LINEAR PROGRAMMING SIMULATIONS OF THE EFFECTS OF 



BYCATCH ON THE MANAGEMENT OF MIXED SPECIES FISHERIES 



OFF THE NORTHEASTERN COAST OF THE UNITED STATES 



B. E. Brown, J. A. Brennan, and J. E. Palmer^ 



ABSTRACT 



We evaluated the results of using historic bycatch (incidental catch) ratios in adjusting fishing 

 regulations by linear programming techniques. We used both 197 1 and 1973 bycatch ratios separately 

 to assess the sensitivity of the results to the reported changes in bycatch ratios in estimating the total 

 1975 catch of countries fishing in the northwest Atlantic. For 4 of the 1 1 countries for which data were 

 examined, the difference between the percentage of a country's species total allowable catches (i.e., 

 those catches allowed a country by regulation) using the 1971 and 1973 bycatch ratios, was at least 

 20% . Only four countries were predicted to catch at least 807f of their species total allowable catches. 

 The predicted total catches of all countries and all species was only 60% of the total species quotas. The 

 simulated directed fisheries constituted only 70% of the total catch using 1971 bycatch ratios and only 

 73% using 1973 bycatch ratios. Examination of the reported 1975 catches indicated that the total 

 allowable catches for herring were most frequently limiting a country's catch. Except for U.S.S.R., the 

 differences between reported and simulated catches were less than 50 metric tons, with the difference 

 less than 10 metric tons for 6 of the 11 countries. There was little difference in reported versus 

 simulated catches between the schemes using the 1971 and 1973 bycatch ratios. 



The control of fishing mortality by means of indi- 

 vidual species catch quotas is difficult in a mixed 

 fishery, i.e., where a significant proportion of the 

 fishing mortality on a given species is generated as 

 a result of the incidental catch, or bycatch, of that 

 species in fisheries directed toward other species. 

 Moreover, if a country is allowed to catch a spec- 

 ified amount of a given species by means of a di- 

 rected fishery for that species, the total species 

 catch may exceed that amount because of the as- 

 sociated bycatch of that species in the other 

 fisheries. 



The International Commission for the North- 

 west Atlantic Fisheries (ICNAF) modified its 

 regulatory measures several times in attempts to 

 account for bycatches of species under quota re- 

 strictions. The initial haddock quota regulations 

 (Subarea 5 and Division 4X, Figure 1) stated that 

 the directed fishery should cease when the ac- 

 cumulated catch (directed catch plus bycatch) re- 

 ported to ICNAF biweekly reached 809f of the 

 quota, anticipating that the catch after closure (a 

 bycatch by definition) would be 209f of the quota 

 (ICNAF 1969). When yellowtail flounder was 

 added to the list of species under quota, the closure 



'Northeast Fisheries Center Woods Hole Laboratory, Na- 

 tional Marine Fisheries Service, NOAA, Woods Hole, MA 02543. 



procedures were changed. The Assessments Sub- 

 committee of ICNAF estimated the expected 

 monthly bycatch after closure of directed fisheries 

 and the decision to cease directed fishing was then 

 made when the accumulated total catch reported 

 to ICNAF on a biweekly basis plus the expected 

 bycatch during the remainder of the year equalled 

 the quota (ICNAF 1970). With the introduction of 

 national quota allocations in 1972, the procedure 

 again changed, requiring each country to control 

 its directed fishery so that the sum of its directed 

 catch and the estimated bycatches would not ex- 

 ceed its quota allocation (ICNAF 1972a). 



The bycatch problem was acknowledged by 

 ICNAF in its decision to establish a TAC (total 

 allowable catch, i.e., that catch allowed a country 

 by regulation) for all species combined that was 

 less than the sum of the individual species TAC's 

 for 1974 and 1975 (ICNAF 1974a). Linear pro- 

 gramming simulations utilizing bycatch ratios 

 from directed fisheries for all countries combined 

 substantiated this policy (Brown et al. 1973; An- 

 thony and Brennan 1974). 



Since 1974, TAC's were set for all species (either 

 singly or in groups) and for national catches (IC- 

 NAF 1974a, 1975a). Under this regime, it was 

 possible to utilize linear programming more 

 realistically to investigate the extent to which the 



Manuscript accepted July 1978. 



FISHERY BULLETIN: VOL. 76. NO. 4, 1979. 



851 



