View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Repositorio Institucional Digital del IEO FISHERIES OCEANOGRAPHY Fish. Oceanogr. 23:3, 191–209, 2014 Larval fish distribution and retention in the Canary Current system during the weak upwelling season M. MOYANO,1,4,* J.M. RODRIGUEZ,2 V.M. sometimes coexisted. Finally, larval connectivity BENITEZ-BARRIOS1,3 AND S. HERNANDEZ- between Islands within the Canary archipelago is sug- LEON 1 gested. The present study thus contributes to the 1Instituto de Oceanografıa y Cambio Global, Universidad de Las understanding of the complex dispersal and retention Palmas de Gran Canaria, Campus Universitario de Tafira, processes in the Canaries-African Coastal Transition 35017, Las Palmas de Gran Canaria, Canary Islands, Spain Zone. However, results also highlight the poor knowl- 2Centro Oceanografico de Gijon, Instituto Espanol~ de Oceanog- edge of this region compared with the other three rafıa, Avda, Prıncipe de Asturias 70Bis, 33212, Gijon, Astu- main Eastern Boundary Upwelling Systems in terms of rias, Spain ichthyoplankton dynamics. The importance of routine 3 Centro Oceanografico de Canarias, Instituto Espanol~ de Ocean- monitoring programs of commercial and non-commer- ografıa, Via Espaldon, Darsena Pesquera, parcela 8, 38180, cial species in the area is emphasized. Santa Cruz de Tenerife, Canary Islands, Spain Key words: connectivity, larval drift, larval fish assemblages, Eastern Boundary Upwelling System ABSTRACT INTRODUCTION The spatial distribution of fish larvae was studied in Dispersal of the early life stages of fish may have dra- the Canaries-African Coastal Transition Zone, outside matic consequences for their survival and, further, for the strong upwelling season. An onshore–offshore population connectivity and recruitment success transition in the larval fish community structure was (Harden-Jones, 1968; Cowan and Shaw, 2002). To observed, from a coastal assemblage dominated by provide population closure and preserve self-recruit- small pelagics (sardine, anchovy, mackerel), bounded ment, retention mechanisms have likely evolved to by the upwelling front, to an offshore assemblage dom- avoid drift to unfavourable areas. These retention inated by mesopelagic species (mainly Myctophidae, mechanisms may be either passive (e.g., accumulation Phosichthydae, Gonostomatidae). Distribution of the of larvae within eddies, Karnauskas et al., 2011) or neritic larvae was deeply influenced by the intense active (e.g., diel vertical migrations, Landaeta and mesoscale activity found in the area, both horizontally Castro, 2013). Understanding how these processes (larvae were advected offshore but were always develop in each environment is critical for performing retained within the upwelling area) and vertically real estimates of larval survival within any modelling (larvae were deepened in the vicinity of two anticy- approach and/or recruitment study. clonic eddies). A combined effect of the upwelling The Eastern Boundary Upwelling Systems (EBUS) front and a cyclonic–anticyclonic eddy dipole is likely constitute very productive, albeit highly dynamic the successful retention mechanism for these larvae. regions where offshore dispersal may lead to massive These results support the current belief that retention losses of fish larvae (Cury and Roy, 1989; Castro and may be higher than previously thought in upwelling Hernandez, 2000). In terms of fish population areas. Oceanic larvae were also collected in higher dynamics, the Canary Current system (Fig. 1) is the abundances near the front and an anticyclonic eddy. least studied of these EBUS (i.e., California, Benguela Neritic and oceanic larvae frequently showed a differ- and/or Humboldt). This system functions rather differ- entiated position in the water column, although they ently than the other three due to the presence of the *Correspondence. e-mail: [email protected] Canary Islands. This archipelago acts as a >600-km- 4 Present address: Institute for Hydrobiology and Fisheries wide barrier to the flow of the Canary Current and Science, University of Hamburg, Olbersweg 24, 22767 high mesoscale activity is thus generated south of the Hamburg Germany. islands (Barton et al., 1998) (Fig. 1). Trade winds Received 6 February 2013 blow persistently in the area during summer (July–Sep- Revised version accepted 1 December 2013 tember), leading to the strong upwelling season on the © 2014 John Wiley & Sons Ltd doi:10.1111/fog.12055 191 192 M. Moyano et al. African coast and also to more frequent island-gener- of Fuerteventura (Fig. 1) has been invoked as a poten- ated mesoscale structures south of the Canary Islands. tial retention mechanism for clupeid larvae (Rodrıguez Mesoscale features generated in the African coast et al., 1999; Rodrıguez et al., 2004). Secondly, offshore (e.g., upwelling filaments, Rodrıguez et al., 1999), and eddies can also lead to a high-growth scenario for lar- south of the islands (island-wakes or eddies) can inter- vae due