楊 剛,徐炳慶,王秀霞,李 凡,袁小楠,呂振波
萊州灣三疣梭子蟹生物學(xué)參數(shù)及生長特性研究
楊 剛1,2,徐炳慶1,王秀霞1,李 凡1,袁小楠1,2,呂振波1
(1.山東省海洋資源與環(huán)境研究院,山東省海洋生態(tài)修復(fù)重點實驗室,山東煙臺 264006;2.上海海洋大學(xué)海洋科學(xué)學(xué)院,上海 210306)
根據(jù)2012年5~11月使用單船底拖網(wǎng)進(jìn)行的7個航次調(diào)查數(shù)據(jù),運用FiSATⅡ軟件相關(guān)模塊對萊州灣三疣梭子蟹(Portunus trituberculatus)生長、死亡參數(shù)及生長特性、種群補(bǔ)充模式、資源量等進(jìn)行研究。結(jié)果顯示:7個航次共捕獲三疣梭子蟹1128 ind,雌雄性比為0.96,雌性甲寬為27~227 mm,雄性為29~207 mm;獲得三疣梭子蟹雌性生長參數(shù)k=1.60、L∞=241.50、W∞=639.29、t0=0.081,雄性為k=1.50、L∞=210.00、W∞=418.23、t0=0.091;經(jīng)體長結(jié)構(gòu)VPA(Length-Structured VPA)模塊估算,穩(wěn)定狀態(tài)下萊州灣三疣梭子蟹雌性漁獲尾數(shù)為734×104ind、種群尾數(shù)為1.15×108ind、資源量為2 682 t,雄性漁獲尾數(shù)為810×104ind、種群尾數(shù)為1.19×108ind、資源量為1 929 t;經(jīng)變換體長漁獲曲線法(Length-Converted Catch Curve)及刀刃式選擇假設(shè)模型(Knife-Edge)估算三疣梭子蟹雌性總死亡系數(shù)Z=4.17、自然死亡系數(shù)M=1.20、捕撈死亡系數(shù)F=2.97、資源開發(fā)利用率E=0.712、平均選擇甲寬Lc=62.38mm、最大效益時開發(fā)利用率Emax=0.515;雄性總死亡系數(shù)Z=3.76、自然死亡系數(shù)M=1.19、捕撈死亡系數(shù)F=2.57、資源開發(fā)利用率E=0.684、平均選擇體長Lc=40.84 mm、最大效益時開發(fā)利用率Emax=0.487。研究表明:1)萊州灣三疣梭子蟹雌雄性比、雌雄性冪指數(shù)均處在正常水平,總體生長狀況良好;2)萊州灣三疣梭子蟹雌、雄性群體資源利用率均顯著高于最適利用率與最大利用率,處于過度開發(fā)水平;3)萊州灣三疣梭子蟹現(xiàn)存資源量低于生態(tài)容量,上升空間較大。
三疣梭子蟹;FiSATⅡ;生長參數(shù);資源開發(fā)率;資源量;萊州灣
三疣梭子蟹(Portunus trituberculatus)隸屬于甲殼綱十足目梭子蟹科梭子蟹屬,是重要的海洋經(jīng)濟(jì)蟹類,也是重要的增殖放流種,廣泛分布于我國大陸架及日本、朝鮮、馬來西亞群島等海域[1]。因其具有較高的營養(yǎng)價值和經(jīng)濟(jì)效益,并擁有成熟的人工繁殖技術(shù),從1981年開始便被列為我國水產(chǎn)養(yǎng)殖對象[2]。
萊州灣位于山東半島北部、渤海東南部,海岸線長達(dá)319 km,擁有6 966 km2海域[3]。沿岸黃河、小清河等眾多河流的注入,使得灣內(nèi)餌料資源豐富,棲息環(huán)境多樣,成為眾多經(jīng)濟(jì)物種的產(chǎn)卵場和索餌場[4]。近年來,隨著過度捕撈、環(huán)境污染等多方面人為因素影響不斷加大[5],灣內(nèi)漁業(yè)資源受到嚴(yán)重破壞[6],群落結(jié)構(gòu)波動較大,生物多樣性指數(shù)不斷降低[7],增殖放流活動成為眾多傳統(tǒng)經(jīng)濟(jì)種類賴以補(bǔ)充的基本途徑[8]。相對于魚類資源衰退,甲殼類資源衰退幅度較小,李凡等[9]對萊州灣底層漁業(yè)資源研究表明,甲殼類資源在萊州灣生態(tài)系統(tǒng)中地位有上升趨勢。作為重要的經(jīng)濟(jì)型甲殼類,我國海洋科學(xué)工作者已分別從各個方面對萊州灣三疣梭子蟹做了大量研究,如生物學(xué)特性[10]、生化遺傳分析[11]、生態(tài)容量[12-13]等。
