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Article Excerpt
Introduction
Shark exploitation in the U.S. Atlantic and Gulf of Mexico, sporadic throughout much of the twentieth century, has greatly increased over the last three decades. Shark stock assessments (NMFS (1,2,3)) have varied in their estimates of stock size, fishing mortality, and maximum sustainable yield (MSY). However, each assessment reached the same general conclusion: shark mortality from a combination of fishing efforts has exceeded the reproductive capacity of certain species to the detriment of overall stock size. These conclusions are corroborated by substantial declines in shark catch-perunit-effort (CPUE) in commercial fishery samples, fishery-independent longline fishing experiments (NMFS (1,2,3)), and recreational fishing tournament data (Hueter (4)).
Sharks are argued to be highly susceptible to overfishing because of their K-selected life history characteristics (Heppell et al., 1999; Cort6s, 1999, 2002). Many of the species important to commercial and recreational fisheries grow slowly, mature at larger sizes, and have limited reproductive capacity. Given the biological constraints on shark production, the intensive fishing of shark resources is believed to be unsustainable.
Various management agencies examined strategies for sustainable utilization of the resource in the early 1990's. Initially, Texas, North Carolina, Virginia, and Florida enacted regulations for shark fisheries within their state waters (NMFS (5)). A Federal Shark Fishery Management Plan (IMP) was implemented in 1993 by the National Marine Fisheries Service (NMFS) for 39 species in the U.S. Atlantic and Gulf of Mexico waters (NMFS (5)). Implementation of this plan, in development for nearly a decade, was hampered by a lack of adequate data.
Initial regulations in the FMP included seasonal commercial quotas, recreational bag limits, and prohibitions of "finning" and recreational catch sales which were all designed to enhance stock rebuilding. The IMP proposed a data collection plan, including utilization of at-sea observers to verify logbook information and gather pertinent data on shark discards and interactions with protected and endangered resources. Subsequent FMP modifications were implemented reflecting results of updated assessments and newly generated biological data (NMFS (6,7,8)).
An onboard observer program is an effective means of rapidly gathering detailed information on: 1) species and size composition of the catch and landings, 2) catch-per-unit-effort (CPUE) (number of sharks caught per 10,000 hook hours), and 3) disposition (released alive, discarded dead, used for bait, etc.) of nonlanded catch. An observer program garners details otherwise not captured by mandatory vessel logbook data, and it simultaneously "ground truths" this information.
In 1994, the Commercial Shark Fishery Observer Program (CSFOP) initiated monitoring of bottom longline (BLL) vessels targeting sharks in the U.S. Atlantic and Gulf of Mexico; the principle U.S. directed commercial fishery for large coastal sharks. The CSFOP has generated one of the most extensive and detailed biological databases in existence for sharks of the western North Atlantic.
The IMP allocated northwest Atlantic shark species into five groupings for potential management purposes. The "large coastal" (LC) shark complex represents an assemblage of 11 species of carcharhinid, sphyrnid, and orectolobid sharks (Table 1), which have historically been the target of the BLL fishery and have been managed as a unit. The "small coastal" (SC) shark complex, another managed complex of three carcharhinids and one sphyrnid species (Table 1), are less frequently targeted by BLL fishermen but are commonly captured as bycatch within the LC-targeted fishery and inshore gillnet, trawl, and hook fisheries. "Prohibited sharks" (PH) are a diverse group of 19 sharks (odontaspid, carcharhinid, and lamnoid sharks) deemed especially vulnerable and banned from landing (Table 1). "Pelagic sharks" (PE) (five lamnoid and carcharhinid sharks) and "dogfish" ((DF) excluded from management through the IMP) (Table 1) are infrequently taken in the BLL fishery (NMFS(9)). This paper characterizes the BLL shark fishery as monitored by the CSFOP in Atlantic waters of the United States from 1994 through 2003.
Materials and Methods
CSFOP observers were trained in the following areas: marine safety, sea turtle handling and resuscitation techniques, fishery and biological data collection, biological sampling, and shark and bycatch species identification. Observers were required to record catch and effort information from each longline set targeting coastal sharks during each sampled trip (a "trip" is defined as the time period between a fishing vessel's departure from port and its return to port with all deployed fishing gear fully retrieved). Data and biological samples were returned to the Florida Museum of Natural History (FLMNH) at the University of Florida for processing and further studies. Data were archived and analyzed using a customized Microsoft Access database. (10) Relevant specimens and biological samples were archived at FLMNH for further study.
