Fish
Nassau Grouper
Epinephelus striatus · also called nassau grouper
The Nassau grouper was for centuries the most important food fish on Caribbean reefs. It was also, it turned out, one of the easiest to destroy. Once a year the whole breeding population of an area travels to the same reef corner on the same full moon to spawn — and once fishers knew that, they could take out an entire generation in a few nights. The species is now Critically Endangered.
Overview
Nassau groupers live on coral reefs of the tropical western Atlantic, from Bermuda and Florida through the Bahamas and Caribbean. They reach about 1.2 m and 25 kg, stout-bodied with a large mouth, and can shift rapidly between pale, dark-barred, and near-black colour patterns. They are ambush predators of fish, crabs, lobsters, and octopuses, and a keystone reef hunter.
The spawning aggregations
For a few days around the winter full moons, Nassau groupers migrate — sometimes over 100 km — to a handful of traditional sites at reef promontories and drop-offs, gathering in the thousands, historically the tens of thousands, to spawn.
The collapse
Because the fish concentrate so predictably, fleets could take enormous catches in a few nights, removing breeding adults faster than they could be replaced. The global population has fallen by more than half, and dozens of aggregation sites no longer form — hence the Critically Endangered listing.
Protection and recovery
Many countries, including the United States, the Bahamas, the Cayman Islands, and Belize, have banned or seasonally closed the fishery and protect the remaining aggregations. Well-enforced sites off Little Cayman and in Belize have stabilised or begun recovering, but many historic sites remain empty, and recovery is slow.
Nassau Grouper: common questions
Why did the Nassau grouper become Critically Endangered?
Its own breeding behaviour made it easy to overfish. For most of the year Nassau groupers are spread out across the reef, but once a year they travel, sometimes long distances, to gather in huge numbers at a small number of traditional spawning sites at specific phases of the moon. Fishers learned exactly where and when these aggregations formed and could take thousands of fish in a few nights, year after year, stripping out the breeding adults. Many aggregation sites that once held tens of thousands of groupers now produce none at all, and the global population has more than halved.
What is a spawning aggregation?
It is a temporary mass gathering of fish, at a particular place and time, for the sole purpose of breeding. For the Nassau grouper these form at reef corners and drop-offs around the winter full moons and last only a few days. The fish release eggs and sperm into the water in large synchronised events, and the fertilised eggs drift as plankton before the larvae settle onto reefs weeks later. Aggregations are efficient for the fish but extremely vulnerable to fishing, because the entire local breeding population is concentrated in one small area.
Is the Nassau grouper recovering?
In places. Where spawning aggregations have been given full legal protection and enforcement, most notably a site off Little Cayman in the Cayman Islands and sites in Belize, grouper numbers have stabilised or begun to climb back after years of decline. Elsewhere many aggregations remain gone and are not reforming, and the species overall is still classed as declining. Recovery is slow because the fish grow slowly, mature late, and depend on rebuilding the traditional aggregations, which appears to require enough surviving adults that know the sites.
Can you still fish for Nassau grouper?
In much of its range, no, or only under tight restrictions. The United States prohibits harvest in federal and most state waters, and the Bahamas, Cayman Islands, Belize, and other jurisdictions have imposed bans or closed seasons that cover the spawning period, along with protected areas around aggregation sites. These measures are relatively recent, and enforcement varies, but the direction across the Caribbean has been toward strong protection of a fish that was once the region's most important reef catch.