Island in the Stream: Oceanography and Fisheries of the Charleston Bump

<em>Abstract.</em>—The Gulf Stream off the east coasts of Florida, Georgia, and the Carolinas is one of the U. S. pelagic fishery regions in which particularly high swordfish discard rates were reported after a regulation limiting the landings of swordfish less than 25 kg whole weight went into effect in 1991. Swordfish <em> Xiphias gladius </em>fishing and catch locations from mandatory longline logbooks for the years 1991 through 1995 were used to explore the distribution patterns of swordfish discard rates in this region. Every 0.1 degree square of latitude and longitude was assigned a discard rate category (very high, moderate, low, none) for each month of the year based on the percentage of the swordfish catch that was discarded in that month over the five year period. Swordfish discard rates varied with latitude and season. The greatest seasonal changes were seen off the Carolinas where discard rates increased in the fall along with changes in fishing patterns.

Island in the Stream: Oceanography and Fisheries of the Charleston Bump

<em>Abstract.</em>—The Charleston Bump is a structural and topographic high on the northern Blake Plateau that overlies a seaward offset of the edge of continental crust. The feature causes the bottom to shoal and deflects the Gulf Stream offshore, causing an intensification of bottom currents. The area has been swept by strong currents since late Cretaceous time, but the strongest currents have occurred in the Neogene (last -25 million years). Nondepositional conditions prevail at present, but erosion of the bottom is checked where the bottom is armored by a hard surficial layer of phosphorite pavement. The phosphorite pavements were formed by re-cementation of eroded residues of phosphorite-rich sediments of early-Neogene age. In some places there are multiple pavements separated by poorly lithified sediments. Submersible observations indicate that the south, or current-facing flank of the Charleston Bump has several deep (>100 m) scour depressions, the southern flanks of which form cliffs characterized by ledges and overhangs. In other areas discrete layers of older Paleogene rocks have been partly eroded away, leaving cliff-like steps of 5 m or more relief. Conglomeratic phosphorite pavement layers up to 1 m thick armor most of the bottom. Where breached by scour, these pavements form both low-relief ledges and rock piles. These features form a reef-like environment of caves and overhangs utilized by wreckfish <em> Polyprion americanus </em>and barrelfish <em> Hyperoglyphe perciformis </em>as shelter from the current and as staging areas to prey on passing schools of squid. Wreckfish and other large fish were often localized in rugged bottom habitat, including caves and other shelter areas. We observed wreckfish darting from shelters to feed on passing schools of squid. Present and past observations, are consistent with the concept that impingement of the Gulf Stream at the Charleston Bump compresses midwater fauna from much thicker water layers, providing food for a flourishing big-fish fauna. During our dives we noted currents often exceeding 1 knot, and ranging to 2.4 knots. Evidence of fossil, manganese-iron-encrusted megaripples suggest even greater current regimes in the past. Investigation of the site of an earlier report of possible freshwater discharge failed to find any evidence of a closed sinkhole or freshwater discharge. Rather, we concluded that the apparent loss of buoyancy experienced by the submarine was probably caused by downward-directed eddy currents generated by currents sweeping across the pavement/void interface of a more than 100-m high cliff 3 km south of the reported location.

Island in the Stream: Oceanography and Fisheries of the Charleston Bump

<em>Abstract.</em>—The animation of daily composites of sea surface temperatures (SST) from a National Oceanic and Atmospheric Administration Geostationary Operational Environmental Satellite (GOES) provides a new method for the detection of dynamics at the surface of the ocean. By rapidly viewing the daily SST composites of hourly images, it is possible for the human eye to separate the fast moving residual clouds from the slowly moving SST patterns associated with ocean currents, eddies, and upwelling. Although each individual daily composite is still partly cloud covered, the rapid display provides the appearance of continuity of the SST patterns. The GOES SST animations were used during 1998 and 1999 to monitor the time dependent deflection of the Gulf Stream due to a rise in bottom topography southeast of Charleston, South Carolina, locally known as the Charleston Bump. Examples of the sea surface temperature animations of the Gulf Stream appear at the website: http:// www. goes .noaa.gov

