David W. Kerstetter

Postrelease Survival of Sailfish Caught by Commercial Pelagic Longline Gear in the Southern Gulf of Mexico

The biomass levels of several target species of the Atlantic pelagic longline fishery, including various tunas of the genus Thunnus and swordfish Xiphias gladius, are estimated to be close to those required to support the maximum sustainable yield. In contrast, several species captured incidentally are severely depleted. Live release of incidental catch is one means of reducing the fishing mortality of these species without sacrificing the target catch, but the efficacy of such a measure is predicated on the assumption that postrelease survival is relatively high. Prior work has evaluated postrelease survival from pelagic longline gear for the larger istiophorid billfishes, such as blue marlin Makaira nigricans and white marlin Kajikia albida, but survival rates are unknown for sailfish Istiophorus platypterus. To estimate the postrelease survival of sailfish caught on pelagic longline gear in the southern Gulf of Mexico, short-duration pop-up satellite archival tags (PSATs) were deployed on captured sailfish for 10-d periods. Of the 29 sailfish captured, 20 (68.9%) were alive at the time of longline haulback, and the first 17 encountered alive were tagged. All tags transmitted at the preprogrammed times, and data from 15 of the 17 PSATs (88.2%) were consistent with the survival of the tagged sailfish for the 10-d tag deployment. Our results clearly demonstrate that sailfish can survive the trauma from interaction with pelagic longline gear and that management measures promoting the release of live individuals from this fishery can significantly reduce sailfish mortality without reducing the catches of target species.

Sailfish Habitat Utilization and Vertical Movements in the Southern Gulf of Mexico and Florida Straits

Abstract Pop-up satellite archival tags (PSATs) were deployed on 19 sailfish Istiophorus platypterus captured in the southern Gulf of Mexico and Florida Straits between 2005 and 2007 on commercial pelagic longline gear (n = 18) and recreational rod-and-reel gear (n = 1). The data from three tags indicated mortality events and were excluded from subsequent analyses. All PSATs were programmed to collect pressure (depth), temperature, and light-level data for 10 d at approximately 90-s intervals. These transmitted point data subsequently allowed the reconstruction of vertical movement patterns. The remaining 16 PSAT data sets indicate that sailfish are primarily associated with the upper surface waters within the top 20 m (75.7% of total time during the day versus 46.7 % at night) but undertake numerous short-duration vertical movements below the local mixed layer to depths of 50–150 m, presumably to feed. Analyses of 2,279 individual vertical movements among all 16 tagged sailfish indicated two distinct types (short-duration “V” and longer-duration “U” movements) similar to those reported for white marlin Kajikia albida. Sailfish also exhibited movement type differences between diel periods (having higher proportions of V movements in daytime), suggesting directed foraging at depth. Although short-duration movement to depths by these tagged fish contribute a small percentage of the total time at depth, these depths overlap with the monitored shallow-set pelagic longline gear depths actively targeting swordfish by the vessel in the local fishery. These results suggest that time-at-depth histograms alone may be insufficient to capture feeding motivations at depth and, therefore, true interaction potentials between individual sailfish and pelagic longline gear.

Using Logbook Data to Determine the Immediate Mortality of Blue Sharks (Prionace glauca) and Tiger Sharks (Galeocerdo cuvier) Caught in the Commercial U.S. Pelagic Longline Fishery

Document Type Article Publication Date 2017 Publication Title Fishery Bulletin ISSN 0090-0656 Volume 115 Issue/No. 1 First Page 27 Last Page 41 Abstract Commercial fisheries are recognized as one of the greatest threats to shark populations worldwide, but factors affecting the likelihood of shark mortality during fishery capture are poorly understood. We used the U.S. pelagic fishery logbook data from 1992 through 2008 to quantify the effects of several variables (fisheries regulatory periods, geographic zone, target catch, and sea surface temperature) on mortality of blue sharks (Prionace glauca) and tiger sharks (Galeocerdo cuvier). Mortality rates and trends in both species closely matched those recorded from other sources, and therefore indicated that the data on sharks discarded dead and discarded alive in the U.S. pelagic fishery logbook are accurate. The introduction of fisheries management regulations (fin weight to carcass weight ratios in 1993 [to prevent finning] and the prohibition of J-hooks in 2004)  Download

Supplemental Table 1 of Using logbook data to determine the immediate mortality of blue sharks (Prionace glauca) and tiger sharks (Galeocerdo cuvier) caught in the commercial U.S. pelagic longline fishery

1 School of Biological Sciences Monash University Wellington Road Clayton, Victoria 3800, Australia Present address for contact author: Washington Department of Fish and Wildlife 600 Capitol Way North Olympia, Washington 98501–1091 2 School of Biological Sciences Flinders University G.P.O. Box 2100 Adelaide, South Australia 5001, Australia 3 Anderson Cabot Center for Ocean Life New England Aquarium Central Wharf Boston, Massachusetts 02110-3399 4 Department of Marine and Environmental Sciences Halmos College of Natural Sciences and Oceanography Nova Southeastern University 8000 North Ocean Drive Dania Beach, Florida 33004