Cranial allometry of the Pacific albacore tuna, Thunnus alalunga and comparisons with three other species of Scombridae: an archaeological study

Modern specimens (N = 165) of albacore, Thunnus alalunga , were collected and 18 measurements made on cranial bones and an element of the caudal peduncle. Allometric equations were calculated to facilitate the reconstruction of live fork length from archaeological bones. Modern fisheries trawl data of albacore, bigeye tuna ( Thunnus obesus ), yellowfin tuna ( Thunnus albacares ), and skipjack tuna ( Katsuwonus pelamis ) provided data for equations linking live fork length to body weight for each species. Examination of power curve fits between bone dimension and fork length for 12 unrelated species showed that most conform to a single growth curve, with specialised small-mouthed browsing species as outliers. The curves of three species within one family were effectively co-linear. Since the cranial anatomy of different species of scombrids is notoriously difficult to identify to species, it was hypothesised that the allometric curve for albacore might therefore be suitable for estimating fork length from archaeological bones of the three other species. Scombrid bones from four archaeological sites (Te Ana Pua, Fa’ahia, Hane and Motupore) were measured and live fork lengths estimated. Size-frequency histograms showed ancient catches of the first three were dominated by skipjack, with very few yellowfin and albacore. By contrast, at Motupore, most fish were a larger species, probably yellowfin. Total live body weight was estimated and found to be similar at each site (265 to 374 kg). When meat weights were calculated and nutrient composition evaluated, the overall MNR was found to be 60:38:2. The slightly elevated value of carbohydrate is due to glycogen reserves in tuna white muscle.