ESTIMATION OF FISHING EFFORT IN THE 

 WESTERN NORTH ATLANTIC FROM AERIAL SEARCH DATA 



M. L. Parrack' 

 ABSTRACT 



Three estimators of days fished were developed from aerial search data obtained by fisheries 

 surveillance operations over the northwest Atlantic off the northeast coast of the United States. These 

 algorithms estimate fishing effort by applying functions of past aerial observations and past reported 

 effort to aerial data from the time period for which effort is to be calculated. An estimator based on the 

 relation of the average number of fishing vessels that were obsen'ed per flight and days fished as 

 reported has produced easily calculated estimates of days fished to within -0.50 of the reported value in 

 90% of all cases, 1971-73. An estimator based on the probability of a day fished if not sighted by fisheries 

 surveillance operations provided an estimate of fishing effort to within *0.50 in 95% of all cases. An 

 algorithm based on the probability of a day on fishing grounds, if not actually observed, and on the ratio 

 of days fished to days on grounds enabled the calculation of days fished with largest error (within -0.50 

 in approximately 80% of all cases). 



Prior to 1961, the waters off the northeast coast of 

 the United States were fished exclusively by the 

 domestic fleet. However, in 1961 distant water 

 fishing fleets of other nations began fishing this 

 area. Concern for the presence of these fishing 

 vessels prompted the United States to observe and 

 record the activities and magnitude of such fleets. 

 These observations over the 160,000 km^' fishing 

 grounds were made from land-based aircraft; one 

 to several flights were made each month. Although 

 fisheries statistics are reported by fishing nations, 

 such statistics are only available at least 6 mo after 

 the close of the reporting period. Overflight ob- 

 servations are therefore the only available up-to- 

 date information on that fishery. 



The fishery in these waters is regulated by the 

 International Commission for the Northwest 

 Atlantic Fisheries (ICNAF), a fisheries man- 

 agement directed treaty organization. Under the 

 objective of maintaining a maximum sustained 

 catch, the Commission sets regulations "to achieve 

 the optimum utilization of the stocks of those 

 species of fish which support international fisher- 

 ies in the convention area."- Intensive fisheries 

 harvest regulations by that agency^ have required 

 progressively larger cutbacks in fishing by fleets 

 other than the United States and Canada in these 



'Northeast Fisheries Center, National Marine Fisheries 

 Service, NOAA, Woods Hole, MA 02543. 



2ICNAF. 1974. ICNAF Handbook. Dartmouth, N.S., Can., 78 p. 



^ICNAF. 1974. Proceedings of the third special meeting, 

 October, 1973, N.S., Can., 34 p. 



waters. (ICNAF Statistical Subareas 5 and 6, 

 Figure 1.) 



The United States has expressed its concern to 

 ICNAF as to adherence to these fisheries regula- 

 tions in 1974.^ This concern originated from 

 preliminary examination of the fisheries over- 

 flight data. 



As a consequence, stochastic methods to monitor 

 the fishery through the analysis of overflight data 

 are of chief importance. In response to such needs 

 three estimators of fishing effort are presented. 

 These estimators of days fished are based on the 

 aerial surveillance data and concomitant reported 

 fishing effort. (Fishing effort as reported by each 

 ICNAF member nation is published annually, 

 usually about 1 yr following the reporting period. 

 Such statistics used in this study were obtained 

 from the ICNAF Statistical Bulletin, Vol. 19-23, 

 Dartmouth, N.S.) In each estimation method, 

 functions developed from aerial surveillance and 

 reported data in a previous time interval are used 

 to calculate fishing effort during a future time 

 interval for which only aerial surveillance data are 

 available. 



METHOD 



Fisheries surveillance flights were approxi- 

 mately 12 h or less in duration and were carried out 



Manuscript accepted March 1976. 

 FISHERY BULLETIN: VOL. 74, NO. 3. 



1976. 



^ICNAF. 1975. Proceedings of the fifth special meeting, 

 November, 1974, N.S., Can., 40 p. 



503 



