Prey body size and anthropogenic resource depression: The decline of prehistoric fishing at Chelechol ra Orrak, Palau

Abstract

Prior investigation at the Chelechol ra Orrak site (3000/1700 -0 BP) in Palau's Rock Islands revealed a decline in fishing and increased reliance on small-bodied, inshore and littoral molluscs, commensurate with evidence for declining foraging efficiency and prey switching that signal potential resource depression. Yet, standard markers for 'overfishing', such as diet-breadth expansion, increased taxonomic richness, and a switch to exploitation of offshore waters, are lacking at the site, undermining the case for anthropogenic resource (exploitation) depression as a cause of the observed patterning.Broad scale climate change similarly fails to account for these shifts. To investigate these conflicting patterns we performed a mean/median size analysis of two parrotfish (Scaridae) taxa, Scarus and Chlorurus, among the most heavily exploited fish at the site. Results indicate that Scarus size remains unchanged through 1500 years of exploitation, while Chlorurus become larger, substantiating previous findings for sustainable resource use at Orrak. With these results in mind, we critically evaluate prey size change as a metric for anthropogenic exploitation depression, noting that size diminution, in particular, may arise epiphenomenally due to multiple causes unrelated to human predation pressure. Results have broader implications for the detection and attribution of resource depression in studies of human paleoecology.

Coastal Subsistence, Maritime Trade, and the Colonization of Small Offshore Islands in Eastern African Prehistory

“…The comparatively higher-intensity exploitation of marine resources in the EIA and potential resulting resource depression might well have played a role in the EIA-MIA economic transition described here, though this hypothesis cannot be addressed without additional research. Such research would clarify the potential for human impacts on nearshore environments during the early phase of island colonization and occupation (e.g., Butler 2001;Giovas et al 2010;Giovas et al 2016;Morrison and Hunt 2007 …”

Reconstructing prehistoric fishing zones in Palau, Micronesia using fish remains: A blind test of inter‐analyst correspondence

“…In a previous publication (Giovas et al . ), we remarked on the absence of evidence for pelagic fishing. Here, a small (5.9% total MNI), but notable, pelagic fishing component is registered because contemporary species checklists (Froese & Pauly ) were used to refine the lamniform identifications to two pelagic‐oceanic shark species, the shortfin mako ( Isurus oxyrinchus ) and the pelagic thresher ( Alopias pelagicus ).…”

“…; Giovas et al . , ). Notably, Analysis B did not record the abrupt appearance of pelagic fishing after 500 calBP in Phase IV.…”

“…At Orrak, where a decline in absolute fish abundance is recorded in later site history, studies show no reductions in fish and mollusc size, suggesting sustainable resource use throughout occupation (Giovas ; Giovas et al . ). The present study was conducted in part to determine if fine‐grained data about fishing areas could be obtained to understand better the historical ecology of Orrak.…”

Pre‐contact fish choice and foraging efficiency at Tula, American Sāmoa

“…We are in agreement with other researchers that direct measurements of elements is preferable (see Lambrides & Weisler for a regional synthesis; see also Giovas et al . for a recent case study). However, in our case and similar studies that rely on re‐analyses of previously published data, it may not be possible to directly measure elements.…”