漁業(yè)資源生物學(xué)參數(shù)、生長特性及開發(fā)利用率等研究在漁業(yè)資源生態(tài)學(xué)中尤為關(guān)鍵,針對萊州灣三疣梭子蟹這幾方面研究報道較少。聯(lián)合國糧農(nóng)組織(FAO)開發(fā)的FiSATⅡ軟件對水生生物生長參數(shù)研究有重要意義,已廣泛應(yīng)用于魚類、甲殼類生物學(xué)參數(shù)的研究[14-22]。本文根據(jù)2012年5~11月在萊州灣海域進(jìn)行的單船底拖網(wǎng)調(diào)查數(shù)據(jù),運用FiSATⅡ軟件中相關(guān)模塊,對該海域三疣梭子蟹漸近甲寬L∞、生長參數(shù)k,總死亡系數(shù)Z等生物學(xué)參數(shù)進(jìn)行估計,并在此工作基礎(chǔ)上對萊州灣三疣梭子蟹資源量、漁獲產(chǎn)量等進(jìn)行分析與討論,以期為三疣梭子蟹增殖放流、資源可持續(xù)利用提供一定的理論基礎(chǔ)。
研究所用數(shù)據(jù)全部來自2012年5~11月每月中下旬在萊州灣逐月進(jìn)行的單船底拖網(wǎng)調(diào)查所采集的三疣梭子蟹,對其進(jìn)行甲寬和體質(zhì)量測定,分別精確至1 mm和0.1 g;調(diào)查船只為“魯昌漁64193”,功率為80 kW,網(wǎng)口周長30.6 m,囊網(wǎng)網(wǎng)目20 mm,拖曳時網(wǎng)口寬度約8 m。
1.2.1 甲寬和體質(zhì)量關(guān)系
采用冪函數(shù)擬合甲寬和體質(zhì)量關(guān)系,公式為:
式中,W為體質(zhì)量(g),L為甲寬(mm),a為條件因子,b為冪指數(shù)。
1.2.2 生長參數(shù)
利用測定三疣梭子蟹甲寬、體質(zhì)量數(shù)據(jù),以10 mm組距建立甲寬頻率數(shù)據(jù)[22],運用FiSATⅡ軟件中的ElefanⅠ(electronic length frequency analysisⅠ)法擬合Von Bertalanffy生長方程(VBGF)對萊州灣三疣梭子蟹生長參數(shù)L∞、k進(jìn)行估算,VBGF公式為:
式中,Lt、Wt分別為t時間時的甲寬與體質(zhì)量;t0為理論生長起點年齡,運用PAULY經(jīng)驗公式[23]求得,公式為:
對生物學(xué)參數(shù)優(yōu)化度的評估,采用PAULY等[24]提出的擬合優(yōu)度Score指數(shù)為判別標(biāo)準(zhǔn),指數(shù)計算于FiSATⅡ軟件中同時完成,公式為:
式中,ESP(explained sum of peaks)表示理論波峰數(shù),ASP(available sum of peaks)表示可獲得總波峰數(shù)的最大值,是曲線能夠得到的最大值。Score指數(shù)值介于0到1之間,是擬合優(yōu)度估計值。不斷更改L∞、k的初始值,通過檢驗擬合優(yōu)度Score指數(shù)大小變化,從而得出Score指數(shù)最大且相應(yīng)參數(shù)在生物學(xué)上能接受的L∞、k值,即最佳值。
1.2.3 死亡系數(shù)及資源利用率
運用FiSAT軟件中的體長變換漁獲曲線法(Length-converted catch curve)估計總死亡系數(shù)Z,公式為:
式中,Nt為t齡甲寬組占總樣品尾數(shù)的比例,Δt為其相應(yīng)體長組下限生長到體長組上限所需時間,t′為對應(yīng)體長組中值年齡,a=ln N0,-b=Z,即總死亡系數(shù)估計值。自然死亡系數(shù)M運用PAULY經(jīng)驗公式[24]求得,公式為:
式中,t為調(diào)查海域全年平均水溫。捕撈死亡系數(shù)為總死亡系數(shù)與自然死亡系數(shù)差值,即F=Z-M。資源利用率為捕撈死亡系數(shù)與總死亡系數(shù)的比值,即E=F/Z。
1.2.4 種群補(bǔ)充模式
