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Life history of wahoo, Acanthocybium solandri, in the Tropical Eastern Atlantic Ocean – the importance of applying a suite of methods for fisheries assessment in data-limited situations


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Figure 1

Locations where wahoo specimens were sampled by the Chinese Longline Fishery Observer in the Eastern Atlantic Ocean between November 2010 and May 2020.
Locations where wahoo specimens were sampled by the Chinese Longline Fishery Observer in the Eastern Atlantic Ocean between November 2010 and May 2020.

Figure 2

Framework process showing methods used to estimate wahoo’s life history parameters and to provide proxies for the stock status in the Tropical Eastern Atlantic.
Framework process showing methods used to estimate wahoo’s life history parameters and to provide proxies for the stock status in the Tropical Eastern Atlantic.

Figure 3

Length frequency distribution (by sex) of wahoo in the Eastern Atlantic.
Length frequency distribution (by sex) of wahoo in the Eastern Atlantic.

Figure 4

Uncertainty in growth parameters L∞ and K for wahoo in the Eastern Atlantic based on length-frequency analysis using the ELEFAN GA-Bootstrap method; N = 1000 bootstrap runs; outer contour – 95% confidence envelope; grey lines – Φ′ isopleths; marginal histograms show univariate density for both parameters.
Uncertainty in growth parameters L∞ and K for wahoo in the Eastern Atlantic based on length-frequency analysis using the ELEFAN GA-Bootstrap method; N = 1000 bootstrap runs; outer contour – 95% confidence envelope; grey lines – Φ′ isopleths; marginal histograms show univariate density for both parameters.

Figure 5

Monthly mean (± SE) gonadosomatic index (GSI) for mature females collected from the Tropical Eastern Atlantic.
Monthly mean (± SE) gonadosomatic index (GSI) for mature females collected from the Tropical Eastern Atlantic.

Figure 6

Monthly percentages of the four wahoo maturity classes. Numbers on class bars indicate the number of females in a given monthly interval.
Monthly percentages of the four wahoo maturity classes. Numbers on class bars indicate the number of females in a given monthly interval.

Figure 7

Percentage of mature female wahoo (n = 182) caught in the Eastern Atlantic was modeled using a logistic function. Length at maturity L50 represents the mean parameter estimate for FL at 50% maturity.
Percentage of mature female wahoo (n = 182) caught in the Eastern Atlantic was modeled using a logistic function. Length at maturity L50 represents the mean parameter estimate for FL at 50% maturity.

Estimated values for VBGP resulting from bootstrapped ELEFAN GA analysis, estimated length (cm) at age (from 0 to 10) and Φ’ by sex, previous results from different geographical areas and age estimation methods (LFDA – length frequency distribution analysis; otolith). F – female; M – male; CS – combined sex.

MethodsAreaGrowth parametersMean parameter estimateSexLongevity (years)
LFDA: ELEFAN-GA-Bootstrap (this study)Eastern AtlanticL(cm)161.2 (CS); 166.5 (M); 164.9 (F)CS10
k(year)−10.47 (CS); 0.31 (M); 0.33 (F)
Φ3.97 (CS); 3.34 (M); 3.76 (F)
tanchor(months)0.64 (CS); 0.62 (M); 0.71 (F)
Sectioned Otoliths (McBride et al. 2008)Northwest AtlanticL(cm)170.1 (CS); 155.5 (M); 179.7 (F)CS9
k(year)−10.381 (CS); 0.44 (M); 0.32 (F)
ΦCS (4.04)
t0(years)–1.63 (CS); –1.64 (M); –1.91 (F)
Whole Otoliths (Zischke et al. 2013)Coral Sea off eastern AustraliaL(cm)149.9 (CS); 141.7 (M); 155.4 (F)CS7
k(year)−11.58 (CS); 2.31 (M); 1.18 (F)
ΦCS (4.55)
t0(years)–0.17 (CS); 0.002 (M); –0.37 (F)
Whole Otoliths (Hogarth 1976)West Central AtlanticL(cm)215.1 (CS)CS4
k(year)−10.152 (CS)
Φ3.21 (CS)
t0(years)–3.67 (CS)
Whole Otoliths (Kishore & Chin 2001)West Central AtlanticL(cm)153.97 (CS)CS10
k(year)−10.34 (CS)
Φ3.76 (CS)
t0(years)–1.54 (CS)
LFDA: MULTIFAN (Lee T.M. 2008)waters off eastern TaiwanL(cm)156.8 (CS)CS9
k(year)−10.245 (CS)
Φ3.43 (CS)
t0(years)–1.63 (CS)

Estimated values of fishing mortality obtained from the equation: fishing mortality rate (F), total mortality rate (Z), and natural mortality rate (M).

Method used to estimate MNatural mortalityMethod used to estimate Z
LCCCBeverton and Holt (BH)
MZFZF
Gislason0.360.750.390.800.44
ChenWatanabe0.670.080.13
Brodziak_K0.370.380.43
Pauly_Linf0.650.100.15
Alverson_Carney0.330.420.47
Then_10.640.120.17
Then_20.440.310.36
Hewitt Hoenig0.470.280.33
Hoenig0.450.300.35

Wahoo fishery status in the Tropical Eastern Atlantic Ocean presented by LBB (Linf, Lc50, F/M, M/K, and B/B0 and B/BMSY and their respective 95% confidence intervals; numbers in parentheses) under different M scenarios.