to increased production compared with the sur- act in the so-called Canaries-African Coastal Transi- rounding ocean waters (California Current, Logerwell tion Zone (Canaries-African CTZ). and Smith, 2001; Canary Current, Becognee et al., Dispersal processes in EBUS are frequent but do not 2009). Besides these common processes observed in necessarily imply larval losses. These processes can be other EBUS (i.e., upwelling filaments and eddies), a linked to other concentration and retention mecha- third transport mechanism present in the Canaries- nisms that lead to a high growth - low predation sce- African CTZ is the larval transport from the African nario for fish larvae: ocean triad (Bakun, 1996). For coast to the Canary Islands by upwelling filaments example, Ekman transport and upwelling filaments (Becognee et al., 2006; Moyano et al., 2009). Connec- have been reported to transport fish larvae and their tivity among islands within the archipelago and with prey tens or hundreds of kilometers away from the other archipelagos (e.g., Madeira, Cape Verde) has coast (Parrish et al., 1981; Hutchings et al., 2002) to a been suggested (Rodrıguez et al., 2000; Rodrıguez lower predation pressure environment. But these et al., 2004) but never observed in the field. filaments can also interact with other structures Besides the above-mentioned passive retention (e.g., eddies) that return the biogenic material back to mechanisms, larval behavior can also favor coastal the shelf (Bakun, 1996). In the case of the NW Afri- retention. For example, in the Humboldt Current can upwelling, a filament–cyclonic eddy complex south postflexion larvae of Peruvian anchoveta perform a 18oW 15oW 12oW 9oW 6oW 39oN IBERIAN N PENINSULA 36oN o 33 N MADEIRA urrent y C Canar Cape Ghir 30oN CANARY ISLANDS Cape Juby 27oN Cape Bojador NORTHWEST AFRICA 24oN Figure 1. Map showing the location of the sampling area. The upper panel indi- 29oN cates the direction of the Canary Current Lanzarote 0 0 and some mesoscale eddies formed near 10 – 40’ the NW African upwelling area and Fuerteventura –200 south of the Canary Islands (red: anticy- –3000 20’ Tenerife clonic eddies; blue: cyclonic eddies). The –1000 Gran Canaria lower panel displays the 78 sampling 47 32 31 16 15T1 28oN 0 67 61 60 48 46 33 30 17 14 1 T2 stations (zonal transects are shown as 78 –20 T9 68 62 59 49 455 34 292 18 13 2 T3 – 77 T1 T9) and four frequent mesoscale –3000 69 63 58 50 44 35 28 19 12 3 T4 40’ 76 structures in the area: northern filament 75 70 64 57 51 43 36 27 20 11 4T5 74 originated near Cape Juby (green arrow) 71 65 56 52 42 37 26 21 10 5 T6 20’ 73 NORTHWEST and its associated cyclonic eddy (blue); 72 66 55 53 41 338 25 22 9 6 T7 AFRICA southern filament generated near Cape 54 40 39 24 23 8 7 T8 27oN Bojador (green arrow) and its associated 17oW 16oW 15oW 14oW 13oW anticyclonic eddy (red). © 2014 John Wiley & Sons Ltd, Fish. Oceanogr., 23:3, 191–209. Larval fish retention in the Canary Current system 193 diel vertical migration (DVM) from depth to shallower although living in depth, these fish are also sensitive waters at night (Landaeta and Castro, 2013). This to climate-driven changes (Koslow et al., 2013). These upwards migration at night, or Type I DVM (Neilson findings thus highlight the need for continuous moni- and Perry, 1990), prevents advection during daytime toring and management of these unexploited species, in which winds, and thus Ekman transport, is stronger. as well as the incorporation of this component in The opposite DVM, Type II DVM (Neilson and Perry, future ecosystem-based management. 1990), has been observed for anchovy in the Benguela The present study focuses on the ichthyoplankton system (Stenevik et al., 2007). But these authors argue community in the Canaries-African CTZ. Previous that this behavior also contributes to larval transport larval fish works in the area investigated the dynamics towards the nursery areas, due to the shallow Ekman of commercial species (mainly clupeids) in the African layer and the deeper onshore current. Despite the shelf (e.g., John, 1982; Ettahiri, 1996; Arkhipov, importance of vertical distribution and diel migrations 2009) but the transition zone has been overlooked. for retention processes on each particular system, there Only a handful studies have analyzed non-commercial have been very few studies investigating them in the species in the Canaries-African CTZ (Rodrıguez et al., NW African upwelling (John, 1985; Rodriguez et al., 1999; 2004, 2006), all cruises conducted during the 2006). Given the complex hydrodynamic scenario strong upwelling season (summer). Our work is the that fish larvae face in upwelling systems in general, first to investigate the entire larval fish community in and in the Canaries-African CTZ in particular, under- the Canaries-African CTZ in winter–spring (during standing the fate of the larvae and quantifying their the weak upwelling season). Our aims were to (i) growth and survival in this environment is essential.