Goliath Grouper Research in PHMR

A recent study was carried out at TIDE by Science Director, James Foley, and Research Assistant, Marty Alvarez, to determine the current status of Goliath groupers in Port Honduras Marine Reserve (PHMR), Toledo.  Data from 2014 was compared with studies conducted by Rachel Graham in 2007-2010 to determine impacts of fishing on Goliath grouper, and to inform national policy on this IUCN listed critically endangered species.


Goliath groupers are the largest of all grouper species in the Caribbean, and have been known to live up to 37 years. They play an important part in maintaining the health of a reef as they predate and balance populations of smaller herbivorous and predatory fish. Also, it is possible larger adults sometimes consume invasive lionfish, highlighting their importance as a potential natural control against lionfish. Being top predators, their survival relies upon healthy smaller fish populations, and their presence therefore indicates a healthy ecosystem.

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PHMR is one of only three known nursery sites for Goliath groupers in the region, the other two being in Florida and Brazil where full bans are in place on fishing of the species. Juveniles are thought to remain in nurseries for 5-6 years, so although there is a relatively high abundance of Goliath groupers in PHMR, populations are depleting throughout its adult range throughout the Mesoamerican Barrier Reef, making it essential to protect their nurseries.

The study determined the size range of catch from PHMR by measuring lengths and weights of market catch in Punta Gorda. Results found that although adults can grow up to three metres in length, the majority of fish landed in Punta Gorda measured between 50-95cm. This means that 100% of the catch sampled from PHMR in 2014 had not yet reached sexual maturity, which could have implications on Goliath grouper populations in the surrounding area; a genetic study by Rachael Graham found Goliath groupers can migrate as far as Mexico after originating from PHMR.

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Foley and Alvarez were also able to compare changes in the average size of Goliath groupers over time by comparing their results with previous data collected by Rachel Graham between 2007-2010. Results found the average catch size has not changed significantly over time but confirmed that only juveniles are being caught.

As the population of Goliath groupers in PHMR is skewed towards juvenile fish, the Belize Fisheries Department is willing to set a size limit regulation of catch from the results of this study. Foley and Alvarez recommend a 60 - 70cm size limit. While this may receive criticism as Goliath groupers mature at around one-metre in length, it would also be more likely to be complied with by fishers. Due to the high number of juveniles, a one-metre catch size would effectively be a ban on catching Goliath grouper in the reserve and would therefore likely push Goliath grouper commercial activity underground. With a smaller size limit, 75% of Goliath groupers could be protected during their juvenile phase, leaving 25% of the population for local fishers to continue harvesting for their livelihoods.

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 It is hoped that by reducing fishing pressure, Goliath groupers will increase in maturity and abundance and reach spawning age within the next 5 – 10 years.  By increasing the population of juveniles, more individuals can migrate to other areas around Belize and Mexico.

 

 

 

 

PHMR is one of only three known nursery sites for Goliath groupers.

 

 

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It is hoped that by reducing fishing pressure, Goliath groupers will increase in maturity and abundance.

Date: August 6, 2014 Author: clarebaranowski
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