FMRI recently provided commission staff members with this briefing document regarding the issue of proportions of foulhooked fish observed in the Boca Grande Pass tarpon study.
The purpose of this document is to clarify our results to date relating to the frequency of foulhooking associated with tarpon caught on breakaway jigs and live bait in Boca Grande. The results from 20022003 observations relative to hook position and hook orientation are summarized in Table 1. For the live bait method, all fish were hooked in the mouth region, 88% were hooked in the jaw with hook orientation inside/out. Three live bait fish were hooked inside the mouth. One live bait fish was hooked in the clipper.
For jig caught fish, 50% (13 out of 26) were hooked in the clipper. Hook orientation is available only for 7 of the 13 fish hooked in the clipper. For these 7 fish, only one was hooked outside/in, the remaining 6 were hooked inside/out. A total of 4 jig caught fish were hooked in a position other than the jaw or the clipper. One fish was hooked inside the mouth, one fish was hooked in the gills, and two fish were hooked elsewhere on the head.
Table 1: Summary of Tarpon Catch and Release Study Boca Grande Pass, 20022003 Landed Tarpon (tagged and untagged)

Hook Position and Orientation


Fishing

Jaw

Clipper 
Mouth

Gills

Head

Total

Method

In/Out

Out/In

In/Out*

Out/In

Unknown ^{1}




Fish

Jig

6

3

6

1

6

1

1

2

26

Live Bait

28

0



1

3



32

Total

34

3

6

1

7

4

1

2

58

^{1}Hook orientation was not recorded for clipper hooked fish in 2002.
*5 of these 6 fish were hooked from the inside corner of the mouth membrane out to the clipper
Definition of Foul Hooking
Our definition of foul hooking for this study was based on definitions used for other areas, published scientific literature, and input from experts in tarpon feeding behavior and fish functional morphology. The most common and widely accepted (AL, CO, MA, TX, Canada, UK, the International Gamefish Association, and virtually all popular glossaries and "Dictionary of Ichthyology")definition of foul hooking is:
"hooking a fish in a part of the body other than the mouth"
More restrictive definitions exist. For example in New Zealand, foul hooking is defined as:
"to hook a sports fish otherwise than from within the mouth"
At least one state (MS) has adopted a less restrictive definition:
"fish hooked further back than the gill covers".
Based on the information we have in hand, we are adopting the following definition of foulhooking for tarpon:
"A foul hooked fish is hooked in a part of the body other than the mouth"
Based on this definition, only 3 fish listed in Table 1 qualify as foulhooked fish. All three of these fish were jigcaught (1 in the gills and 2 on the head). These results indicate that 11.5% (3 out of 26) jig caught fish were foul hooked. No live bait caught fish were foulhooked based on this definition.
Statistical Analysis of Foul Hooking Data
Based on the definition of foulhooking above, results from the first two years of sampling may be summarized as follows:
Observed Data




hook

hook

Row

method

nofoul

foul

Totals

livebait

32

0

32

jig

23

3

26

All Grps

55

3

58

The analyses of these data are complicated by the relatively small sample size. The small sample size results in a zero cell for livebait foul hooked fish  theoretically, even if the frequency of foul hooking for live baiters is extremely low we would get at least one instance of foul hooking as sample size increases. Statistically, it is appropriate to view these count data as generated by a Poisson process and the use of chisquared test for a two way contingency table is an appropriate analysis. The chisquared test tests the null hypothesis of independence, i.e. that fishing method and number of foul hooked fish are completely independent. Rejection of the chisquared test indicates dependence, i.e. the tendency to foul hook fish depends on fishing type.
Expected frequencies under the assumption of independence are easily computed:
Expected Frequencies



hook

hook

Row

method

nofoul

foul

Totals

livebait

30.34

1.66

32

jig

24.66

1.34

26

All Grps

55

3

58

Under the assumption of independence, and with our sample size of 58, we should have observed approximately 2 foul hooked fish from the livebait method and one foul hooked fish from the jig method. Again, these small expected values are an artifact of the small sample size.
The chisquare test yields the following results:


Chisquare 
df

p

Pearson Chisquare


3.893706

df=1

p=.04847

ML Chisquare


5.016453

df=1

p=.02511

Yates Chisquare


1.896576

df=1

p=.16847

Phi for 2 x 2 tables

.2591001




The Pearson Chisquare and the MaximumLikelihood Chisquare test the hypothesis of independence, the only difference is that the ML chi square is based on MaximumLikelihood theory. In practice, the ML Chisquare is usually very close in magnitude to the Pearson Chisquare statistic. Both the Pearson Chi Square and the ML Chi Square result in rejection of the null hypothesis at the 5% significance level  i.e. the number of foul hooked fish depends on fishing technique. It must be noted that the only assumption underlying the use of the Chisquare (other than random selection of the sample) is that the expected frequencies are not very small. The reason is that the Chisquare inherently tests the underlying probabilities in each cell; and when the expected cell frequencies fall, for example, below 5, those probabilities cannot be estimated with sufficient precision.
The approximation of the Chisquare statistic in small 2x2 tables can be improved by reducing the absolute value of differences between expected and observed frequencies by 0.5 before squaring (Yates' correction). This correction, which makes the estimation more conservative, is usually applied when the table contains only small observed frequencies, so that some expected frequencies become less than 10  exactly the case we have with tarpon. This correction results in the test statistic labeled Yates Chisquare in the table above. The Yates corrected test fails to reject the hypothesis of independence at the 5% level, it does, however, reject the null at the 10% level. Again, we have uncertainty generated by our relatively low sample size.
The Phisquare statistic in the table above is a measure of correlation between two categorical variables in a 2x2 table. Its value can range from 0 (no relation between factors; Chisquare=0.0) to 1 (perfect relation between the two factors in the table). The calculated correlation of 0.26 indicates a low degree of correlation between fishing method and frequency of foul hooked fish. As with the other results, the interpretation of this correlation is hampered by the relatively small sample size.
Power Analysis
Statistical power in this case is simply the probability that we reject the null hypothesis (independence of fishing type and frequency of foul hooked fish) when it is in fact false (i.e. the probability of detecting a statistical effect if one exists). The most effective way to increase statistical power is to increase sample size. A statistical methodology has been developed to determine the power of the Pearson chi squared test for 2x2 contingency tables. The plot below presents statistical power on the y axis and sample size (number of fish) on the x axis. The current dataset results in a statistical power of about 0.5 based on a sample size of 58 fish. One commonly accepted baseline for a powerful experiment is Power = 0.7 or greater. For this study, a sample size of approximately 90 fish will be required to achieve a power of 0.7. It should be noted that 1) sample sizes in this study were set relative to the catch and release mortality assessment portion of the project and 2) this power analysis may change as another year of data on foul hooking are collected. The total number of fish necessary to achieve Power=0.7 may decline, but will likely not increase with additional data collection.
* Prior to July 1, 2004, the Fish and Wildlife Research Institute (FWRI) was known as the Florida Marine Research Institute. The institute name has not been changed in historical articles and articles that directly reference work done by the Florida Marine Research Institute.