2 Heavy Metal Sampling Programme

Before 1984, MAF Fisheries co-ordinated the collection of tissue samples for heavy metal analysis of commercial fish and shellfish species. This was to provide heavy metal level guidelines for health requirements and for the MAF export certification system. By 1984 most commercial species had been analysed for heavy metals and the formal heavy metal sampling programme was wound down. Total heavy metal levels in several species of commercially important fish have been summarised by Fenaughty et al. (1988).

In 1990, a further forty-eight black cardinalfish (Epigonus telescopus) were sampled from a major commercial fishery off the east coast of the North Island to determine their flesh mercury (Hg) levels. The results from this study have been published in Tracey (1990).

Muscle tissue was taken from the left dorsal side of fish specimens, directly posterior to the operculum, except with skate (Raja spp.), where flesh was taken from the wings, stargazer (Kathetostama giganteum), where flesh was taken from the posterior body, and southern bluefin tuna (Thunnus maccoyi), from which both tail and belly flesh were taken. An additional subcutaneous muscle sample was taken from some orange roughy (Hoplostethus atlanticus).

Mantle, digestive gland, and gonad tissue were sampled from squids; the whole organism was homogenised for shellfish analysis.

Total mercury was analysed by the method of Robertson et al. (1975), with minor modifications (van den Broek et al. 1981). Later samples were generally acid-digested then analysed for Hg using cold-vapour atomic absorption spectrometry along with a reference sample of a known Hg value (Louie et al. 1985). The analytical techniques used for determining cadmium, copper, zinc, and lead concentrations were those of Gorsuch (1959) and Brooks and Rumsey (1974). Selenium levels were analysed by the method of Watkinson (1966). Organochlorine insecticide levels were examined by the technique of Solly and Harrison (1972).

Lengths and weights were not recorded for all samples. In some instances only partial lengths and weights (i.e., of trunked and gutted fish) were recorded, particularly with factory samples. Lengths were measured by the appropriate measurement method (see Appendix).