Movements and spawning of white marlin (Tetrapturus albidus) and blue marlin (Makaira nigricans) off Punta Cana, Dominican Republic

With a focus on white marlin (Tetrapturus albidus), a concurrent electronic tagging and larval sampling effort was conducted in the vicinity of Mona Passage (off southeast Hispaniola), Dominican Republic, during April and May 2003. Objectives were 1) to characterize the horizontal and vertical movement of adults captured from the area by using pop-up satellite archival tags (PSATs); and 2) by means of larval sampling, to investigate whether fish were reproducing. Trolling from a sportfishing vessel yielded eight adult white marlin and one blue marlin (Makaira nigricans); PSAT tags were deployed on all but one of these individuals. The exception was a female white marlin that was unsuitable for tagging because of injury; the reproductive state of its ovaries was examined histologically. Seven of the PSATs reported data summaries for water depth, temperature, and light levels measured every minute for periods ranging from 28 to 40 days. Displacement of marlin from the location of release to the point of tag pop-up ranged from 3l.6 to 267.7 nautical miles (nmi) and a mean displacement was 3.4 nmi per day for white marlin. White and blue marlin mean daily displacements appeared constrained compared to the results of other marlin PSAT tagging studies. White marlin ovarian sections contained postovulatory follicles and final maturation-stage oocytes, which indicated recent and imminent spawning. Neuston tows (n=23) yielded 18 istiophorid larvae: eight were white marlin, four were blue marlin, and six could not be identified to species. We speculate that the constrained movement patterns of adults may be linked to reproductive activity for both marlin species, and, if true, these movement patterns may have several implications for management. Protection of the potentially important white marlin spawning ground near Mona Passage seems warranted, at least until further studies can be conducted on the temporal and spatial extent of reproduction and associated adult movement.

Transboundary Movement of Atlantic Istiophorid Billfishes Among International and U.S. Domestic Management Areas Inferred from Mark-Recapture Studies

Billfish movements relative to the International Commission for the Conservation of Atlantic Tunas management areas, as well as U.S. domestic data collection areas within the western North Atlantic basin, were investigated with mark-recapture data from 769 blue marlin, Makaira nigricans, 961 white marlin, Tetrapturus albidus, and 1,801 sailfish, Istiophorus platypterus. Linear displacement between release and recapture locations ranged from zero (all species) to 15,744 km (mean 575, median 119, SE 44) for blue marlin, 6,523 km (mean 719, median 216, SE 33) for white marlin, and 3,845 km (mean 294, median 98, SE 13) for sailfish. In total, 2,824 (80.0%) billfish were recaptured in the same management area of release. Days at liberty ranged from zero (all species) to 4,591 (mean 619, median 409, SE 24) for blue marlin, 5,488 (mean 692, median 448, SE 22) for white marlin, and 6,568 (mean 404, median 320, SE 11) for sailfish. The proportions (per species) of visits were highest in the Caribbean area for blue marlin and white marlin, and the Florida East Coast area for sailfish. Blue marlin and sailfish were nearly identical when comparing the percent of individuals vs. the number of areas visited. Overall, white marlin visited more areas than either blue marlin or sailfish. Seasonality was evident for all species, with overall results generally reflecting the efforts of the catch and release recreational fishing sector, particularly in the western North Atlantic. This information may be practical in reducing the uncertainties in billfish stock assessments and may offer valuable insight into management consideration of time-area closure regulations to reduce bycatch mortality of Atlantic billfishes.

Atlantic Blue Marlin, Makaira nigricans, and White Marlin, Tetrapterus albidus, Bycatch of the Japanese Pelagic Longline Fishery, 1960–2000

ABSTRACT—Since the late 1950’s, a multi-national longline fishery has operated throughout the Atlantic Ocean to supply the growing global demand for tunas (Scombridae) and swordfish, Xiphias gladius. Two species caught as bycatch include Atlantic blue marlin, Makaira nigricans, and white marlin, Tetrapterus albidus, referred to in this paper as “Atlantic marlin.” Pelagic longlining has consistently been the principal source of adult mortality for both species, which are currently depleted and have been so for more than two decades. In this paper, we examined aspects of the Atlantic marlin bycatch of the Japanese pelagic longline fishery from 1960 to 2000. Temporal and spatial patterns in effort, target catch (species combined), marlin bycatch, marlin catch-per-unit-effort (nominal CPUE), and ratios of marlin bycatch to target catch (B: T ratios) were analyzed. An objective was to reveal changes, if any, in marlin bycatch associated with the fishery’s target species “switch” (ca. 1980–87) from mostly surface-associated tunas to mostly the deeper-dwelling bigeye tuna, Thunnus obesus. The highest values of all variables examined occurred during the 1960’s and then fell by the second half of that decade. Since 1970, mean levels of fishing effort, target fish catches, and blue marlin landings have increased significantly, while blue marlin CPUE and B:T ratios have remained relatively stable. Concurrently, white marlin landings, CPUE, and B:T ratios have all declined. While results suggest the fishery’s target species change may have been a factor in lowering white marlin bycatch, the same cannot be said for blue marlin. Relative increases in blue marlin B:T ratios off the northeastern coast of South America and in the wider eastern Atlantic are cause for concern, as are continuing trends of CPUE decline for white marlin in this data set as well as others.