Efficacy of an established marine protected area at sustaining a queen conch Lobatus gigas population during three decades of monitoring

Abstract

Marine Protected Areas (MPAs) are designed to conserve and preserve the ecosystems and cultural resources of the ocean. In theory, protected populations flourish, replenish adjacent regions, and are self-sustaining. However, describing the efficacy of MPAs requires long-term monitoring. Queen conch Lobatus gigas are iconic Caribbean denizens with populations that have been decimated by overfishing and are slow to rebound due to density-dependent breeding. The Exuma Cays Land and Sea Park (ECLSP) is a well-enforced, no-take, old, and large MPA. Surveys in 1994, 2011, and 2016 were used to track changes in the abundance, size, and age structure of conch within the park. Statistical models suggested that abundances of adults in 50 km of repeated towed-observer surveys had declined by 71% in 2016 relative to 2011. Further, the remaining conch populations were associated with tidal channels, and these model results agreed with independent observations in 40 km of expanded survey area. Measurements of shell lip thickness, an estimator of relative age, showed an increase relative to 1994 with the greatest effect in 2016, indicating senescence. The ECLSP population appears to be slowly dying of old age, and an early life history process has been altered. Upstream populations have been heavily fished while habitats within the park remain productive, suggesting that low local retention and a lack of exogenous larval sources are driving the decline. A network of MPAs encompassing the entire life cycle and dispersal envelope of targeted organisms is needed for proper conch conservation. Surveys focused on tidal channels could locate candidate upstream populations of conch.

Declining size of adults and juvenile harvest threatens sustainability of a tropical gastropod, Lobatus gigas, fishery

“…Given the heavy reliance on RZs to the overall management of conch in Belize and elsewhere, it is critical to quantify the net spillover to the surrounding fishing grounds (Acosta, ; Hernandez‐Lamb et al, ; Singh‐Renton et al, ; Tewfik & Béné, ). Such a strategy should also strive for a RZ network that includes the entire life cycle (Kough et al, ) and associated components of the fishery for conch (Figure ).…”

“…Therefore, as conchs age, the volume within the shell, regardless of maximum SL attained, decreases (Randall, ), resulting in old conchs (lip thickness, LT > 22 mm) having slight decreases in overall soft tissue mass and gonad mass, indicating some decrease in fecundity but no loss in reproductive capability when compared with younger adult conchs of similar SL (Stoner, Mueller, et al, c). This indicates that overall fecundity is mostly a function of size (maximum SL achieved as juveniles) at onset of lip formation, but also age (relative shell volume), and suggests that thick‐lipped small SL phenotype (‘samba’) queen conchs have smaller tissue and gonads and therefore lower fecundity (Kough, Cronin, Skubel, Belak, & Stoner, ; Stoner, Mueller, et al, ). In very old conchs of any size the rate of external bio‐erosion of the shell, varying depending on the local environment, may outpace the growth of the interior areas of the shell, resulting in a reduced SL while making LT an unsatisfactory means of absolute ageing when compared with younger adults (Buckland, ; Stoner & Sandt, ; Tewfik, ; Tewfik, Guzmán, & Hácome, ).…”

Contemporary and emerging fisheries in The Bahamas—Conservation and management challenges, achievements and future directions

“…No‐take marine protected areas (MPAs) have also been a partially effective management strategy for queen conch. The Exuma Cays Land and Sea Park (ECLSP) had historically healthy adult queen conch populations, but repeated surveys have shown that deep‐water populations inside the no‐take MPA are sharply declining and the overall population is ageing with little signs of recruitment (Kough, Cronin, Skubel, Belak, & Stoner, ). However, conch densities inside the ECLSP still surpass those outside the MPA (Stoner et al., ).…”

Shell morphology and color of the subtidal whelk Buccinum undatum exhibit fine‐scaled spatial patterns

“…Clines in species’ phenotypic traits are an important part of ecological and evolutionary studies (Levin, ) and can be extremely useful in quantifying the degree of connectivity among populations and for delineating population boundaries (Jones, Srinivasan, & Almany, ; Kough, Cronin, Skubel, Belak, & Stoner, ; Leis, van Herwerden, & Patterson, ; Woods & Jonasson, ). Geographical patterns in morphology can result from direct environmental control of physiological processes and body shape (Vermeij, ), differential adaptation to variable surroundings (Pinkert, Brandl, & Zeuss, ; Reinecke et al., ), or, alternatively, from random changes in genetically distinct populations (Kimura & Maruyama, ).…”

“…However, there is a noticeable paucity of knowledge on geographical patterns, population connectivity, and within‐species diversity in marine species (Conover, Clarke, Munch, & Wagner, ), particularly in deep sea (>200 m depth) habitats (Mengerink et al., ; Taylor & Roterman, ) but also in shallower, coastal seas. These coastal zones are home to many commercially harvested gastropods, for which spatial management and conservation strategies are hampered by a scarcity of data on population processes (Jones et al., ; Kough et al., ; Leis et al., ; Machkour‐M'Rabet, Cruz‐Medina, García‐De León, De Jesús‐Navarrete, & Hénaut, ; Woods & Jonasson, ). Moreover, marine molluscs with direct development (e.g.…”