依據(jù)甲寬頻率數(shù)據(jù),在FiSATⅡ軟件補(bǔ)充模式(Recruitment Patterns)模塊中輸入L∞、k及t0數(shù)據(jù),重構(gòu)萊州灣三疣梭子蟹每年種群補(bǔ)充期,從而確定種群補(bǔ)充模式[14]。
1.2.5 平均選擇體長
采用FiSATⅡ軟件Beverton-Holt模塊中的刀刃式選擇假設(shè)模型(Knife-edge)進(jìn)行相關(guān)單位補(bǔ)充量漁獲分析。在FiSATⅡ軟件中開發(fā)率E包括以下幾種水平:Emax為獲得最大漁獲量的開發(fā)率,E10為Y′/R邊際增長減少10%時的開發(fā)率,E50為資源量降至原始水平50%時的開發(fā)率[24]。
1.2.6 漁獲尾數(shù)、資源尾數(shù)與資源量估算
對漁獲尾數(shù)、資源尾數(shù)與資源量的估算采用體長結(jié)構(gòu)實際種群分析(Length-Structured VPA)模塊[18]進(jìn)行,模型公式為:
式中,NL+ΔL為L+ΔL體長組資源量,CL為L體長組漁獲量,F(xiàn)L、ZL分別為體長組L的捕撈死亡系數(shù)與總死亡系數(shù),△t由軟件程序根據(jù)所使用生長方程計算。
1.2.7 單位補(bǔ)充量產(chǎn)量與單位補(bǔ)充量資源量估算
運用FiSATⅡ軟件中的Beverton and Holt Y/R Analysis模塊進(jìn)行單位補(bǔ)充量產(chǎn)量(Y′/R)和單位補(bǔ)充量資源量(B′/R)的估算[15],公式為:
式中,Y′/R為相對單位補(bǔ)充量產(chǎn)量(g);B′/R為相對單位補(bǔ)充量資源量;E為開發(fā)率;Lc為平均選擇體長;L∞為極限體長;M為自然死亡系數(shù);k為生長系數(shù);Z為總死亡系數(shù);F為捕撈死亡系數(shù)。
通過對萊州灣海域7個月跟蹤監(jiān)測,共捕獲并測量三疣梭子蟹1 128 ind,總重100.48 kg,其中雄性575 ind,50.19 kg,雌性553 ind,50.29 kg,雌雄性比為0.96,雌雄個體數(shù)量差異不顯著(P>0.5)。雌性甲寬范圍為27~227 mm,其中46~156 mm的個體占總數(shù)的93.07%,雄性為29~207 mm,其中46~166 mm的個體占總數(shù)的92.65%(圖1)。
分別對萊州灣三疣梭子蟹雌、雄性個體甲寬與體質(zhì)量數(shù)據(jù)進(jìn)行冪指數(shù)曲線擬合,結(jié)果得出三疣梭子蟹甲寬與體質(zhì)量的關(guān)系(圖2):
三疣梭子蟹雌性♀:W=5.81×10-5L2.955
三疣梭子蟹雄性♂:W=7.75×10-5L2.899
圖1 萊州灣三疣梭子蟹甲寬分布Fig.1 Frequency distribution of carapace w idth of Portunus trituberculatus in the Laizhou Bay
圖2 萊州灣三疣梭子蟹甲寬與體質(zhì)量關(guān)系Fig.2 Relation curves between carapace w idth and weight of Portunus tritubercu latus in the Laizhou Bay
根據(jù)甲寬頻率數(shù)據(jù),運用FAO開發(fā)的FiSATⅡ軟件中EIEFANΙ模塊對萊州灣三疣梭子蟹生長參數(shù)進(jìn)行估算,并應(yīng)用Pauly經(jīng)驗公式計算t0值,結(jié)果為:
三疣梭子蟹雌性♀:
三疣梭子蟹雄性♂:
獲得三疣梭子蟹甲寬生長方程為:
三疣梭子蟹雌性♀:
三疣梭子蟹雄性♂:
根據(jù)生長方程繪制生長曲線(圖3)。
采用FiSATⅡ軟件中的變換體長漁獲曲線法,估算三疣梭子蟹雌性、雄性總死亡系數(shù)分別為Z♀=4.17、Z♂=3.76(圖4);將漸近甲寬、生長系數(shù)及調(diào)查海域平均溫度數(shù)據(jù)帶入PAULY經(jīng)驗公式(2)即由軟件估算可得三疣梭子蟹雌性、雄性自然死亡系數(shù)分別為M♀=1.20、M♂=1.19,并計算得捕撈死亡系數(shù)分別為F♀=2.97、F♂=2.57;開發(fā)率分別為E♀=0.712、E♂=0.684(表1)。
