The Influence of Otolithes ruber Consumption on Prey and ...

Journal of the Persian Gulf (Marine Science)/Vol. 3/No. 9/September 2012/9/53-61

The Influence of Otolithes ruber Consumption on Prey and Comparison with that Harvested by Fisheries Eskandari, Gholamreza1*; Koochaknejad, Emad1; Savari, Ahmad2 Koochenian, Preeta3;Taghavi Motlagh, Seyedamin4; 1-South Iran Aquaculture Research Center, Ahwaz, IR Iran

2- Dept. of Marine Biology, Faculty of Marine Science, Khorramshahr University of Marine Science and Technology, Khorramshahr, IR Iran 3- Dept. of Fisheries, Faculty of Marine Natural Resources, Khorramshahr University of Marine Science and Technology, Khorramshahr, IR Iran 4- Iranian Fisheries Research Organization, Tehran, IR Iran

Received: March 2012

Accepted: May 2012

© 2012 Journal of the Persian Gulf. All rights reserved.

Abstract The Otolithes ruber is considered a valuable fish in the Indo-West Pacific. Estimates of the Q/B ratio and parameters of equations to ‘predict’ Q/B values for O. ruber in northwestern part of the Persian Gulf and the effects of different age-groups (age 1 to 6 year) on prey are presented. The age and food item of O. ruber were recorded on data collected from monthly samplings by bottom trawl during Oct 2007 to Sep 2008 and size frequency data were collected from commercial catches between Apr 2002 to Mar 2012. Food composition was analyzed by quantitative method. The effects of different age-groups on prey were calculated by biomass of the predator and the consumption rate of different age-groups. Six age group were identified. The biomass of stock was dominated by age-group 2 (3069 tons). Stomach contents of O. ruber included mostly shrimps and fish. Daily consumption of shrimp and all food items were 54 and 100 tons respectively. The highest and the lowest consumption rate and ratio of consumption to the stocked biomass were in age-groups 1 and 6, respectively. The Q/B ratios for shrimp and all food items were 3 and 5.57, respectively. Age-groups 2 and 3 had the most and age-group 6 the least effect on prey community. Shrimp consumption was greater during 2008-2009 than the minimum recorded in 2002-2003. Despite increasing biomass of O. ruber and increasing the consumption of shrimp, the shrimp catch was not much affected. Keywords: Otolithes ruber, Persian Gulf, Shrimp, Consumption, Biomass

been suggested as permanent food of juvenile and adult tiger toothed croaker in Alzobair creek (Nasir, 2000). Several studies in North of the Persian Gulf and Oman Sea have been suggested small fishes and crustaceans (particularly shrimp) as the main food of O. ruber (Niamaimandi, 1999, Kamali et al., 2006, Azhir, 2008). The O. ruber diet composition in Khuzestan coastal waters consists of smaller fish such as species of Mugilidae, Engraulidae and shrimp as secondary food (Eskandari, 1997). Species within any ecosystem unit interact with each other and with species in other ecosystem units

1. Introduction The Tiger toothed croaker (Otolithes ruber) is a demersal fish living both in the bottom and on the surface of the water and obtains its food from the bottom, column and surface of the water (Fischer and Bianchi, 1984). Numerous teeth accompanied by short and few gill rakers and large stomach indicate carnivore habit of Otolithes ruber. Food of tiger toothed crooker generally consists of such crustaceans as shrimp and other invertebrates. Zoobenthos has *

E-mail: [email protected] 53

Eskandari eet al. / The Inffluence of Otolithes ruber C Consumption on o Prey and…

1997 7, Nair, 19 980, Pillai, 1983, Eu uzen, 1987,, Passo oupathy and Natarajan, 11987, Nasir, 2000). Also,, Buck kel et al. (1999) haas compareed biomasss conssumption by predator p fishh and fishing g harvest.

