Age and growth of one of the world's largest carnivorous gastropods, the Florida Horse Conch, Triplofusus giganteus (Kiener, 1840), a target of unregulated, intense harvest.

The Florida Horse Conch, Triplofusus giganteus, one of the largest marine gastropods in the world, has been intensely exploited by shell collectors, curio dealers, and commercial harvest for over a century and is now in decline. Effective management of horse conch populations requires better data on commercial and recreational harvest intensities but also on the species' intrinsic capacity to recover. Here, we use stable oxygen and carbon isotope sclerochronology to investigate the horse conch's life history, including its maximum life span, growth rates, age at first spawning, and number of lifetime spawning seasons. The largest two shells studied (460 and 475 mm linear shell length) grew for 13 and 11 years, respectively. Growth curves for these shells, extrapolated out to the length of the record size shell (606 mm linear shell length) predict a maximum age of just 16 years. Carbon isotopes and field photographs of spawning females suggest that females mature relatively late in life. However, the largest horse conchs remaining in the wild are also smaller and younger than those studied here. Thus, the largest females left in the wild could have few lifetime spawning events. High fecundity can buffer horse conchs from overfishing but only if females reach spawning age and reproductive-age females are protected. Our study highlights the usefulness of stable isotope sclerochronology for characterizing the life histories of molluscan species now too uncommon to study through traditional mark and recapture approaches.

Prehistoric baseline reveals substantial decline of oyster reef condition in a Gulf of Mexico conservation priority area.

The Gulf of Mexico (GoM) is home to the world's largest remaining wild oyster fisheries, but baseline surveys needed to assess habitat condition are recent and may represent an already-shifted reference state. Here, we use prehistoric oysters from archaeological middens to show that oyster size, an indicator of habitat function and population resilience, declined prior to the earliest assessments of reef condition in an area of the GoM previously considered pristine. Stable isotope sclerochronlogy reveals extirpation of colossal oysters occurred through truncated life history and slowed growth. More broadly, our study suggests that management strategies affected by shifting baselines may overestimate resilience and perpetuate practices that risk irreversible decline.