Koeller; Influence of temperature and effort cfianges on lobster catchies 



63 



\ ^ LFA31A 

 4i N"^ 



 ~ 4 "-^ ^"^ 



4, -c^ ^. -V "<^. 





<^\ 



* ^ "*"*. \ % ^\ \ 





^^ 



<" ^ 'c. 



^ ^%. >/^ \ '^ 



LFA31B 



LFA33 



\ 



LEA 32 



50 km 



Figure 1 



Study area, including locations of ports along the eastern shore where fishermen provided 

 catch and effort information. The number of index fishermen at each location providing data 

 in 1994 is given in brackets after the port name. The dashed lines show the boundaries be- 

 tween lobster fishing areas (LFAs) and statistical districts (SDsi. The location of ports that 

 are discussed in the text are circled. 



Materials and methods 



Annual lobster catch is recorded by statistical dis- 

 trict from purchase slips by the Department of Fish- 

 eries and Oceans (DFO). These data are summarized 

 by larger geographical units for assessment purposes, 

 usually by lobster fishing areas (LFAs). In order to 

 examine the large scale relationships between 

 catches and temperature, catches were summarized 

 in a similar manner for this analysis. The Atlantic 

 coast of Nova Scotia (Fig. 1) was bisected into coast- 

 lines of approximately equal length, named the east- 

 ern shore (LFAs 31 A, 3 IB, and 32) and south shore 

 (LFA 33). Long-term records of sea surface tempera- 

 tures (SSTs) are available from Halifax harbour which 

 is located on the boundary between these areas and 

 can be considered representative of both. 



The three data series, i.e. total annual catches from 

 the south and eastern shore and average annual 

 SSTs, were smoothed with a 3-yr running average. 

 Examination of the plots suggested that the series 

 could be divided into two periods, a pre-1974 period 

 of high-frequency, low-amplitude cycles, and a single 



post-1974 cycle of high amplitude. Correlations at 

 lags of 0-10 years were then run for each period sepa- 

 rately and combined. 



Daily catch and effort information is collected for 

 DFO by selected index fishermen in some areas of 

 Nova Scotia. At minimum these fishermen provide 

 total lobster catches (usually weight in pounds) and 

 the number of traps hauled on a daily basis during 

 the fishing season. The number of index fishermen 

 varies between areas but tends to cluster around key 

 ports that are also sampled for length frequencies 

 by port samplers. On the eastern shore, about 20 fish- 

 ermen have kept log books along a 200-km stretch of 

 coastline between Canso and Halifax, some begin- 

 ning as early as 1986. In 1994 an additional 28 fish- 

 ermen associated with the Fishermen's and Scien- 

 tists' Research Society (FSRS) kept logs in this area. 

 Most FSRS fishermen also deployed continuous tem- 

 perature recorders (Vemco Ltd., Halifax, N.S.) on 

 their traps during the 1994 fishing season, which 

 extended from 20 April to 20 June in LFAs 3 IB and 

 32, and from 1 May to 31 June in LFA 31A. Because 

 effort information is available only for a limited num- 



