Long-term trends in reef fish populations in Bonaire Marine Park

Abstract

Management of reef fish populations requires insight in their resilience to anthropogenic stressors. Studies on temporal variations in reef fish populations and their abundance responses to environmental changes are crucial to the development of ecosystem-based management.  Nineteen years of voluntary fish survey data of reef fish at the west coast of Bonaire Marine Park (Caribbean) were analysed to investigate the effect of environmental changes on local reef fish populations. Various anthropogenic stressors that influence the coral reefs of Bonaire were studied in recent years. This study studies to what extent these stressors and protective management measures can be related to the observed population trends. In addition, reef fish population responses to specific events were analysed. In general fluctuations in sighting frequencies were species-specific and difficult to interpret.  Although some noise in the data couldn’t be filtered out they show an overall negative trend in sighting frequencies in the 155 studied species.. A comparison of the average frequencies between the first five years of this study with the last five years resulted in an over 10% decrease in 64 of the species, while 30 species increased over 10%.  Three large parrotfish species decreased by approximately 50% over time and there were indications of a slight negative trend in mid-sized parrotfish as well. In fishery targets, the most intensive fished group, large to mid-sized groupers, decreased strongly. After the abundance of these groupers decreased to near zero, two species belonging to other fish families started to show signs of sequential overfishing.  It is unclear if larval import will compensate for the loss in reproductive capacity of the species in decline. Recent literature on recruitment distances suggest that the level of larval import is low on isolated islands like Bonaire, resulting in dependence of self recruitement.  Another event with strong effect on population dynamics are the mass mortality events in moray eels. Especially in two Enchelycore species these resulted in sigmoid like trends. The 2008 and 2022 mass mortality events were first noted at the onset of a period of sea water warming, paralleling various reef fish species in the Red Sea. This gives further support to the hypothesis that the current increase in warming events will lead to more frequent mass mortalities.  f.p.bennema@gmail.com