On a bright, sunny, calm day in the Port Honduras Marine Reserve of southern Belize, a team of TIDE’s community researchers and research intern Miwa Takahashi went fishing for Queen conch. This fieldwork is part of a larger project, led by Science Director James Foley, to ensure the best available science is being used to inform fisheries management in southern Belize.
Abalone Caye - PHMR Ranger Station
Conch fishing is an important livelihood for many fishers in the Toledo District, therefore TIDE’s science team is continually working to improve data, share their findings, and ultimately contribute to better fisheries management.
Queen conch is an endangered species throughout the Caribbean and also a valuable commercial species for many fishers. In the Port Honduras Marine Reserve (PHMR), TIDE’s monitoring activities indicate that up until 2012, the density (individual conchs per hectare) was relatively stable; however since 2012 we have seen declining trends in overall population and in density.
Landings data collected through fisheries-dependent surveys show that the proportion of harvested conch in the large ‘mega-spawner’ size class (≥25 cm shell length) declined from 45% in 2009, to 26% in 2010, 14% in 2011, and just 3% in 2012.
The current regulations on conch harvesting in PHMR consist of a closed season from July 1 through September 30, a minimum legally harvestable shell length of 178 mm (7 inches) or minimum meat weight of 85 g (3 oz), and a ban on use of SCUBA while harvesting. Shell length is used as an indicator for sexual maturity of the conch. Knowing whether a conch has reached sexual maturity is important because it ensures that the species has had time to reproduce before it is harvested.
Community Researcher Jenny Ramirez diving for conchs
Researcher Miwa Takahaski measuring shell length
However, shell length may not be the best indicator for sexual maturity. Data from other areas of the Caribbean suggest that conch lip thickness may be a better indicator for determining sexual maturity. Stoner et al. (2012) determined that male and female queen conch in the Bahamas reached sexual maturity when their shell lips were 9 mm or 12 mm thick, respectively. The proportion of conch caught in PHMR with lip thickness less than 9 mm (and therefore probably juvenile) increased from 30% in 2009 to 90% in 2012, indicating that potentially mature conch are rapidly being fished out.
However, both shell length and the shell length to lip thickness ratio vary at local and regional scales due to differences in diet, water temperature, and water chemistry. Therefore, localized studies that correlate shell length and lip thickness with sexual maturity in Belize are needed. This is precisely the research TIDE is undertaking.
TIDE interns measuring, weighing, and dissecting conch samples at Abalone Caye
The preliminary data are showing some encouraging results: there seems to be a stronger relationship between lip thickness and gonadosomatic index (GSI) than with shell length. GSI is a measure of the ratio of gonad mass to total body mass and it is used as a tool for measuring the sexual maturity of animals.
Data on conch caught in PHMR show that fishers are complying very well with the legal shell length-based size limits. If it is determined that lip thickness serves as a more accurate proxy indicator of conch maturity in PHMR, TIDE will work with local fishers and the Belize Fisheries Department to determine the best way forward for legislation. It within TIDE’s interest to establish the most ecologically and socioeconomically viable recommendations for updating legislation for long term sustainability of conch extraction in PHMR.
At the end of this month, we anticipate to have more data that will help us to make more conclusions. Please stayed tuned in to our Facebook and website as we progress through this important research at TIDE!
For more information about this research, please contact our Science Director James Foley at email@example.com.