First attempt to assess the viability of bluefin tuna spawning events in offshore cages located in an a priori favourable larval habitat

Abstract

SUMMARY: Most of the Atlantic bluefin tuna caught by the purse-seine fleet in the Mediterranean Sea are transferred alive into transport cages and towed to coastal facilities where they are fattened. This major fishery is targeting aggregations of reproductive bluefin tuna that continue spawning within the transport cages. Our study is the first attempt to assess the viability of the spawning events within transport cages placed offshore in a priori favourable locations for larval survival. The study was conducted in June 2010 in the Balearic Sea, a main spawning area for bluefin tuna in the Mediterranean. The location of two transport cages, one with wild and one with captive tuna, coincide with the situation of the chlorophyll front using satellite imagery as a proxy for the salinity front between resident surface waters and those of recent Atlantic origin. The results showed that bluefin tuna eggs were spawned almost every day within the two cages but few or no larvae were found. The expected larval densities estimated after applying mortality curves to the daily egg densities observed in the cages were higher than the sampled larval densities. The trajectories of the eggs after hatching estimated from a particle tracking model based on observed geostrophic currents and a drifter deployed adjacent to the cage suggest that larvae were likely to be caught close to the cages within the sampling dates. Spawning events in captive tuna in transport cages may hatch into larvae though they may experience higher mortality rates than expected in natural populations. The causes of the larval mortality are further discussed in the text. Such studies should be repeated in other spawning areas in the Mediterranean if spawning in cages located offshore in areas favourable a priori for larval survival is likely to be considered a management measurement to minimize the impact of purse-seine fishing on tuna.Keywords: bluefin tuna, larvae, geostrophic currents, transport cage, Mediterranean. RESUMEN: Primer intento de evaluación de la viabilidad del desove de atún rojo en jaulas en alta mar ubicadas en un hábitat a priori favorable para las larvas. -La mayor parte del atún rojo atlántico capturado por la pesquería de cerco en el mar Mediterráneo es transferido vivo a jaulas de transporte y remolcado a instalaciones de engorde localizadas en la costa. Esta importante pesquería tiene como objetivo las agregaciones de reproductores de atún rojo que continúan aún su puesta en las jaulas de transporte. Nuestro estudio es el primer intento de evaluar la viabilidad del desove que tiene lugar en jaulas de transporte que están localizadas en alta mar en zonas que a priori favorecen la supervivencia larvaria. La zona de estudio está situada en el mar Balear, una de las zonas de puesta de atún rojo más importantes del Mediterráneo, en junio del 2010. La ubicación de las dos jaulas de transporte, con atún recién capturado y en cautividad respectivamente, coincide con la situación del frente de clorofila utilizando imágenes de satélite como...

Reproductive investment of the pen shell Pinna nobilis Linnaeus, 1758 in Cabrera National Park (Spain)

“…Observations of recruitment in the Bay of Palma (Cabanellas-Reboredo et al, 2009a) have pointed to a second larval peak in January; however, this data shows that our particular shallow population cannot be the source of this second peak. It is possible that populations at greater depths are responsible for a second spawning period, as bivalve spawning triggers are related to water temperature and the thermocline around the island of Mallorca is approximately 20 m depth during the summer months and 60 m during the winter months (Reglero et al, 2013;Olivar et al, 2014).…”

An overview of stress physiology of fish transport: changes in water quality as a function of transport duration

“…Some larger species may even be transported in cages within the sea itself, as in the case of Atlantic Bluefin tuna (Thunnus thynnus, Scombridae) (Reglero et al 2013). The main differences are related to the type of container, fish density inside the container, fish species and the duration of the transport.…”

“…They may be individually packed or packed as a group. Some larger species may even be transported in cages within the sea itself, as in the case of Atlantic Bluefin tuna (Thunnus thynnus, Scombridae) (Reglero et al 2013). Fish density during transport is an important factor because high densities correspond to lower costs.…”

“…Water conditions can, and most probably will, adversely change during fish transport. Fish transport is a global necessity, related to several activities/goals: (i) human feeding (Marc ßalo et al 2008;Reglero et al 2013); (ii) transport of fry from hatchery sites to growth/fattening ponds (Abreu et al 2008) or for human recreation fishing (angling); and (iii) transport of wild animals for aquaculture facilities (Marc ßalo et al 2008;Oyoo-Okoth et al 2011), release of juveniles for stocking programmes (Iversen et al 1998;Gomes et al 2003), for public aquaria Harmon 2009), for ornamental (Wright et al 2007;Gomes et al 2009;Brinn et al 2012), or even for research (Corrêa et al 2014). Stress can lead to infectious diseases or even cause animal mortality (Bernoth and Crane 1995;Murphy and Lewbart 1995).…”

Fish Domestication: An Overview

“…Nevertheless, the aquaculture production truly started in the middle of the 1980s in the Mediterranean Sea, with the evolution of new technics allowing to provide fish to fattening farms [71,72]. Despite significant progress, notably thanks to the work of a consortium of European researchers, the reliable control of the life cycle of the Atlantic bluefin tuna in captivity was never reached [73,74]. Consequently, this…”