Abundance and population structure of queen conch inside and outside a marine protected area: repeat surveys show significant declines

Abstract

Effectiveness of a marine protected area (MPA) in supporting fisheries productivity depends upon replenishment patterns, both in supplying recruits to surrounding fished areas and having a sustainable spawning stock in the MPA. Surveys for queen conch Strombus gigas were made in 2011 at 2 locations in the Exuma Cays, The Bahamas, for direct comparison with surveys conducted during the early 1990s at Warderick Wells (WW) near the center of the Exuma Cays Land and Sea Park (ECLSP) and at a fished site near Lee Stocking Island (LSI). There was no change in adult conch density and abundance in the shallow bank environment at LSI where numbers were already low in 1991, but numbers declined 91% in the deeper shelf waters. At WW, the adult population declined 69% on the bank and 6% on the island shelf. Unlike observations made in the 1990s, queen conch reproductive behavior near LSI is now rare. Average age of adult conch (indicated by shell thickness) at LSI decreased significantly during the 20 yr period between surveys, while average age increased at WW and juvenile abundance decreased. These results show that the LSI population is being overfished and the WW population is senescing because of low recruitment. In 2011, the ECLSP continued to be an important source of larvae for downstream populations because of abundant spawners in the shelf environment. However, it is clear that the reserve is not self-sustaining for queen conch, and sustainable fishing in the Exuma Cays will depend upon a network of MPAs along with other management measures to reduce fishing mortality. KEY WORDS: Marine protected area · Population structure · Reproduction · Queen conch · Bahamas Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 460: [101][102][103][104][105][106][107][108][109][110][111][112][113][114] 2012 lacking, a large amount of literature has accumulated discussing reserve location and size and the role of MPA networks in the context of population connectivity, stock replenishment, and fisheries management (Lubchenco et al. 2003, Jones et al. 2007, Kininmonth et al. 2011.The efficacy of an MPA for both preservation of a stock and contributions to surrounding fisheries will depend upon either the self-sustaining capacity of the population within the MPA or recruitment from outside. Despite considerable optimism about the role of MPAs as an important tool in fisheries management, the limitations of MPA design and the importance of broader impacts outside the reserves themselves have become clear (Allison et al. 1998, Gaines et al. 2003, Mora et al. 2006, Botsford et al. 2009). Botsford et al. (2001) pointed out a decade ago that the reserve areas likely to be implemented by local governments may not be large enough to sustain natural communities unless fishing and other deleterious effects outside the reserves are limited. Stochastic processes associated with larval transport and population processes including recruitment, along with the human component of fisheries m...

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

“…The Exuma Cays Land and Sea Park (ECLSP) is an appropriate MPA due to its age, size, and regular enforcement. Further, as the ECLSP conch population has been studied for decades, our study is supported by a long history of work, and it has been suggested that the park population is in senescence (Stoner et al 2012c). Here, our goal was to examine how the abundance, age, and size structure of the conch population in the ECLSP changed during surveys in 1994, 2011, and 2016.…”

“…1C) within the ECLSP. The 2016 data (tows and measurements) were collected during late May when adult conch were actively mating (Aldana Aranda et al 2014), and thus captured similar environmental and ecological conditions as previous surveys (Stoner & Ray 1996, Stoner et al 2012c. Following previous protocols (Stoner & Ray 1996, Stoner et al 2012c, an observer was towed behind a skiff (~4 km h −1…”

Maturation and age in queen conch (Strombus gigas): Urgent need for changes in harvest criteria

“…Earlier studies have shown that spawning behavior in the abalone Haliotis laevigata parallels histological maturity (Wells and Mulvay, 1995); new observations on egg-laying frequency and actual fecundity by SL and LT criteria would be particularly useful in evaluating reproductive capacity of queen conch. This will be especially critical in light of increasing numbers of small phenotype adults observed in heavily fished populations (Stoner et al, 2012a), but density-dependent oogenesis observed in strombids (Appeldoorn, 1988b) and density-dependent mating behavior in queen conch (Stoner et al, 2012b) will complicate any analysis of reproductive output.…”

“…(9.5 mm) are required for harvest (Theile, 2005). Despite attempts to manage the queen conch fisheries, the species continues to be listed in Appendix II of the Convention on International Trade in Endangered Species (CITES) (Daves and Fields, 2004), and numbers continue to decline throughout the geographic range because of ever-increasing fishing pressure (Bell et al, 2005;Posada et al, 2007;Stoner et al, 2012a).…”

Redrawing the boundaries: planning and governance of a marine protected area—the case of the Exuma Cays Land and Sea Park

“…This implies that the park's role in protecting marine biodiversity depends on the protection of other near-marine areas (Chiappone and Sealey 2000), and that a single MPA does not ensure marine metapopulation. Although the ECLSP produces large number of conch eggs and larvae, it is not large enough to retain them, and northwest marine currents carry them out of the park (Stoner et al 2012).…”