National Shark Research Consortium
Shark Research Program - Virginia Institute of Marine Science
Featured Projects
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NSRC Featured Project: History of the VIMS Longline Survey
The Virginia Institute of Marine Science (VIMS) longline survey began in 1973 and will continue into its 31st year during the summer of 2004. This project allows VIMS scientists to assess the abundance of local shark stocks and to monitor changes in this abundance over time. The survey is a depth-stratified field survey of the Chesapeake Bay and Virginia coastal waters. Eight standard stations plus ancillary locations are fished each month from May or June through September or October. Five of these stations occur in coastal waters and represent three depth strata, < 10m, 10-20m, and 20 - 100m, two of these stations occur in the Chesapeake Bay, and the last station is found in the Eastern Shore seaside lagoons of Virginia (Figure 1).
Figure 1. Longline stations occupied by the VIMS shark project during 1973-2002. Standard stations are labeled: K, M, W, Q, T, C, L, and V.
Courtesy VIMS
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At each station a 100-hook longline covering approximately 1.25 nautical miles is fished for 3-4 hours. Each hook is baited with one third or one half of an Atlantic menhaden (Brevoortia tyrannus). Each fish that is captured is measured, sexed, and biological samples are taken as needed for genetic, age/growth, trophic, and reproduction analyses.
Healthy specimens not needed for these analyses are tagged and released for long-term studies on migration, habitat utilization, and age and growth. Sandbar sharks (Carcharhinus plumbeus) up to 150 cm total length are tagged with Hallprint nylon dart tags, specifically designed for juvenile sharks. All other sharks are tagged with "M"-type steel dart tags, supplied by the National Marine Fisheries Service (NMFS) Apex Predator Program. During the course of this survey over 1,000 sets have been made and over 99,000 hooks have been set catching a total of 7,434 sharks of 21 different species (Figure 2).
Figure 2. Shark species caught by the Virginia Institute of Marine Science longline survey from 1973 - 2002. Courtesy VIMS
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The most common shark species captured by the VIMS longline project include the sandbar shark, the dusky shark,
the smooth dogfish, and the Atlantic sharpnose shark. In addition to sharks, the longline project also captures many species of skates and rays, including clearnose skate, southern stingray, roughtail stingray, bluntnose stingray, spiny butterfly ray, smooth butterfly ray, cownose ray, and bullnose ray. Virginia waters undergo large yearly temperature changes and most shark and ray species only inhabit these waters during the warmer summer months. The Chesapeake Bay and Eastern Shore lagoons of Virginia constitute one of the primary sandbar shark summer nursery areas.
Figure 3. A juvenile sandbar shark caught in the Chesapeake Bay nursery. Courtesy VIMS.
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The principal goal of this project is to provide a fishery-independent assessment of the relative abundance, species, size, and sex composition of Virginia sharks so that the current population status of individual shark species may be compared with historical trends. Catch per unit effort (CPUE) data is determined each year for the large coastal shark management group, as well as sandbar, dusky, sandtiger, tiger, and Atlantic sharpnose sharks. This project has documented the drastic decline of large coastal sharks, which began in the 1980s and continued into the 1990s with CPUE's of large coastal sharks reaching a minimum in 1992 (Figure 4).
Figure 4. Log catch per unit effort for large coastal shark abundance from 1974-2002. Courtesy VIMS.
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Catch rates of large coastal sharks increased for a few years beginning in 1993 but have leveled off in the past 4-7 years well below pre exploitation catch rates. Species-specific CPUE for four individual species: the sandbar shark C. plumbeus, the dusky shark C. obscurus, the tiger shark Galeocerdo cuvier, and the sandtiger shark C. taurus also reflect this same general pattern. Length frequencies of the more common species caught by the survey are also examined by VIMS scientists to determine if growth overfishing has occurred during the period of study. A noticeable change in the mean size of sandbar sharks captured in coastal Virginia waters has been documented. The mean size has declined from over 100cm precaudal length in the early 1980s through the early 1990s to the 75-85 cm range in recent years (Figure 5).
Figure 5. The mean precaudal length of sandbar sharks captured in coastal Virginia waters from 1980 to 2002 (error bars are standard error). Courtesy VIMS.
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The first 30 years of this program have documented the population decline of local shark stocks and, more specifically, serious and potential recruitment failure for dusky and sandbar sharks. These data can be extrapolated to indicate the status of the northwest Atlantic stock, as these individuals that seasonally occupy the mid-Atlantic region migrate northward from southern locales each spring. These data were supported by stock assessments for large coastal shark species of the northwest Atlantic that were used to develop a fishery management plan (FMP) for shark resources of the Atlantic Ocean, Gulf of Mexico and Caribbean Sea. Data from this program suggest that current shark stocks remain stable and have not increased above depressed, pre-management levels. This project has provided the longest (1973-present) reliable, fishery-independent assessment of relative abundance of East Coast shark stocks. Continued collection of these fishery-independent data to estimate shark abundance will contribute significantly to evaluating the effectiveness of management measures implemented in the FMP, and is essential for continued monitoring of shark population status.
Figure 6a. Traditional longline gear used by the VIMS survey including orange buoys, standard gangions consisting of 3/16" braided nylon with stainless steel leaders (on left), and monofilament gangions (on right) used to sample juvenile sandbar sharks in the Chesapeake Bay and Eastern Shore nursery areas. Courtesy VIMS.
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Figure 6b. Bait used by the VIMS longline survey. Courtesy VIMS.
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