Spillover of the Atlantic bluefin tuna offspring from cages in the Adriatic Sea: A multidisciplinary approach and assessment

Abstract

During routine monitoring of commercial purse seine catches in 2011, 87 fingerling specimens of scombrids were collected in the southern Adriatic Sea. Sequencing of the mitochondrial DNA control region locus inferred that specimens belonged to the Atlantic bluefin tuna, Thunnus thynnus (Linnaeus, 1758) (N = 29), bullet tuna, Auxis rochei (Risso, 1810) (N = 30) and little tunny, Euthynnus alletteratus, Rafinesque, 1810 (N = 28). According to previously published growth parameters, the age of the collected specimens was estimated at approximately 30–40 days, suggesting they might have been spawned in the Adriatic Sea, contrary to the current knowledge. A coupled modelling system with hydrodynamic (ROMS) and individual based model (IBM—Ichthyop) was set up to determine the location of the spawning event. Numerical simulations with the IBM model, both backward and forward in time, indicate commercial tuna cages in the middle Adriatic coastal area as possible spawning location. The two other non-commercial species likely opportunistically use the positive environmental (abiotic and biotic) conditions to spawn in the same area.

Spatial connectivity pattern of expanding gilthead seabream populations and its interactions with aquaculture sites: a combined population genetic and physical modelling approach

“…This is further supported by parental test analysis where six parent–offspring pairs were identified, connecting parents from the farm surroundings of Brač and Ugljan Islands with offspring from all three nurseries (Raša, Pantana and Neretva) situated along the coastline. In addition, the coupled numerical system with ROMS and Ichthyop models successfully utilized in tuna offspring distribution studies within the Adriatic 54 , has confirmed a possible passive transport between tuna-farms areas off the islands of Brač and Ugljan and the Raša and Pantana nursery grounds in 2016.…”

“…Two different ROMS setups were used to calculate input fields for IBM (hourly averaged current, temperature and salinity fields) for the period from 1 January, as seabream spawning regularly occurs during first two months of the year, to 15 May 2016 when juvenile sampling was conducted. The first ROMS setup (Adriatic ROMS) 54 covered the entire Adriatic Sea with a resolution of 2.5 km, while the second ROMS setup (ASHELF2 ROMS) 32 had a smaller domain encompassing the eastern coastal area of the middle Adriatic, with a resolution of 1 km (Fig. 4).…”

Interaction between small pelagic purse seine fishery and its top predators

“…2a). Although tuna presence was recorded through the year, its lower occurrence in May and June could be connected with tuna spawning migration to open sea waters, where this fishing gears do not operate (JARDAS, 1996;DŽOIĆ et al, 2017). Monthly occurrence of dolphins and swordfish showed opposite pattern -dolphins were mostly noted during summer (August, 24 %; Fig.…”

Marine Aquaculture Impacts on Marine Biota in Oligotrophic Environments of the Mediterranean Sea – A Review

“…This form of aquaculture activity has a range of both positive and negative impacts on marine biota within the ecosystem. Grubišić et al (2013) reported spontaneous spawning of bluefin tuna (Thunnus thynnus) during rearing practices within cages, which could possibly increase the abundance of juvenile tunas in the open sea (Džoić et al, 2017), and have a positive effect on the resilience of this species to intensive fishery exploitation.…”