Spatial distribution of spawning groupers on a Caribbean reef from an autonomous surface platform

Abstract

Many commercially important groupers (Epinephelidae) form fish spawning aggregations (FSA) at specific sites where the spawning stock is concentrated to spawn within a couple of months each year. The concentrated nature and short duration of these FSAs render these species susceptible to fishing pressure leading to their disappearance or decrease in the number of spawning fish. As a result of directed fishing during FSAs many large-bodied groupers are now International Union for Conservation of Nature (IUCN) Red-listed. Puerto Rico within the US Caribbean is where protective measures have been designated for the recovery of grouper species that aggregate to spawn, in particular the threatened (Endangered Species Act) Nassau grouper (Epinephelus striatus) and sustainability of the red hind (Epinephelus guttatus). The regulations at three marine managed areas (MMAs) off the west coast of Puerto Rico, have been focused on reproductive seasons, through seasonal closures. However, these management zone boundaries may fail to fully encompass fish migration paths and temporal variability in FSAs, exposing threatened species like the Nassau grouper to incidental fishing and poaching. In addition to traditional methods used to study FSAs, passive acoustics represent a relatively new approach to assess the presence and spatio-temporal distribution of aggregating species. Sound production is common among many fishes, including the Nassau and red hind groupers, and is most often associated with courtship and spawning behavior. In this study, we present the results from the deployment of an autonomous surface vehicle equipped with a passive acoustic monitoring system along the insular shelf break that surveyed the MMAs during their peak spawning season. Our observations suggest that known FSA sites are critical habitat for both species and the existence of potential, previously unknown FSAs for multiple grouper species as well, highlighting the importance of spatial and temporal expansion of existing regulations.