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

Alexander Tewfik, Elizabeth A Babcock, Richard S. Appeldoorn, Janet Gibson

Research output: Contribution to journalArticle

Abstract

Queen conch (Lobatus gigas) is a large herbivorous gastropod, found across the Caribbean, which forms the basis of important dive fisheries. Conch have a two-phase shell growth pattern, first in shell length (SL), which ceases well before maturity, followed by growth in shell lip thickness (LT) into maturity. This growth pattern must be considered in determining the ideal size and associated maturity for sustainable harvest. Shell morphology, sex organ development and soft tissue masses indicated that mature adult conchs at Glover's Atoll, Belize, were those with thick shell lips (≥10 mm), eroded shells and heavier soft tissue masses. Therefore, SL-based regulations cannot serve as a proxy for maturity and harvest. The use of inappropriate minimum size limits (SL = 178 mm, 85 g market clean meat mass) has allowed significant juvenile harvest and the fishery appears to have truncated the SL size distribution of conchs with a flared shell lip (i.e. adults) over the last 15 years. The reduced SL observed in lipped conchs may lead to a significant impact on the reproductive success of the population as well as diminished economic yield from the fishery, as smaller adult conchs of the same age have lower gonad and meat weight. We believe this to be the first documentation of a decline in the SL of adult queen conchs, and that the SL-based size limits have contributed to this decline. Refinement of the individual size-based regulations for conch in Belize to LT will probably facilitate local recovery as well as regional harmonization of regulations. Future research in Belize should include movement dynamics of conch in relation to replenishment zone size and spillover as well as the importance of deep-water conch to shallow-water recruitment, which is thought to be limited.

Original languageEnglish (US)
JournalAquatic Conservation: Marine and Freshwater Ecosystems
DOIs
StatePublished - Jan 1 2019

Fingerprint

shell (molluscs)
gastropod
Gastropoda
fishery
fisheries
sustainability
shell
lips
Belize
meat
Lobatus gigas
harvest
atoll
reproductive success
gonads
shallow water
deep water

Keywords

  • Belize
  • coral reef
  • management measures
  • overfishing
  • queen conch
  • seagrass
  • small-scale fisheries

ASJC Scopus subject areas

  • Aquatic Science
  • Ecology
  • Nature and Landscape Conservation

Cite this

Declining size of adults and juvenile harvest threatens sustainability of a tropical gastropod, Lobatus gigas, fishery. / Tewfik, Alexander; Babcock, Elizabeth A; Appeldoorn, Richard S.; Gibson, Janet.

In: Aquatic Conservation: Marine and Freshwater Ecosystems, 01.01.2019.

Research output: Contribution to journalArticle

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abstract = "Queen conch (Lobatus gigas) is a large herbivorous gastropod, found across the Caribbean, which forms the basis of important dive fisheries. Conch have a two-phase shell growth pattern, first in shell length (SL), which ceases well before maturity, followed by growth in shell lip thickness (LT) into maturity. This growth pattern must be considered in determining the ideal size and associated maturity for sustainable harvest. Shell morphology, sex organ development and soft tissue masses indicated that mature adult conchs at Glover's Atoll, Belize, were those with thick shell lips (≥10 mm), eroded shells and heavier soft tissue masses. Therefore, SL-based regulations cannot serve as a proxy for maturity and harvest. The use of inappropriate minimum size limits (SL = 178 mm, 85 g market clean meat mass) has allowed significant juvenile harvest and the fishery appears to have truncated the SL size distribution of conchs with a flared shell lip (i.e. adults) over the last 15 years. The reduced SL observed in lipped conchs may lead to a significant impact on the reproductive success of the population as well as diminished economic yield from the fishery, as smaller adult conchs of the same age have lower gonad and meat weight. We believe this to be the first documentation of a decline in the SL of adult queen conchs, and that the SL-based size limits have contributed to this decline. Refinement of the individual size-based regulations for conch in Belize to LT will probably facilitate local recovery as well as regional harmonization of regulations. Future research in Belize should include movement dynamics of conch in relation to replenishment zone size and spillover as well as the importance of deep-water conch to shallow-water recruitment, which is thought to be limited.",
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