by means of a complex neetwork calleed a food weeb (beergh and Baarkai, 1993). Aquatic food webs havve beeen studied intensivelyy with resspect to thhe intteraction of cconsumer (‘‘top-down’’)) and resourc rce (‘‘b bottom-up’’)) effects on species com mposition annd abu undance (W Worm and Myers, M 2003 3). Biologiccal intteractions in marine ecoosystems, intterspecies annd inttraspecies innteractions may have a significaant inffluence on sstock dynam mics and can n contribute to thee high variabbility which is frequentlly observed in reccruitment andd stock sizess (Magnússo on, 1999). Fi sh sto ock dynamicc is highly affected a by predators annd fish hers (Whippple et al., 20000). of The effect of predator fishes on composition c aqu uatic ecosysstems could be significcant. Mortaliity ind duced by prredation cann reduce preey abundancces loccally and m may limit prey p recruitm ment in som me sysstems. Predaation by fishhes is often size-dependeent leaading to increeased mortaliity at specificc life stages of preey and to ppotential shiffts in size distribution of surrviving indivviduals. To begin b to quaantify potentiial efffects of fish predation onn community y structure annd preey populationns, detailed innformation iss needed on th the feeeding habits of importaant predatorss (Scharf annd Sch hlicht, 2000).. The main eemphasis in theoretical and empiriccal stu udies of speccies interactioons has been n on predatioon, sin nce it is relativvely easy to observe and probably moore imp mportant than competitionn. However, demonstratinng thaat predation hhas a measurrable and sig gnificant effeect on stock dynam mics and lonng-term stock k sizes is moore diffficult (Magnnússon, 19999). Shrimp is onne of the harvvestable inverrtebrate speciies in the muddy hhabitats in thee northwestern areas of th the Perrsian Gulf. T The catch ratte has been reported aboout 300 00 tons in 20009. Young O. O rubers indiv viduals feed oon shrrimp species (Eskandari, 1997) 1 and as such, stocks of prrey and predaator could proobably be afffected with anny chaange in popullation size off either (Figurre.1). O. ruber is distributed in the Oman n Sea and thhe Perrsian Gulf. Many studies have beeen carried oout reg garding feedding habit of fish in Iraan (Eskandaari,

Fig. 1: 1 Variations of o shrimp and O. ruber catch h in Khuzestann coastaal waters (2000-2010).

Th he consum mption rate and pro oportion off conssumption to biomass andd relationshiip with preyy has yet y to be stud died. Therefoore, the aim of this studyy was to determiine proportiion of conssumption too biom mass stock (Q Q/B), prey coonsumption rate, harvestt of prey p and prrey-predatorr relation using u virtuall popu ulation analysis data. 2. Materials M and d Methods Monthly M seaa sampling surveys for collectingg biolo ogical data were w carried out in coasttal waters off Khuzzestan provin nce in the noorthwestern Persian P Gulff betw ween 48°45' and a 49°50' E and 29°48 8' and 30°06'' N ussing fish traw wl, during 22007 to 2008 8 (Figure.2).. Samp ples were seelected randoomly and theen, stored inn ice boxes b and traansferred to tthe lab for id dentificationn of fo ood items an nd age struccture. Later, total lengthh and fresh weigh ht of each sppecimen werre measuredd urately. Stom mach contentts of all speccimens weree accu identtified. The total num mber, wet weight, w andd frequ uency of occcurrence off each prey item in thee stom mach of the fishes weree recorded and a weighedd separately. Otoliiths (sagittaae) were rem moved from m 1500 0 sampled fish, andd analyzed d using a stereeomicroscopee by an exxpert single age readerr coun nting annulii in the w whole otolith h. The agee 54

Journal of thhe Persian Gu ulf (Marine Science)/Vol. 3/N /No. 9/Septemb ber 2012/9/533-61

estimates deerived after annuli a countiing were repported as ``true'' agge using for age a – length - keys.

Food comp position was ddetermined using quantitattive nalysis technique of Sánchhez and Olaso (2004). an Predator sttock consum mption rate was w determinned fiirstly, by ob btaining requuired data fo or the modell of virtual populaation analysiis (VPA) (W Weizhong et al., d South of Iran I 2003) from local fisheryy offices and Research C Aquaculture A Center to estimate Croaaker biomass in different d agee-groups durring 2002-20012 an nd secondly, using the following fo ormula (Lillyy et all., 2000) to calculate c dailly consumptiion rate.

Ci= prey co onsumption rrate Si=prey weig ght, in the stomach at a the time of saampling B=predatorr size T=temperaature (ºC) Constants: γ = 0.13 β = 0.48 δ = 0.46 αi =117 for shrimp,,75 for fish, 70 for all in nvertebrates, and 73 for innvertebrates and a fish (Lillyy et all., 2000). Thirdly, th he daily connsumed prey y biomass was w ob btained by multiplyingg prey biom mass by prey p co onsumption in different aage-groups and a accordingly, th he annual consumption c rate by multiplying m d daily co onsumption rate to 365.. The consum mption - to biomass ratio (Q/B) was obtained from m dividing sum s to otal of annuaal consumptioon in differen nt age-groupss by prredator biomaass. In additioon, (Q/B) waas also calculaated using Pauly an nd Palomares (1998) formu ula as followss: Q/B =10^ (7.964 - 0.2044 * log Winf - 1.965 * 10000 / (T+273.15)) + 0.083 * A + 0.532 * h + 0.398 * d) d In carnivorrous species: h = 0, d = 0 A (aspect ratio of cauudal fin) = (height of the caaudal) 2/ squ uare centimeeters for surfface area forr O. ru uber in this study s A=1.322 Winf = Weiight infinite

Fig. 2: Samplling area of O. ruber in Nortthwestern part of the Persian Gulf.

