Assessing fish stock status is always challenging, but this is especially true for reef fish without catch or effort data. A promising approach is to combine length measurements with life history parameters, using the LBSPR or LIME assessment frameworks. Together with the REEF Grouper Moon Project and Cayman Islands DOE scientists, we use diver-operated laser calipers and stereo cameras to obtain lengths from Nassau Grouper spawning aggregations in the Cayman Islands.

Pulse recruitment of Cayman Islands Nassau Grouper

We used 17 years of laser caliper length data in an assessment model to show that biomass of Little Cayman Nassau Grouper recovered largely thanks to one strong year class from 2011 spawning. Length distributions were bimodal in 2017-2019 on two islands, Little Cayman and nearby Cayman Brac, which suggests that a large recruitment pulse occurred in 2011 on both islands. Our study demonstrates that collecting time-series of in situ length data is an effective method for monitoring protected fish spawning aggregations and is especially promising for situations where catch, effort, and invasive length data are unavailable.

Stock BC, Heppell SA, Waterhouse L, Dove IC, Pattengill-Semmens CV, McCoy MC, Bush PG, Ebanks-Petrie G, and Semmens BX. Pulse recruitment and recovery of Cayman Islands Nassau Grouper (Epinephelus striatus) spawning aggregations revealed by in situ length-frequency data. ICES Journal of Marine Science. Paper, code + data.