Our Well Intervention revenues decreased by 7% for the six-month period ended June 30, 2021 as compared to the same period in 2020, primarily reflecting lower vessel utilization in the North Sea, lower utilization on the Q4000 and lower rates on the Q5000 in the Gulf of Mexico, and our short-term extension at lower rates on the Siem Helix 1 in Brazil in 2021, offset in part by higher utilization on the Q7000 in Nigeria.
Robotics revenues decreased by 38% for the six-month period ended June 30, 2021 as compared to the same period in 2020, primarily reflecting fewer vessel days due to a significant drop in spot vessel days attributable to site clearance projects in the North Sea as well as decreased utilization of ROVs and ROVDrill, offset in part by an increase in trenching activities. Our results included 401 vessel days and 156 trenching days during the six-month period ended June 30, 2021 as compared to 904 vessel days and 161 trenching days during the same period in 2020.
Our Production Facilities revenues increased by 5% for the six-month period ended June 30, 2021 as compared to the same period in 2020, primarily reflecting higher HFRS revenues and oil and gas production.
Gross Profit (Loss). Our consolidated gross profit decreased by $13.8 million for the six-month period ended June 30, 2021 as compared to the same period in 2020, primarily reflecting lower gross profit in our Well Intervention and Robotics segments, offset in part by higher gross profit in our Production Facilities segment.
The gross profit related to our Well Intervention segment decreased by $7.8 million for the six-month period ended June 30, 2021 as compared to the same period in 2020, primarily reflecting higher costs associated with our increased activity in the North Sea and West Africa, offset in part by our overall cost reduction efforts.
The gross profit related to our Robotics segment decreased by $9.3 million for the six-month period ended June 30, 2021 as compared to the same period in 2020, primarily reflecting lower revenues due to fewer spot vessel days on site clearance projects, offset in part by lower operating costs.
The gross profit related to our Production Facilities segment increased by $4.4 million for the six-month period ended June 30, 2021 as compared to the same period in 2020, primarily reflecting higher HFRS revenues, higher oil and gas production revenues and a reduction in direct costs.
Goodwill Impairment. The $6.7 million charge in the six-month period ended June 30, 2020 reflects the impairment of the entire goodwill balance, which related to our acquisition of a controlling interest in STL (Note 10).
Selling, General and Administrative Expenses. Our selling, general and administrative expenses were $28.6 million for the six-month period ended June 30, 2021 as compared to $32.2 million for the same period in 2020, primarily reflecting lower credit loss reserves. Our selling, general and administrative expenses for the six-month period ended June 30, 2020 included a $2.4 million provision for current expected credit losses (Note 14).
Net Interest Expense. Our net interest expense totaled $12.0 million for the six-month period ended June 30, 2021 as compared to $12.8 million for the same period in 2020, primarily reflecting lower interest expense due to a reduction in our overall debt levels and the elimination of accretion of debt discounts associated with our 2022 Notes, 2023 Notes and 2026 Notes as a result of the adoption of ASU No. 2020-06 beginning January 1, 2021 (Note 5), offset in part by the cessation of interest capitalization with the completion of the Q7000 in 2020. Net interest expense for the six-month period ended June 30, 2020 excluded $1.2 million in capitalized interest associated with the Q7000 (Note 5).
Other Income (Expense), Net. Net other income was $2.6 million for the six-month period ended June 30, 2021 as compared to net other expense of $12.5 million for the same period in 2020, primarily reflecting foreign currency transaction gains due to the strengthening of the British pound.
Income Tax Benefit. Income tax benefit was $1.9 million for the six-month period ended June 30, 2021 as compared to an income tax benefit of $21.4 million for the same period in 2020. The effective tax rates for the six-month periods ended June 30, 2021 and 2020 were 10.0% and 71.6%, respectively. The decrease in the effective tax rate was primarily attributable to the earnings mix between our higher and lower tax rate jurisdictions and the impact of the CARES Act and the foreign subsidiary restructuring in 2020 (Note 6).