Stephanie Archer, who will be joining FIU next year, with a neat paper
on Nassau Grouper color phases. Her guest post below.
Nassau grouper (Epinephelus striatus) are iconic throughout the Bahamas and Caribbean and are one of the most easily recognizable species on the region’s reefs. These fish are critically important in the maintenance of healthy reef communities and also support the region’s economy as a draw for dive-related tourism and as a fishery. Nassau grouper are typically solitary, maintaining individual territories on home reefs. But, once or twice a year they congregate in a specific location for the express purpose of spawning. This congregation is called a spawning aggregation or SPAG for short. The fish typically spend from 4-11 days on the aggregation before participating in 1-3 nights of spawning then returning home. Unfortunately for the Nassau grouper, the timing and location of their SPAGs are highly predictable. Because of this predictability and the ease at which Nassau can be caught on SPAGS, the Nassau grouper is now listed as endangered by the IUCN. Fisherman can simply not resist the lure of thousands of large fish all gathered in one place at one time, and once an aggregation has been discovered it does not take long for the spawning population to be wiped out. Aggregations were once between 30,000 and 100,000 fish strong. Today, more than 75% of Nassau grouper SPAGS are thought to be defunct or declining and aggregations considered healthy are rarely larger than a couple thousand fish.
This paper is the result of a long-term study of one of the regions healthiest remaining SPAGs. The Nassau grouper spawning aggregation off of the West end of Little Cayman Island, Cayman Islands, British West Indies has been protected from fishing for the past nine years and supports a spawning population of around 4,000 Nassau grouper. Since 2004 a team of scientists from the Reef Environmental Foundation (REEF), Cayman Islands Department of the Environment, and Oregon State University have been monitoring the behavior of the fish returning to the Little Cayman spawning aggregation. While on the spawning aggregation Nassau grouper exhibit three color patterns they do not display during other times of the year. Changes in color patterns are typically thought to be a means of conveying information between members of a population and changes associated with spawning are often thought to convey information such as health of the potential mate and readiness or willingness to spawn. We used video footage collected on the aggregation to attempt to determine if there was evidence that Nassau grouper use the different color patterns to convey information related to spawning activities. One color pattern often described as bicolor (the fish is extremely dark on top with a completely white belly) has been associated with the act of spawning since Nassau grouper spawning behavior was first described. Our paper showed that the bicolor color pattern is not only associated with the act of spawning but is also used to convey readiness and willingness to spawn in the days leading up to spawning. Additionally we have shown that two color patterns previously assumed to be displayed only by females are actually displayed by fish of both sexes.
The website of the Little Cayman grouper team: http://www.reef.org/groupermoonproject