Estimation Methods
Generally speaking, to estimate total catch, you need to estimate both the number
of angler trips (effort) and the catch per angler trip (catch rate):
 What species are being caught
 How many fish are being caught
 How many fish are kept
 How many fish are discarded, and the condition of the discarded fish
 Size and weight of fish caught
 How many people are fishing
 Where people are fishing
 How often people go fishing
On the Atlantic and Gulf coasts, MRIP uses three main surveys to gather the information needed to generate these estimates. For a more detailed description of these estimation methods, please review the information provided below. To understand methods and surveys used in other regions, see Coverage for links to the various state and regional survey programs.
Basic Estimation Methods
The MRIP catch and effort estimates are produced using information from three complementary surveys.
 The Coastal Household Telephone Survey (CHTS) of private households is used to monitor the number of fishing days for shore and private boat fishermen. The CHTS collects fishing activity data that can be used to estimate the total number of shore and private mode angler trips (effort).
 The ForHire Survey (FHS) is a telephone survey of forhire boat operators that is used to monitor the number of day trips made by fishermen using charter boats and head/party boats. The FHS collects fishing activity data that can be used to estimate the total number of charter/head boat angler trips (effort). Additionally, the Southeast Region Headboat Survey samples and monitors the recreational headboat fishery in the south Atlantic and Gulf of Mexico.
 The Access Point Angler Intercept Survey (APAIS) is a survey at fishing/marina sites that monitors the catch rates of fishing participants in the shore, private boat, and charter boat modes. The APAIS collects data that are used to estimate catch by species per angler fishing trip. The APAIS interviews are completed onsite and inperson by trained interviewers. In the Northeast, catch rate for head boats is determined from the observations of atsea samplers who monitor catch aboard sampled head boat trips.
We calculate effort through the two telephone surveys and average trip catch rates through the onsite APAIS interviews. The effort estimate can be used to expand the mean catch rate to get an estimate of the total number of fish caught.
Effort x Catch Rate = Total Catch
For example, if 5 people made 3 trips each (15 angler trips total) and averaged one black sea bass and two cod per trip, we would estimate their total catch to be:
15 angler trips x 1 black sea bass per trip = 15 black sea bass
15 angler trips x 2 cod per trip = 30 cod
We produce estimates for every species, every type of fishing (mode), and three different catch types. 1) Type A catch estimates are based on fish brought back to the dock and observed and identified by trained interviewers. 2) Type B1 catch estimates are based on reported fish that were used for bait, released dead, or filleted ( i.e. they are killed but identification is by individual anglers and not samplers). 3) Type B2 catch estimates are based on reported fish that were released alive (again, identification is by individual anglers).
This is the most fundamental approach to estimating total catch. However, it is usually necessary to make adjustments to the effort estimates produced by the CHTS and FHS. For example, the CHTS only samples coastal households and therefore does not reach people in inland states. We use information from the onsite APAIS survey, where we ask what state a person is from, to adjust the estimates accordingly. A similar adjustment is made for the FHS charter angler trip estimate to account for angler fishing trips on charter boats not included in that survey (it's voluntary).
Example: Basic Estimation with Effort Adjustment
The following table is an example of the various components from the complementary surveys that are used to generate catch estimates for private boat mode in Massachusetts. Use the numbers in the table below to follow these steps to estimate catch estimates:
 Start with the original estimated private boat mode effort for Massachusetts from the CHTS for twomonth sample intervals Waves 3 (MayJune), 4 (JulyAugust), and 5 (SeptemberOctober) for the years 2011, 2012, and 2013.
 Calculate the coverage adjustment factor (Adjustment on the table, accounts for people not able to be surveyed) for that wave, and multiply it by the original effort to get an adjusted effort estimate.
 Calculate the weighted mean catch per angler trip (Catch Per Effort on the table) from the APAIS survey (for private boat mode, in this case)
 Multiply the adjusted effort estimate of angler trips by the catch per trip estimate to obtain the catch estimate.
Massachusetts Private Boat Mode Example*  
Year  2011  2011  2011  2012  2012  2012  2013  2013  2013 
Wave  3  4  5  3  4  5  3  4  5 
Original Effort  237,114  392,138  301,444  359,247  562,259  133,695  333,813  503,932  365,785 
Adjustment  1.3688  1.3162  1.3104  1.3794  1.3646  1.3634  1.4499  1.3306  1.1763 
Adjusted Effort  324,558  516,118  395,008  495,548  767,233  182,279  484,010  670,539  430,270 