Fishing vessel participation in the CSFOP was voluntary from 1994 to 2001. CSFOP personnel (Principal Investigators or observers) personally solicited individual longline vessel owners and/or captains for permission to monitor their fishing trips. Due to the voluntary nature of the program at this time, monitoring was nonrandom by nature and certain vessels were observed repetitively, particularly during the latter part of this period. Percent observer coverage was calculated by dividing the total number of LC sharks landed on observed trips by the total number of commercially landed LC sharks during the same time period according to National Marine Fisheries Service (NMFS) records (Cortex and Neer (11)). Sampled trips were responsible for approximately two percent of total recorded commercial landings.
As NMFS regulatory measures were enacted and implemented, it became increasingly difficult to identify vessels willing to voluntarily accept observers (Burgess (12)). Placement of observers was made mandatory by NMFS in 2002. Vessels were selected by NMFS from a pool developed after consulting data generated by mandatory NMFS landing logbooks (Rilling (13)). Vessels identified as actively landing sharks were matched with vessels holding valid Federal shark permits for the upcoming fishing season. Those vessels that documented sharks as more than 25% of their total landings from the same fishing season of the previous year were deemed eligible for selection. A pseudo-random number generator was used to select vessels within three subregions (Mid-Atlantic Bight, southeastern U.S. Atlantic, and Gulf of Mexico). The number of vessels selected for monitoring in a given season was based on the number of fishing days projected by NMFS for the fishery in that season.
Owners/captains of selected vessels were required to contact the observer coordinator at least 48 hr prior to departing port on any trip where LC sharks were targeted or caught incidentally using BLL fishing gear. Individual observers were then deployed to vessels by the observer coordinator. To carry an observer, the vessels were required to have a Commercial Fishing Vessel Safety Decal (CFVSD), issued by the U.S. Coast Guard, and be capable of providing room and board for the observer that was equivalent to that given to the crew. In addition to these NMFS mandated requirements, the CSFOP did not deploy observers aboard vessels smaller than 30 ft in length (because of space and safety considerations), vessels operated by a captain or crew known to abuse alcohol or drugs at sea, or other safety issues reported by observers and documented by the CSFOP.
When deployed on BLL vessels, observers recorded specific details regarding the fishing gear utilized and associated catch during each set for the duration of the trip. The term "set 'refers to an individual BLL set, which includes the deployment and retrieval of fishing gear and associated catch. Recorded were the size and number of hooks, time and latitude and longitude coordinates when the first and last hooks entered and were removed from the water, bait utilized, and length of the deployed mainline. For analytical purposes, we divided the sampled area into three geographical subregions for our analysis: the Mid Atlantic Bight (MAB), the Atlantic coast of the southeastern U.S. (SE US), and the eastern Gulf of Mexico (EGM). The boundaries of these regions and the locations of observed BLL sets are identified in Figure 1.
Vessel captains calculated and provided the length of the mainline from their Global Positioning System (GPS) readings. GPS or Loran geographic positions were recorded. Loran coordinates were converted to latitude/longitude using the Coast Guard POSAID2 version 2.1 a computer program. Water depth at the location of each set was measured with sonar, and bottom water temperature was recorded by a Stowaway XTI temperature recorder (14) fastened to one end of the longline. Air and sea surface water temperatures were recorded using a glass-stem thermometer.
Soak time was defined as the temporal interval between entry of the first hook and removal of the first hook from the water. CPUE for each set was calculated as the number of sharks caught per 10,000 hook hours (CPUE = catch x 10,000/(hooks x soak time)). CPUE calculations do not include or adjust for hook type and size, type of bait used, distance between hooks, gangion length and material (monofilament, steel), or the specific sharks targeted (SC or LC, sandbar or blackfip).
All catch was identified to the lowest possible taxon, and disposition of it was recorded. Disposition categories included: landed, used for bait, released alive, discarded dead, tagged (with a NMFS M-style dart tag), released, archived as museum specimens, or another category. To determine at-vessel mortality rates observers recorded the condition (alive or dead) of hooked animals when brought on board. Animals were deemed alive if there was any response to tactile stimuli (there were no varying degrees of alive) and dead if there...
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