Rebuilding Atlantic Cod: Lessons from a Spawning Ground in Coastal Newfoundland

Abstract

Atlantic cod (Gadus morhua) was studied at the Bar Haven, Placentia Bay, Newfoundland (NAFO 3Ps stock unit) spawning ground from 1996 to 2003. Lessons applicable to management of rebuilding stocks derived from these studies are reviewed: (1) cod spawn in the same area each year, but numbers and timing vary (spawning biomass varied from 2,000 to 25,000 t, with timing protracted over at least 100 days); (2) courtship and spawning behavior is complex, and includes lekking, sound production, and vertical rituals; (3) large fish in good condition are necessary to large egg potential because fecundity increases exponentially with fish size-total egg potential varied considerably from year to year with spawning abundance, age changes, and mean liver condition in spawning females; (4) retention of early life stages did not explain local recruitment and rankings of annual densities of eggs, larvae and juveniles did not match with local recruitment during three years of study; (5) dispersal of early life stages, juveniles, and adults was density-dependent; (6) individual adults homed to the same spawnAuthorship assigned alphabetically after senior author. 198 Rose et al.-Rebuilding Atlantic Cod ing ground in sequential years, but others strayed; (7) egg potential was correlated with the return of adults to the spawning ground 4-5 years later (r 2 = 0.33, d.f. 3), and with recruitment to the full stock area (NAFO subdivision 3Ps) (r 2 = 0.96, d.f. 5), with only weak compensation in survival at low stock size; (8) fishing on spawning aggregations may harm reproductive potential; and (9) seasonal fisheries influence fishing mortality, commercial yield, and value. Management implications are discussed.

Seasonal spawning and wind‐regulated retention‐dispersal of early life stage Atlantic cod (Gadus morhua) in a Newfoundland fjord

“…Lawson and Rose (2000) found female cod in spawning condition as late as November in Placentia Bay, with a late peak in egg potential evident in ichthyoplankton surveys (Bradbury et al. , 2000; Rose et al. , 2008).…”

“…, 2007). Conversely, dispersal of eggs and larvae from inshore spawning grounds may help counter density‐dependent mortality resulting from food competition and predation, or lead to increased survival in what are undoubtedly highly variable environments (Economou, 1991; Rose et al. , 2008).…”

Acoustic markers of Atlantic cod (Gadus morhua) spawning in coastal Newfoundland

“…Very few studies have simultaneously described distributions of spawning adults and resultant eggs and larvae with resultant links made between the life stages (see Rose et al, 2008). Egg and larval surveys in conjunction with temperature dependent development models can provide estimates of spawning times and locations but are restricted by assumptions and uncertainties about drift patterns (Pepin and Helbig, 1997).…”

“…Knowing when and where harvested fish stocks spawn is an essential component of spatial and ecosystem-based fisheries management (Auster and Shackell, 2000;Rose et al, 2008;Sadovy de Mitcheson et al, 2008). This knowledge is important not only to stock assessment, recruitment studies and surveys, but also for management as spawning areas are often closed or limited to various types of fishing.…”

Fish spawning aggregations: where well‐placed management actions can yield big benefits for fisheries and conservation

“…; Rose et al . ). This occurs via disruptions of complex courtship rituals and mate encounter rates, impairment of visual or auditory communication, alterations of operational sex ratios and social structure during mating (Rowe and Hutchings ; Rowe et al .…”