ScenariosM/K*Linf (CI)M/K (CI)F/M (CI)Lc50 (CI)B/BMSY (CI)B/B0 (CI)Stock status
M/K Median (Then_2)0.94165 (164–167)0.89 (0.79–1.02)0.76 (0.48–1.1)115 (112–118)1.4 (0.38–3.1)0.58 (0.16–1.3)Healthy
M/K Upper (Chen and Watanabe)1.42165 (164–167)1.3 (1.17–1.44)0.4 (0.26–0.67)120 (116–124)1.9 (0.53–3.8)0.76 (0.21–1.6)Healthy
M/K Lower (Alverson_Carney)0.70164 (163–165)0.73 (0.57–0.86)1.48 (1–2.24)112 (109–115)1.3 (0.35–3.3)0.56 (0.15–1.4)Healthy

Von Bertalanffy growth parameter (VBGP) estimates generated by various length-frequency analysis programs for the wahoo stock sampled in the Eastern Atlantic. Parameter estimates by different methods are presented with AIC and BIC values. NB: ELEFAN-FI and SHEPHERD (ELEFAN and Shepherd methods in FiSAT II), ELEFAN-LFDA (ELEFAN method in LFDA v 5), ELEFAN-GA, ELEFAN-SA (TropFishR package) and ELEFAN-GA-Bootstrap, ELEFAN-SA-Bootstrap (fishboot package).

MethodsParameterMean parameter estimateAIC ScoreBIC Score
ELEFAN-FIL(cm)183.75−10602−10617
k(year−1)0.69
t0(years)−0.518
SHEPHERDL(cm)175987965
k(year−1)0.12
t0(years)−3.22
ELEFAN-LFDAL(cm)163.3−1058310598
k(year−1)0.57
t0(years)−0.652
ELEFAN-G.A.L(cm)159.94805790
k(year−1)0.49
tanchor(months)0.68
ELEFAN-S.A.L(cm)194.51−10309−10324
k(year−1)0.08
tanchor(months)0.54
ELEFAN-SA-Bootstrap*L(cm)201.56−10648−10663
k(year−1)0.12
tanchor(months)0.64
ELEFAN-GA-Bootstrap*L(cm)161.21−11407−11422
k(year−1)0.47
tanchor(months)0.64

Natural mortality (M) methods and equations used. L∞, K and t0 are von Bertalanffy growth function parameters, Tmax is the maximum observed age, a and b are length–weight relationship parameters. L50 is length at first maturation, L is the observed length, T is temperature (°C), and t is age. In this study, the temperature was T = 18.43°C.

AcronymEquationsM by ageReferences
Gislasonln (M )=0.55−1.61 ln (L)+1.44 ln (L)+ln (K )YesGislason et al. 2010
ChenWatanabeM=K1=eK*(tt0)M = \frac{K}{{1 = e^{ - K_* (t - t_0 )} }}; t = ageYesChen and Watanabe 1989
Brodziak_KM=K*L50lengthM = K_* \frac{{L_{50} }}{{\user1{length}}}YesBrodziak et al. 2011
Pauly_LinfM=e0.0152+0.6543*ln(K)0.279*ln(L))+0.4634*ln(T)M = e^{ - 0.0152 + 0.6543*\ln (K) - 0.279*ln\left( {L_\infty )} \right) + 0.4634*\ln (T)}NoPauly, 1980
Alverson_CarneyM=3Ke(0.38*Tmax*K)1M = \frac{{3K}}{{e^{\left( {0.38*\user1{Tmax}*K} \right) - 1} }}NoAlverson and Carney, 1975
Then_1M = 4.899 *Tmax0.916NoThen et al. 2014
Then_2M = 4.118 *K0.73*L−0.33NoThen et al. 2014
Hewitt HoenigM = e1.44−0.98*ln (Tmax)NoHewitt and Hoenig 2005
HoenigM = e1.46−0.101* ln (Tmax)NoHoenig 1983

Per-recruit results. Current F/F0.1 and Current E references obtained for different Z and M parameters. Stock state indication per M method; green color indicates healthy state, red indicates overfished state, and yellow indicates one of the two references indicating overfished state.

Z-MCurrent FF0.1FmaxCurrent F/F0.1Current EStock state indication
LCCC-GislasonF10.360.470.530.770.52Overfished in terms of E
LCCC-ChenWatanabeF20.670.490.591.370.11Overfished in terms of F
LCCC-Brodziak_KF30.370.460.530.800.51Overfished in terms of E
LCCC-Pauly_LinfF40.650.490.591.330.14Overfished in terms of F
LCCC-Alverson_CarneyF50.330.470.530.700.56Overfished in terms of E
LCCC-Then_1F60.640.500.581.280.15Overfished in terms of F
LCCC-Then_2F70.440.460.530.960.41Healthy
LCCC-Hewitt HoenigF80.470.460.541.020.37Overfished in terms of F
LCCC-HoenigF90.450.460.540.980.39Healthy
BH-GislasonF100.440.490.560.900.55Overfished in terms of E
BH-ChenWatanabeF110.130.530.620.250.17Healthy
BH-Brodziak_KF120.430.490.560.880.54Overfished in terms of E
BH-Pauly_LinfF130.150.530.620.280.19Healthy
BH-Alverson_CarneyF140.470.490.560.960.59Overfished in terms of E
BH-Then_1F150.170.540.620.310.21Healthy
BH-Then_2F160.360.490.570.730.45Healthy
BH-Hewitt HoenigF170.330.490.580.670.41Healthy
BH-HoenigF180.350.490.580.710.43Healthy
Median-LCCC0.980.40Healthy
Mean-LCCC1.020.35Overfished in terms of F
Median-BH0.710.43Healthy
Mean-BH0.630.39Healthy
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