posted on March 25, 2003 13:20
Eric N. Powell, Allison J. Bonner, Roger Mann and Sarah E. Banta
Haskin Shellfish Research Laboratory, Rutgers University
6959 Miller Avenue, Port Norris, NJ 08349, USA
Source - Journal of Northwest Atlantic Fishery Science, Volume 32: 39-55
The Illex illecebrosus fishery in the northwestern Atlantic Ocean is a trawl-based fishery. Illex illecebrosus normally lives less than one year, thus managing the fishery using a standard stock assessment approach is difficult. Real-time management is an attractive option. The purpose of this study was to investigate the validity and utility of data reported by commercial vessels for application in real-time management in the I. illecebrosus fishery. The assessment includes evaluating the frequency of erroneous reports, identifying the best measures of effort for catch per unit effort (CPUE) analysis, and examining the influence of vessel type and vessel behavior on subsequent analyses of trends in catch and effort.
Incomplete reports occurred 24% of the time in the commercial data. Misreported times and positions occurred less than 1% of the time. Searching time was not discriminated consistently. Searching times and distances were recovered from the more accurately-reported data on tow times and tow positions. Tow duration was more accurately estimated from Captains' reports than tow distance. True distances were underestimated by 10-20% using the position of net deployment and retrieval to measure tow distance because tows did not follow a straight-line path. Effort could be estimated based on tow distance or tow duration. Duration was the most accurate effort term. Searches between tows did not improve subsequent catch. Similarly, overnight transits, arguably a type of searching behavior, did not improve the subsequent day's catch. Thus, vessels, on the average, would have improved trip economics by not searching. Because of the apparent absence of a positive effect of searching and the lower accuracy of searching time and searching distance in comparison to tow-based metrics, particularly tow duration, addition of searching time or searching distance to effort did not materially improve the measurement of CPUE.
RSW (refrigerated seawater) trawlers search much less often than freezer trawlers. As a consequence of lower catch and longer duration tows, the CPUE for RSW trawlers is distinctly lower than for freezer trawlers. Catch per tow was higher by more than a factor of two for larger vessels. As a consequence of the higher catch and longer tows, CPUE was significantly higher also for the larger vessels. Managing the I. illecebrosus fishery using an industry-based reporting scheme would require information from freezer and RSW trawlers and specified vessel size categories.
Language - English
Publisher - Northwest Atlantic Fisheries Organization (NAFO), Dartmouth, N.S., Canada
Publication Date - 2003
Publication Type - Journal Article
Descriptors - catch, commercial vessel, effort, fishery, Illex illecebrosus