ACTA ICHTHYOLOGICA ET PISCATORIA (2012) 42 (1): 21–30 DOI: 10.3750/AIP2011.42.1.03 BIOLOGY, FEEDING, AND HABITAT PREFERENCES OF CADENAT’S ROCKFISH, SCORPAENA LOPPEI (ACTINOPTERYGII: SCORPAENIFORMES: SCORPAENIDAE), IN THE BALEARIC ISLANDS (WESTERN MEDITERRANEAN) Francesc ORDINES1*, María VALLS1, and Adam GOURAGUINE1, 2 1 IEO-Centre Oceanogràfic de les Balears, Palma, Spain 2 University of Glasgow, Division of Ecology and Evolutionary Biology, Glasgow, United Kingdom Ordines F., Valls M., Gouraguine A. 2012. Biology, feeding, and habitat preferences of Cadenat’s rockfish, Scorpaena loppei (Actinopterygii: Scorpaeniformes: Scorpaenidae), in the Balearic Islands (western Mediterranean). Acta Ichthyol. Piscat. 42 (1): 21–30. Background. Scorpaena loppei Cadenat, 1943 is a small benthic scorpion fish, distributed in the eastern Atlantic from the Bay of Biscay to Mauritania and the Mediterranean Sea. This work constitutes the first complex attempt to study aspects of biology, feeding, bathymetric distribution, and habitat preferences of S. loppei. Materials and methods. The biological samples of S. loppei, as well as the data on its abundance and distribu- tion, were collected during the annual bottom trawl survey series BALAR-MEDITS carried out from 2005 through 2010. The biological sampling included: weighing and measuring the fish, gonad weighing, determina- tion of sex and maturity stage, age estimation through otolith readings, and stomach content analysis. Results. The sampled individuals ranged from 5.5 to 12.8 cm in total length (TL). The females predominated in the smaller size classes, and males being more abundant in the larger ones. All females sampled were mature (or approaching maturity). The age determined ranged from 0 to 5 years and from 1 to 5 years, for females and males, respectively. The estimated values of the von Bertalanffy asymptotic length L∞ (cm) and growth coefficient k (year–1) for females and males were 10.9 and 0.53 and 12.4 and 0.49, respectively. According to the age–length key, all females of S. loppei should be attaining their first maturity during their first year of life. The diet of S. loppei consisted predominantly of crustaceans (mysids and decapods) followed by teleosts fishes. A spe- cialized feeding behaviour was indicated by the Levin’s index for numerical composition and frequency of occur- rence assuming values of 0.18 and 0.28, respectively. The presence of S. loppei was restricted to sandy-mud deep continental shelf bottoms from 90 to 180 m depth. This distribution did not overlap with that of other small scor- pion fish species inhabiting the area. Conclusion. Unlike its congeners, S. loppei demonstrated specialised feeding habits and habitat requirements. Being the only small scorpion fish inhabiting this benthic habitat in the study area might have reduced the inter- specific competition, facilitating feeding and growth and allowing an early achievement of sexual maturity. Keywords: Scorpaena loppei, small scorpion fish, deep continental shelf, bottom trawl surveys, biological traits, distribution, Balearic Islands, western Mediterranean INTRODUCTION Mediterranean the biology of the majority of the The genus Scorpaena occurs worldwide in tropical and Scorpaena species such as Scorpaena scrofa L.; temperate seas accommodating 62 valid species (Froese Scorpaena porcus L.; Scorpaena notata Rafinesque, 1810; and Pauly 2011). Six of them are present in the Scorpaena elongata Cadenat, 1943; and Scorpaena Mediterranean, where in some littoral communities such as maderensis Valenciennes, 1833 have been studied (Bradai rocky reefs and/or meadows of Neptune grass, Posidonia and Bouain 1988, 1990a, 1990b, 1991, Harmelin-Vivien et oceanica, the biomass of the scorpionfish of the genus al. 1989, Morte et al. 2001, Ragonese et al. 2003, La Mesa Scorpaena is substantial in relation to other fish species et al. 2005, Muñoz et al. 2005, Ordines et al. 2009), leav- (Harmelin-Vivien et al. 1989). Scorpaena species have ing Scorpaena loppei Cadenat, 1943 as the only species of received relatively little attention worldwide, with the excep- this genus whose biology is almost unknown. tion of Scorpaena guttata Girard, 1854 and Scorpaena car- The Cadenat’s rockfish, S. loppei Cadenat, 1943, is dinalis Solander et Richardson, 1842 (see: Love et al. 1987, a small benthic scorpion fish, distributed in the eastern Stewart and Hughes 2010). In contrast, in the Atlantic from the Bay of Biscay to Mauritania and the * Correspondence: Francesc Ordines, IEO-Centre Oceanogràfic de les Balears, Moll de Ponent s/n, 07015 Palma, Spain, phone: (34) 971 40 41 02, fax: (34) 971 40 49 45, e-mail: [email protected]. 