Island in the Stream: Oceanography and Fisheries of the Charleston Bump

<em> Abstract.</em>—The status of the wreckfish <em> Polyprion americanus </em>stock caught on the Blake Plateau in the southeastern United States Atlantic was analyzed by calibrated virtual population analysis (VPA) to estimate trends in fishing mortality and population (or stock) biomass. Calibration of the FADAPT VPA program was to fishery-dependent catch-per-unit effort (CPUE) for a range in assumed values for natural mortality (M). Age-length keys were developed from two aging studies of wreckfish (1988– 1992 and 1995–1998). Keys were developed annually (pooled across seasons to create three “annual” age-length keys to represent 1988–1990, 1991–1993, and 1994–1998) and seasonally (pooled across years to create three seasonal age-length keys to represent April–June, July–September, and October to end of fishing year on 15 January). Analyses based on both annual and seasonal catch matrices showed similar patterns and values, with the seasonal catch matrix producing slightly lower estimates of fishing mortality rates (F) and higher estimates of biological reference points based on F. Fishing mortality rates peaked in 1989, as did the maximum annual U.S. landings (4.2 million pounds). Subsequently, both landings and fishing mortality rates have generally declined. Although stock biomass has generally declined over the study period, recruitment at age 7 has risen since about 1994. Meanwhile, annual estimates of static spawning potential ratio (SPR), which are inversely related to F, have risen since 1994. Fishing mortality rates from recent low landings are at or near the South Atlantic Fishery Management Council’s threshold definition of overfishing (static SPR of 30%), while the process of rebuilding with improving recruitment appears to be underway. Concern persists because the assessment is based on the underlying assumption that wreckfish from the Blake Plateau form a single stock separate from the eastern North Atlantic and genetic evidence suggests the stock encompasses the entire North Atlantic.

Island in the Stream: Oceanography and Fisheries of the Charleston Bump

<em>Abstract.</em>—Competition between commercial and recreational fishers for fishery resources is common throughout the United States. This competition for resources occurs throughout the south Atlantic region. However, competition around an area known as the Charleston Bump led to controversy and public calls for closure of that area to commercial fishing. In 1997, controversy erupted over the proposed lease of a fish processing facility at the newly completed Charleston Maritime Center. A group of commercial fishermen proposed to open the Maritime Center’s facilities to all types of commercial fishing craft, but with emphasis on longline vessels. The high level of public awareness and knowledge of South Carolina’s offshore fisheries helped to catapult the Charleston Bump to the forefront of state and federal marine fisheries policy, research, and management. Parties to this dispute looked to state fisheries managers for interpretation of technical information upon which to base their decisions. However, fisheries managers soon learned that the data on the significance of the Charleston Bump as a nursery area were inconsistent and spotty. This lack of reliable data left the managers in a policy dilemma: how to make technical recommendations on the management of the fisheries of the Charleston Bump given the lack of data. The fisheries managers responded by acknowledging the lack of data and suggesting that a comprehensive ecological analysis of the Charleston Bump be performed. In addition, the fisheries managers responded by interpreting the data based on the precautionary principle (i.e., do no harm to the resource) and advised the parties to the Maritime Center dispute against any move that might consolidate fishing effort on the Charleston Bump. The purpose of this paper is to: (1) document the approach taken by the State of South Carolina to analyze this public controversy and; (2) describe how public involvement in the development of a local public policy issue can create the need for further scientific inquiry and research. The authors present an overview of this controversy and highlight how public perceptions and demand for action resulted in a policy stance. The authors describe how the public’s direct involvement led not only to the colloquium but also to a renewed scientific interest in the Charleston Bump.

