Distribution, Biology and Management

Atlantic mackerel, Scomber scombrus, is a fast swimming, pelagic, schooling species distributed in the Northwest Atlantic between Labrador and North Carolina. There are two major spawning components in the population: a southern group that spawns primarily in the Mid-Atlantic Bight during April and May, and a northern group that spawns in the Gulf of St. Lawrence in June and July. Both groups winter between Sable Island (off Nova Scotia) and Cape Hatteras in waters generally warmer than 7°C (45°F), with extensive northerly (spring) and southerly (autumn) migrations to and from spawning and summering grounds (Figure 23.1). The two groups are managed as a unit stock. Maximum observed size in recent years is about 42 cm (16.5 in) in length and 1.0 kg (2.2 lb) in weight. Sexual maturity begins at age 2 and is usually complete by age 3. Maximum age is about 20 years.

Assessment Results

Fishing mortality (ages 4-6, unweighted) was high during 1969-1975, peaking at 0.54 in 1975 (Figure 23.6 [Fig 23.6 Data]), and then sharply declined to 0.05 in 1978 followed by a very low and stable period during 1979-1986. Fishing mortality increased very slightly in 1988 to 0.09, (coincident with the joint venture (JV) fishery that operated for several years), and then declined and has since been below 0.06. Spawning biomass peaked in 1972 at 1.7 million mt, declined until 1976, and has increased thereafter reaching a record high of 2.3 million mt in 2003-2004 (Figure 23.7 [Fig 23.7 Data]). Recruitment ranged between 0.1-5.8 billion fish during 1962-2004 and averaged 1.1 billion fish (Figure 23.8 [Fig 23.8 Data]). Three large year-classes were produced during this period, the 1967, 1982, and 1999 cohorts. The 2003 and 2004 cohorts appear to be above average but their magnitude is still uncertain.

Biological Reference Points

Yield and spawning stock biomass reference points are shown Table 23.2. These reference points were re-estimated in the most recent (fall 2005) assessment as F_0.1 = 0.25 and F_40% = 0.24 (NEFSC, 2006).

The spring stock recruitment relationship for Atlantic mackerel is highly variable with strong year classes produced at both high and low spring stock levels. Survival ratios have been relatively low during 1962-2005 with the exception of the four largest year-classes (Figure 23.9 [Fig 23.9 Data]). Recent R/S ratios have been very low except for the 1999 year-class.

MSY reference points were estimated in the most recent (Fall 2005) assessment and MSY = 89,000 mt, SSB_msy = 644,000 mt, and F_msy = 0.16 (NEFSC, 2006).

Summary

Spawning stock biomass has increased steadily since 1978, reaching a recent high of 2.3 million mt in 2004, for B_MSY (644,000 mt). Fishing mortality has remained very low (below F=0.06) since 1992. Therefore, the stock is not overfished and overfishing is not occurring.