RESEARCH ARTICLE Christin L. Pruett Æ Eric Saillant Æ John R. Gold Historical population demography of red snapper (Lutjanus campechanus) from the northern Gulf of Mexico based on analysis of sequences of mitochondrial DNA Received: 30 April 2004 / Accepted: 1 March 2005 / Published online: 5 May 2005 Ó Springer-Verlag 2005 Abstract We evaluated stock structure and demographic (population) history of red snapper (Lutjanus campech- anus) in the northern Gulf of Mexico (Gulf) via analysis of mitochondrial (mt)DNA sequences from 360 indi- viduals sampled from four cohorts (year classes) at three localities across the northern Gulf. Exact tests of genetic homogeneity and analysis of molecular variance both among cohorts within localities and among localities were non-significant. Nested clade analysis provided evidence of different temporal episodes of both range expansion and restricted gene flow due to isolation by distance. A mismatch distribution of pairwise differences among mtDNA haplotypes and a maximum-likelihood coalescence analysis indicated a population expansion phase that dated to the Pleistocene and probably rep- resents (re)colonization of the continental shelf follow- ing glacial retreat. The spatial distribution of red snapper in the northern Gulf appears to have a complex history that likely reflects glacial advance/retreat, habi- tat availability and suitability, and hydrology. Habitat availability/suitability and hydrology may partially re- strict gene flow among present-day red snapper in the northern Gulf and give rise to a metapopulation struc- ture with variable demographic connectivity. This type of population structure may be difficult to detect with commonly used, selectively neutral genetic markers. Introduction The Gulf red snapper (Lutjanus campechanus) is a highly exploited marine fish found primarily along the conti- nental shelf of the Gulf of Mexico (Hoese and Moore 1977; Allen 1985) and subjected to both recreational and commercial fishing (Goodyear and Phares 1990). Red snapper abundance in the northern Gulf of Mexico (Gulf) has decreased by almost 90% since the 1970s (Goodyear and Phares 1990), leading to intensive man- agement beginning in the early 1990s (Christman 1997). A central question regarding conservation and man- agement of red snapper resources in the northern Gulf is whether multiple management units (stocks) exist within the fishery. The question is of importance because sep- arate management of regional stocks, should they exist, is necessary to avoid regional over-exploitation and maintain potentially adaptive genetic variation (Carv- alho and Hauser 1995; Hauser and Ward 1998). Prior genetic studies on adult red snapper sampled across the northern Gulf have generally revealed homogeneity among localities, consistent with the exis- tence of a single stock (Camper et al. 1993; Gold et al. 1997; 2001; Garber et al. 2004; but see Bortone and Chapman 1995). The genetic data, however, are not fully consistent with studies of post-juvenile life history and with most tag-and-recapture experiments that indicate adult red snapper are sedentary and exhibit high site fidelity (Fable 1980; Szedlmayer and Shipp 1994; Szedlmayer 1997; but see Patterson et al. 2001). Two hypotheses forwarded to account for these seemingly disparate observations are (1) gene flow, perhaps occurring from hydrodynamic transport of pelagic eggs and larvae across the northern Gulf (Goodyear 1995), is sufficient to preclude genetic divergence, or (2) gene flow across the northern Gulf is limited but there has been insufficient time for semi-isolated lineages to completely sort into monophyletic assemblages (Gold and Rich- ardson 1998; Gold et al. 2001). A third hypothesis is (3) that gene flow/isolation among assemblages or lineages Communicated by P.W. Sammarco, Chauvin C. L. Pruett Æ E. Saillant Æ J. R. Gold (&) Center for Biosystematics and Biodiversity, Department of Wildlife and Fisheries Sciences, Texas A&M University, TAMU 2258, College Station, TX 77843-2258, USA E-mail: goldfish@tamu.edu Fax: +1-979-8454096 Marine Biology (2005) 147: 593–602 DOI 10.1007/s00227-005-1615-8