Population Genetic Structure of the Goosefish, Lophius americanus.
Mark Kuzirian 
Tony Lee 
Lophius americanus Cuvier & Valenciennes 1837 (1), the goosefish, anglerfish, or monkfish, is common in coastal waters of the northeastern United States. Its geographic range extends from the northern Gulf of St. Lawrence south to Cape Hatteras, North Carolina [2, 3]. The highest fish concentrations are found along the shallower depths of the shelf from 70 to 100 m, but there is also a significant deep-water population below 190 m. Adult fish migrate seasonally in response to spawning, food availability, and optimal temperatures (3[degrees]-9[degrees]C) . The species is also dispersed through the drifting of egg rafts. Total dispersal time from embryonic development through larval and juvenile stages can extend to several months until benthic recruitment occurs. Sexual maturity is reached between 3 and 4 years of age .
Goosefish is the fourth largest commercial species in the U.S. fishery, and number one in demersal species landings. Goosefish landings have risen steeply through the 1980s, reaching approximately 28,800 mt ($35 million) for 1997 . Since the 1980s, the Canadian contribution to the fishery has declined precipitously, and now the major landings occur in the southern regions of the species range. In their autumn survey data, the Northeast Fisheries Science Center, Woods Hole, Massachusetts, has documented recent sharp declines in goosefish abundance, from 2.24 kg/tow in 1986 to 0.74 kg/tow in 1996. The New England and Mid-Atlantic Fishery Management Councils (NEFMC and MAFMC) consequently designated goosefish as overexploited and at low abundance . The 23rd Stock Assessment Workshop at the Northeast Fisheries Science Center concluded that it was not possible to delineate the stock structure for goosefish because of the lack of genetic, tagging, or migration studies. Nevertheless, the Councils divided the coastal population into northern and southern stocks (41[degrees]N latitude) for stock management purposes. This formula led to fishing restrictions being placed geographically, and made certain areas uneconomical to fish. Because of the lack of definitive stock data for goosefish , we undertook a population genetic study of goosefish in eastern waters from the Canadian border to North Carolina. We used random amplification of polymorphic DNA and PCR (RAPD-PCR)  to analyze the genetic structure of the sampled populations.
Eight representative sampling sites were chosen, extending from Maine (42[degrees]40' N, 68[degrees]20' W) to North Carolina (35[degrees]40', 75[degrees]00'), from depths to about 300 m. Fish were collected from September 1999 to June 2000. Up to 45 fish were sampled at each location. Tissue samples were collected in tissue preservation buffer . Genomic DNA was purified by standard phenol-chloroform procedures, and was finally dissolved in Tris-EDTA (TE) buffer (8). DNA fingerprinting was performed by RAPD-PCR , using 10 [micro]1 per reaction. Amplification products were separated by electrophoresis on 1.2% agarose gels in 0.5x TBE . Gels were stained with ethidium bromide and photographed under UV light. The presence or absence of amplification products was scored manually. Cluster analysis was performed with the RAPDistance package .
Six fish, three each from Georges Bank and New York/New Jersey sites were first screened with the seven primers shown in Table I. As expected, the number of amplification products per primer varied, ranging from 2 to 9, and very few bands were polymorphic (Table I). On the basis of the initial screening, a subset of 6-8 DNA samples from each site was analyzed, using primers 101 and 103; Figure 1 shows data for primer 103.
There appeared to be no significant differences between individuals or between populations, with either primer. Polymorphic bands were present in a minority of individuals, usually one or two. A set of eight fish collected off Martha's Vineyard, Massachusetts, by the Marine Biological Laboratory, was examined with an additional set of primers (115, 119, 130, and 143). Again, the band distribution was very homogeneous (data not shown). Of the 22 identifiable bands produced by these primers, 21 were present at a frequency of 100%. Band 22 was present at a frequency of 58%. All the MBL samples were clustered as one group by the RAPDistance package. These results taken together imply that the fish populations are relatively homogeneous genetically across all geographic sampling sites, the level of polymorphism within populations being as low as that between populations. Fish caught at shallower ([greater than]200 m) depths could not be differentiated from those at lower ([less than]200 m) depths, neither could t hose collected north or south of the 41[degrees]N line. For the primers tested, there was no amplification product (or the absence of one) that uniquely characterized a particular population. The trend in the data is clear even though only a subset of samples was analyzed with two primers. We are currently examining the entire sample set with more primers to reinforce the validity of our results.
The homogeneity of the goosefish populations off the eastern coastline of the United States suggests that there is unrestricted gene flow across the region. This is very plausible considering the preferred temperature profile and migratory patterns of the adults, and the long dispersal times of the embryos, larvae, and postlarval juveniles [2, 3]. These data will have serious implications for management of the goosefish fishery. The study results run counter to the current NEFMC/MAFMC policy of dividing the fishery into northern and southern stocks. Any management plan will be difficult to implement because the spawning stock biomass is unknown. More data is also needed to determine the location of the standing reproductive population, and to assemble specific temporal data on when spawning occurs over the fish's geographic range. Integration of the published data on seasonal abundances (NMFS Spring/Autumn Bottom Trawl Surveys) with yearly temperature profiles along the coastlines might suggest some possible avenues to pursue these answers. Such data will assist in defining the natural and fishing mortality rates (F) and what the [F.sub.threshold] should realistically be for this commercially important species.
This work was supported in part by the Monkfish Defense Fund. H.M.C. and A.M.K. are indebted to Kathy Downey of the MDF for acquainting them with the problems of the goosefish fishery, and for organizing the fishermen for sample collection. We thank the Aquatic Resources Division, MBL, for collecting some goosefish used in this study.
(1.) Cape Cod Community College, W. Barnstable, MA.
(2.) University of Rhode Island, Kingston, RI.
(3.) Duke University. Durham, NC.
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|Author:||Chikarmane, Hemant M.; Kuzirian, Alan M.; Kozlowski, Robbin; Kuzirian, Mark; Lee, Tony|
|Publication:||The Biological Bulletin|
|Date:||Oct 1, 2000|
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