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Chapter 8 - Small Pelagic FishJacobson 2006). The lack of recovery of the Illex squidpopulation may be due to extreme overfishing in the1970s, as well as depressed populations of capelin, a keyforage species for Illex at the northern limit of their migratoryrange (i.e. Nova Scotia and Labrador) (Macy2008). Finally, butterfish reached historic lows around2000 and the population is still depressed. Though fishingpressure is low, there is significant bycatch in otherfisheries (Overholz 2006c).Sand lance populations exploded during the early 1980s,a response to release from predation pressure due to overfishingof species which prey on them. As some stockshave recovered, most notably herring and mackerel, sandlance numbers have declined. As the only species amongthe small pelagic group assessed here that are not subjectto significant fisheries, sand lance populations are regulateddirectly by predation which in turn is influenced byfishery impacts (Weinrich et al. 1997).Ecosystem Interactions and EcologicalDependenciesSmall pelagic species are crucial to the health and functioningof marine ecosystems (Read and Brownstein2003). On a very broad scale, they capture energy fromlower trophic levels (phytoplankton, zooplankton, andsmall planktivorous fish) and transfer it to higher levelcarnivores including mammals, birds, and numerous speciesof pelagic and demersal fish and marine invertebrates.Because of their seasonal migrations and other life historytraits, they also provide a significant link between coastaland pelagic systems by transporting energy and biomassseasonally from coastal embayments and nearshore watersto offshore waters (Gottleib 1998).Herbivorous or omnivorous small pelagic species also arecapable of removing significant amounts of phytoplanktonfrom the water column. As a result of the often massivenumbers and dense schooling behavior of some of thesespecies, they can significantly alter water chemistry on alocalized scale by increasing nutrients and depleting oxygen(Oviatt et al. 1972). On a bay- or estuary-wide scale,small pelagic species serve as net exporters of nitrogenfrom these systems (Gottleib 1998).Some species in this group compete with one another andwith species outside the group, serving as predator or preydepending on life stage. Atlantic herring and Atlanticmackerel consume sand lance. Sand lance competes forCalanus finmarchicus (a zooplankton) with endangerednorthern right whales (Kenney et al. 1986). Both speciesof squid are piscivorous, and squid are also cannibalistic.Also of note is the importance of small pelagic species to ahost of large pelagic fish, as well as cetaceans and birds.Northwest Atlantic Distribution andImportant AreasMethodsSee methods overview in Chapter 5.Limitations of Data for Small Pelagic SpeciesSpatial data for determining distribution and importantareas was obtained from NMFS bottom trawl surveys.These surveys represent more than four decadesof fishery-independent data collection throughout theNorthwest Atlantic region, primarily in federal waters butin some state waters as well (inside three miles). Whenused for sampling small pelagic species, the survey methodhas some limitations with regard to fish behavior andecology. These species tend to be found near the surfaceand/or can outswim the gear, so these species are not sampledas effectively as many demersal species in the trawlsurveys. In addition, these fish can make diurnal verticalmigrations or exhibit other behaviors that can causethem to be more difficult to catch at certain times of day.A number of experts have cautioned that there are bettermethods for sampling populations of small pelagic species,such as acoustics, purse seines, or midwater trawls. Thereis some likelihood that the trawl surveys have missed someimportant locations where small pelagic fish tend to beclose to the surface, and the data may be biased towardareas where these species can be caught in a bottom trawl.It is unclear the extent to which these issues affect thevalidity of the maps created for this assessment.Another important limitation of the data is the relativelyshort time frame (six weeks) in spring and fall withinNorthwest Atlantic Marine Ecoregional Assessment • Phase 1 Report 8-