For Atlantic bluefin tuna fisheries, the linked issues of population structure and mixing remain of paramount significance in optimizing utilization of a species well known for its pan-oceanic migrations. Due in part to increased evidence of trans-Atlantic migrations (Lutcavage et al. 1998), there has been increased scrutiny by scientists and resource representatives of the two stock hypothesis, which guides stock assessments and management projections for western Atlantic tuna (Magnuson et al. 1994). There is strong belief by commercial and recreational sectors of the bluefin tuna fishery (Chase et al. 2001) that the harvest of undersized (sub-legal) juveniles in the Eastern Atlantic is curtailing the recovery of Western stock bluefin tuna, despite stringent harvest limits that have been promulgated upon North American fisheries.

There is a clear need for empirical methods to directly estimate contributions of recruits originating from primary nurseries (currently believed to be the Mediterranean Sea / Eastern Atlantic and the Gulf of Mexico / Western Atlantic) to the fisheries that depend upon these recruits. The National Marine Fisheries Service and other agencies are currently supporting the development of three methods that have bearing on estimating mixing rates:

1. Electronic pop-up tags,
2. Biochemical markers, and
3. Otolith microconstituent analysis

Through support by the NMFS, and with strong collaboration with Dr. Jay Rooker (Texas A&M University, Galveston), we are developing and applying otolith microconstituent analysis, which we believe has particular relevance to the problem of mixing.

Bluefin Tuna Sampling Network: We are working with most categories of fishers on Atlantic tuna to obtain samples of otoliths for small bluefin tuna (<15 lb and <27 inch curved fork length; special 'Scientific Collectors Permits' are required) ....

	Bluefin Tuna Sampling Network [96 Kb; will open in a new window]

Secor,D.H., S.E. Campana, V.S. Zdanowicz, J.W.H. Lam, L. Wang and J.R. Rooker. In press. Inter-laboratory comparison of Atlantic and Mediterranean Bluefin tuna otolith microconstituents. ICES J. Mar. Sci.

	Bluefin Tuna Otolith Microconstituents [96 Kb; will open in a new window]

Rooker, J.R., D.H. Secor, V.S. Zdanowicz, G.De Metrio and L.O. Relini. In press. Identification of Atlantic Bluefin tuna stocks from putative nurseries using otolith chemistry. Fish. Oceanogr.

Secor, D.H. 2002. Is Atlantic Bluefin Tuna a Metapopulation? ICCAT SCRS/01/056. Collective Volume of Scientific Papers, Madrid, Spain.

	Bluefin Tuna Metapopulations [160 Kb; will open in a new window]

Rooker, J.R., D.H. Secor, V.S. Zdanowicz and T. Itoh. 2001. Discrimination of northern bluefin tuna from nursery areas in the Pacific Ocean using otolith elemental fingerprints. Mar. Ecol. Progr. Ser. 218: 275-282.

Rooker, J.R., V.S. Zdanowicz and D.H. Secor. 2001. Otolith chemistry of Atlantic tunas: Assessment of natural variation and post-mortem handling effect. Mar. Biol. 139: 35-43.

Secor, D.H. and V. Zdanowicz. 1998. Otolith microconstituent analysis of juvenile bluefin tuna (Thunnus thynnus) from the Mediterranean Sea and Pacific Ocean. Fish. Res. 36: 251-256.