Distribution, Biology and Management
I. illecebrosus live for less than one year, experiences high natural mortality rates, and exhibit a protracted spawning season whereby overlapping “microcohorts” enter the population throughout the year over a wide geographic area and exhibit variable growth rates. Age estimation, accomplished by counting daily growth increments in the statoliths, has been validated for I. illecebrosus (Dawe et al. 1985; Hurley et al. 1985). Back-calculated hatch dates from statolith-based aging studies indicate that spawning occurs throughout most of the year (Dawe and Beck 1997; Hendrickson 2004). The only confirmed spawning area is located in the Mid-Atlantic Bight where the winter cohort spawns during late May (Hendrickson 2004). Spawning may also occur offshore in the Gulf Stream/Slope Water frontal zone, where Illex sp. paralarvae have been collected (O’Dor and Balch 1985; Rowell et al. 1985), and south of Cape Hatteras, during winter, where Illex sp. hatchlings have been collected (Dawe and Beck 1985). The lifespan of the winter cohort in U.S. waters ranges from 115 to 215 days (Hendrickson 2004). The species is semelparous and fishing mortality and spawning mortality occur simultaneously on the U.S. shelf (Hendrickson and Hart 2006). The species inhabits offshore shelf and slope waters primarily during spring through autumn (Hendrickson and Holmes 2004). Species distribution and abundance are strongly influenced by oceanographic factors (Dawe and Warren 1993; Dawe et al. In Press). Annual survey indices of relative abundance and biomass and average body size suggest that the stock has experienced low and high productivity periods (Hendrickson and Showell 2006; NEFSC 2006). The information provided herein reflects the results of the most recent peer-reviewed assessment of the U.S. component of the I. illecebrosus stock.