Modernizing Recreational Fisheries Management Act of 2018 (Sec. 3) This bill defines "mixed-use fishery" to mean a federal fishery in which two or more of the following occur: (1) recreational fishing, (2) charter fishing, or (3) commercial fishing. TITLE I--CONSERVATION AND MANAGEMENT (Sec. 101) The Government Accountability Office must conduct a study and submit to Congress a report on mixed-use fisheries in the South Atlantic and Gulf of Mexico. (Sec. 102) The bill authorizes a regional fishery management council to use management measures in developing a plan or proposed regulations for a recreational fishery or the recreational component of a mixed-use fishery. (Sec. 103) The Ocean Studies Board of the National Academies of Sciences, Engineering, and Medicine must complete a study on the use of limited access privilege programs to harvest fish in mixed-use fisheries, including an assessment of the social, economic, and ecological effects of the program on businesses, coastal communities, and the environment. TITLE II--RECREATION FISHERY INFORMATION, RESEARCH, AND DEVELOPMENT (Sec. 201) The Department of Commerce must develop a report on facilitating greater incorporation of data, analysis, stock assessments, and surveys from state agencies and nongovernmental sources into fisheries management decisions. (Sec. 202) Commerce must also establish partnerships with states and make grants to improve recreational fisheries data collection.