Atlantic Herring Conservation Lauren Keyes Yu Kawakami Brigette Jones Herring Stocks Spawning Sites Larval Dispersal Spawning Fish migrate from offshore to inshore coastal waters at various locations in the Gulf of Maine to spawn Females spawn once a year for several years External fertilization Egg mats (masses of eggs) laid on the ocean floor Eggs Egg mats attract variety of predators, contributing to high egg mortality Eggs hatch 7-10 days after fertilization Larvae Larvae are 5-7mm long upon hatching Have attached yolk sac with food supply for +/- 10 days Gradual switch from yolk to feeding on plankton; critical transition period with extremely high mortality Only about 1% of larvae survive to become juveniles at 6 months Juveniles Larvae metamorphose into juveniles in the spring at about 4cm in length Begin to look more like adults: scales form, body deepens Do not join adults yet; as adults move inshore to spawn, juveniles move offshore Adults Juveniles mature into adults at 3-4 years Measure about 10in Can live up to 12 years in the Gulf of Maine Migration Not very well understood, but in general Adults migrate against the currents from feeding grounds (offshore) to spawning grounds (inshore) Larvae drift passively with the currents Juveniles eventually join the adults Feeding Herring survive entirely by feeding on plankton, specifically Calanus finmarchicus, the dominant copepod in the Gulf of Maine Even larval herring eat a lot of larval (naupliar) copepods Herring distribution depends on copepod distribution Herring growth rates vary with copepod availability and abundance Predators Lots of things eat herring Herring Habitat Fully marine Spawn in coastal waters Depths above 100 meters Level bottom Substrates: rocks, cobble, gravel, pebbles, beds of seaweed, fragments of shells Pelagic larvae Exposed to currents, tides, and winds Brit (Juvenile) closer to shore Environmental Factors Temperature Salinity Oxygen Density Light Temperature Spawning happens in temperatures between 10C and 15C Spawning progresses from north to south Egg hatching dependent on temperature 7-10 days Water temperature determines length of larval stage 3-11 months (avg: 6 months) Oxygen Eggs deposited on upper level of egg mat exposed to more oxygen in moving currents Con: eggs on upper level of egg mat exposed to higher predation Density Juveniles migrate together in dense schools near surface Growth dependent on density Exceeding optimal number decreases growth rates Light Juveniles (brit) migrate vertically in response to light cycles Dispersed throughout water column during day Collect at surface waters at night Feeding on zooplankton prey We must consider these environmental factors when considering conservation Changes in Abundance Peak landings in complete collapse on Georges Bank 6X higher in than in Lowest from after crash Increased from 1985 onward 3 semi-independent stocks GoM, Nantucket Shoals, GB 1970-Continental Shelf from Nantucket to Chesapeake Bay Highest abundances off Long Island and NJ, Nantucket Shoals Late 70s-mid 80s-most south of Cape Cod Latitudinal shifts from o N in Late 60s to between 40 o 30-44 o 10N by 1984, back to 41 o N since 1989 Longitudinal shifts from West of 70 o W farther East (offshore) through 1986 and then back to 70 o W in Distribution Catch locations and abundances from Spring bottom trawl data Causes of the Collapse Excessive fishing mortality ICNAF (International Commission for the Northwest Atlantic Fisheries) TAC limits routinely set above scientific recommendations for sustainable fishing Concentration of fishing efforts on spawning areas Spawning stock and egg and larval decrease Complete absence of larvae on Georges Bank for 10yrs Mechanisms and Pattern of Recovery Recovery of Georges Bank began in 1984 Full recovery has required nearly 2 decades Spawning area closures and restrictions on GB beginning in the 1980s No offshore landings Abundances and biomass improved steadily on GB Stepwise recovery because of non-uniform distribution of larvae Gulf of Maine Nantucket Shoals Georges Bank Progression of larval abundances-colonization Water circulation patterns support pattern Current Conditions and Recommendations Have recovered to pre- 1960s biomass and abundance One of top 5 species in abundance and biomass Annual landings ranged from metric tons in early-mid 1990s Continue to prevent concentrated fishing of spawning stock Possibly rolling closures and/or localized closures of spawning areas Recovery of Atlantic Herring was possible because of almost totally releasing the populations from fishing pressures, and because larval dispersal between distinct areas was possible