Feeding biology of the introduced fish Roi (Cephalopholis argus), and its impact on Hawaiian coral reef-fishes and fisheries
The Ciguatera Problem Ja...
2. Ciguatera analysis (continued) • MIA test procedure
• MIA test output:
2. Ciguatera analysis (continued) • MIA test Ciguatera scores: Teststicks No coloration: Faint blue coloration: Blue coloration: Strong blue coloration:
Score 0 0.5 1 2
Total score for each fish sum of three tissue samples (head, body, tail): Actual range of possible fish-scores: 0 to 6 (min.: 3 x 0 = 0; max.: 3 x 2 = 6)
Conventional interpretation: Safe to eat Usually safe, but incident possible Incident possible Incident likely
Results • The overall sample • Ciguatoxin levels by Site and Island • Ciguatoxin level and Roi size Switch between SCORES and the SCORECLASSES with more practical implications
The overall sample
+
90 80
Frequency
70 60 50 40 30 20 10 0 0
1
2
3
4
Ciguatera score
5
6
The overall sample Ciguatera levels, frequency & percent 40; 14% 13; 4% 104; 36%
0-0.5 1-2 2.5-4 4.5-6
n = 292 135; 46%
The overall sample - conclusions • Majority of Roi safe to eat, but close to 1/5th of fish in positive category, and 4% strongly positive (likely to cause Ciguatera) • Question: how does this compare to other reef fish species?
Site d sewer pipe
S Kiholo
Red Hill N
Puako
Mahukona
ne Tree Arch
na resort 3/4
na resort 1/2
ona Paradise
ko Arches 2
aneohe 6/7/8
Kaneohe 4/5
Kaneohe 2/3
Kaiwi Point
Honaunau S
lden Arches
Alahaka
Score (Jan)
Ciguatoxin level by Site Boxplots of Score (J by Site (means are indicated by solid circles)
6
5
4
3
2
1
0
Ciguatoxin level by Site
100%
Strong pos. 60%
Positive 40%
Marginal
20%
Negative
M
K-
ah u
ko
n Ki a ho K- lo L K - on e Go l K - de n Ko lo K- ko Ka K - iw i K - Pu Ho a k na o un K- au Ko n K- a K - Re d Al ah ak a OK2 OK4 O- O-K Ko 6 ol in a 2 Al l
0%
K-
F re q u e n c y
80%
Site One-way ANOVA: Score versus Site Analysis of Variance for Score
Source Site Error Total
DF 16 275 291
SS 69.55 499.20 568.75
MS 4.35 1.82
F P 2.39 0.002
M ah u K-
ko
n Ki a ho K- lo Lo K- ne Go l K - de n Ko lo K- ko Ka K - iw i K - Pu Ho a k na o un K- au Ko n K- a K - Re d Al ah ak a OK2 OK4 O- O-K Ko 6 ol in a 2 Al l
Ciguatoxin level by geographic location - conclusions • Significant association of location & Ciguatoxin level • Sites differ significantly in Ciguatoxin levels • Mean Roi Ciguatoxin scores low at some sites, however, strongly positive outliers can occur at these sites • Roi from Oahu and Hawaii Island differ significantly in Ciguatoxin levels, mean level on Oahu less than half as high as on the Big Island
Ciguatoxin level and Roi size
6
Ciguatera score
5 4 3 2 1 0 15
25
35
Standard length
45
Ciguatoxin level and Roi size 6
Ciguatera score
5 4 3 2 1 0 15
25
35
45
Standard length
Regression Analysis: Ciguatera score versus Standard length The regression equation is: Score = 0.146 + 0.0411 Standard length Predictor Constant Standard
Coef SE Coef 0.1459 0.3942 0.04106 0.01430
S = 1.381
T P 0.37 0.712 2.87 0.004
R-Sq = 2.8%
R-Sq(adj) = 2.4%
Analysis of Variance: Source Regression
DF 1
SS 15.713
MS 15.713
F 8.24
P 0.004
Ciguatera level and Roi size - conclusions • Fish length and Ciguatera toxicity are positively associated, however, only a very small degree (2.8%) of variation in toxicity is explained by fish length
General conclusions 1. Is the problem really as bad as perceived by the public? • While the majority of Roi in Hawaii appears safe for consumption, a significant amount of fish is ciguatoxic – the current public caution is therefore justified
2. What are the factors influencing Ciguatera in Roi? • Geographic location and Ciguatera are associated • Significant differences between Ciguatera levels at different sites suggest that Roi from certain sites are predictably safer than from other sites. However, ciguatoxic fish can occur at the ”relatively safe” sites
• Roi from Oahu are significantly safer for consumption than Roi from the Big Island. However, high variation in Ciguatera levels means that ciguatoxic and strongly ciguatoxic fish nonetheless occur.
• Ciguatera and Roi size (standard length) are positively associated. Size only explains a very small amount of variation in Ciguatera, and is therefore not a useful indicator of Roi toxicity levels.
General conclusions Key management question: Feasibility of Roi fishery in Hawaii Æ At this time, data do not indicate potential for risk-free fishery
Next steps Ciguatera: • Enhance statistical analysis • Look at remaining factors that may influence Ciguatera levels as information becomes available • Age and Ciguatera • Prey type and Ciguatera
Other: Feeding biology component of study
Next HCRI presentation: Stomach content analysis results
Prey items found in preliminary run through Roi stomachs of our sample
Acknowledgments • HCRI • UH specialization in Ecology, Evolution and Conservation Biology