Landing surveys occcurred between 2002 and t the land ding sites off the 2012. Routtine visits to commerciall fishery were w perforrmed alongg the Khuzestan coast. The total lengthss (TL) of laanded meter. fishes weree measured to the nearest centim Annual sam mpled numbers-at-length h were convverted to annual tootal catch num mbers-at-length and age uusing informationn on landing statistics by y year taken from the South oof Iran Aquaaculture Reseearch Centerr. The catch-at-agee data havee been anaalyzed usingg the software forr VPA tuninng described. VPA is a paart of the age-struuctured stockk assessmentt techniques.. This method is based on determining the t life circcle of n and m cohorts, andd finding thee mean fish number mean biomass in the exploiteed stock. Th he denominattor is the biomasss term (B) which iss the weighht of individual fish at agee t (Wt) multiplied m byy the number of ffish (Nt) at age t ( Buckell et al., 19999). Populatioon consumptiion rate of one speciess was calculated bby food estim mation, populaation biomasss and food consum mption coefficcient. To calcculate consum mption rate, followinng approachees were used: 55


simillar trend, with h slight decreease in 2010 (Figure ( 3).

T= average aannual temperature of waater Stock numbeer trend, biom mass, consum mption and aggegro oups, and im mpacted predator biomasss during 200092012 were anaalyzed. The average bio omass of pre rey con nsumption byy predator waas calculated and compare red to landed catchh. Finally, preedator prey interaction i w was con nsidered. Similarities iin diet compoosition betweeen age-group ups weere comparedd using nonpaarametric multi-dimensionnal

Fig. 3: 3 The annual Q/B Q estimates foor O. ruber stocck in Khuzestann coastaal waters (2002-2012).

scaaling (MDS) (Clarke and Warwick, W 199 94).

Th he (Q/B) is decreasing d w with increase in size. Thee

3. Results

smalllest size classs had the mosst (Q/B) for shrimp s (12.6)) Stomach conntents of O. ruber were composed ffor

and total t consum mption (13.7) and the largeest size classs

vertebrates annd fish. The shrimp s consu umption rate bby inv

had the lowest (Q/B) for shrimp (0 0) and totall

agee-group 1 was higherr than otheer age-group ups

consu umption (2.6) (Figure 4).

deccreasing sharrply in olderr age-groups. 54.55 tons of and fish weere shrrimp and 1000.1 tons of invertebrates i con nsumed dailyy (Table 1). The daily annd annual (Q Q/B) of shrim mp were 0.0008 and d 3, respectivvely based on o VPA estim mation. For aall foo od items thee annual (Q Q/B) were 0..015 and 5.557 (Taable 1). The annual (Q/B)) for all food d was estimateed 6.1 1 by using Paauly's model (1998). ( The annual a (Q/B) of preey consumedd showed rellatively stable trend durinng

Fig. 4: 4 The Q/B esstimates for O. ruber by eacch age class inn Khuzeestan coastal waaters.

200 00-2009. Thhe annual (Q Q/B) of shrrimps showeed

Table 1. Estimate of daily y and annual pre rey consumption n of O. ruber po opulation by agge class. Age (years) 1 2 3 4 5 6

Prey (all foo od items) consumption rate (g/(g.d d)) 0.04 4 0.014 4 0.013 3 0.011 0.009 96 0.007 7

S Shrimp connsumption ratee (g/(g.d))

O. O ruber biomass b 3 (kg*10 ( )

Biomass of con nsumed shrimpp peer day (kg*103)

Biomasss of consumed prey per day (kg g*103)

0.035 0.008 0.007 0.001 0 0

338 3069 2252 939 482 221 7301

11.7 25.5 16.4 0.95 0 0

12.7 42.5 28.5 10.2 4.6 1.6

54.55

100.1

0.008 3

0.015 5.57

Sum Dailyy consumpption Q/B daiily Q/B annnual

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Journal of thhe Persian Gu ulf (Marine Science)/Vol. 3/N /No. 9/Septemb ber 2012/9/533-61

The greaatest numberr of O. rubeer stock oveer the period of 2005 to 20010 was at age-group 1. It decreased iin older agee-groups reaching the loowest number at age-group 6 (Figure.5A)). O. ruber stock biomass peaaked about agge-groups 2 and a 3 (Figuree.5B). The maximuum and minnimum daily consumptionn rate for shrimp and all foodd items weree at age-grouups 1 and 6, respeectively (Figuure.5C).