A Catch Per Effort  0.0070  0.0024  0  0.0226  0  0.0122  0.0739  0.0153  0.1212 
B1 Catch Per Effort  0.2315  0.0687  0.0511  0.5350  0.0101  0.3058  0.0616  0.0569  0.0443 
B2 Catch Per Effort  0.4513  0.1671  0.1164  0.8452  0.2625  0.6488  0.3519  0.8898  0.5697 










A Catch Estimate  2,270  1,228  0  11,214  0  2,232  35,769  10,275  52,139 
B1 Catch Estimate  75,127  35,477  20,201  265,101  7,774  55,745  29,816  38,185  19,065 
B2 Catch Estimate  146,481  86,245  45,988  418,828  201,393  118,257  170,333  596,664  245,145 
*Note: Due to rounding error, if you calculate the estimates above, you won't get exactly the same numbers shown. 
Weighting Estimation
In the basic estimation example, we indicate that we obtain a weighted estimate of the mean catch per angler trip from the APAIS data. Per standard survey design methodology, survey weights account for the fact that some people and sites are more likely to have interviews than others . If we did not try to account for this, our estimates would be less accurate. For basic weighting, if a given sample unit had a 1/10 chance of being selected, the assigned weight would be the inverse of that probability, or 10/1 = 10. In the APAIS, there are multiple stages of sample selection that require weighting . An example is provided below to clarify how this is done. The following numbers are for illustrative purposes only, and do not represent actual numbers used in our survey estimates.
Primary Stage Weights
The first sampling unit for the APAIS is a specific fishing site and time interval. The probability of selection for a given sitetime combination depends on how active the fishing site is expected to be during the time interval, as predicted from historical information. For example, let's say that we have three types of fishing sites and their expected activity during an assigned time interval for interviewing:
L for low activity, expected to have about 10 angler trips
M for medium activity,expected to have about 40 angler trips
H for high activity, expected to have about 100 angler trips
Let's say for a given area we have 40 Lsites, 20 Msites, and 8 Hsites. Based on the known activity levels, the probability of selection for each site is:
probability of selection for a given sitetime combination =
activity level (L, M, or H) / (L*Lsites + M*Msites + H*Hsites)
Lsites: each site has a 1/200 chance of being selected (10 / (10*40+40*20+100*8)=1/200)
Msites: each site has a 1/50 chance of being selected (40 / (10*40+40*20+100*8)=1/50)
Hsites: each site has a 1/20 chance of being selected (100 / (10*40+40*20+100*8)=1/20)
Now, let's say we take a small sample of 5 sitedays and end up selecting 1 Lsite, 2 Msites, and 2 Hsites. The site weights are the inverse of the selection probabilities, so in this example the primary stage weights for Lsites would be 200, Msite weights would be 50, and Hsite weights would be 20.
Secondary Stage Weights
When visiting an assigned site in an assigned time interval, each APAIS interviewer tries to interview as many anglers who have completed fishing for the day as he/she can while keeping track of how many total trips were completed at the site. For the lower activity sites, it may be easy to interview every angler trip, while at the higher activity sites, people may be leaving at the same time and the interviewer may not be able to interview every angler. For each assignment, we calculate a second stage selection probability, and also create a weight for each interview that is based on the inverse of that probability.
Working with our example:
At the Lsite, there were 10 trips as expected and all 10 were interviewed, so the probability is 10/10, or 1 and the weight is also 1.