表1 萊州灣三疣梭子蟹死亡系數(shù)與開發(fā)率Tab.1 Mortality coefficient and exp loitation rate of Portunus trituberculatus in the Laizhou Bay
圖3 萊州灣三疣梭子蟹生長曲線Fig.3 G row th curve of Portunus tritubercu latus in the Laizhou Bay
圖4 變換體長漁獲曲線法估算的總死亡系數(shù)Fig.4 Estimation of the totalmortality coefficient from length-converted catch curve
萊州灣三疣梭子蟹雌、雄性都呈現(xiàn)連續(xù)性、單峰補(bǔ)充模式,主要補(bǔ)充期分別為8~9月和4~8月(圖5)。
通過計算圖4擬合線性關(guān)系中未利用點的ln(N/t)的觀察值與期望值之比的累計率,估算出當(dāng)前三疣梭子蟹雌雄性漁業(yè)被捕獲概率達(dá)50%的甲寬,即平均選擇甲寬Lc分別為62.38 mm、40.84 mm(圖6)。
根據(jù)甲寬頻率數(shù)據(jù)和生長參數(shù)L∞、k數(shù)據(jù),應(yīng)用體長結(jié)構(gòu)VPA(Length-Structured VPA)模塊對穩(wěn)定狀態(tài)下漁獲尾數(shù)、資源尾數(shù)與資源量進(jìn)行估算。結(jié)果為穩(wěn)定狀態(tài)下三疣梭子蟹雌、雄性漁獲尾數(shù)分別為734×104ind、810×104ind;種群尾數(shù)分別為1.15×108ind、1.19×108ind;資源量分別為2 682 t、1 929 t(圖7)。
圖5 萊州灣三疣梭子蟹種群補(bǔ)充模式Fig.5 Recruitment pattern of Portunus trituberculatus population in the Laizhou Bay
圖6 根據(jù)變換體長漁獲曲線的保留百分?jǐn)?shù)估算平均選擇甲寬Fig.6 M ean selected carapace w idth from the proportional retention of length-converted catch curve
圖7 各甲寬組的現(xiàn)存量、死亡量、漁獲量和捕撈死亡系數(shù)曲線Fig.7 Survivors,losses,catches and fishingmortality curves of dfferent carapace w idth classes
萊州灣三疣梭子蟹當(dāng)前資源的開發(fā)程度可以由相對單位補(bǔ)充量漁獲量Y′/R與開發(fā)率E的二維分析圖表示,Y′/R邊際增長減少10%時三疣梭子蟹雌、雄性開發(fā)率分別為E10=0.449、E10=0.416,資源量下降到原始水平50%時開發(fā)率分別為E50=0.326、E50=0.313,最大漁獲量的開發(fā)率分別為Emax=0.515、Emax=0.487(圖8)。
Von Bertalanffy生長方程對魚類體長與年齡數(shù)據(jù)的擬合應(yīng)用廣泛,較適合用于描述魚類的生長[25]。三疣梭子蟹生長過程與蝦類相似,在斷續(xù)蛻殼過程中生長,由于其生長非連續(xù)性特征,不適合于Von Bertalanffy生長方程。但BERGMAN等[26]研究認(rèn)為,由于繁殖群體所有成員不是在同一時間蛻皮生長,總體生長呈連續(xù)性,三疣梭子蟹生長同樣擁有此特征[1],所以生長可以應(yīng)用Von Bertalanffy方程描述。本研究運用FiSATⅡ軟件擬合的Von Bertalanffy方程生長參數(shù)及繪制的生長曲線,從客觀上反映了三疣梭子蟹生長速度快、生命周期短等特征,與鄧景耀等[27]通過三疣梭子蟹頭胸甲長頻數(shù)推定的其年齡相一致,也與吳強(qiáng)等[10]的研究結(jié)果相似,由此可以認(rèn)為,應(yīng)用FiSATⅡ軟件進(jìn)行三疣梭子蟹生物學(xué)參數(shù)研究是可靠的。
