Adapting to the wild: the case of aquaculture‐produced and released meagres Argyrosomus regius

Abstract

The performance of juvenile Argyrosomus regius released off the coast of Mallorca Island (Balearic Islands, Spain) was assessed by comparing the body condition, stable isotope signature and stomach contents of aquaculture‐produced A. regius that had been released, fished and returned by fishermen after spending from a few days to >1 year at liberty with A. regius reared under controlled conditions on two contrasting diets (well‐fed and unfed). During the first 40 days of the experiment, the condition index (KR) of the returned A. regius and the unfed A. regius followed the same decreasing trend. Thereafter, the KR values of the returned A. regius were significantly higher than those of the unfed A. regius but never reached the values of well‐fed A. regius. The δ13C signal of the returned A. regius clearly increased (in comparison with the well‐fed A. regius) after they had spent a few months at liberty. The temporal pattern depicted by the stable isotopes and the most likely prey composition inferred from this pattern strongly suggest a shift in diet. The stomach contents of the returned A. regius that had spent <100 days at liberty consisted almost exclusively of decapods. The diet of the few returned A. regius that had spent >100 days at liberty consisted entirely of fishes. Wild A. regius from the remaining fishery on the Spanish coast exhibited the same ontogenetic diet shift from invertebrates to fishes, but at a smaller size threshold. Overall, the results demonstrated that culture‐reared A. regius experience adverse conditions during the first days after release into the wild but that at least some A. regius are able to adapt to the natural environment after a few months at liberty.

Comparing tagging strategies: Effects of tags on retention rate, mortality rate and growth in hatchery-reared juvenile meagre, <em>Argyrosomus regius</em> (Pisces: Sciaenidae)

“…However, some tag losses were observed on the recaptured meagre several months after the release (Gil et al 2014a). In this study, T-bar tags showed a high variability in retention time in juvenile meagre, as has been observed in other studies.…”

“…Therefore, an optimal nutritional condition may result in an increased activity pattern, thus favouring tag loss. Released meagres in the Balearic restocking programme need a relatively long time to adapt to wild food (Gil et al 2014a). Shortterm tag loss seems to be smaller, and may be related to suboptimal diet of recently released fish, which may be less active than fully feed fish, as suggested by the tank experiment.…”

“…Tag loss may cause underestimation of survival rate for the hatchery-reared juveniles, and therefore an underestimation of restocking success. Results obtained from the meagre restocking programme conducted in the Balearic Islands showed that some tag loss occurred on the recaptured specimens several months after the release (Gil et al 2014a). In the same study, the recaptured meagre juveniles showed that the released specimens experienced difficulty feeding during the first weeks after release into the wild (Gil et al 2014a).…”

“…Results obtained from the meagre restocking programme conducted in the Balearic Islands showed that some tag loss occurred on the recaptured specimens several months after the release (Gil et al 2014a). In the same study, the recaptured meagre juveniles showed that the released specimens experienced difficulty feeding during the first weeks after release into the wild (Gil et al 2014a). Therefore, studies on tagging methodologies in meagre juveniles and the influence of the nutritional status on the tag retention appear to be necessary.…”

Stock enhancement by hatchery-released turbot, <em>Psetta maxima</em>, in the southeastern Black Sea: capture, migration, growth and diet analyses

“…The condition factor values of recaptured fishes are expected to decline, reflecting the consumption of energy reserves without replacement. The same pattern has also been observed in the aquaculture-produced and released meagre Argyrosomus regius (Gil et al 2014). The growth performance index estimations provide an indication of the reliability of estimates since it is suggested that growth performance index values are similar for the same species and genera.…”