Baker, Nicole

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    Effectiveness of management regulations and updated analysis of population health and trends of Queen Conch, Strombus gigas, in Puerto Rico
    (2014) Baker, Nicole; Appeldoorn, Richard S.; College of Arts and Sciences - Sciences; Garcia, Jorge; Stoner, Allan; Corredor, Jorge; Department of Marine Sciences; Rosario, Héctor
    The queen conch resource continues to support a commercial fishery in Puerto Rico, despite a history of overfishing and low conch densities. The primary goal of this study was to generate density estimates for queen conch off western Puerto Rico using diver-based visual surveys and to assess trends and evaluate hypotheses of management interest using generalized linear mixed models. Density data were supplemented by size/age data. The spawning stock was also calculated and compared to a population (Abrir La Sierra) recently discovered at depths of 38-44m. Forty-six sites were surveyed and data on habitat, depth, estimated length, age class and reproduction were collected. Total density was 14.05/ha (adults = 7.32/ha; juveniles = 6.63/ha). Year (current and past surveys), depth and location were all significant factors influencing adult density. Lower densities of both juvenile and adult conch were observed in 1997 compared to 2006 and 2013. This result alone indicates some level of improvement in the population, though not recently. A location effect compared sites within the US EEZ (greater than 9NM from Puerto Rico) which is closed to fishing versus local waters which are open to fishing. Adult density was higher in shallower water; and regardless of depth or year, adult densities were higher in the EEZ than in local waters, though a greater proportional increase occurred in the EEZ. This suggests that though not statistically significant, the closure of the EEZ is having a positive effect on conch density. Length-frequency diagrams showed an increase in the proportion of adults within the 16-20 cm size class in 2006-2013 pooled relative to 1997. This suggests an effect of the 9inch minimum size limit implemented in 2004. In 1997, juveniles comprised 70% of the population, and no very old adults were found. In 2013, 50% of the population was juveniles, and adults were found in all the age classes, including very old adult. This suggests an overall decrease in fishing mortality. The spawning stock on the broad, shallow shelf was estimated at 172,705 individuals, significantly greater than the 29,092 individuals reported at Abrir La Sierra. Changes in survey methodology are recommended, including but not limited to shortening the transects, not utilizing scooters, standardizing area surveyed, stratifying between depth and habitats, and increasing sites in the EEZ area.