Food of the yellowtail amberjack Seriola lalandi from the south-west Atlantic

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Food of the yellowtail amberjack Seriola lalandi from the south-west Atlantic
  Food of the yellowtail amberjack   Seriolalalandi  from the south-west Atlantic m. vergani 2 , e.m. acha 1,2,3 , j.m. diaz de astarlon 1,2 and d. giberto 2,3 1 Universidad Nacional de Mar del Plata, Argentina,  2 Consejo Nacional de Investigaciones Cientı´ficas y Te´cnicas (CONICET), 3 Instituto Nacional de Investigacio´n y Desarrollo Pesquero (INIDEP), Paseo Victoria Ocampo N 8  1, B7602HSA Mar del Plata,Argentina Keywords: Q1 The stomach contents of 66 adult (50–86 cm total length) Seriola lalandi  were examined, and comprised primarily  Trachurus lathami , with some small pelagic cephalopodsalso consumed.Yellowtail amberjack ( Seriola lalandi , formerly   S. dorsalis ;Carangidae) (Schmitt & Strand, 1982; Poortenaar  et al. ,2001) is a cosmopolitan carangid inhabiting tropical and sub-tropical waters, between 40 8 N and 40 8 S. It is exploited in com-mercial and recreational fisheries in several regions of theworld, and is also used in aquaculture in Japan, Australia,New Zealand and Hawaii (Poortenaar  et al. , 2001). Itsbiology and life-history are poorly known, with little pub-lished information on its food and feeding habits. The few existing reports show that the entire diet comprises schooling species (Schmitt & Strand, 1981; Marı´n, 1993).Historically, two species of yellowtail amberjack ( S. lalandi and  S. rivoliana ) were thought to occur in the south-westAtlantic (see Cosseau  et al. , 1975). However, those authorsbased on the homogeneity found in morphometric and mer-istic characters of 186 specimens, concluded that  S. lalandi is the only species occurring in Argentine waters.Adult  S. lalandi  migrate to Argentine waters during thesummer months (January–April), as also noted in other pelagicfish, and is reported as associating with Atlantic bonito Sarda sarda  (Bloch) in commercial catches. They have beenreported from Argentine waters in depths of 20–36 mbetween 36 8 S and 38 8 S (Figure 1) and, as reported elsewherein the world, are often associated with rocky reefs (Cousseau et al. , 1975; Marı´n, 1993).Samples of   S. lalandi  were caught using trolling lines during daytime (08:00–18:00 h), around rocky reefs at 35 8  52 0 –35 8 58 0 S and 54 8  45 0 –54 8  48 0 W, on 15 to 22 February 2002(Figure 1). These sparse rocky reefs may concentrate  S.lalandi  schools, but our knowledge on their role as fishhabitat is limited. Surface and bottom water temperature atthe study site ranged from 22.2–22.5 8 C and 19.6–19.9 8 Crespectively, with a seasonal thermocline at 15–16 m depth.A weak halocline was also present at the same depth, with sali-nities of 29.17–31.41 at the surface, and 32.72–32.86 at thebottom, showing the influence of the freshwater dischargefrom the Rı´o de la Plata.Sixty-six adult  S. lalandi  were analysed, with specimensmeasured (L T ) and weighed (W T ) on board and the stomachslabelled and frozen. In the laboratory, stomachs were weighedand their contents identified to the lowest possible taxon.Total length and total weight ranged from 50–86 cm, and1000–3770 g, respectively (L T  mean value 59.30 þ / 2 7.36 cm, W T  mean value 1918.35 þ / 2  611.33 g). Based onthese data, the length–weight relationship was estimated as:W T ¼ 0.2112 TL 2.2224 . The low value of b ( , 3) may be asso-ciated with high energetic costs after spawning and / ormigrations.The following indices were estimated from the stomachsamples: (i) coefficient of repletion (C R  ), the proportion of stomachs containing food; (ii) numerical index (N I ), percen-tage of specimens of a particular prey species in relation tothe total number of all prey; (iii) frequency index (F I ), percen-tage of stomachs with prey of a particular species in relation tothe number of stomachs with food; (iv) weight index (W I ),percentage by weight of all specimens of a particular prey species in relation to the total weight of all prey; and (v)index of relative importance, IRI ¼ F I (N I þ W I ), which wassubsequently expressed as a percentage (%IRI).Seventy-six per cent of stomachs contained food, indicating a relatively high feeding activity during the study period. Thenumber of prey items per stomach ranged between 7 and 45(mean value 16.9  þ / 2 6.3). Total length and food weight(stomach free) were negatively correlated (r ¼  2 0.545;  P  , 0.0001), while total length and number of prey itemsshowed no correlation ( P  . 