對三疣梭子蟹生長狀況的研究,能夠?qū)ζ滟Y源合理利用提供一定理論基礎(chǔ),具有重要意義。本次研究表明,調(diào)查海域三疣梭子蟹性比為0.96,雌雄個體數(shù)量差異不顯著(P>0.05),處于正常水平,甲寬和體質(zhì)量關(guān)系式中雌雄性冪指數(shù)值分別2.955和2.899,說明萊州灣三疣梭子蟹個體處于近勻速生長狀態(tài),生長狀況總體較為良好[28]。與2006年對山東近海三疣梭子蟹研究相比,本次研究冪指數(shù)數(shù)值有所增大,更接近理論勻速生長冪指數(shù)數(shù)值,這可能得益于多年持續(xù)的三疣梭子蟹增殖放流。
三疣梭子蟹屬于沿岸型類群,游泳能力較弱,不做長距離洄游,但有明顯季節(jié)性移動[29]。通常在春、夏季(4~9月份)定向移動至3~5 m的淺海區(qū)域、特別是港灣或河口處產(chǎn)卵活動,到秋、冬季則移動至10~30 m的海底泥沙越冬[30]。目前6~8月份萊州灣內(nèi)伏季休漁(三疣梭子蟹開捕時間較早,為8月20號左右[31])。由研究中所得種群補(bǔ)充模式來看,三疣梭子蟹群體主要的種群補(bǔ)充期為4~9月,恰好與三疣梭子蟹生活習(xí)性及萊州灣伏季休漁政策吻合,同時,同時也與吳強(qiáng)等[10]的研究相符。
根據(jù)GULLAND[32]所提理論,種群最適開發(fā)利用率為0.5,本研究發(fā)現(xiàn)雌雄群體獲得最大漁獲量時理論開發(fā)率分別為0.515、0.487,與最適開發(fā)率相近。然而,研究同時發(fā)現(xiàn)當(dāng)前萊州灣三疣梭子蟹雌、雄性開發(fā)利用率分別為0.712、0.684,都顯著大于種群最適利用率和獲得最大漁獲量時理論開發(fā)率。這就說明,當(dāng)前萊州灣三疣梭子蟹應(yīng)該處于過度開發(fā)狀態(tài)。這與叢旭日等[33]、吳強(qiáng)等[10]的研究結(jié)果相符。
圖8 單位補(bǔ)充量產(chǎn)量和單位補(bǔ)充量資源量2D分析曲線(雌性♀:Lc=62.38 mm;雄性♂:Lc=40.84 mm)Fig.8 2D analysis curve for the relative yield per recruit and the relative biomass per recruit(female Portunus trituberculatus:Lc=62.38 mm;male Portunus trituberculatus:Lc=40.84 mm)
本次研究,獲得萊州灣三疣梭子蟹雌雄總資源量為4 611 t,與以往的研究相近[13]。萊州灣三疣梭子蟹的生態(tài)容量可達(dá)到7 412 t[13],由此判斷萊州灣三疣梭子蟹總資源量嚴(yán)重不足,尚擁有很大的增殖放流空間。
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On biological parameters and grow th characteristics of Portunus trituberculatus in the Laizhou Bay
YANG Gang1,2,XU Bing-qing1,WANG Xiu-xia1,LIFan1,YUAN Xiao-nan1,2,LV Zhen-bo1
(1.Shandong Provincial Key Laboratory of Restoration for Marine Ecology,Shandong Marine and Fishery Research Institute,Yantai 264006,China;2.Institute of Marine Science,Shanghai Ocean University,Shanghai 201306,China.)
