fiscal year 2020 due to increased demand in these categories as a result of increased demand in these products as consumer spending increased. Our hunting and shooting, fishing, and camping departments saw decreases of $11.5 million, $6.1 million and $1.1 million, respectively, in the second quarter of fiscal year 2021 compared to the comparable 13-week period of fiscal year 2020. Within hunting and shooting department, our firearm and ammunition categories saw decreases of $11.2 million or 13.3% and $1.4 million or 2.6%, respectively, in the second quarter of fiscal year 2021 compared to the comparable 13-week period of fiscal year 2020. The decrease seen in these categories is due to lower demand as we anniversaried the social unrest and pending presidential election of the prior year period.
With respect to same store sales, during the 13 weeks ended July 31, 2021, our footwear, clothing, and optics, electronics, and accessories, departments had increases of 7.1%, 6.7%, and 0.6%, respectively, for the second quarter of fiscal year 2021 compared to the comparable 13-week period of fiscal year 2020. Our fishing, hunting, and camping departments saw decreases of 14.1%, 11.7%, and 5.5%, respectively, as we anniversaried the demand driven in the prior year by the COVID-19 pandemic, social unrest, and the pending political process. As of July 31, 2021, we had 107 stores included in our same store sales calculation.
Gross Profit. Gross profit decreased to $120.1 million during the 13 weeks ended July 31, 2021 compared to $129.1 million for the corresponding period of fiscal year 2020 primarily as a result of decreased sales. As a percentage of net sales, gross profit decreased to 33.2% for the 13 weeks ended July 31, 2021, compared to 33.9% for the corresponding period of fiscal year 2020 due to higher freight costs. The higher freight costs were partially offset by an increase in product margins across all categories and increased vendor incentives. We expect higher transportation costs to continue to impact the business during the remainder of fiscal 2021.
Selling, General, and Administrative Expenses. Selling, general, and administrative expenses increased by $12.3 million, or 14.7%, to $95.9 million during the 13 weeks ended July 31, 2021 from $83.6 million for the comparable 13-week period of fiscal year 2020. This increase was primarily due to an increase in our payroll expense of $4.4 million, which was the result of opening 8 new stores since the end of the second quarter of fiscal year 2020, and minimum wage increases impacting 12 of our stores in fiscal year 2021. We also had an increase in acquisition costs of $2.5 million due to costs relating to the pending merger with Great Outdoors Group, as well as increases in other selling, general and administrative costs, rent, depreciation, and pre-opening of $2.0 million, $1.7 million, $1.0 million, and $0.8 million, respectively, during the 13 weeks ended July 31, 2021 primarily related to the opening of 8 new stores since August 1, 2020. As a percentage of net sales, selling, general, and administrative expenses increased to 26.5% of net sales in the second quarter of fiscal year 2021, compared to 21.9% of net sales in the second quarter of fiscal year 2020, as a result of the decrease in net sales we experienced in the second quarter of fiscal year 2021 compared to the second quarter of fiscal year 2020 and the increase in expenses noted in second quarter of fiscal year 2021 compared to the second quarter of fiscal year 2020.
Interest Expense. Interest expense decreased by $0.7 million, or 73.8%, to $0.3 million during the 13 weeks ended July 31, 2021 from $1.0 million for the comparable 13-week period of fiscal year 2020. Interest expense decreased primarily as a result of decreased borrowings on our revolving line of credit during the second quarter of fiscal year 2021 compared to the second quarter of fiscal year 2020.
Income Taxes. We recognized income tax expense of $6.2 million compared to an income tax expense of $12.0 million during the 13 weeks ended July 31, 2021 and August 1, 2020, respectively. Our effective tax rate for the 13 weeks ended July 31, 2021 and August 1, 2020 was 25.9% and 27.0%, respectively. Our effective tax rate will generally differ from the U.S. Federal statutory rate of 21.0%, due to state taxes, permanent items, and discrete items relating to stock award deductions.
Twenty-Six Weeks Ended July 31, 2021 Compared to Twenty-Six Weeks Ended August 1, 2020
Net Sales. Net sales increased by $60.9 million, or 9.7%, to $688.8 million during the 26 weeks ended July 31, 2021 compared to $627.8 million in the corresponding period of fiscal year 2020. Our net sales increased due to a variety of reasons including: increased participation in outdoor activities, increased demand through our e-commerce platform, and demand driven by the change in consumer behavior associated with the COVID-19 pandemic, partially offset by lower demand during the second quarter of fiscal 2021 compare to the same period last year in certain categories as we anniversaried the demand driven in the prior year by the COVID-19 pandemic, social unrest, and the pending presidential election. Stores that have been open for less than 12 months and were, therefore, not included in our same store sales, contributed $46.3 million to net sales. Same store sales increased by 3.4% for the 26 weeks ended July 31,