Connectivity and Estuaries: Historically, estuarine fisheries biology has focused on the theme of estuarine dependency, with an emphasis on microhabitat use. Ironically, however, few fishes that we associate with estuaries are in fact obligatory users (anadromous fishes are a notable exception). What then are the causes and consequences of estuarine habitat vs. coastal habitat use? To address this issue, we investigate "connectivity" in the life cycles of fishes. Connectivity here refers to the dependence of fish production and population dynamics on dispersal and migration among multiple habitats. I am especially interested in migration and habitat use as behaviors that control and regulate population dynamics, and cause individuals to be differentially vulnerable to exploitation and pollution. A recent emphasis in our laboratory is to use otolith tracers to reconstruct habitat histories and nursery use in estuarine and coastal fishes. Still, because migration and dispersal are complex in measurement, we utilize a battery of approaches.

An example of otolith tracers in a striped bass otolith .... This X-ray map image shows evidence of early exploration of marine habitats by Hudson River striped bass, followed my annual spawning migrations into low salinity environments (red = high strontium levels)

The Contingent Hypothesis: The concept of closed population structure - the unit stock concept - has been fundamental to marine fisheries science for nearly a century (Secor 2002). We have argued that anomalous individual migration and habitat use patterns - those that diverge from expected ontogenetic circuits of migration - represent modalities, and that these modalities confer resiliency in populations where mortality risk and production is related to specific spatial behaviors. These modalities are well represented by the retentive and migratory forms of salmon and chars, but have been observed increasingly in marine and coastal fishes through the use of otolith microchemistry (Secor 1999). Groups of individuals with similar migration trajectories are called contingents, a term coined initially by Hjort (1914). The prevalence of contingent behaviors provides insight into the evolution of estuarine dependency, as well as the consequences of patterns of estuarine dependency to population dynamics and pollution ecology. We are actively testing hypotheses that can explain contingent structure and its consequences, using white perch as a model species.

An example of contingent structure .... Two otolith strontium x-ray maps from white perch young-of-the-year (YoY) juveniles, one giving evidence of freshwater residency during its first year of life (blue), and another exhibiting dispersal to brackish habitats (green)

Secor, D.H. 2002. Historical roots of the migration triangle. ICES J. Mar. Sci. 215: 329-335.

	Historical Roots [96 Kb; will open in a new window]

Secor, D.H. 2002. Estuarine dependency and life history evolution in temperate sea basses. Proc. 70th Anniv. Internat. Symp. Jap. Sci. Fish. Soc.

	Estuarine Dependency & Life History Evolution [224 Kb; will open in a new window]

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]

Secor, D.H., J.R. Rooker, E. Zlokovitz and V.S. Zdanowicz. 2001. Identification of riverine, estuarine, and coastal contingents of Hudson River striped bass based upon otolith elemental fingerprints. Mar. Ecol. Progr. Ser. 211: 245-253.

Secor, D.H. 1999. Specifying divergent migration patterns in the concept of stock: The Contingent Hypothesis. Fish. Res. 43: 13-34.

	The Contingent Hypothesis [3.5 Mb; will open in a new window]

Secor, D.H., T.E. Gunderson and K. Karlsson. 2000. Effects of salinity and temperature on growth performance in anadromous (Chesapeake Bay) and non-anadromous (Santee-Cooper) strains of striped bass, Morone saxatilis. Copeia xx: 291-296.

Secor, D.H. and J.R. Rooker. 2000. Is otolith strontium a useful scalar of life-cycles in estuarine fishes? Fish. Res. 46(1-3): 359-371.

Kimura, R, D.H. Secor, E.D. Houde and P.M. Piccoli. 2000. Up-estuary dispersal of young-of-the-year bay anchovy Anchoa mitchilli in the Chesapeake Bay: Inferences from microprobe analysis of Sr in otoliths. Mar. Ecol. Progr. Ser. 208: 217-227.

Secor, D.H., T. Ota and M. Tanaka. 1998. Use of otolith microanalysis to determine estuarine migrations of Ariake Sea Japanese seabass. Fish. Sci. 64: 740-743.

Secor, D.H. and P. M. Piccoli. 1996. Age- and sex-dependent migrations of the Hudson River striped bass population determined from otolith microanalysis. Estuaries 19: 778-793.

Secor, D.H., A. Henderson-Arzapalo and P.M. Piccoli. 1995. Can otolith microchemistry chart patterns of migration and habitat utilization in anadromous fishes? J. Exp. Mar. Biol. Ecol. 192: 15-33.

Ashley, J.T.F, D.H. Secor, E. Zlokovitz, J.E. Baker and S.Q. Wales. 2000. Linking habitat use of Hudson River striped bass to accumulation of polychorinated biphenyl congeners. Environ. Sci. Techn. 34: 1023-1029.

Zlokovitz, E.R. and D.H. Secor. 1999. Effect of habitat use on PCB body burden in Hudson River striped bass (Morone saxatilis). Can. J. Fish. Aquat. Sci. 56 (Suppl.1): 86-93.

Ongoing NOAA supported research.