Bluefin tuna caught in the Gulf of Maine are less abundant and much leaner than a decade ago, according to University of New Hampshire scientists.

The premium tuna for Japanese sushi lovers are in poorer condition than in the early 1990s, with slimmer body shapes and steadily declining oil content. High oil content is the tuna's best overall health indicator, and the oil-rich fish fetch the highest prices.

Arriving in late May to fatten up before departing for warmer waters, tuna are primarily caught by small boats. Possible causes for the decline include poor local herring stocks, and purse seine fishing, which can catch entire families, a very disruptive harvest method.

Similar declines have also recently been noted in Canada's Gulf of St. Lawrence.