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

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.

The potential of marginal coastal nursery habitats for the conservation of a culturally important Caribbean marine species

“…All queen conchs who departed the inlet had a predicted syphonal length between 200 and 264 mm, indicating significant growth during the period the individuals remained in the inlet. This is consistent with observations in marine nursery grounds (Boman et al, ; Stoner, Davis, Davis, & Booker, ; Tewfik, Babcock, Appeldoorn, & Gibson, ). The majority of individuals with a lip thickness >5 mm at the time of tagging departed the inlet.…”

“…The majority of individuals with a lip thickness >5 mm at the time of tagging departed the inlet. Siphonal length does not allow for the determination of sexual maturity, which is largely based on lip thickness (Boman et al, ; Tewfik et al, ). However, there is currently no reliable lip thickness growth model available for queen conchs so we were unable to determine whether the individuals who departed the inlet were sexually mature.…”

Impact of the the COVID-19 pandemic on a queen conch (Aliger gigas) fishery in The Bahamas

“…The decreasing size of conch fished throughout the study, even as catch volume declined, suggests serial depletion of large individuals in the fishing grounds. Such intense fishing of juveniles as well as all large adults, risks long-term overfishing and stock depletion ( Tewfik et al, 2019 ).…”

Queen ConchLobatus gigaspopulation estimates and age structure suggest a potential natural refuge on the Cay Sal Bank, The Bahamas

“…Despite the sometimes drastic policy changes, overfished conch populations have been slow to recover, most noticeably in the Florida Keys, where depleted stocks have failed to fully rebound despite a moratorium on the fishery spanning almost three decades (Delgado & Glazer, 2007). Sizebased harvest criteria have shown to be an ineffective technique for long-term sustainability (Tewfik, Babcock, Appeldorn, & Gibson, 2019). Marine protected areas (MPAs) have yielded mixed effects for management.…”