Distribution, Biology and Management

Northern or pink shrimp, Pandalus borealis, occur in boreal waters of the North Atlantic, North Pacific, and Arctic Oceans. In the Gulf of Maine, northern shrimp are considered to constitute a unit stock. They inhabit soft mud bottom at depths of approximately 10 to 300 m (2 to 165 fathoms), most commonly in the cold waters of the southwest Gulf of Maine (Figure 33.1). The Gulf of Maine is the southern limit of the northern shrimp distribution in the North Atlantic, and temperature affects growth and development rates and reproductive success in the stock.

Northern shrimp are hermaphroditic, maturing first as males at roughly 2½ years of age and then transforming to females at about 3½ years of age. In the Gulf of Maine, spawning begins in offshore waters in late July. In late autumn and winter egg bearing females move inshore, where the eggs hatch. Juveniles remain in coastal waters for a

The Fishery

A directed otter trawl fishery for northern shrimp in coastal waters of the Gulf of Maine began during the winter months in the 1930s. Landings peaked at 12,800 mt in 1969 with the expansion of an offshore, year-round fishery; but markedly declined in the mid-1970s and a fishery closure was enacted in 1978 Figure 33.2 [Fig 33.2 Data]). Thereafter, landings increased steadily to over 5,000 mt by 1987. Landings ranged from 2,300-4,400 mt between 1988-1994, and then rapidly increased to 9,200 mt in 1996. Landings declined between 1996 and 2002 but increased afterwards Landings in the 2003 38-day season were 1,211 mt, 1,933 mt (preliminary data) in a 40-day season in 2004 and 2,146 mt (preliminary data) in the 70-day season in 2005 (Table 33.1)

Maine accounted for 84% (1,808 mt) of the 2005 season while New Hampshire and Massachusetts landed 14% (290 mt) and 2% (48 mt), respectively. This distribution of landings among states is similar to recent years, but has shifted since the 1980’s when Massachusetts accounted for about 30% of the total, (Figure 33.3 [Fig 33.3 Data]). Most shrimp in the Gulf of Maine are landed by otter trawls, although traps accounted for 4 – 20% of the annual landings during 2000 - 2005.

There has been no northern shrimp fishery in the Canadian portion of the Gulf of Maine since the early 1970s.

Research Vessel Survey Indices

Biomass of the northern shrimp stock is monitored in the NEFSC autumn bottom trawl survey and the ASMFC summer shrimp survey. The NEFSC autumn survey biomass index declined in the early and mid-1970s, remained relatively stable from 1980 to 2001 and has since slightly increased (Figure 33.4 [Fig 33.4 Data]). A joint State-Federal shrimp survey has been conducted from the summer of 1984 to present. Biomass and abundance indices from this series are the major source of information used in an annual assessment by the ASMFC northern shrimp Technical Committee. These indices are similar in trend to those from the NEFSC autumn bottom trawl series. They are relatively stable from 1984 – 1990 then decline throughout the 1990s. Until 2003 the summer indices remained low and have increased in the last 3 years. (Figure 33.4) . Exploitation rates, calculated during fishing seasons, increased from 20 to 38% between 1985 and 1995, peaked at 60% in 1997 before declining to 6% during 2002 (Figure 33.5 [Fig 33.5 Data]). The drop in exploitation rate is consistent with the decline in nominal effort during the same period. Since that time, exploitation has increased to 15%. Exploitation rates at or near the 1997 level occurred at the time of the stock collapse in the mid-1970s.

Figure 33.2

Figure 33.3

Figure 33.4

Figure 33.5

Figure 33.6

Figure 33.7

Figure 33.8

Biological Reference Points

Fishing mortality and biomass reference points (Table 33.2) for northern shrimp were developed in 2004 (NSTC 2004) and adopted by AMFC (ASMFC 2004). F_Target was estimated to be 0.22 based on the average estimates from 1985 through 1994, which represents a relatively stable period covered by the assessment series. F_Limit = 0.6 represents the level of fishing mortality that would reduce egg production below 20% of maximum (NSTC 2006). This level of fishing is comparable to that preceeding the stock collapse in the late 1970s. The stock biomass threshold of B_Threshold = 9,000 metric ton and limit of B_Limit = 6,000 metric ton are based on historical abundance estimates and response to fishing pressure. Biomass dynamics during 1985 through 2006 are shown in (Figure 33.8 [Fig 33.8 Data]).

Summary

Table 33.1 Commercial landings of GOM northern shrimp (thousand metric tons).

Table 33.2 Fishing Mortality and Biomass reference points for Gulf of Maine northern shrimp.