Young Brothers Ltd.’s interisland cargo volume remained virtually flat during the second quarter as shipments of locally grown agriculture, automobiles and recyclable materials remained weak.

The state’s largest interisland cargo carrier said Tuesday that volume edged up 0.6 percent from the year-earlier period as only two of the six neighbor island ports showed increases. It was the second consecutive quarter that volume rose 0.6 percent.

“While we remain hopeful for a stronger second half, two consecutive quarters of this weak growth in cargo volumes to and from the neighbor islands is consistent with our low volume projection for the year,” Young Bros. Vice President Roy Catalani said in a statement.

The company said agricultural shipments were down in both the second quarter and the first six months of the year, auto shipments declined for the second straight quarter primarily due to reduced volume from rental car agencies, and demand for recyclable materials continued to lag due to depressed prices. Shipments of construction equipment also declined in both the second quarter and the first half of the year.

Young Bros. said air and ground transportation companies utilized more barges for interisland shipping, while shipments of renewable-energy and certain construction materials also grew in the second quarter compared with a year ago.

Young Bros.’ cargo volume has been up marginally in recent years with gains of 1.1 percent in 2015, 0.5 percent in 2014 and 1.5 percent in 2013.

The 116-year-old company signed a contract in June with Louisiana-based Conrad Shipyard to buy four new tugboats for close to $20 million apiece to replace much of its aging fleet. The new tugs are scheduled for delivery in 2018 and 2019.

Young Bros. has nine tugboats — six for towing and three for providing assistance in harbors. The four tugs slated for replacement are 40 to 43 years old. Young Bros. said the new tugs are expected to be useful for 35 years and will lower crew expenses because they will provide faster transit, improve fuel efficiency and reduce downtime and maintenance needs.

In the most recent quarter, Kahului, the largest neighbor island port in terms of volume with more than one-third of the shipments, saw its volume inch up 0.4 percent. Hilo, the only other port to show a gain, posted a volume increase of 5.3 percent. Volume includes both inbound and outbound shipments.

Elsewhere, cargo volume declined 3.1 percent for Nawiliwili on Kauai, fell 5.8 percent for Molokai and dropped 6.5 percent for Kawaihae on Hawaii island.

On Lanai volume plunged 10.8 percent, marking a big reversal from the first quarter, when shipments jumped 21.9 percent as major construction companies shipped large amounts of supplies and equipment from the island with the completion of resort renovation projects in the first three months of the year.

Young Bros., which is regulated by the state, tracks cargo volumes using a standard unit measurement called container/platform equivalents, or CPEs.

For the second quarter the volume of interisland cargo totaled 33,200 CPEs, compared with 32,994 CPEs in April-June 2015.

The agricultural sector was weak again as outbound volume declined 6.8 percent to 1,904 CPEs during the quarter from 2,043 in the year-earlier period. In the first quarter agricultural shipments declined 8.8 percent.

Molokai and Maui bucked the downward trend with increases of 10 percent and 1.8 percent, respectively. Hilo incurred the largest decline of the ports at 13.6 percent while the port of Kawaihae, on the Kona side, fell 10.7 percent.

At the other ports, agricultural volume was down 7.4 percent on Kauai and 3.4 percent on Oahu. There were no outbound agricultural shipments from Lanai.

Agricultural volume consists of locally grown cargo that qualifies for the company’s island agricultural product discount of 30 to 35 percent.