Research Document - 2006/095
Atlantic mackerel (Scomber scombrus L.) fishery, biology, diet composition and predation in NAFO Subareas 3 and 4 in 2005
By Grégoire, F., C. Savenkoff and D. Chabot
Abstract
In 2005, landings of Atlantic mackerel (Scomber scombrus L.) in the northwest Atlantic totalled 93,512 t, which represents a decrease of 14,020 t from 2004. In eastern Canada, 51,918 t were landed, including 40,724 t in Newfoundland only. Most of the landings of the west coast of Newfoundland were from unit areas 4Rb, 4Rc and 4Rd with 4,576 t, 1,334 t, and 7,614 t. On the east coast of Newfoundland, the most important landings were from unit areas 3Kd, 3Kh, 3Ki, 3Lb, and 3Lf with 8,570 t, 10,647 t, 3,380 t, 1,856 t, and 1,552 t, respectively. Mackerel catches of this importance are unusual for the east coast of Newfoundland. The other important unit areas were 4Tg and 4Tl in the southwestern Gulf of St. Lawrence with landings of 944 t and 625 t, respectively, and unit areas 4Xm and 4Xo, in Nova Scotia, with 3,513 t and 3 577 t. Since 2000, the most striking feature of the commercial mackerel fishery has been the presence of a high abundance and very large proportion of fish from the 1999 year-class. Over the past six years, this year-class has accounted for between 30% and 77% of the total number of fish caught, which hasn’t been seen since the late 1960s. In 2005, this year-class was dominant during the second and fourth quarter compared to the 2004 and 2003 year-classes for the third quarter. The analyses of the biological data indicate that the proportion of mature fish at age has decreased in recent years. The size at which 50% of the fish were mature, or L50, was 254.9 mm in 2005. Since 1999, the annual L50 values have been below or slightly above the minimum legal catch size of 250 mm. Data collected in the mid-1980s showed that mackerel in the Northern Gulf of St. Lawrence (Divisions 4RS) fed mainly on small (< 5 mm) and large (≥ 5 mm) zooplankton. During the mid-1990s and the beginning of the 2000s, the importance of the small and large zooplankton in the diet slightly decreased and was replaced by shrimp (Pandalus borealis) and capelin (Mallotus villosus). As shown by the results of different models of the Northern Gulf of St. Lawrence marine ecosystem, the main causes of mortality for mackerel in the mid-1980s were cetaceans, large cod (Gadus morhua), and large demersals. Cetaceans were still the main predators of mackerel in the mid-1990s and the beginning of 2000s. The same models showed that fishery related mortalities gradually increased from 2% in the mid-1980s to 15% in the mid-1990s, and finally to 30% of total mortality in the early 2000s. The main sources of uncertainty related to the present assessment are the unrecorded catches and the contribution of mackerel from Canadian waters in the American catches from the Gulf of Maine and Georges Bank areas. Because of this imprecision, of the recent increase of fishing effort and of the uncertainty regarding the results from the recent abundance surveys, the current TAC level of 75,000 t could be lowered over the next year.
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