0.05). Seriola lalandi  fed almost exclusively on juveniles horsemackerel  Trachurus lathami  (%IR I ¼ 99.66), and this prey species occurred in all the stomachs containing food(Table 1), and ranged from 42–74 mm L T , with a meanlength of 60.4 mm þ / 2  6.15. Other prey items were  Loligosanpaulensis  and  Serranus auriga  (F I ¼ 14% and 2%respectively).The coastal waters of the Buenos Aires province are anursery ground for juvenile horse mackerel, with spawning occurring in coastal waters during spring and summer, and juveniles remaining there until reaching sexual maturity (Saccardo & Katsuragawa, 1995). Corresponding author: M. VerganiEmail: 1  Journal of the Marine Biological Association of the United Kingdom , page 1 of 2.  # 2008 Marine Biological Association of the United Kingdomdoi:10.1017/S0025315408000477 Printed in the United Kingdom 123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263  The percentage of the stomach with contents showed twopeaks during daytime: one in the morning (08:00–10:00 hC R  ¼ 91%) and other during the afternoon (16:00–18:00 hC R  ¼ 95%). The lowest values of C R   (40%) were observedbetween 11:00 and 15:00 hours. Schmitt & Strand (1982)observed a similar pattern in feeding activity for  S. lalandi in the Gulf of California.Predation by   S. lalandi  on small schooling pelagic fish (e.g.sardines, anchovies, jack mackerel and Pacific mackerel) andcephalopods has been reported off California, Australia,New Zealand and in the Gulf of Mexico, and has also beenobserved in related species, including   S. quinqueradiata , S. dumerili  and  S. rivoliana  (Schmitt & Strand, 1982;Poortenaar  et al. , 2001). There have been fewer studies onthe diet of   S. lalandi  food in the south-western Atlantic,with Marı´n (1993) reporting the diet as comprising juvenileArgentine anchovy   Engraulis anchoita  (81%),  T. lathami(  7%) and  Scomber japonicus  (1.9%).The coastal waters of the study area are productive, duein part to the outflow from the Rı´o de la Plata, and thesewaters have a high biomass of small pelagic fish suchas anchovy and horse mackerel (e.g. Saccardo & Katsuragawa, 1995). As a consequence, the region may bean important summer feeding ground for migratory species such as  S. lalandi ,  S. sarda  and  Pomatomus saltatrix  ,which come from the continental shelf of southern Braziland neighbouring oceanic regions. In Argentinean waters, S. lalandi  tend to be restricted to rocky reefs, which havea scarce and patchy distribution in the region, and thisaffinity to reef habitats may be related to their feeding behaviour. Observations by Schmitt & Strand (1982) onthe feeding tactics of   S. lalandi  in the Gulf of Californiashowed a high degree of cooperation among individualswhile performing well-coordinated foraging behaviour thatinvolved, fish enclosing schooling prey against the rocky reefs prior to feeding.  ACKNOWLEDGEMENTS This research was partially supported by CONICET PIP 5009and Universidad Nacional de Mar del Plata EXA 355 / 06. Thisis INIDEP contribution No. 1466. REFERENCES Cousseau M.B., Cotrina C.P. and Roa B.H.  (1975) La ubicacio´n sistema´-tica del pez limo´n pescado en la Argentina.  Physis Secc. A. Bs. As.  34,89, 371–376. [In Spanish.]  Q2 Marı´n Y.  (1993)  Estructura de la poblacio´n y explotacio´n del pez limo´n (Seriola lalandi,  Cuvier, 1833) . Technical Report 43, INAPEUruguay, pp. 54. [In Spanish.] Poortenar C.W., Hooker S.H. and Sharp N.  (2001) Assessment of yel-lowtail kingfish ( Seriola lalandi ) reproductive physiology, as a basisfor aquaculture development.  Aquaculture  201, 271–286. Saccardo S.A. and Katsuragawa M.  (1995) Biology of the rough scad Trachurus lathami , on the southeastern coast of Brazil.  Scientia Marina  59, 265–277.and Schmitt R.J. and Strand S.W.  (1982) Cooperative foraging by yellowtail, Seriola lalandei , on two species of fish prey.  Copeia  3, 714–717. Correspondence should be addressed to: M. VerganiConsejo Nacional de InvestigacionesCientı´ficas y Te´cnicas (CONICET)Paseo Victoria Ocampo N 8  1B7602HSA Mar del PlataArgentinaemail: Submitted xx xx xxxx Accepted xx xx xxxx Published xx xx xxxx on MBA website  Q3 Fig. 1.  Sampling site and rocky bottoms distribution ( † ) at the study area. Greyed squares (15 8  latitude  15 8  longitude) show   Seriola lalandi occurrence from the Argentine purse-seine fleet during January to May.Insert: geographical distribution of   S. lalandi  in South American waters. Table 1.  Diet composition of adult  Seriola lalandi;  number of fishexamined ¼ 66; coefficient of repletion ¼ 76%; average number of prey per stomach ¼ 16.9. Food items F I  N I  W I  IRI %IRI Trachurus lathami  (TELEOSTEI) 100 97.92 85.10 18301.8 99.66 Loligo sanpaulensis  (CEPHALOPODA) 14 1.22 1.19 33.7 0.18 Dules auriga  (TELEOSTEI) 2 0.17 2.73 5.8 0.03Unidentified fish remains 2 0.69 10.96 23.3 0.13F I , frequency index  ;  N I , numerical index; W I,  weight index; IRI, index of relative importance. 646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126 2 m. vergani  et al .
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