506 



Fishery Bulletin 103(3) 



directly related to vessel length. With increasing vessel 

 length, horsepower would increase as would the vessel's 

 ability to use larger nets. Vessel length (a surrogate vari- 

 able for horsepower) could be a significant covariate in 

 the relationship between CPUE and cumulative catch. 



Results 



Bottom trawl survey 



Mean CPUE (kg/km 2 ) of Pacific cod in the smaller HSE 

 survey stratum was almost three times higher than 

 in the larger LSE stratum, resulting in mean biomass 

 estimates of 31,312 t and 17,720 t of Pacific cod, respec- 

 tively (Table 2 and Fig. 3). The highest recorded CPUE 

 of cod was recorded for a haul on the northeast side of 

 Unimak Pass (Fig. 3). Hauls with CPUEs above the 

 mean were distributed throughout the HSE stratum in 

 depths less than 200 m. Only one of the 18 hauls in the 

 LSE stratum had a CPUE larger than the mean. For the 

 HSE stratum, the 95% confidence interval on the mean 

 biomass estimate was 19.284-43,339 t. 



where C, = catch in time period t; 



f t = effort in t; 



q = catchability; 11 



B = underlying (or initial) biomass; and 



K t = cumulative catch through /. 



Current catch, effort, and cumulative catch are required 

 by the model, whereas catchability and initial biomass 

 are estimated from it. The catch and effort time series 

 used in these analyses were 1) daily aggregates of 

 observed cod catch in metric tons (t) and effort by ves- 

 sels targeting cod by area (i.e., the high sampling-effort 

 [HSE] area, the low sampling-effort area [LSE], the 

 area east [AE] and the area south [AS] of the survey 

 area), and 2) daily cumulative catch of cod by area for 

 all vessels. CPUE metrics were defined for each gear: 1) 

 trawl as the catch of cod (t) per hour of observed trawl- 

 ing per day; 2) pot as the catch of cod (t) per 20 pots 

 observed per day; and 3) hook and line as the catch of 

 cod (t) per 1000 hooks observed per day. These metrics 

 were chosen so that the CPUE for each gear would be in 

 approximately the same range to permit being plotted 

 together on the same axis. Changing the unit-of-effort 

 definition (number of pots or hooks fished, for instance) 

 has no effect on the significance of the results. Hauls for 

 which cod was the target species were defined as those 

 in which the catch of cod was at least 20% of the total 

 groundfish catch; target levels of 40% and 60% were also 

 explored for trawl fisheries. Catch and effort from these 

 hauls alone, in which cod was the target species, were 

 used for CPUE calculations, whereas cumulative catch 

 was derived from the total catch of cod from all vessels 

 regardless of their target species. 



The relationship between trawl vessel length and 

 CPUE was investigated but was not included in the 

 Leslie analyses. It was expected that CPUE would be 



Fishery data 



Total catch of Pacific cod Approximately 30,500 t of 

 Pacific cod were caught in the four areas of the south- 

 eastern Bering Sea from 1 January to 30 April 2001 

 (Table 3 and Fig. 4). Almost 60% of this total catch was 

 collected in the HSE survey stratum, whereas 25% and 

 12% of the total catch were collected in the AE and AS 

 of the survey area, respectively; only 4% was collected 

 in the LSE survey stratum. Based on the distribution of 

 the observed catch of cod by gear, approximately half of 

 the total catch was collected by trawls, a third by hook 

 and line (=longline), and 14% by pots. 



The distribution of cod catch by area primarily re- 

 flects the distribution of the fishery targeting Pacific cod 

 (Fig. 4). Of the 5813 t of cod that was observed caught 

 by the cod trawl fleet (with at least 20% of each haul 

 composed of cod), 86% was caught in the HSE stratum 

 in over 4600 hours of observed trawling. Most of the 

 remainder (13% or 781 t) was caught east (AE) of the 

 survey area, primarily between the HSE stratum and 

 the 20 nautical mile (nmi) radius trawl exclusion zone 

 encompassing sea lion critical habitat around Sea Lion 

 Rocks and Amak Island (Figs. 1 and 4). There was little 

 trawl effort targeting Pacific cod in the LSE stratum 

 (only 10 observed hours of trawling) or south (17 hours 

 observed) of the survey area. The cod pot fleet worked 

 primarily south of the survey area (57% of their catch) 

 and in the HSE stratum (31%) in areas where conflicts 

 with trawl gear would be minimized. The cod longline 

 fleet worked in both the HSE stratum and to the east 

 of the survey area, and had only trace amounts of catch 

 in the other areas (Table 3). 



Percentage of Pacific cod in the haul The distribution 

 of the percentage of cod in the total catch of each haul 



