming Mediterranean marine protected area

Temporal trends in the recovery of exploited species in marine protected areas (MPAs) are useful for a proper assessment of the efficacy of protection measures. The effects of protection on the fish assemblages of the sublittoral rocky reefs in the \u201cPenisola del Sinis-Isola di Mal di Ventre\u201d MPA (W. Sardinia, Italy) were evaluated using a multi-year series of data. Four surveys, conducted 7, 10, 13 and 15 years after the area was designated as an MPA and carried out in the period spanning June and July, were used to estimate the abundance and biomass of commercial species. The surveys were carried out in zones with decreasing levels of fishing restrictions within the MPA (zones A, B, C) and in unprotected zones (OUT1 and OUT2), and underwater video visual census techniques were used. Protected zones only occasionally showed higher levels of abundance or biomass, and the trajectories of those metrics were not consistent across the years. In addition, the zone with the highest level of protection (zone A) never presented levels of abundance and biomass higher than those in zones B and C. This study shows that even 15 years after designation, protection has had no appreciable effect in the MPA studied. It is argued that this is emblematic of several shortcomings in the planning, regulation and enforcement frameworks of the MPA

Life history traits and historical comparison of blue whiting (Micromesistius poutassou) growth performance from the western Pomo/Jabuka Pits area (central Adriatic Sea)

Although fishing is considered the primary cause of the decline in fish populations, increasing evidence of the significant role of climate change has been provided recently in the Mediterranean Sea, which shows one of the highest warming trends in the world. In this area, the most important environmental driver is represented by the increase in seawater temperature. Though several studies have addressed the effects of sea warming on thermophilic species, little attention has been paid to cold-water species. Among these, blue whiting (Micromesistius poutassou) constitutes one of the most important traditional fisheries resources in the northern part of the basin, particularly in the central Adriatic Sea. This area has experienced intense fishing exploitation by the Italian and Croatian fishing fleets. Since 2015, the Pomo/Jabuka Pits area, the fleets' main fishing ground, has been subject to a series of fishing regulations over time and space. In the present study, we investigated the age structure and growth performance (by means of otoliths) of blue whiting, comparing samples collected during 1985-86 and 2020-21 in the Pomo/Jabuka Pits. Our results show that the 2020-21 blue whiting specimens had a lower length-at-age compared to 1985-86. The asymptotic length estimate decreased from 29 cm TL in 1985-86 to 25 cm TL in 2020-21. The pattern observed might be related to a modification in the cold and dense water formation dynamics in the northern Adriatic Sea, as a consequence of climate change, resulting in higher temperatures and lower nutrient and oxygen exchange, which may have hampered the optimal growth of the species. Moreover, data on the historical trend of landings from the Adriatic Sea reveals a clear decline in catches starting from 2000 onwards. Although the introduction of a fishing ban in the Pomo/Jabuka Pits was an important milestone, the abundance of this species in the area remains at low levels, highlighting a potentially alarming situation for the stock of blue whiting in the central Adriatic Sea

First direct evidence of reproductive behaviour of the white grouper, Epinephelus aeneus (Geoffroy Saint-Hilaire, 1817)

This study describes the first ever reported direct observation of a pair spawning event and the reproductive liveries of the white grouper, Epinephelus aeneus. Spawning took place on a rocky bank located in the Marine Protected Area (MPA) of Tavolara-Punta Coda Cavallo (NE Sardinia, Italy), in the Western Mediterranean Sea. In the evening of August 4th, 2018, the spawning of two large-sized individuals (~90 cm total length), displaying distinct colour patterns, was observed using SCUBA diving. This direct observation is the first record of E. aeneus male reproductive livery, characterized by a darker coloration on the head, the dorsal part of the body and the caudal fin. In addition, information on the environmental conditions in which reproduction occurred was collected. At the study site, relatively high seawater temperatures were recorded at the time of the E. aeneus spawning (24 °C at 24.7 m), as well as over the 2018 summer months (July-September), even in deep waters (>35 m), compared to previous summers. The spawning event occurred in a coralligenous-dominated seascape where fishing is prohibited, while diving activities are allowed. The site hosts abundant populations of ecologically and commercially valuable fish species (e.g., groupers, sparid fishes), with significant proportions of large-sized individuals (i.e. reproducers). Further studies are needed to advance our knowledge of the white grouper, with a particular emphasis on reproduction and the importance of implementing effective protection measures. Prioritizing management actions at key reproductive sites, such as rocky banks, is essential for ensuring the protection and/or recovery of over-exploited species

Pelagia benovici sp. nov. (Cnidaria, Scyphozoa): a new jellyfish in the Mediterranean Sea

A bloom of an unknown semaestome jellyfish species was recorded in the North Adriatic Sea from September 2013 to early 2014. Morphological analysis of several specimens showed distinct differences from other known semaestome species in the Mediterranean Sea and unquestionably identified them as belonging to a new pelagiid species within genus Pelagia. The new species is morphologically distinct from P. noctiluca, currently the only recognized valid species in the genus, and from other doubtful Pelagia species recorded from other areas of the world. Molecular analyses of mitochondrial cytochrome c oxidase subunit I (COI) and nuclear 28S ribosomal DNA genes corroborate its specific distinction from P. noctiluca and other pelagiid taxa, supporting the monophyly of Pelagiidae. Thus, we describe Pelagia benovici sp. nov. Piraino, Aglieri, Scorrano & Boero

Ontogenetic trophic segregation between two threatened smooth-hound sharks in the Central Mediterranean Sea

Elasmobranchs are among the species most threatened by overfishing and a large body of evidence reports their decline around the world. As they are large predators occupying the highest levels of marine food webs, their removal can alter the trophic web dynamic through predatory release effects and trophic cascade. Suitable management of threatened shark species requires a good understanding of their behaviour and feeding ecology. In this study we provide one of the first assessments of the trophic ecology of the \u201cvulnerable\u201d smooth-hounds Mustelus mustelus and M. punctulatus in the Central Mediterranean Sea, based on stomach contents and stable isotope analyses. Ontogenetic diet changes were addressed by comparing the feeding habits of three groups of individuals: juveniles, maturing and adults. Our results highlighted that the two species share a similar diet based mostly on the consumption of benthic crustaceans (e.g. hermit crabs). Their trophic level increases during ontogeny, with adults increasing their consumption of large-sized crustaceans (e.g. Calappa granulata, Palinurus elephas), cephalopods (e.g. Octopus vulgaris) and fish (e.g. Trachurus trachurus). Our results provide also evidence of ontogenetic shifts in diet for both species showing a progressive reduction of interspecific trophic overlap during growth. The results of this study contribute to improve the current knowledge on the trophic ecology of these two threatened sharks in the Strait of Sicily, thus providing a better understanding of their role in the food web