August 24, 2018 - Rebecca G AschGrouper Conservation efforts Climate Change

OBIS data reveals that climate change will exacerbate the impact of historical overfishing on an iconic Caribbean reef fish

The Nassau Grouper (Epinephelus striatus) is an endangered fish species whose population has been reduced to a fraction of its historical abundance due to overfishing at spawning aggregation sites. Like many other groupers and snappers, Nassau Groupers solely reproduces during spawning aggregations where hundreds-to-thousands of fish migrate to specific sites to engage in spawning. Since Nassau Grouper spawning aggregations recur each year at predictable times linked to the phase of the moon, they are an easy target for fishermen once the location of an aggregation site has been identified. As a result, many Nassau Grouper spawning aggregation sites have been extirpated throughout the Greater Caribbean region. While some populations are recovering due to conservation, the management of this species has not yet considered how climate change could impact Nassau Grouper.

This topic was explored in a recently published paper appearing in the journal Diversity and Distributions. Here researchers from East Carolina University and the University of Texas at Austin utilized data from OBIS and a database of spawning aggregation sites to generate separate species distribution models for non-spawning adult Nassau Grouper and spawning fishes. While both of these life history stages were affected by temperature and hydrodynamic features, preferred habitat conditions differed by life history stage. In particular, spawning aggregations were characterized by a narrower thermal niche and occurred at cooler temperatures. This suggests that the spawning life stage may form a bottleneck constraining how this species responds to climate change. Indeed, under a business-as-usual climate change scenario, spawning aggregations were projected to experience an 82% decline in available habitat by the end of the 21st century. In contrast, habitats used by non-spawning adult Nassau Grouper were projected to undergo a comparatively smaller 46% decline. Even under the RCP 2.6 climate change scenario, which includes implementation of strong climate change mitigation measures, spawning habitats for Nassau Grouper are projected to decline by 30%. These decreases in habitat availability were accompanied by northward shifts in Nassau Grouper distribution and a shortening of the spawning season.</p>

Overall, this study indicates that many current-day conservation measures meant to protect Nassau Grouper may need to be adjusted to provide adequate future protection for this species. For example, the dates of seasonal closures at spawning aggregation sites will need to be adjusted to account for changes in the seasonality of spawning. Similarly, this paper tentatively identifies a few regions that could serve as climate change refugia for Nassau Grouper, which may deserve to be the focus of future conservation efforts.</p>

Reference: Asch, R.G.; Erisman, B. (2018). Spawning aggregations act as a bottleneck influencing climate change impacts on a critically endangered reef fish. Diversity Distrib. Online first.

Photo credit: Alfredo Barroso Ruiz