The Laizhou Bay is the spawning and feeding ground formany important economic marine species and thus,is rich in fishery resources.However,in recent years,frequent occurring of overfishing in this region leads to destruction of local fishery resources.As an importantmarine economic species and themain species for propagation and releasing,Portunus trituberculatus in the Laizhou Bay is also subject to severe impairment.Therefore,the study on the biological parameters and growth characteristics of Portunus trituberculatus is necessary.Based on the data of bottom trawl surveys on Portunus trituberculatus from May 2012 to November 2012,using FiSATⅡsoftware,the growth,mortality parameters as well as recruitment pattern,standing crop were studied.The results showed that 1 128 ind of Portunus trituberculatus were captured and the female-male ratio was 0.96.The carapace width of female Portunus trituberculatus ranged from 27 to 227 mm,and the male ranged from 46 to 185 mm.According to the measured data and then estimated by the Electronic Length Frequency Analysis,the growth parameters of Portunus trituberculatus were obtained as follows:for female Portunus trituberculatus:k=1.60,L∞=241.50,W∞=639.29,t0=0.081;formale Portunus trituberculatus:k=1.50,L∞=210.00,W∞=418.23,t0=0.091.All of the parameters conformed to the growth characteristics of Portunus trituberculatus.Through the Length-Structured VPA module,itwas estimated that there were 115 million individuals of female Portunus trituberculatus for 2 682 tons and 119 million individuals ofmale Portunus trituberculatus for 1 929 tons in the Laizhou Bay,in which 7.34 million individuals of female Portunus trituberculatus and 8.10 million individuals of male Portunus trituberculatus had been captured.Through the Length-Converted Catch Curve,Pauly Empirical Formula and Beverton and Holt Y/R Analysismodule,themortality,the exploitation ratio and the optimum utilization rate of Portunus trituberculatus were estimated.The results were as follows:for female Portunu strituberculatus:totalmortality(Z)=4.17,naturalmortality(M)=1.20,mean selection length(Lc)=62.38 mm,fishingmortality(F)=2.97,exploitation rate(E)=0.712,optimum utilization rate(Emax)=0.515;formale Portunus trituberculatus:total mortality(Z)=3.76,natural mortality(M)=1.19,mean selection length(Lc)=40.84 mm,fishing mortality(F)=2.57,exploitation rate(E)=0.684,optimum utilization rate(Emax)=0.487.All these indices could well descripe the realities,indicating that there was serious overexploition.The results also showed that the level of sex ratio of Portunus trituberculatus in the Laizhou Bay was normal,which meant the growth of this species was in a good condition.The exploitation ratio of the Portunus trituberculatusis was significantly higher than the normal level(P<0.05),indicating the overdeveloping occurring to the Portunus trituberculatus in the Laizhou Bay.Finally,the resource amount of Portunus trituberculatusis was below the ecological capacity,which meant there could be more quantities of this species existing in the Laizhou Bay waters.
Portunus trituberculatus;FiSATⅡ;biological parameters;exploitation rate;resources;Laizhou Bay
S 932.5+2
A
1004-2490(2017)04-0401-10
2016-09-26
海洋公益性行業(yè)科研專項經(jīng)費項目(201405010);農(nóng)業(yè)部漁業(yè)種質(zhì)資源保護(hù)項目(17162130135252058);水生動物營養(yǎng)與飼料“泰山學(xué)者”崗位經(jīng)費(TS200651036)
楊 剛(1989-),男,山東臨沂人,碩士研究生,主要從事漁業(yè)資源研究。E-mail:yg9005@126.com
呂振波,研究員。E-mail:ytlvzhenbo@163.com