FISHKKY MUI.LKTIN: VOL. 86, NO 1 



tively. Vessels fishing the relatively nearshore 

 Cape Cod grounds remained in the 34-50 GRT 

 range. Larger vessels continued to enter the fish- 

 ery during the 1970's and, by 1983, several ves- 

 sels were in the 311-400 GRT range. Since 1964, 

 vessel CRT's have been categorized by tonnage 

 class (TO as given in Table la. 



A review of Lux's (1964) data from 1942 to 1961 

 and the distribution of more recent yellowtail 

 flounder landings from 1964 to 1983 (Figs. 3-5) 

 reveal that vessels of similar size have continu- 

 ally fished the same general areas over the past 

 40 years. The TC 21-24 vessels fish primarily on 

 Southern New England and Cape Cod grounds 

 (Fig. 3 1, although TC 24 vessels occasionally 

 enter the southwest part of Georges Bank. The 

 TC 25-33 vessels fish on both Georges Bank and 

 Southern New England grounds (Fig. 4), while 

 TC 41-43 vessels concentrate on Georges Bank 

 (Fig. 5). Although TC 41 vessels operate at times 

 on the eastern part of the Southern New England 

 grounds, the TC 42 and 43 vessels fish exclusively 

 on Georges Bank. 



The distribution plots (Figs. 3-5) reveal a grad- 

 ual phaseout of smaller (TC 21-24) vessels on the 

 inshore Southern New England and Cape Cod 

 grounds and a concurrent increase in the activity 

 of large (TC 41-43) vessels on Georges Bank, 

 Southern New England, and, to a lesser extent, 

 on the Cape Cod grounds. In evaluating trends in 

 CPUE we must ask whether these changes in the 

 yellowtail fishery over the past 20 years (i.e., the 

 shift in the predominant vessel size on two of the 



Table 1. — Definition of vessel tonnage classes (a) and depth 

 ranges and corresponding zones (b) included in analysis of vari- 

 ance of yellowtail flounder CPUE. 



three grounds and the addition of larger vessels to 

 the fieet on all three grounds) affect CPUE as 

 calculated by the traditional method (Lux 1964). 

 If the same size range of vessels (5-100 GRT) had 

 fished for yellowtail flounder throughout the 

 years, a shift in the dominant vessel class would 

 not affect CPUE estimates since effort would be 

 standardized against the same class and is, there- 

 fore, relative. However, the maximum vessel size 

 has increased and the predominant TC now repre- 

 sents vessels larger than 100 GRT. Since landings 

 and effort data contributed by these larger vessels 

 were not incorporated into previous CPUE calcu- 

 lations, CPUE estimates will not necessarily rep- 

 resent overall fleet performance in recent years. 

 The following procedures, therefore, were devel- 

 oped to calculate new fishing power coefficients 

 that encompass the entire size range of vessels 

 currently in the fishery. 



METHODS OF ANALYSIS 



Catch and effort data recorded by trip were ob- 

 tained from Northeast Fisheries Center (NEFC) 

 detailed commercial landings files. Fishing effort 

 or days fished (df) is defined on a 24-h basis as 

 number of hours of actual fishing time divided by 

 24. Only trips landing 50% or more of yellowtail 

 flounder were analyzed; trips included within the 

 qualification level generally accounted for 70- 

 90% of the total yellowtail landings over the en- 

 tire period, except on Cape Cod grounds where 

 qualified trips accounted for 40-60% of the total. 

 Catch per day fished (CPUE) was computed for 

 each trip and transformed to In CPUE since pre- 

 liminary analysis indicated a positive correlation 

 of the arithmetic mean CPUE with the variance. 

 Use of the log transformation, however, stabilized 

 the variance and created a lognormal distribution 

 as noted by Gulland (1956) and Steel and Torrie 

 (1980). 



Trips landing between 1964 and 1983 are clas- 

 sified in the data base by vessel tonnage class, 

 statistical area, and depth zone fished. Vessels 

 ranging in size from 5 to 310 GRT (Table la) and 

 statistical areas corresponding to the three major 

 stocks were selected for analysis as follows: 

 Georges Bank (areas 522-525), Southern New 

 England (area 526 and 537-539), and Cape Cod 

 (areas 514 and 521) (Fig. 6). Because of their spo- 

 radic representation, TC 21-23 vessels have been 

 excluded from the Georges Bank analyses and 

 have been combined as one category on the South- 

 ern New England grounds. Depth zones 1, 2, and 



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