At the Msites, there were 40 trips but only 32 were interviewed, so the probability is 32/40 = 4/5, and the weight is 5/4 = 1.25.
At the Hsites, there were 100 trips but only 40 were interviewed, so the probability of selection is 40/100 = 2/5, and the weight is 5/2 = 2.5.
Combining Weights
The overall weights assigned to each trip can then be calculated by multiplying the sitetimeselection (primary stage) weight by the tripselection (secondary stage) weight. The overall weights assigned to each trip in our example are:
Lsites: 200*1 = 200
Msites: 50*1.25 = 62.5
Hsites: 20*2.5 = 50
Calculating Catch per Unit Effort
To calculate the weighted catch per unit effort for a particular species, we sum the product of the number of fish caught by the respective trip weight and then divide by the total sum of the weights themselves. This produces a weighted average that correctly reflects the sample design. To continue with our example, let's say that we're interested in species X. A the Lsite that was selected, a total of 6 fish of species X were caught among the 10 interviewed trips. Across the selected Msites, a total of 30 fish of species X were caught among the 64 total interviewedtrips. Across the selected Hsites, a total of 34 fish of species X were caught among the 80 total interviewed trips.
Combining the information above, we can calculate the weighted catch estimate for species X by multiplying the number of fish caught at each site by the appropriate weight and summing them. In this case, the weighted catch estimates are:
Lsites: 6*200 = 1,200
Msites: 30*62.5 = 1,875
Hsites: 34*50 = 1,700
Sum: 1,200+1,875+1,700 = 4,775
To calculate the weighted catch per unit effort, we need to divide this by the total sum of the weights. We can calculate that by multiplying the combined weights by the total number of interviewed trips for a particular site. In this example, the sum of the weights would be 10*200+64*62.5+80*50=10,000. Therefore, the weighted mean catch per angler trip would be 4,775/10,000=0.4775.
The "unweighted" mean catch per angler trip could be calculated by taking the total number of fish caught and dividing by the total number of interviewed trips, or 70/154=0.4545. However, this is a biased estimate of the actual catch per unit effort because it doesn't reflect the sampling design. This may not look like a large numerical difference from the weighted estimate, but the difference could be much larger for other examples.
Example: Weighted Estimation
The table below shows the weighted estimation example described in the previous tab. Each of the steps in calculating weighted estimates is demonstrated below.
Numerical Weighting Example  
Site Type  L  M  H  Total  Notes  
Number of Sites  40  20  8  68 
 
Expected Trips per Site  10  40  100 

 
Total Expected Trips  400  800  800  2000 
 
Probability of Selection  1/200  1/50  1/20 

 
Site Weight  200  50  20 
 (Inverse of probability of selection)  
# of Trips at Each Site  10  40  100 

 
# of Interviewed Trips/Site  10  32  40 
 (Average trips interviewed per site)  
Probability of Selection  10/10  32/40  40/100 
 (# interviewed trips/total trips )  
Interview Weight  1  1.25  2.5 
 (Inverse of probability of selection)  
Overall Trip Weight  200  62.5  50 
 (Site weight*interview weight)  





 
Total Trips Across Sites  10  80  200  290 
 
Total Interviewed Trips  10  64  80  154 
 
Total # of Species X Caught  6  30  34  70 
 





 
Weighted Catch Species X  1,200  1,875  1,700  4,775 
 
Sum of Weights  2,000  4,000  4,000  10,000  (Sum of interviewed trips*weights)  
Weighted Catch per Effort 


 0.4775  (Weighted Catch/Sum of Weights)  





 
Unweighted Catch  6  30  34  70 
 
Trips Interviewed  10  64  80  154 
 
Unweighted Catch per Effort 


 0.4545  (Total Catch/Trips Interviewed) 