The only retailer who passed the tuna report? It's Aldi.

Is it safe to say many grocery retailers do not know how tuna arrived at their stores? That is a tough call. The environmental nonprofit Greenpeace attempted to get more transparency with its second "High Cost of Cheap Tuna" report, but in many cases the information was incomplete.

Greenpeace asked retailers questions including: Do they require vessels to comply with international safety standards? Are vessel crews provided with adequate rest, nutrition and potable water at no cost? Do vessels spend a maximum three consecutive months at sea? Sixteen grocery chains were surveyed and some did not provide all of the information that was required. Therefore, only one retailer received a passing grade … and it is not something to write home about.

Aldi scored a D rating (62%) while Ahold Delhaize (55%), Whole Foods Market (50%), Hy-Vee (50%), Target (48%), Walmart (44%), Sprouts (40%), Albertsons (36%), Giant Eagle (31%), Kroger (27%), Costco (27%), H-E-B (24%), Publix (19%), Wegmans (17%), and Meijer (16%) all failed. It is important to point out that incomplete or missing information counted against the retailer. In those cases, researchers used information that was publicly available.

The scores were weighted with human rights and labor protections accounting for 25% of the overall score, followed by tuna procurement policy, traceability, and current sourcing (20% each), advocacy and initiatives (10%), and customer education and labeling (5%). A total of 14 of the stores did not respond to the question about requiring vessels to provide adequate access to drinking water. Albertsons and Hy-Vee said yes to vessel safety, rest, nutrition and potable water, while Whole Foods indicated a commitment to a maximum of three months at sea.

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"The thinking here was that while it's important for retailers to engage in advocacy, which means advocating for better regulations at the national level or even at the international level, the focus of the change that we want them to make is within their own supply chains," Greenpeace Senior Oceans Campaigner Mallika Talwar, the report’s lead author, said. "Often the easiest thing to do is sign a letter asking someone else to change regulations, but that's not enough. We want them to take responsibility for their own supply chains, and the sale of their tuna properly."

Talwar urged U.S. retailers selling tuna to enhance their transparency efforts for their own supply chains and to commit to phasing out sourcing from tuna that has undergone transshipment at sea. Though many of the retailers claim they can trace their tuna right back to the supply vessels, in reality, continued opacity in tuna supply chains is allowing obscuring of labor rights and environment issues, according to Talwar.

Related:Whole Foods tuna policy raises the bar

Retailers, however, do face challenges when it comes to tuna sources, and most receive pushback when it comes to requesting working conditions outlined by Greenpeace. The ILO Convention 188 sets international standards for safety, food, accommodation, medical care, employment practices, insurance, and liability on board fishing vessels and at sea. Some countries do not follow the ILO Convention 188.