Alemany, F. (Francisco)

Reglero, P. (Patricia)

Torres, A.P. (Asvin Pérez)

English

Repositorio Institucional Digital del IEO

Environmental variability on the distribution, abundances and growth rates of the larvae of bullet tuna. Pérez-Torres A , Alemany F,  and Reglero P. Instituto Español de Oceanografía (IEO), Centro Oceanográfico de Baleares. Muelle de Poniente s/n, Apdo. 291, Palma de Mallorca, Spain.Bibliography1. Field Manual ICCAT. Chapter 2.1.11.2Bullet tuna2. Fishes of the North-eastern Atlantic and the Mediterranean. Unesco3. Fowler and Smith, 1983; Kruse and Dalley, 1990; Jennings, 19914. Tanaka et al 2008, Sawada et al. 2005 Miyashita et al 20015. Alemany et. al 2008 (Acceptet)6. Chambers and Legget, 19877. Houde, 1987, 19889MethodologyResults & ConclusionsBullet tuna is the tuna species among Bluefin tuna andalbacore whose larval stages are more ubiquitous andshow the highest abundances. Results from previousstudies (5) indicate that bullet tuna larvae can be foundin a wider range of temperatures than other tuna larvae,from 18.5 to 28.5, but showing preference fortemperatures over 23.5ºC. The larvae analyzed in thisstudy showed SL vs age potential relationships and thetemperature had a clear positive influence on the growthrates, as have been widely reported (6). The GAMsshow how the presence of yolk-sac and pre-flexionlarvae have a positive relationship with temperature,salinity and highest with zooplankton biomass, althoughthe flexion and post-flexion larvae only have it withtemperature and zooplankton biomass. Bullet tuna hadhigher growth rates compared to laboratory estimatesfrom the literature for Bluefin tuna.Since recruitment variability has been related to earlylarval and juvenile growth (7), higher temperatures inthe surface layers where tuna larva inhabits could resultin higher growth rates if food is not limiting and hence inhigher recruitment success.ICES CM 2009/G:17 Poster (Session: Comparative study of climate impact on coastal and continental shelf ecosystems in the ICES area: assessment and management )Auxis rochei, is distributed worldwide in tropical and subtropical waters (1), including ICES areas asatlantic coast of Iberian Peninsula, isolated records from the British Islands and coasts of Belgium andScandinavia (2). Auxis rochei larvae were captured off Balearic Islands (Western Mediterranean)within the framework of an ichthyoplankton survey carried out between 29th July and 11th August 2008,by means of double oblique tows from the thermocline to surface realized with Bongo 90 nets fittedwith 500 microns meshes. CTD (Seabird-911) casts were performed at each station to characterizehydrographic scenario. Plankton samples, after sieving, were preserved in 96% ethanol. In the lab,fish larvae were picked up and identified at species level. Standard lengths (SL) of the target specieswere measured to the nearest 0.1 mm with an Image Analysis System (Image-Pro). Shrinkage, onaverage, may be as 7 %, based on estimates for others genders of fish larvae preserved in ethanol (3)but since all samples were preserved following the same methodology, it was assumed that theshrinkage would not influence the comparison of growth rates among analyzed specimens. Sagittaeand lapilli otoliths were teased out with tungsten needles down stereostopic microscope, being thelarvae placed on a cover glass submerged in distilled water. The otoliths were dried and sealed withresin “Eukitt”. Then, the sagitta otoliths were analyzed under a light microscope at 1000magnifications. Daily rings were counted, measuring their widths and distance to otolith center, usingan Image Analysis System based on the software Image-Pro. Once agreed the lecture criteria, eachotolith was read independently by two different readers.AbstractSmall tunas, as bullet tuna (Auxis rochei) play a key role in coastal marine ecosystems since they can have a major impact in small pelagic fish stocks. At their larvalstages they can interact, as competitors or prey/predators, with other tuna larvae, as those of Thunnus thynnus or T. alalunga. It is a well known fact that environmentallydriven variations in larval survivorship rates, potentially induced by climate changes, can result in large fluctuations in population abundances. Therefore, studiesproviding information on the ecology of small tuna species larvae are useful to assess both the impact of climate changes on the dynamics of small pelagic fishes andother tuna stocks. Here we provide a review on the information available up to now of this species overall ICES areas, focusing on the distribution, abundances andgrowth rates of the larvae of bullet tuna. Since water temperature may be of crucial importance in larval stage dynamics we assess/explore the relationship betweentemperature and distribution patterns and growth of bullet tuna larvae using data obtained within the framework of ichthyoplankton surveys directed to tuna larvaesampling carried out during the last decade off the Balearic islands, recognized as one of the main spawning grounds of tuna species in the Mediterranean. Theserelationships are compared to other tuna species and other ICES areas where information is available. Our findings highlight the role that temperature plays at these earlystages of development and the impact that increasing temperature may have on the distribution and growth of these species, and hence in recruitment success.Keywords: tuna, coastal ecosystem, bullet tuna, distribution, growth, larvaeImage 1. Auxis rocheilarvae with 5.09 mm SLand 9 days of lifeYear Tº C Potential p-value R²2008 27 SL = 1,240DL0,629 0,001 0,712008 26 SL = 1,220DL0,594 0,001 0,682008 25 SL = 1,327DL0,547 0,001 0,71Fig. 1 and Table 1. Temperature effect in Bullet tuna larvae growth ratesFig. 2. The weight at age relative to the estimated initialweight. The symbols are the estimated data from differentlaboratory experiments with Bluefin tuna (T thynnus) larvae(4). The black squares are our observations for BT at 25 °Cfrom otolith data. The continuous lines represent the fits forbullet and bluefin tuna.Image 2. Map of spatial distribution bullet tuna larvae within the community duringsummer 2008 in Balearic Islands. Bullet tuna print in redTable 2. Based on GAM models the estimated significance relationship between thepresence/absence of two ontogenetic stages, yolk-sac and pre-flexion larvae and flexionand post-flexion larvae with respect to the temperature, zooplankton biomass, andsalinity. ns: no significant; *: significant (<0.05); **glm instead of gamFig. 2. Results of Single Parameter Quotient analysisconsidering all the data about average temperature in theupper mixing layer, above the thermocline, and Auxis rocheilarval abundances calculated from Bongo 60 standard obliquetows, available from Tunibal surveys carried out annually from2001 to 2005.Acknowledgements  This work is financed by the IEO and Conselleria de Agricultura I Pescadeles Illes Balears. We want to thank to Agurtzane Urtizberea that help usto make GAMs and Fig. 2Environmental variableYolk-sac and pre-flexion larvaeDev. % UBREFlexion and post-flexion larvaeDev. % UBRETemperatureZooplankton biomassSalinity6.12 0.31 *11 **6.94 0.31 *4.16 0.11*2.79 0.11*1.01 0.14ns050100150200N. stations

Environmental variability on the distribution, abundances and growth rates of the larvae of bullet tuna

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