Scad are small, schooling marine fish belonging to the Carangidae family, which also includes jacks and pompanos. They have streamlined bodies and deeply forked tails. Scad play a significant role in various oceanic environments globally, impacting marine food webs and human economies.
Geographic Distribution and Habitat
Scad inhabit tropical and subtropical waters worldwide, including the Atlantic, Indian, and Pacific Oceans. They are found in coastal and pelagic zones, forming large schools near shore or in open waters.
For instance, the mackerel scad, Decapterus macarellus, is circumglobal, occurring from Nova Scotia to Brazil in the western Atlantic and across the Indian and eastern Pacific Oceans. Yellowtail scad, Atule mate, are widespread throughout the Indo-Pacific, from East Africa to Hawaii. These fish congregate around islands, bays, and coral reefs. While occasionally observed near the surface, they are caught at depths ranging from 40 to 200 meters.
Ecological Role in Marine Ecosystems
Scad serve an important role as “forage fish” within marine food webs, transferring energy from lower to higher trophic levels. Their diet consists of zooplankton, small crustaceans, and fish larvae, with larger adult scad also preying on small fish.
This position in the food chain makes them a primary food source for diverse marine predators. Larger fish like tuna, mackerel, snapper, grouper, barracuda, and sailfish depend on scad. Marine mammals such as dolphins and various seabirds also rely on scad populations. The availability of scad directly influences the well-being of these predator populations.
Commercial Importance and Fishing Pressure
Scad are extensively targeted for various uses, driving commercial fishing. Scad are consumed, available fresh, dried, canned, or prepared by frying, boiling, and steaming.
They also serve as a widely used baitfish in larger commercial and recreational fisheries, particularly for species like tuna, mackerel, and snapper. Furthermore, scad are processed into fishmeal and fish oil, used in aquaculture feeds and as nutritional supplements.
Primary fishing methods include purse seines, trawls, gillnets, and beach seines for large-scale harvesting of their schooling aggregations. This high demand creates considerable pressure on scad populations globally.
Population Status and Conservation Concerns
The status of scad populations varies, with some stocks experiencing considerable exploitation while others remain more stable. Despite many individual scad species, such as mackerel scad and yellowtail scad, being listed as “Least Concern” by the IUCN, approximately 90 percent of global marine fish stocks are either fully exploited or overfished.
Overfishing is the primary threat to scad populations, as fish are removed faster than they can reproduce, leading to declines. Beyond direct fishing pressure, scad populations face other environmental challenges. Climate change impacts water temperatures and the availability of their food sources, while habitat degradation and pollution compromise their marine environments.
To promote sustainable scad populations, various fishery management strategies are used. These measures include implementing catch quotas, establishing gear restrictions, enacting seasonal closures, and setting annual catch limits to prevent overfishing and support stock rebuilding.