The peak daily d consum mption of shriimp (Figure.55D) an nd all food d items (Figgure 6), occcurred betw ween ap pproximately y age-group 2 and age-gro oup 3. No shriimp co onsumption was observeed in age-gro oup 5 and agea group 6.

Fiig. 6: Daily con nsumption ratess by O. ruber in n Khuzestan coaastal waters w (2002-2012).

Shrimp con nsumption by O. ruber was w much higgher th han its land ding during 2002-2012. The averrage co onsumption of shrimp bby O. ruberr was 12,1775 t (6 6,202–21,158 8 t) from 20002 to 2012 2 (Figure.7). O. ru uber biomasss does not shhow inverse relationship r w with sh hrimp catch during d that peeriod (Figure..8).

Fiig. 7: Estimateed biomass off shrimp consu umed by O. ruuber po opulation in Khu uzestan coastal w waters and harv vested by Khuzeestan fisheries (2002-20 012).

Fig. 5: Estimaates of O. ruberr impact on prey y by age class ffor the northwestern ppart of Persiann Gulf O. ruber stock during 20092012. Numberrs of O. ruber (A) ( and O. rubeer weight at agee were used to calcullate O. ruber biiomass (B). Im mpact (kg) on pprey by each age classs (D) was caalculated by multiplying m O. ruber biomass by maaximum consum mption rate for each age class (C).

Fiig. 8: The relationship betweenn O. ruber biom mass and harveested sh hrimp in Khuzesstan coastal wateers (2002-2012)..

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recreeational valu ue and mightt insert impo ortant effectss on estuarine community c structure (Scharf ( andd Schlicht, 2000). There is a ppositive relattion betweenn nd prey sizee, both in penaeid p andd predator size an wever, the laargest predattor size classs pisciine prey. How appaarently selected fewer bbut larger teeleostei preyy (Kru umme et al., 2005). 2 Due too low depth and a estuarinee cond dition of the northwestern n n part of the Persian P Gulf,, Juvenile fishes an nd shrimps w were observed d throughoutt year.. Therefore, the t young O.. ruber indiviiduals fed onn smalll shrimps which w were available ass a frequentt prey in the region. The aduult O. ruber immigratedd into the region n from aut utumn to early e springg (spaw wning migraation). Durinng this perio od, the adultt O. ru uber (age-group 4 to agee-group 6) mainly m fed onn fish. However, in this studdy, larger sh hrimps weree obseerved in their food item ms. In addittion to sizee facto or, the differences in prefferred prey were w closelyy linkeed to temporal changees in prey availabilityy (Sch harf and Schllicht, 2000) because con ncurrent withh the immigration of adult croaakers in the region, r adultt shrim mps migrated d to deeper zoone for spawn ning. Th he MDS plo ot showed thhat diet comp position wass affeccted by the size. Specim mens were divided intoo threee different groups g basedd on their diet. d In factt youn ng O. ruber preferred p shrrimp but witth increasingg size they started d to consum me fish and in larger O. rubeer fish domin nated the diet et. Finally, th he diet of thee largeest size class was only fissh. Th he estimated “Q/B” basedd on the VPA A was lowerr than its estimatio on with Paully and Palom mares modell (1998). This diffference couuld be resullt of under-mation of thee “Q/B” of aadult fishes in the VPA.. estim Sincee, species haave different growth rate, “Q/B” wass diffeerent among species so inn general, “Q Q/B” has ann inverrse relationsship with L Linf and trrophic levell (Ang gelini and Ag gostinho, 20055). Fish with h high growthh rates reach their Linf L at fasterr rates and "Q Q/B" value iss higheer in older in ndividual (fissh). Thereforre, the "Q/B"" valuees in youngeer age-groupss of O. rubeer are higherr than older age-g groups becauuse the gro owth rate off nger age-grou ups are higheer than olderr age-groups.. youn

The MDS pplot showedd three distin nguished aggegro oups based on their diiet composition with thhe stress value of 0.01. The sm mallest size age-group a (agge 1 year) y had ddifferent diett compositio on from othher sizze age groups. The age-ggroups 2 and d 3 had simillar dieets and were separated frrom larger siize age-groupps (ag ge 4,5,6 yearr) (Figure.9).

