Abstract

Groupers are among the most important yet vulnerable fishes in the Caribbean and in tropical waters worldwide. Vulnerability comes from their habit of forming spawning aggregations predictable in space and time, yet these same factors make aggregations focal points for both management and assessment. However, in situ assessments are often difficult due to wind and wave conditions and limited resources, especially where multiple spawning sites exist. Passive acoustic recordings using benthic hydrophones offer a potential solution. Groupers are soniferous fishes, and males make specific sounds related to courtship activities. These calls can be distinguished among species. For the red hind at the Abrir la Sierra (ALS) aggregation site off western Puerto Rico, the number and sound level of calls were sufficiently correlated to overall fish density to be able to use sound as a predictor of density, or relative abundance. We address the reliability of this predictive capacity by comparing the relationship between red hind sound production to density at ALS over two years and between ALS and Mona Island, which is separated from ALS by 47 km and depths of 400 to 600 m. Red hind calls were recorded using a bottom-mounted hydrophone while density was measured using diver visual census surveys. Due to low sample size and greater inherent variability, the relationship between sound production and density at Mona Island in 2010 was not statistically significant, but the slope was similar to that observed at ALS in 2012. The relationships between sound production and density at ALS in 2011 and 2012 were both significant, but their slopes differed. In 2012 there was greater sound production at a lower density. Seasonal profiles of sound production during a spawning season are seen as useful predictors of density, but the dynamics of this across years may be variable.

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