Banggai cardinalfish (Pterapogon kauderni) populations (stocks) around Banggai Island, a geometric and classical morphometric approach

Background. The identification and characterisation of appropriate management units (stocks) is important as a basis for responsible fisheries management as well as conservation of within species biodiversity. The Banggai cardinalfish Pterapogon kauderni (F.P. Koumans,1933), a mouthbrooding apogonid with Endangered status (IUCN Red List) has been shown to have a high level of genetic population structure across the endemic distribution in the Banggai Archipelago. With a life-cycle making recovery frrm extirpation extremely unlikely, this indicates a need to conserve each reproductively isolated population (stock), in particular to support zonation of Banggai Island in the context of the proposed district marine protected area. Genetic and morphological variations are often but not always related, and ideally both should be used in stock identification. However there were no data on classical or geometric morphometric characteristics of P. kauderni populations. Methods. Adult P. kauderni for classical and geometric morphometric analyses were collected randomly at six sites on Banggai Island (31-34 adult fish/site, total 193). Eleven morphometric parameters were measured and 10 dimensionless ratios were compared using the ANOVA function in Microsoft Excel 2007. A landmark set for P. kauderni was developed. Each specimen was photographed, digitised (tps.dig and tps.util). Characteristics of the six populations were analysed using Canonical Variate Analysis (CVA) and Discriminant Function Analysis (DFA) in MorphoJ geometric morphometric software to identify significant between-site variation. The results were compared with genetic, geophysical, bio-ecological and socio-economic data to determine meaningful stocks or management units. Results. Except for one site pair (Monsongan and Tinakin Laut) we found significant or highly significant differences between sites (sub-populations) in morphometric characteristics, as well as from the CVA and DFA results. The greatest morphometric difference was between sub-populations at the north (Popisi) and southeast (Matanga) extremities of the Banggai Island P. kauderni distribution. The Popisi population was characterised by short/high head shape, Matanga by a more hydrodynamic shape (elongated with a more pointed head). The findings were consonant with genetic study results. We propose a population model with four closed populations and one metapopulation resulting in five P. kauderni stocks around Banggai Island. Discussion. Observed patterns of morphometric variation could be related to geographical spread (radiation or North-South gradient), habitat-driven selection or growth patterns, stochastic events, or a combination. Such fine-scale characterisation calls for intra-species conservation, with implications for the management of this restricted range ornamental fish around Banggai Island and throughout the P. kauderni endemic distribution.