Depth-dependent effects of culling—do mesophotic lionfish populations undermine current management?

Abstract

Invasive lionfish (Pterois volitans and P. miles) have spread widely across the western Atlantic and are recognized as a major threat to native marine biodiversity. Although lionfish inhabit both shallow reefs and mesophotic coral ecosystems (MCEs; reefs from 30 to 150 m depth), the primary management response implemented by many countries has been diver-led culling limited to reefs less than 30 m. However, many reef fish undergo ontogenetic migrations, with the largest and therefore most fecund individuals found at greatest depths. Here, we study lionfish density, body size, maturity and dietary patterns across the depth gradient from the surface down to 85 m on heavily culled reefs around Utila, Honduras. We found lionfish at increased densities, body size and weight on MCEs compared with shallow reefs, with MCEs also containing the greatest proportion of actively spawning females, while shallow reefs contained the greatest proportion of immature lionfish. We then compared lionfish behaviour in response to divers on shallow culled and mesophotic unculled Utilan reefs, and on shallow unculled reefs in Tela Bay, on the Honduran mainland. We found that mesophotic lionfish exhibited high alert distances, consistent with individuals previously exposed to culling despite being below the depth limits of removal. In addition, when examining stomach content, we found that fish were the major component of lionfish diets across the depth gradient. Importantly, our results suggest that despite adjacent shallow culling, MCEs retain substantial lionfish populations that may be disproportionately contributing towards continued lionfish recruitment onto the shallow reefs of Utila, potentially undermining current culling-based management.

Depth-Dependent Structuring of Reef Fish Assemblages From the Shallows to the Rariphotic Zone

“…Lionfish have been widely reported from MCEs in the western Atlantic, including Bermuda (Andradi-Brown et al, 2017b). Although shallow reef culling has been shown to structure lionfish populations across depth (Andradi-Brown et al, 2017a), it seems that, for our study area at least, water temperature might have been a more important driver (Goodbody-Gringley et al, 2019). In Bermuda, shallow inshore reefs experience lower winter temperatures (14-15 • C) compared to the deeper offshore reefs (Coates et al, 2013), and crucially, these lower inshore winter temperatures fall below the thermal threshold (16.1 • C) under which lionfish have been experimentally shown to cease feeding (Kimball et al, 2004).…”

The lionfish Pterois sp. invasion: Has the worst‐case scenario come to pass?

“…Moreover, culling can have unintended consequences: lionfish behaviour can change to make further culling less effective (Côté et al, ) and lionfish recruitment spiked on culled reefs after a hurricane (Smith et al, ). Equally troubling is emerging evidence that the largest and most fecund lionfish might reside on mesophotic reefs at depths beyond the reach of diver‐led culls, which potentially undermines culling efforts by providing a continuous supply of recruits to adjacent, shallow‐water reefs (Andradi‐Brown et al, , ). Overall, the initial enthusiasm for culling as a viable management strategy might be tempered somewhat as new studies uncover some of the nuances and complexities of lionfish behaviour and movement.…”

“…S . S M I T H Côté et al, 2013a;Andradi-Brown et al, 2017a, 2017b, relatively easy to catch, tag and release Akins et al, 2014) and many aspects of their ecology and behaviour are now well understood (Fig. 1).…”

Testing the efficacy of lionfish traps in the northern Gulf of Mexico

“…Over 557,000 km 2 of benthic habitat in western Atlantic invaded range of lionfish lies within mesophotic depths of 40–300 m [24] where lionfish populations densities are often higher than shallower depths [9,25–27]. Deepwater lionfish populations likely disrupt food webs on mesophotic reefs [7] and provide refuge for larger and more fecund individuals [28]. These protected source populations can provide larvae for sink regions [29,30] and undermine shallow-water control efforts [8,28].…”

“…Deepwater lionfish populations likely disrupt food webs on mesophotic reefs [7] and provide refuge for larger and more fecund individuals [28]. These protected source populations can provide larvae for sink regions [29,30] and undermine shallow-water control efforts [8,28]. Population and ecosystem models predict high levels of fishing mortality over a broad geographic range will be necessary to control lionfish populations on a regional scale [15,29,31,32].…”