Research Document - 2006/090
An Assessment of the Eastern Scotian Shelf Shrimp Stock and Fishery in 2006 and Outlook for 2007, including an estimate of bycatch and evaluation of alternative fishery independent abundance indicators
By Koeller, P., M. Covey and M. King
Abstract
Stock biomass remains high - the 2006 DFO-industry survey index was the third highest of the 12 year series. It decreased slightly from the previous year, mostly due to decreases in SFA13 which has been fished relatively heavily recently. The bulk of the biomass continues to concentrate in the offshore part of SFA 14 (i.e. survey stratum 14, SFA14 or the Misaine Hole). The spawning stock biomass (females) also decreased slightly from 2005, mainly because of slower growth and delayed sex change of the large 2001 year class, but it remains high and is likely to remain high or increase as this year class changes sex during 2006-2007. It should support the higher TAC (5000mt) effected in 2005 for at least one more year. The 2002-2005 year classes are weaker, consequently a biomass decrease is expected following the passage of the 2001 year class through the population. This is similar to what occurred during the last strong recruitment event (1994-1995 year classes), suggesting the establishment of a cyclical population dynamic often seen in established shrimp fisheries. Such a pattern may be indicative of decreased population stability, re-enforcing the need for continued good monitoring information and a precautionary approach in managing this fishery, including decreases in TACs during population downturns. Commercial counts in 2006 were the highest on record because of the prominence of the 2001 year-class, which is increasingly recruiting to the gear as it grows, but shrimp from this year-class are still relatively small for 5-year olds. It constituted the majority of the catch by numbers in 2006. Effort in SFA 14 increased significantly as fishers took advantage of high catch rates and accumulated biomass in this area. Although increased fishing activity occurred again during the ovigerous fall months due to the higher TAC and other factors the proportion of the catch taken during the ovigerous period decreased in 2006. The percentage of females in the catch also decreased due to the large numbers of males from the 2001 year class. Commercial catch rates reached a record high in 2006. Spatial indicators show that the area with the highest commercial catch rates remains large. Analysis of shrimp catches in the eastern Scotian Shelf snow crab surveys indicate that it could produce more accurate and precise abundance estimates than the shrimp survey. However, the selectivity of the nephrops trawl for shrimp is not known, so its usefulness for determining population length composition and recruitment must be determined. .Analysis of bycatch data from shrimp survey and commercial catches indicate that the Normore grate effectively reduces bycatch to an average of 3.6% and 2.3% by weight in the survey and fishery, respectively. However, the numbers of small fish caught by the fishery annually can be relatively large e.g. about 0.5 million small plaice. The impact on the population dynamics of these species is not known.
Accessibility Notice
This document is available in PDF format. If the document is not accessible to you, please contact the Secretariat to obtain another appropriate format, such as regular print, large print, Braille or audio version.
- Date modified: