The recent resurrection of a Tridacna maxima sensu Rosewater (1965) ecotype as a distinct species, Tridacna noae (Röding, 1798), has raised concerns that inadvertent confusion of the two species in the past may have led to overestimates of T.maxima densities and errors in determining demographic parameters. To assess the potential impacts of such a scenario, this study examined the population demographics of T. noae within the center of its geographic distribution in the Kavieng lagoonal system of New Ireland Province, Papua New Guinea. The study found that 42% of the T. maxima sensu Rosewater population could be delineated as T. noae, with T. noae being the most abundant giant clam species at 7 of the 20 study sites. Past confusion of the two species is likely to be of the greatest concern on reef sites with high or medium levels of exposure to oceanic influences where T. maxima (2.08 ± 0.41 per 400 m2, 1.86 ± 0.59 per 400 m2, respectively) and T. noae (2.06 ± 0.36 per 400 m2, 1.25 ± 0.28 per 400 m2, respectively) densities were similar (P > 0.05). In analyzing size (shell length) frequency distributions, it was determined that the T. noae population had a larger mean size (206 ± 6 mm) than that of T. maxima (161 ±6 mm, P < 0.001). Thus, in areas where the two species have overlapping distributions and fisheries regulations are based on size, reassessment of T. maxima stocks should be considered a priority given the high frequency at which the larger T. noae may comprise historical populations of T. maxima sensu Rosewater.
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Vol. 34 • No. 2