How is the Information Given to the California Recreational Fisheries Survey’s Samplers Used?

Casey AllenEducation

By Otis Horning, CDFW Environmental Scientist

After a great day on the water fishing, you have done your part and participated in the California Recreational Fisheries Survey (CRFS). The friendly California Department of Fish and Wildlife (CDFW) employee (or “CRFS sampler”) has asked you a series of questions about your fishing trip and has measured and weighed your catch. Now the question is: what happens to this information and how is it used?

CRFS is a statewide survey that occurs at over 450 sites along the coast from just south of San Diego past Crescent City and includes all recreationally caught marine finfish in California. This survey began in 2004, replacing a similar survey formerly called the Marine Recreational Fisheries Statistical Survey, which started in 1980. Other states such as Oregon and Washington have similar surveys to CRFS. The primary purpose of CRFS is to produce monthly catch and fishing effort estimates. Each time an angler participates in the survey this valuable information helps CDFW gather important sample data to produce these estimates. Because each fishing trip is unique anglers are encouraged to participate in this survey each time they are asked. The more accurate sample data CDFW gets, the better the estimates will be.

Survey data is collected in four different fishing modes: Private/rental boat mode (personal fishing boats, kayaks, and rental skiffs), man-made mode (piers, jetties, and other man-made structures), party/charter boat mode, and beach/bank mode (shore anglers). Since each site cannot be sampled every single day, sites and days sampled are randomly selected. The data collected by random sampling is expanded to estimate the effort/catch for the rest of the days that are not sampled. In addition, data is also collected through a telephone survey in which licensed anglers are contacted at random. This is used to estimate fishing effort that cannot be estimated through field observations, such as night fishing and fishing that occurs out of private marinas.

So now that CDFW has collected your information, what happens next? All the survey data is reviewed carefully for errors and entered into a database. Each month, catch estimates are calculated for the previous month. There are two main components needed to calculate total catch: An estimate of effort (total number of angler trips) and catch-per-unit-effort (CPUE, or the success rate of anglers measured by the number of fish caught per trip). Basically, the effort multiplied by the CPUE will give a catch estimate in numbers of fish.

You may wonder how are these two components are obtained? The first component (the effort estimate) is generated by conducting counts of daily effort (such as number of anglers on a pier or number of anglers on fishing boats at a launch ramp) and these counts are expanded for the days that are not sampled. To do this, the daily effort counts are averaged and multiplied by the total number of available fishing days within the sampled month. The average of the counts is considered unbiased due to the random selection of sample days and a sufficient sample size of days surveyed. Both together produce a representative measure of fishing effort. For example, surveys conducted during periods of low effort caused by poor ocean conditions will be balanced out by surveys conducted during blue weather days with high effort. The second component (the estimate of CPUE) is calculated for individual fish species for each angler trip that is sampled. This is then averaged across all estimated trips for the month. Using these two components allows CDFW to expand samples to calculate an estimate of total catch without sampling every single available fishing day in the month. Counting fish alone cannot be used since it does not account for days not sampled and for anglers who are missed or choose not participate in the survey.

So, how are the fish measurements and weights taken by CRFS samplers used? Fishery managers use the total weight of fish harvested or kept during the fishing season to guide season structures or to make adjustments to the regulations. To convert numbers of fish into a metric tonnage, the catch estimate is multiplied by the average weight for that fish species. Average weight is calculated from the fish CRFS samplers have measured or weighed in the field. Sampled fish with only length measurements are converted to weight using regression analysis (e.g., the strong relationship between fish length and weight). It is necessary to continuously obtain weight and length data on all fish species to ensure a true representation, which takes into account regional differences and changes in catch size over time. If CRFS samplers did not collect fish measurements year round, in every mode and location the conversions would be biased toward the areas or time periods that samples were taken. For example average weights are calculated regionally, ensuring those smaller Vermilions typically caught in Southern California are not applied to the catch in Northern California where they tend to be larger.

Now that you know how the catch estimates are made the last question is: how are they used? The CRFS catch estimates are used in a variety of ways by CDFW as well as other organizations to help manage California’s diverse marine fish populations. CDFW biologists as well as other fisheries scientists often use CRFS catch estimates when conducting research on individual fish species. CRFS catch trends, catch location data, and length and weight data are often valuable information when fisheries scientists are preparing stock assessments on a particular fish species. These stock assessments can be used to evaluate how fish populations may be affected by potential management actions and to forecast future conditions of the population

( Another way CDFW uses these catch estimates is in the development of new fishing regulations or to change existing ones. Trends in catch estimates over time often alert fishery managers to when fishing regulations may need to be changed in order to maintain a sustainable fishery or when new fishing opportunities can be opened. There are various tools that fishery managers may use to help manage the many different fish species. Some of these include daily bag limits, size restrictions, season closures, and depth restrictions. These tools can ensure that the number of fish being harvested is sustainable for future generations to come.

So as you can see the information gathered from anglers on the launch ramps, on the piers, aboard the party boats, and along the shore by the CRFS samplers is an important part in the management of California’s marine resources. The accuracy of the CRFS catch estimates depends heavily on the cooperation of anglers. So, if approached by a sampler after your next fishing trip or if you are contacted randomly on the telephone, do your part by saying “Yes” and provide answers to the best of your knowledge and allow the CRFS samplers to examine, weigh, and measure your catch in the field. The future fish populations of California will thank you!