Snapper perished of natural causes

MYSTERY SOLVED: A few of the snapper that washed ashore on Tokerau Beach late last year.

Large number of snapper that washed up on Tokerau Beach late last year died of natural causes according to the Ministry for Primary Industries.

The strong local suspicion at the time was that they had been dumped from a commercial fishing boat.

A spokesman for the ministry said a member of the public had alerted fisheries staff. Approximately 60 snapper washed up on to some eight kilometres of the beach over a three-day period. They were whole and showed no obvious signs of disease. Nor was there evidence of net damage, handling or hook injuries. There had been rough weather in the area over that period.

Samples collected for examination by MPI pathologists and histopathological examination did not reveal anything unusual, but histology showed that the snapper had been suffering a well established systemic bacterial infection, where the bacteria existed in small pockets in the blood vessel walls.

The predominant bacteria were usually "opportunistic" and secondary, invading an already immuno-compromised animal and "finishing it off", but this particular species could be, and in this case appeared to actually be, a primary pathogen.

The ministry said that, according to literature, infection with V. harveyi had been seen before in post-spawn snapper (which these were), and that could have been a factor in rendering them immuno-compromised, quite possibly along with extremely warm water temperatures (or according to one commercial fisherman unseasonably cold water temperatures).

"V. Harveyi exists in high levels in the environment anyway, so this suggests there must be something that is making the snapper more susceptible to it than any other species, which is probably, at least in part, the post-spawning condition [or lack thereof]," the spokesman added.

"It was certainly a natural event that appears to have come to a natural conclusion, and the investigation was closed. However, it will be of note if this phenomenon happens again in the future."