Abstract
Connectivity among subpopulations of organisms is a primary focus in marine ecology and this knowledge is particularly imperative to the development of regulations in the management of fisheries (Cowen et al., 2007). The structure of local populations can be identified using intrinsic markers such as morphological and life history characteristics, as well as genetic markers (Bailey, 1997, Begg and Waldman, 1999). Genetic techniques are limited in that they cannot detect low levels of exchange (Thresher, 1999). Life history, morphological and meristic characteristics have been regularly employed to identify differentiation between local populations and in order to create a robust study it is reccomended that a combination of traits be examined (Begg and Waldman, 1999).
The objective of the present study is to determine the level of connectivity among subpopulations of the flatfish species Peltorhamphus novaezeelandiae in the neighbouring Otago and Southland regions of New Zealand. I endeavoured to determine whether these fish form a single panmictic population over this geographical landscape or, are in fact segregated into discrete sub-populations. Flatfish as a group are an important component in New Zealand’s annual commercial catch particularly in the Otago and Southland regions, yet there is little biological information available on each species including Peltorhamphus novaezeelandiae. Fish from each region were sampled by otter trawl and morphological, stable isotope, stomach content and age determination analyses were conducted. As a result of these analyses I concluded that Peltorhamphus novaezeelandiae exhibit a complex population structure within the Otago and Southland regions of New Zealand. These subpopulations experience connectivity whether it be via the dispersal and recruitment of eggs, larvae or juveniles or through the migration of adults. Subpopulations are subject to enough separation over spatial and temporal scales to enable and maintain significant differences in life history characteristics. It is evident that the population structure of P.novaezeelandiae occurs at smaller spatial scales than is currently recognised by the Quota Management System and it is hoped that the knowledge gained through the completion of this study enables more informed management decisions and the sustainability of this important fish stock.