NOAA Fisheries' Center for Coastal Fisheries and Habitat Research (Beaufort Laboratory) has conducted coastwide biological sampling of Atlantic menhaden for length and weight at age since 1955, developing one of the longest and most complete time series of biostatistical fishery data in the nation. Biological sampling is based on a two-stage cluster design, and it has been conducted over the range of the reduction fishery, both temporally (weekly) and geographically (port). The catch-at-age matrix for Atlantic menhaden landed for reduction is one of the most accurate and precise catch matrices used in the U.S.. Bait landings of Atlantic menhaden are available since 1985. Because of limited age composition data, bait landings were separated into the three geographic areas (New England; Middle Atlantic and Chesapeake Bay including coastal Virginia waters; and South Atlantic). Length frequency distributions and age-length keys for the summer period were developed by area in three-year increments from 1989-2000 to convert bait landings to catch in numbers at age. Hence, catch-at-age estimates from the reduction fishery were combined with catch-at-age estimates from the bait fishery to create a combined Atlantic menhaden catch-at-age matrix for the period 1985-2000.

The Murphy virtual population analysis (VPA) approach has been applied to Atlantic menhaden for many years. This method does not provide for calibration to fishery independent surveys, although preliminary runs have been made of a calibration approach based on a forward projection model implemented by AD Model Builder. The Murphy VPA has been conducted on the reduction catch matrix only and on the reduction and bait catch matrices combined. Because the benchmarks developed in Amendment 1 were based on Murphy VPA output from reduction data only, alternate benchmarks were estimated based on Murphy VPA output from the reduction and bait data combined. Estimates of fishing mortality (full F), recruits to age-1 (R1), and spawning stock biomass (SSB) were obtained from the Murphy VPA applied to the two catch matrices.

Fishing mortality rates on fully recruited ages (referred to as full F) are calculated as the weighted average of age-specific F's for ages 2-8, weighted by catch in numbers. Both temporal series show a downward trend in full F since the early 1970s. Preliminary estimates for 2000 are F = 0.6 based on the reduction and bait catch matrices combined. Current F is well below its 25th percentile of the 46-year set of estimates.

Similarly, short-term losses to the Atlantic menhaden stock due to the fishery can be assessed by considering the exploitation rate (U), which is the fraction of the remaining stock removed by the fishery during some specified period of time (usually 1 year). Exploitation rates of Age 1-8 menhaden by the reduction fleet have steadily declined since the mid-1960's:

Exploitation rate (U) for age-0 and ages 1-8 menhaden, 1955-1999.

Historical trends in spawning stock biomass (SSB) have shown considerable variability over the 46-year period. Extremely large values of SSB were present during the late 1950s and early 1960s, resulting primarily from two very large year classes (1951 and 1958).

With mostly poor recruitment during the 1960s, SSB declined to low levels. Rebuilding of the SSB occurred during the 1970s and 1980s when recruitment was good to excellent, and SSB recently peaked in 1997. Preliminary estimates in 2000 are SSB = 90,100 t based on the reduction and bait catch matrices combined. Current SSB is above its 75th percentile of the 46-year set of estimates.

Relative survival from spawning stock biomass to subsequent recruits to age-1 was estimated for 1955-1999 as an index that permits one to judge the relative survival from egg production (assuming proportionality with female biomass) and subsequent recruitment to age-1. A particularly high index of relative survival was estimated during the mid-1970s, aiding in the rebuilding of the menhaden stock. Only in recent years has the index of relative survival been very low, on par with the 1950s and early 1960s (with the exception of the 1958 year class).

Observed survival (millions of recruits to age 1 per metric ton spawning biomass) of Atlantic menhaden. Recent survivorship of age-0 fish has been very low due to environmental conditions (e.g. heavy predation by predators), resulting in low recruitment to age-1.

Also available to scientists are juvenile abundance indices from North Carolina, Virginia and Maryland, which have all recently been below their 25th percentile. The indices from Chesapeake Bay (Maryland and Virginia) have been low for some time, while the North Carolina indices showed a recent decline, possibly due to several hurricanes during the previous fall. The SEAMAP indices for ages 1 and 2 are between their median and 75th percentiles. The juvenile abundance indices from Connecticut and Rhode Island, however, are well above their 75th percentiles. The recent coastwide index (North Carolina through southern New England) falls just above its 25th percentile.

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