Vasapollo, C. | Search bioRxiv

bioRxiv2024

Stock identification of Mediterranean horse mackerel (Trachurus mediterraneus) through the analysis of morphometric characters in the Adriatic Sea.

Phenotypical differentiation among stocks of Mediterranean horse mackerel Trachurus mediterraneus in the Adriatic Sea was investigated through the analysis of several individual morphometric characters. Overall, 426 individuals of Mediterranean horse mackerels were sampled from the northern, central and southern Adriatic Sea in 2012 and 2013, and then compared using multivariate techniques (linear discriminant analysis). Discriminant analysis suggested a scarce intermingling between the northern and central Adriatic with the southern part. The former two areas showed more stable populations, overlapping both in space and time. The latter seemed to be more variable over the years. A possible hypothesis for this, to be investigated, is the flow of individuals from the Ionian and Aegean Seas populations through the Otranto Channel. When the morphometric variables were investigated, the results showed that most of the variability was associated with the head characters. In particular, the northern and central Adriatic Sea individuals had shorter and thicker heads than the southern ones. This could be due to different feeding habits: the former mainly feed on small fishes, the latter mainly on euphausiids. A short mouth could reduce the power of suction of bigger preys, while a long mouth could increase the volume of water to be filtered to feed on small planktonic crustaceans. From this study, it comes clear that the Mediterranean horse mackerel populations should not be managed as a single stock in the Adriatic Sea as it was evident that morphological two different populations are present in the basin.

ecology↗

bioRxiv2019

Bottom trawl catch comparison in the Mediterranean Sea: Flexible Turtle Excluder Device (TED) vs traditional gear

The Mediterranean Sea is a hotspot of biodiversity, but the high fishing pressure results in high bycatch rates of protected (sea turtles and cetaceans) and top predator species (sharks). The reduction of bycatch is challenging for fishery scientists, as conservation of these species has become a priority. Among the animals threatened by fishing activities, the loggerhead (Caretta caretta) represents a charismatic species considered as \"vulnerable\" at the global scale by IUCN.\n\nIn the Mediterranean Sea, trawl nets show the highest probabilities of bycatch of protected species, with high rates of mortality. A new flexible Turtle Excluder Device (TED) has been tested for the first time on a commercial scale in the Mediterranean Sea to assess its effectiveness in reducing bycatch. The results did not show any significant ( = 0.05) loss in terms of commercial weight, but a significant reduction of debris in the codend of the nets mounting the TED respect to traditional nets. The catch comparison of the main commercial species showed similar rates without any significant loss of sizes, with the only exception of anglerfishes (Lophius spp.) that showed a loss of the largest individuals by TED. In terms of bycatch, the traditional nets captured mostly rays and sharks, while no turtles were captured, at all. In this regard, the authors were informed by other vessels operating in the same areas at the time of the trials about some accidental catches of loggerhead turtles. Our results demonstrated that the flexible TED represents a practical and effective solution to reduce the bycatch of endangered species in coastal Mediterranean demersal multispecies fisheries, as demonstrated experimentally also in other areas of the world. The measures involving technical modifications of fishing gears require significant investments but are technically feasible and could guarantee the success of the conservation.

ecology↗