22 Ordines et al. Mediterranean Sea, commonly not exceeding 12 cm in total length (Hureau and Litvinenko 1986). In the eastern Mediterranean it is considered a rare species (Filiz et al. 2010), reported from the Aegean Sea, Israeli waters (Papaconstantinou 1988, Golani 2005), and recently also Turkey (Keskin and Eryilmaz 2008, Filiz et al. 2010). In the western Mediterranean S. loppei seems to be more abundant and has been reported as a usual component of demersal assemblages in areas such as the Gulf of Lions and the Catalan coasts (Gaertner et al. 1999, Demestre et al. 2000), and as a by-catch of the bottom trawl fleet from the Balearic Islands (Merella et al. 1997). The presently reported study was intended to be the first major contribution on the main biology traits of S. loppei. Particularly, we focused on age and growth, feeding habits, bathymetric distribution, and habitat pref- Fig. 1. Map of the western Mediterranean indicating the erences of this fish. study area (dashed rectangle) MATERIAL AND METHODS observed macroscopically and under a binocular micro- Trawl sampling. The data used in this study was col- scope and assigned to a maturity stage according to the lected during the series of BALAR (2005–2006) and scale described in Brown-Peterson et al. (2011). Stomachs MEDITS (2007–2010) annual bottom trawl surveys car- were preserved in plastic vials containing 96% alcohol ried out during spring–early summer (May through June). solution for a subsequent food content analysis (see In all, 323 hauls covering the continental shelf and the below). The sagittal otoliths of all specimens were also slope off the Balearic Islands (western Mediterranean) removed, cleaned, and stored dry. In total, 175 individu- from 38 to 750 m depth (Fig. 1) were analysed. The sam- als of S. loppei were sampled. pling design and gear used (GOC73) were the same for Biological indexes and parameters. Length frequency both series of surveys, and were those commonly used distributions by sex were created. The Chi-square test was throughout the Mediterranean within the MEDITS used to test for differences from 1 : 1 in the sex-ratio by size Programme since 1994 (Bertrand et al. 2002). class and for the whole population. The gonadosomatic index The hauls were conducted during daylight hours and (GSI) was calculated as follows: GSI = 100 · GW · EW–1, had a duration that ranged from 20 minutes on the shelf to where GW and EW are gonad weight and eviscerated 60 minutes on the slope. The average towing speed was weight, respectively. The relation between GSI and indi- ≈1.54 m · s–1 (3 knots). The arrival and departure of the vidual total length was studied by means of linear regres- net to the bottom, as well as the horizontal and vertical sion. Length–weight relations of all individuals and by sex gaps (on average 16.4 and 2.8 m, respectively), were were established by fitting a power regression, W = a · TLb, measured using a SCANMAR system. Depth and position where W is the individual total weight in g, TL is the total were recorded every five min. length in cm, a is the intercept and b is the allometric con- Biological sampling. A total of 175 individuals of stant. The 95% confidence intervals of the b parameter S. loppei (Fig. 2), caught during the surveys, were were calculated by using the regression analysis tool retained for biological studies. For each individual, the included in EXCEL, and it were used to assess the allom- total length (TL, to the nearest mm), total and eviscerated etry of the increase in weight (confidence intervals weight (to the nearest 0.01 g), sex, and gonad weight (to lower/higher or including 3 indicate negative/positive the nearest 0.01 g) were recorded. Female gonads were allometry, or isometric growth, respectively). Analysis of Fig. 2. Individual of Scorpaena loppei , from the Balearic Islands; arrow points a single anterior mandibular pore (characteristic trait of S. loppei not shared by its congeners from the Mediterranean) Biology, feeding, and distribution of Cadenat’s rockfish 23 covariance (ANCOVA) was applied to test for differences software version 7.0; Krebs 1999). In order to minimize in the length–weight relations between males and females. problems derived from different states of prey digestion, Previously to the application of ANCOVA both W and TL the index was calculated using both %n and %F. This were log-transformed in order to obtain linear relations. index ranges from 0 to 1, low values indicating a special- Age and growth. The sagittal otoliths were immersed ized feeding strategy, whereas high ones indicate a gener- in a 50% mixture of glycerol and alcohol. The number of alist diet. The vacuity index (percentage of empty stom- translucent rings was counted with a compound micro- achs, v) was also calculated. scope using reflected light. The increment periodicity of Distribution. The abundance of S. loppei was stan- the rings could not be validated, because the individuals dardised to 1 km2 by using the distance covered and the sampled in the frames of this study were all collected dur- horizontal opening in each haul. Since it has been ing spring–early summer, and hence the marginal incre- observed that species typically show unimodal (bell- ment evolution throughout the year could not be analyzed.