Cod removal involves extracting cod species from marine ecosystems, primarily through commercial fishing. Cod, such as the Atlantic Cod (Gadus morhua) and Pacific Cod (Gadus macrocephalus), have historically been foundational species in marine food webs and a significant economic resource for coastal communities. Their removal profoundly impacts both ecological balance and human societies.
The History of Cod Fishing and Stock Status
Cod fishing has a long history, dating back centuries, with early methods of salting and drying fish. The North American east coast developed due to abundant cod, with early European fishermen, including the Basques, focusing on the Grand Banks off Newfoundland. Industrial-scale fishing transformed the industry in the 1920s and 1930s with methods like gillnets and draggers, and advancements in fish processing and factory ships that froze catches at sea. These advancements led to a boom in commercial cod catches in the 1950s, increasing fishing capacity.
Intense fishing pressure led to the collapse of major cod stocks, notably the Atlantic Cod fishery on the Grand Banks. By 1968, the cod catch peaked at 810,000 tons, three times the historical maximum before super-trawlers. Overfishing since the 1950s depleted cod stocks faster than replenishment. This led to the Canadian government declaring a moratorium on the Northern Cod fishery in July 1992, as populations fell to about 1% of historical levels, with spawning biomass dropping by 93% from 1.6 million tonnes in 1962 to 72,000-110,000 tonnes in 1992.
Stock assessments gauge cod population health by measuring biomass, recruitment, and fishing mortality. For Atlantic Cod, stocks in areas like the Gulf of Maine and Georges Bank are currently overfished, though management plans aim for population growth. The Southern Gulf of St. Lawrence Atlantic Cod biomass in 2018 was 2.4% of its 1917 level, due to overfishing since 1955. While Canada’s northern cod stock shows signs of recovery, the Gulf of St. Lawrence stock faces a dire situation with high mortality, partly due to gray seal predation. In contrast, Pacific Cod stocks in the Bering Sea and Gulf of Alaska are not overfished, nor are their fishing rates causing overfishing.
Ecological Consequences of Cod Removal
Removing cod from marine ecosystems triggers ecological changes, often through trophic cascades. As a top predator, cod regulate their prey species’ populations. When cod populations decline, their prey, such as forage fish and invertebrates, experience increased abundance.
This shift impacts other species that rely on these prey or compete with cod. For instance, after the collapse of Atlantic Cod, the abundance of its prey, sprat, increased in the Baltic Sea, leading to a decrease in the copepod Pseudocalanus acuspes, which sprat prey on. Similarly, cod population reduction leads to an increase in their predators, such as harp and grey seals, due to reduced competition. These seals exert increased predation pressure on remaining cod, hindering their recovery.
Prey availability influences cod health; when capelin stocks in the Barents Sea collapsed, cod exhibited reduced growth, delayed maturation, and increased cannibalism. Fishing gear for cod fishing impacts marine habitats. Bottom trawling, where heavy nets are dragged across the seafloor, acts like an underwater bulldozer. This damages benthic habitats like coral reefs and seagrass meadows, which are nurseries for marine species and carbon sinks. This destruction eliminates spawning grounds and feeding areas, reduces biodiversity and disrupts the entire food web.
Managing Cod Removal for Sustainability
Effective management of cod removal relies on strategies and policies for sustainable fisheries. Total Allowable Catch (TAC) limits, determined by scientific assessments, set the maximum tonnage of cod that can be harvested periodically. These limits are set to achieve objectives like maintaining healthy stock levels or facilitating stock rebuilding. However, if TACs are set unrealistically high, or if enforcement is lax, fishermen may engage in a “race to fish” to secure their share, undermining conservation.
Seasonal and area closures are another management tool, to protect cod during vulnerable periods, such as spawning, or to safeguard aggregations. For example, an area of the Firth of Clyde in Scotland is closed for eleven weeks annually from February to April to protect spawning cod, as they are susceptible to disturbance and capture then. Such closures aim to allow cod to reproduce successfully before being fished, contributing to stock replenishment.
Gear restrictions contribute to sustainable cod fishing, regulating net mesh sizes and requiring bycatch reduction devices. Larger mesh sizes in trawl nets help reduce the catch of juvenile cod while maintaining the catch of target species. Innovations like the ultra-low-opening trawl (ULOT) net exploit behavioral differences, allowing cod to swim upward and escape while retaining other groundfish like flounder, reducing unwanted cod bycatch.
Marine Protected Areas (MPAs) are areas managed for long-term conservation, where fishing is restricted or prohibited to allow depleted fish stocks and habitats to recover. These areas serve as refuges, protecting spawning grounds and juvenile habitats, leading to increased fish populations that can spill over into surrounding fishing areas. International cooperation through Regional Fisheries Management Organizations (RFMOs) is important for managing shared cod stocks that cross national boundaries. These treaty-based bodies establish binding conservation and management measures, including quotas and technical regulations, for species in international waters.
Despite these efforts, challenges persist. Illegal, unreported, and unregulated (IUU) fishing undermines conservation measures, contributing to overfishing and habitat destruction. IUU fishing accounts for a significant portion of total catches, with illegal catches estimated at 40% of the total for Baltic Sea cod. Climate change impacts cod distribution and productivity, with warming waters influencing spawning grounds and causing shifts in population locations, adding complexity to management. Consumer choices, supported by sustainable seafood certifications like the Marine Stewardship Council (MSC) label, encourage responsible fishing and increase demand for sustainably sourced cod.