Fig g. 9: Multi-dimeensional scalingg plot of the similarities in foood com mposition of diffferent age-grouups.

4. Discussion western part of the Persiaan The O. rubeer in northw ulf feeds on shhrimps and fish. fi The geneeral diet patteern Gu is related r to sizee (age) of thee O. ruber. Th he age-groupp 1 usu ually fed onn shrimps buut age-group ps 4, 5 and 6 preeferred fish in their diiet similar to t the dietaary com mposition off blue fin tunaa which has been shown to be dependent oon prey availlability and tu una body sizze. For a numbeer of piscivvorous species, prey siize inccreases with iincreasing preedator size. Previous P studiies of piscivores hhave found that minimu um-sized pre rey rem mained relatiively constannt with increeased predattor sizze, whereas the maximuum and median prey sizzes inccreased signnificantly. Prrey-predator length ratiios gen nerally averagge 20-30% foor piscivores (Butler, 20077). Comparisonns of prey sizzes consumed by red druum witth sizes occcurring in thhe field indicated that reed dru um fed in neear shore shallow water habitats, h whicch serrve as nurserry areas for many juven nile fishes annd cru ustaceans. T These findinggs demonstrrated that reed dru um fed on seeveral prey species s of co ommercial annd 58


of O. ruber preys was increased with increasing age and food sources were formed from different species of fish and shrimp, but it decreased in older agegroups. The age-group 2 had the most impact on prey population. It appeared that the different age classes had different impact rates on population of their prey. Buckel et al. (1999) suggested the same result about bluefish. The fluctuation of fish populations may be affected by prey density and many other factors (Liu et al., 2006). Comparison of annual shrimp consumption by O. ruber and shrimp landing during 2002-2012 showed that the prey abundance did not influence the population of predators because the low abundance of shrimps led to changes in dietary composition and consumption of other food items. In some species (Carcharhinidae), prey density might not be the factor affecting variations of predator abundance (Liu et al., 2006). Various factors affected population variations of O. ruber. However, it could not be concluded that young O. ruber preferred shrimp in their diet. The relation of consumption to stocked biomass in the young fishes were more than that of older age-groups. Age-group 2 had the most effect on shrimps but shrimp frequency did not have significant influence on O. ruber variations.

Moreover, in some years the "Q/B" value of O. ruber is lower than other years which could be due to the population structure of O. ruber. We know that fish eat shrimps and that many small demersal fish feed on organisms are also consumed by shrimps. Thus, generally speaking, fish are both the predators and the competitors of shrimps, while both fishes and shrimps are prey of a demersal fishery. The demersal fishery, by offsetting the natural balance between shrimps and fishes, can indirectly increase the survival of shrimps by removing their predators and competitors. In Gulf of Thailand, recruitment of shrimp stocks is determined solely by biological and fishery-induced changes in biomass and species composition, and not, as in temperate waters, predominantly by fluctuations in the abiotic environment (Pauly, 1982). Over 50 years of research on Arcto-Norwegian cod feeding in the Barents Sea indicated that cod predation was one of the most important factors influencing northern shrimp population dynamics. Analysis of the RussianNorwegian cod stomach data base showed that cod at age 3-6 have the strongest impact on the Barents Sea shrimp stock and preferred to consume shrimp with a total length range of 5-10 cm (Berenboim et al., 2000). In another study, the timing of both the increase in the shrimp stock and the decline in the cod stock remained unclear and there was considerable uncertainty in the estimates of consumption of shrimp by cod (Lilly et al., 2000). In Massachusetts (USA), coastal waters most consumption by individual striped bass of ages 3–8 came from crustaceans and fish (Nelson et al., 2006). The direct impacts of predators on prey required that predator and prey overlap in time and space and that prey was available for capture during that time (Bax, 1998). The per capita feeding rate on shrimp was highest for cod in the 63-71 cm length-group, but population consumption of shrimp was highest in the 45-53 cm group. The rate of consumption of shrimp by cod was calculated to be 57 tons per day (Lilly et al., 2000). The diversity

Acknowledgment This study was funded by the Khuzestan Fisheries Office with contribution of South of Iran Aquaculture Research Center. The authors would like to thank Dr Mogheinami, Mr Hassanzade and Dr Marammazi for supporting the project. We also thank Yosef Mayahi for collecting samples. Reference Angelini, R. and Agostinho, A., 2005. Parameter estimates for fishes of the upper paraná river floodplain and Itaipu reservoir (Brazil). World Fish Center Newsletter. 28 (1&2): 53-57. 59

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