Table 10. — Effect of price differences on lobster catch when effort and 

 sea temperature are approximately the same. 



Table 1 1 . — Changes in catch in years in which temperatures were 

 approximately the same, effort comparable or even increasing. 



duced 6,323 lobsters. Although the catch per trap per 

 day was slightly lower for those traps fished on a set- 

 over basis, the total catch for the year was 2.8 times 

 greater. Average trap haul catches were greater for 

 set-over fishing during October. November, March, 

 April, and May, while daily haul catches were greater 

 in August, September, December, and February. It is 

 doubtful, however, if these results have any signifi- 

 cance as far as seasonal differences are concerned. Too 

 many other factors, including weather conditions and 

 demand, influence fishing effort and would, thereby, 

 modify results. Results of this study indicate that set- 

 over fishing has no catch per trap advantage over daily 

 fishing (2.524 to 2.526 per trap haul) and catch per trap 

 remained nearly as high during 198 fishing days (2.524) 

 as it did during 71 fishing days (2.546). It may, there- 

 fore, be concluded that annual catch per unit of gear is 

 more an index of the number of fishing days than it is of 

 fluctuations in year-to-year abundance. 



Although catch per unit of gear cannot be used as 

 an index of abundance, the number of traps fished can 



be used as an approximate index of gross fishing ef- 

 fort. 



In years when seawater temperatures are approxi- 

 mately the same, differences in catch have been as- 

 sociated with differences in effort. //; addition to being 

 the most reliable index of gross fishing effort, the av- 

 erage annual number of traps being fished is the 

 longest history of recorded effort data available, con- 

 sistint^ of 55 individual vears spanning the period 

 1897-1971. 



These data have been plotted as an effort-yield 

 curve (Fig. 6). Using the available data on catch, fish- 

 ing effort, and temperature the yield functions shown in 

 Table 12 were compiled.'^ According to the catch- 

 effort function (without the inclusion of seawater 

 temperature as a variable) the maximum sustainable 

 yield (MSY) from the Maine lobster fishery is esti- 

 mated at 22,108,200 pounds [equation (2)]. This catch 

 can be caught by the equivalent of 642,000 pots hauled 

 130 times during the year. The actual number of pots 

 fished in 1970 was 895,000 and in 1972 more than 1.2 

 million. On the basis of these calculations, there is a 

 strong indication that the Maine lobster resource is 

 significantly overfished." We also felt that the yield 

 equation should be computed with the inclusion of 

 seawater temperature as an independent variable in- 

 fluencing the catch. (See Fig. 5 for fluctuations in all 

 these variables.) The results indicated that seawater 

 temperature within the observable range has a positive 

 influence in the level of the catch and was statistically 

 significant at the 1 percent level. (See Fig. 7 for actual 

 and predicted catch.) Using the 1970 seawater tempera- 

 ture, the maximum sustainable yield was estimated to 

 be 22,021,000 pounds [equation (1)]. The catch is esti- 

 mated to require 667,000 pots. Although the pots fished 

 series is a crude proxy for fishing effort, the above 

 analysis does indicate a significant trend toward over- 

 fishing. 



Effort trends throughout the major lobster producing 

 areas of the Northwest Atlantic are similar to those 

 observed in Maine (Fig. 5). 



The limit of Maine lobster supply when the resource 

 is being intensively fished correlates very well with 

 seasonal fluctuations in seawater temperature. Al- 

 though seasonal temperatures appear to be more in- 

 fluential than annual averages, it is necessary to use 

 annual averages to compare conditions in different 

 years as well as to compare climatic trend influences 

 on different species. 



^The years 1971 and 1972 were omitted from the regression be- 

 cause of their extreme deviation from the traditional Schaefer 

 model. (See footnote 6 for further explanation.) In addition, a re- 

 viewer of this manuscript has commented as to whether one can get 

 a long-run equilibrium curve using annual data, but admits that it 

 will serve as the best approximation available. 



"Observations from 1970-72 certainly do not seem to conform to 

 the traditional Schaefer parabolic models. When further observa- 

 tions are obtained the reader may want to apply two other steady 

 state models which allow for a flatter yield function. See Pella and 

 Tomlinson. 1969 and Bell, Carlson and Waugh, 1973. 



15 



