Ferocious, blood thirsty schools of yellow-eyed predators of the pelagic have hit local New Jersey estuaries and coastal rivers in mass the past few springs. Slashing through schools of baitfish in localized feeding frenzies and leaving trails of dead and mangled prey in their wake, bluefish of the sizes we are seeing in the spring can consume up to twice their weight each day, sometimes even regurgitating so they can feast again!
The magnitude of this recent spring slammer fishery has some anglers wondering where all these big fish come from and what they’re doing in the bounds of inshore waters.
Bluefish are a highly migratory pelagic species that typically travel in schools of similar sized individuals and undergo extensive migrations that are likely environmentally induced. They roam western Atlantic waters and are seasonally abundant from as far north as Nova Scotia to the Gulf of Mexico, as well as along the South America coast off Brazil and Argentina; however, they are rarely found in warm tropical waters of south Florida and the Caribbean.
On the east coast of the US, it is believed that bluefish generally overwinter off the southeastern coast and subsequently migrate to northern waters in spring. For the most part, these fish typically return south again sometime in the fall. However, there is also evidence that there may be different migration patterns among bluefish age groups. Scientists now believe that, while younger fish largely move north to south and south to north, older fish may actually follow an onshore-offshore movement pattern, particularly in the mid-Atlantic region.
Bluefish are oceanic spawners. They aggregate offshore in fairly deep continental shelf waters to reproduce. Early research on bluefish allowed scientists to establish that spawning occurs when water temperatures are between about 64 to 77 degrees, with optimum temperatures for spawning in the 70s. The results of these studies also led scientists to initially hypothesize that bluefish have multiple, but distinct, spawning areas and spawning seasons along the east coast. For example, in the south Atlantic researchers verified that spawning occurs offshore near the edge of the Gulf Stream from southern North Carolina, south of Cape Hatteras to Cape Canaveral, Florida in spring (March through May).
In the Mid-Atlantic/southern New England region a second spawning season was documented to occur from Cape Cod, Massachusetts to Cape Hatteras, North Carolina on the mid-continental shelf in summer (June through August) with peak activity typically in July. In addition, another minor spawning season was also documented off the coasts of Georgia and northern Florida in fall (September to November).
More recent studies confirm that bluefish are indeed multiple spawners and some scientists have even speculated that they may actually spawn continuously from about March to September with spawning beginning off the southeastern coast in spring, continuing during their migration to the mid-Atlantic and ending in southern New England waters in the late summer/early fall. However, uncertainty persists among fishery scientists as to whether the spawning period is truly continuous or whether there is a lull in reproduction between the spring and summer spawning periods.
In any event, it now seems apparent that each year bluefish spawn over a prolonged period and produce multiple larval groups at multiple locations along the east coast of the US.
Early Stages of Life
The seasonal migrations of bluefish, along with their spawning behavior, delivers juvenile bluefish to nursery habitats throughout the east coast. For example, after they spawn in the south Atlantic during the spring, their larvae are generally moved inshore by prevailing currents where they begin to develop into small juveniles. These young fish will subsequently spend most of the summer in nearshore and estuarine habitats.
Prevailing oceanographic circulation also transport some of the spring-spawned larvae north into the Mid-Atlantic. As waters warm and these larvae develop into juveniles, they will subsequently move inshore in early to mid-June to spend their first summer in the bays and estuaries of the mid-Atlantic region.
In late summer or early fall, juvenile bluefish spawned in the mid-Atlantic and southern New England also make their way into nearshore ocean habitats or enter estuaries in that region. Scientists have found that this inshore arrival of juvenile bluefish usually happens as a sudden pulse and the actual timing varies from year to year as a result of environmental conditions, including increased daylight and water temperatures corresponding to longer days.
While inshore, young bluefish can grow up to 10 inches in their first year of life. However, maximum size varies depending on when they were spawned. Since spring-spawned individuals have a longer growing season, they may be slightly larger than summer spawned bluefish at the onset of the fall migration.
As previously discussed, scientists have speculated that some of the northern contingent of adult bluefish, especially larger individuals, may forego a southern migration in fall and simply move offshore to overwinter along the edge of the outer continental shelf.
In the spring, these big blues may be hitting the coast in mass to feast before eventually moving back offshore in and around the mid-Atlantic and southern New England region to spawn. This inshore movement is likely spurred on by favorable environmental conditions including longer days stimulating warmer temperatures in shallow coastal waters and plentiful food availability as schools of baitfish also become stimulated by the same environmental conditions.
The recent spring arrival of schools of slammer blues that we have been seeing seem to match up with these circumstances. Let’s hope this pattern continues to repeat itself in the form of another solid run of slammer blues in our local coastal rivers and estuaries.
Start sorting out those old plugs this month, swapping trebles for straight “j” and siwash style hooks, as the spring run of racers should be well on their way for expected arrival.
The author is the Assistant Dean in the Monmouth University School of Science and Director of the Marine and Environmental Biology and Policy Program. A lifelong resident of New Jersey, John has spent his career working on marine and environmental issues affecting the state’s coastal zone. When not at work he can be found fishing or surfing along New Jersey’s northern coast.