Island in the Stream: Oceanography and Fisheries of the Charleston Bump

<em>Abstract.</em>—Atlantic blue marlin are primarily harvested as bycatch in fisheries targeting tunas and swordfish. These target species are managed for maximum sustainable yield (MSY) based largely on guidance from surplus production models that lack age structure. Simulation models were constructed around the life history characteristics of Atlantic blue marlin and yellowfin tuna, one of the target species. Each simulated population was exposed to fishing mortality and the resulting time streams of catches and abundances were used as surplus production model inputs using the computer program ASPIC. The slopes of the stock-recruitment curves of the simulated populations were adjusted until the ASPIC estimates of the intrinsic growth rates for the simulations were equivalent to the estimates derived for these populations in the last ICCAT stock assessments. The equilibrium curves of production on fishing mortality for the age-structured populations were then compared to the logistic production model fitted by ASPIC. For blue marlin, the underlying production curve shifted to the left, and F<SUB> MSY </SUB>was lower than the value estimated by ASPIC. For yellowfin tuna, the underlying production curve shifted to the right and F<SUB> MSY </SUB>occurred at a higher fishing mortality rate than that estimated by ASPIC. These results suggest that the Atlantic blue marlin stock is more vulnerable to fishing mortality than indicated by the production model fitted in the last assessment. Also, the fishing mortality rate that produces MSY for yellowfin is near the extinction level for blue marlin. This characteristic is likely shared by other highly productive stocks that support the fisheries in which blue marlin are killed as bycatch. These results indicate that fishing target species at MSY may result in continued serious depletions of Atlantic blue marlin unless the catchability can be reduced relative to the catchability of the target species.

Island in the Stream: Oceanography and Fisheries of the Charleston Bump

<em>Abstract.</em>—Recent observations from trawling and submersibles have shown several species of cephalopods to be common in slope-waters of the western North Atlantic Ocean. The slope-water cephalopods include the commercially-important genus <em> Illex</em>, taxonomy of which remains troubling in the area off Charleston because of the possibility that <em> I. oxygonius </em>is a hybrid. Other common species include another ommastrephid <em> Ornithoteuthis antillarum</em>, single species of <em> Mastigoteuthis</em>, <em> Brachioteuthis</em>, and <em> Pholidoteuthis</em>, several cranchiids, histioteuthids, and sepiolids, two octopodids, the pelagic incirrate octopod <em> Haliphron atlanticus</em>, and the cirrate octopod <em> Stauroteuthis syrtensis</em>. Behavior and distribution of these species contrast with those of truly open-ocean cephalopods, which also are present in slope waters. In-situ observations have shown that several of the squids are more strongly associated with the bottom than was previously supposed and that many of the slope-water cephalopods exhibit unexpected behaviors.

Island in the Stream: Oceanography and Fisheries of the Charleston Bump

<em>Abstract.</em>—Recent advances in the analyses of tag-and-recapture data and an increase in the type and sophistication of commercially available electronic tags are combining to provide insight into horizontal and vertical movements of pelagic fishes. This information can be used to evaluate the importance of specific geographic areas to the overall movement patterns of a species and to explain exploitation patterns and vulnerability to different fishing gear types. Different types of tag are briefly reviewed and an example given of combining traditional tag-and-recapture with electronic tag data to focus on a specific fishery that targets an aggregated tuna resource. The possibility is discussed of applying similar techniques to address questions surrounding the Charleston Bump.

Island in the Stream: Oceanography and Fisheries of the Charleston Bump

<em>Abstract</em>.—The geological structure and characteristic community members of four relatively distinct benthic habitats, and their associated subhabitats, are described on the upper- and middle-continental slope just north of the Charleston Bump and below the deflection of the Gulf Stream eastward. The predominant habitats, identified from submersible surveys, included moderate-relief capped mounds, moderate-relief coral mounds, low-relief substrates and cohesive-mud substrates. Moderaterelief capped-mound habitats (185–220 m) due east of Charleston, South Carolina, were characterized by high local relief (about 20 m) outcroppings having abundant and diverse fish and sessile invertebrate communities. Moderate-relief coral-mound habitats, at depths of 503–555 m southeast of Charleston, consisted of mounds of dead coral fragments with a local relief of 15–23 m. Associated with the coral mounds was a depauperate assemblage of live coral and rare fish species. Yet, this habitat had a more diverse biological community than most of the low-relief subhabitats. Low–relief habitats at 293–567 m southeast of Charleston primarily consisted of fine sediments distributed in current generated patterns. Although epibenthic fish and invertebrate species were associated with this habitat, their abundance and diversity was relatively low. Cohesive-mud habitats at 150–250 m were distributed along depth contours for a long distance. Many of the species found here were associated with widely distributed tilefish <em> Lopholatilus chamaeleonticeps </em>burrows that impart negative relief to large areas of this flat habitat.