Chapter 16 Case Study: Blue and Mako Shark Catch Rates in US Atlantic Recreational Fisheries as Potential Indices of Abundance Gregory Skomal, Elizabeth A. Babcock and Ellen K. Pikitch Abstract Generalized linear models were used to derive indices of abundance for blue (Prionace glauca) and shortfin mako (Isurus oxyrinchus) sharks based on two components of the US Atlantic recreational fishery: (1) the private and charter boat recreational anglers covered by the Marine Recreational Fisheries Statistics Survey (MRFSS, 1981–2002) of the National Marine Fisheries Service and (2) Massachusetts shark tournaments (1991–2004). From the MRFSS data, blue shark catch per unit effort (CPUE) showed different trends for different regions, seasons, and fishing modes, implying that CPUE is not tracking blue shark abun- dance. Mako shark CPUE differed by mode for private versus charter boats, and showed no trend in either boat type. From the Massachusetts tournament data, blue shark CPUE showed different trends north and south of Cape Cod. Mako shark CPUE declined in the late 1990s in Massachusetts tournaments, then increased again in 2002. Key words: blue shark, mako shark, Prionace glauca, Isurus oxyrinchus, recreational fishing, shark tournaments, angling, game fishing, CPUE. Introduction The blue shark (Prionace glauca, Carcharhinidae) and the shortfin mako (Isurus oxyrin- chus, Lamnidae) are subject to extensive offshore recreational fisheries along the East Coast of the United States. From May through September each year, both species are sought by charter and private vessels, primarily from Virginia to Maine. Moreover, several big-game fishing tournaments that target these species are held annually in this region. The primary source of information about recreational fishing effort and catch in the United States is the Marine Recreational Fisheries Statistics Survey (MRFSS, 2002) of the National Marine Fisheries Service (NMFS). Total catch and effort data are also collected at shark tournaments by the Massachusetts Division of Marine Fisheries. We evaluate the Sharks of the Open Ocean: Biology, Fisheries and Conservation. Edited by M. D. Camhi, E. K. Pikitch and E. A. Babcock © 2008 Blackwell Publishing Ltd. ISBN: 978-0632-05995-9